JP2020031860A - Medical image processing apparatus, X-ray diagnostic apparatus, and medical image processing program - Google Patents

Abstract

To inhibit a rapid change in a pixel value while securing contrast of an X-ray image.SOLUTION: A medical image processing apparatus includes a timing acquisition unit and a pixel value correction unit. The timing acquisition unit acquires information on a switching timing of tube voltages in a plurality of X-ray images captured in time series accompanied by switching of the tube voltages. The pixel value correction unit executes correction of pixel values of at least one of a plurality of first X-ray images before the switching timing and a plurality of second X-ray images after the switching timing, in the plurality of X-ray images.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a medical image processing apparatus, an X-ray diagnostic apparatus, and a medical image processing program.

  2. Description of the Related Art In an X-ray diagnostic apparatus for a circulatory organ, a digital subtraction angiography (DSA) method and a digital angiography (DA) method are widely used when imaging a blood vessel such as a head, abdomen, a liver, a lower limb or a limb. .

  DSA is an imaging technique for displaying only a contrast blood vessel by calculating a difference between an image at the time of injection of a contrast agent (contrast image) and an image before injection (mask image). The contrast image is usually collected not as one but as a continuous image. DSA displays a DSA image created by subtracting a mask image from a continuous contrast image as a moving image. The operator understands the blood flow of the blood vessel by observing the moving image. In such a DSA, when the X-ray tube voltage is constant, the contrast is high because the blood vessel is thick immediately after the contrast medium is injected from the catheter and the contrast medium is thick. In addition, as the contrast agent goes to the peripheral blood vessels, the blood vessels become thinner and the contrast agent is diluted, so that the contrast becomes lower. Note that the contrast in DSA is equal to the pixel value because the DSA image has no background.

  On the other hand, DA is an imaging method for displaying a contrasted blood vessel and its background as an image (contrast image) at the time of injection of a contrast agent, and does not take a difference unlike DSA. Also in DA, a contrast image is usually collected not as one but as a continuous image. DA displays a continuous contrast image (DA image) as a moving image. The operator understands the blood flow of the blood vessel by observing the moving image. In such DA, when the X-ray tube voltage is constant, the contrast increases immediately after the injection of the contrast agent, and the contrast decreases as the contrast agent goes to peripheral blood vessels, as described above. Note that the contrast in DA (hereinafter, also referred to as blood vessel contrast) is different from the pixel value because the DA image has a background. The blood vessel contrast C in DA is defined by the following equation using the average pixel value P0 of the ROI of the image before the injection of the contrast agent and the average pixel value P1 of the ROI of the image after the injection of the contrast agent.

C = (P0−P1) / P0
However, in any case of DSA and DA, the contrast is still a value corresponding to the pixel value of the contrasted blood vessel. For this reason, in DSA and DA, it is preferable to secure the contrast of the X-ray image and prevent a rapid change in the pixel value.

JP-A-2005-226768

  The problem to be solved by the present invention is to secure the contrast of an X-ray image and prevent a rapid change in pixel value.

The medical image processing device according to the embodiment includes a timing acquisition unit and a pixel value correction unit.
The timing acquisition unit acquires information on the switching timing of the tube voltage in a plurality of X-ray images that are taken in time series with the switching of the tube voltage.
The pixel value correction unit is configured to calculate a pixel value of at least one of a plurality of first X-ray images before the switching timing in the plurality of X-ray images and a plurality of second X-ray images after the switching timing. Perform the correction.

FIG. 1 is a block diagram illustrating a configuration of the X-ray diagnostic apparatus according to the first embodiment. FIG. 2 is a schematic diagram for explaining a method for setting a region of interest in the first embodiment. FIG. 3 is a schematic diagram for explaining another method for setting a region of interest in the first embodiment. FIG. 4 is a graph for explaining correction of a pixel value after kV switching in the first embodiment. FIG. 5 is a schematic diagram for explaining correction of a pixel value after kV switching according to the first embodiment. FIG. 6 is a block diagram illustrating a configuration of the X-ray diagnostic apparatus in a case where the image data processing unit and the system control unit according to the first embodiment are implemented by processing circuits. FIG. 7 is a flowchart for explaining the operation in the first embodiment. FIG. 8 is a graph for explaining correction of a pixel value after kV switching in the first modification of the first embodiment. FIG. 9 is a flowchart for explaining the operation in the first modification of the first embodiment. FIG. 10 is a graph for explaining a change in the range of pixel values indicated by colors after kV switching in the second modification of the first embodiment. FIG. 11 is a block diagram illustrating a configuration of an X-ray diagnostic apparatus according to a second modification of the first embodiment. FIG. 12 is a block diagram illustrating a configuration of an X-ray diagnostic apparatus when the image data processing unit and the system control unit according to the second modification of the first embodiment are implemented by processing circuits. FIG. 13 is a flowchart for explaining the operation in the second modification of the first embodiment. FIG. 14 is a block diagram illustrating a configuration of a medical image processing apparatus according to the second embodiment. FIG. 15 is a graph for explaining correction of a pixel value before kV switching according to the second embodiment. FIG. 16 is a schematic diagram for explaining correction of a pixel value before kV switching according to the second embodiment. FIG. 17 is a graph for explaining the correction of both the pixel values before and after the kV switching in the second embodiment. FIG. 18 is a flowchart for explaining the operation in the second embodiment. FIG. 19 is a schematic diagram for explaining two curves in the first modified example of the second embodiment. FIG. 20 is a schematic diagram for explaining correction of a pixel value by comparing two curves in the first modified example of the second embodiment. FIG. 21 is a graph for explaining correction of a pixel value before kV switching in the second modification of the second embodiment. FIG. 22 is a graph illustrating the correction of both the pixel values before and after the kV switching in the second modification of the second embodiment. FIG. 23 is a block diagram illustrating a configuration of a medical image processing apparatus according to a third modification of the second embodiment. FIG. 24 is a flowchart for explaining the operation in the third modification of the second embodiment. FIG. 25 is a flowchart for explaining the operation of the X-ray diagnostic apparatus according to the third embodiment. FIG. 26 is a flowchart for explaining the operation of the medical image processing apparatus according to the first modification of the third embodiment.

  Hereinafter, each embodiment will be described with reference to the drawings. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and repeated description will be made only when necessary.

<First embodiment>
FIG. 1 is a block diagram illustrating a configuration of the X-ray diagnostic apparatus according to the first embodiment. The X-ray diagnostic apparatus 1 includes, as a data acquisition system, an X-ray generator 3, an X-ray detector 5, a bed 7, a C arm 9, an X-ray controller 11, a high voltage generator 13, and a C arm / bed mechanism control. A section 15 is provided. Further, the X-ray diagnostic apparatus 1 includes a position data memory 21, a system control unit 22, an input interface 23, a display 24, and an image data processing unit 25 as a data processing system.

  Here, the X-ray generation unit 3 includes an X-ray tube 3a and an X-ray diaphragm 3b.

  The X-ray tube 3a is a vacuum tube that generates X-rays, accelerates thermoelectrons emitted from a cathode (filament) by a high voltage, and collides the accelerated electrons with a tungsten anode to generate X-rays.

  The X-ray diaphragm 3b is located between the X-ray tube 3a and the X-ray detector 5, and is made of a lead plate as a metal plate. The X-ray stop 3b is controlled by the X-ray controller 11, and shields the X-rays outside the aperture region so that the X-rays generated by the X-ray tube 3a are irradiated only to the region of interest of the subject P. Refine. For example, the X-ray diaphragm 3a has a plurality of diaphragm blades, and by sliding these diaphragm blades, an area where X-rays are shielded is adjusted to an arbitrary size. The aperture blades of the X-ray aperture are controlled by the X-ray controller 11 according to the region of interest set by the region setting circuit 25c, and are driven by a driving device (not shown).

  The X-ray detector 5 detects X-rays transmitted through the subject P. As such an X-ray detector 5, one that directly converts X-rays into electric charges and one that converts X-rays into light and then converts them into electric charges can be used. Here, the former will be described as an example, but the latter will be described. It does not matter. That is, the X-ray detector 5 is, for example, a flat FPD (Flat Panel Detector) that converts X-rays transmitted through the subject P into electric charges and accumulates the X-rays, and driving for reading out the electric charges accumulated in the FPD. A gate driver for generating a pulse. The size of the FPD is typically between 8 and 12 inches. The FPD is configured by two-dimensionally arranging minute detection elements in a column direction and a line direction. Each of the detection elements senses X-rays and generates a charge according to the incident X-ray amount, a charge storage capacitor that stores the charge generated in the photoelectric film, and a charge stored in the charge storage capacitor. TFT (thin film transistor) that outputs at the timing shown in FIG. The accumulated charges are sequentially read by a driving pulse supplied from a gate driver.

  At the subsequent stage of the X-ray detector 5, a projection data generation circuit (not shown) is provided. The projection data generation circuit includes a charge / voltage converter, an A / D converter, and a parallel / serial converter. The charge / voltage converter converts charges read in parallel from the FPD in row units or column units into a voltage. The A / D converter converts the output of the charge / voltage converter into a digital signal. The parallel-to-serial converter converts the digitally converted parallel signal into a time-series serial signal. The projection data generation circuit outputs this serial signal to the image data processing unit 25 as time-series projection data.

  The couch 7 has a mechanism capable of raising and lowering and positioning with the subject P mounted. The bed 7 is provided with a state detector (not shown) for detecting information on a geometrical arrangement such as its position. The state detector outputs information on the geometric arrangement of the bed 7 to the C-arm / bed mechanism control unit 15.

  The C-arm 9 holds the X-ray generation unit 3 and the X-ray detector 5 so as to face each other with the subject P and the couch 7 interposed therebetween. More specifically, the C arm 9 is rotatable about an axis in the X direction perpendicular to both the Z direction perpendicular to the table top of the bed 7 and the Y direction along the long axis direction of the table 7. (Not shown). The C-arm 9 has a substantially circular arc shape centered on the axis in the Y direction, and is slidably held by the holding portion along the substantially circular arc shape. Alternatively, the C-arm 9 can rotate about the axis in the X direction about the holding section, and it becomes possible to observe X-ray images from various angular directions by a combination of slide and this rotation. . The C-arm 9 is provided at an appropriate place where a plurality of power sources for realizing such a sliding operation and a rotating operation are applicable. Further, the C-arm 9 is provided with a state detector (not shown) for detecting information relating to the geometric arrangement such as the angle or the posture or position. The state detector includes, for example, a potentiometer that detects a rotation angle and a movement amount, an encoder that is a position detection sensor, and the like. As the encoder, for example, a so-called absolute encoder of a magnetic system, a brush system, a photoelectric system, or the like can be used. Various types of position detection mechanisms, such as a rotary encoder that outputs a rotational displacement as a digital signal or a linear encoder that outputs a linear displacement as a digital signal, can be appropriately used as the state detector. This type of state detector outputs information on the geometrical arrangement of the C-arm 9 to the C-arm / bed mechanism control unit 15. The information on the geometrical arrangement of the C-arm 9 corresponds to the information on the geometrical arrangement of the X-ray tube and the X-ray detector.

  The X-ray controller 11 is controlled by the system control unit 22 and the switching timing acquisition circuit 25d, and controls the X-ray diaphragm 3b, the X-ray control unit 13a, and the high voltage generator 13b.

  The high voltage generator 13 includes an X-ray controller 13a and a high voltage generator 13b.

  The X-ray control unit 13a supplies a tube current, a tube voltage, an application time, an application timing, and a repetition frequency in the high-voltage generator 13b based on the X-ray irradiation conditions of the X-ray tube 3a supplied from the X-ray controller 11. And so on.

  The high-voltage generator 13b is controlled by the X-ray controller 11 and generates a high voltage applied between the anode and the cathode to accelerate thermoelectrons generated from the cathode of the X-ray tube 3a. Output to

  The C-arm / bed mechanism control unit 15 is controlled by the system control unit 22. The C-arm / bed mechanism control unit 15 individually drives and controls the C-arm 9 and the bed 7, and also receives information on the geometric arrangement of the C-arm 9 received from a state detector (not shown) and the geometry of the bed 7. The information relating to the target arrangement is written into the position data memory 21.

  The position data memory 21 stores information on the geometrical arrangement of the C-arm 9 and information on the geometrical arrangement of the bed 7.

  The system control unit 22 is a central processing unit that performs control related to collection of image data and control related to image processing, image reproduction processing, and the like of the collected image data. The system control unit 22 temporarily stores information such as a command signal input from the input interface 23 and various initial setting conditions, and then stores the information in the X-ray controller 11, the C-arm / bed mechanism control unit 15, And / or sends it to the image data processing unit 25.

  The input interface 23 performs input of subject information, setting of X-ray imaging conditions including X-ray irradiation conditions, input of various command signals, and the like. The input interface 23 includes, for example, a trackball, a switch button, a mouse, a keyboard, a touchpad for performing an input operation by touching an operation surface, for performing a movement instruction of the C-arm 9, setting a region of interest (ROI), and the like. It is realized by a touch panel display or the like in which a display screen and a touch pad are integrated. The input interface 23 is connected to the system control unit 22, converts an input operation received from an operator into an electric signal, and outputs the electric signal to the system control unit 22. In the present specification, the input interface 23 is not limited to one having physical operation components such as a mouse and a keyboard. For example, an example of the input interface 23 includes an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the device and outputs the electric signal to the system control unit 22. It is.

  The display 24 includes a display main body for displaying a medical image, an internal circuit for supplying a display signal to the display main body, and peripheral circuits such as a connector and a cable connecting the display main body and the internal circuit. The internal circuit generates display data by superimposing supplementary information such as subject information and projection data generation conditions on the image data supplied from the image data processing unit 25, and performs D / A conversion on the obtained display data. The TV format is converted and displayed on the display body.

  The image data processing unit 25 includes an image operation circuit 25a, an image data memory 25b, an area setting circuit 25c, a switching timing acquisition circuit 25d, and a display data generation circuit 25e. The display data generation circuit 25e includes a pixel value correction circuit 25f and a color image creation circuit 25g. The image data memory 25b, the area setting circuit 25c, the switching timing obtaining circuit 25d, the display data generating circuit 25e, the pixel value correcting circuit 25f, and the color image creating circuit 25g constitute a medical image processing device 200.

  The image calculation circuit 25a generates an X-ray image based on the detection result by the X-ray detector 5. More specifically, the image calculation circuit 25a sequentially stores time-series projection data output from the projection data generation circuit of the X-ray detector 5 in a projection data storage circuit (not shown) and includes two-dimensional projection data. Generate an X-ray image. This X-ray image is stored in the image data memory 25b.

  The X-ray images that can be generated by the image calculation circuit 25a include a mask image (non-contrast image), a contrast image (contrast image), and a DSA image (difference image). The mask image is an X-ray image before the injection of the contrast agent, and is a projection image having a bone image. The contrast image is an X-ray image after the injection of the contrast agent, and is a projection image having bone and blood vessel images. The DSA image is an X-ray image representing a difference between the contrast image and the mask image, and is a projection image having a blood vessel image. For example, the DSA image can be generated by calculating the difference between the mask image stored in the image data memory 25b and the contrast image generated from the output of the X-ray detector 5. The mask image is generated for each X-ray irradiation condition. For example, when there are a first irradiation condition including a first tube voltage and a second irradiation condition including a second tube voltage, a first mask image based on the first irradiation condition, And a second mask image based on the second irradiation condition.

  In addition to this, the image arithmetic circuit 25a receives the projection data collected by rotating the X-ray tube 3a and the X-ray detector 5 continuously around the subject P, and stores the projection data stored in the image data memory 25b. 3D image data may be generated by performing a predetermined reconstruction process. The obtained 3D image data is stored in the image data memory 25b. In this case, the image calculation circuit 25a may generate a 3D roadmap image by superimposing the 3D image data on a two-dimensional X-ray image in real time. Note that “real time” indicates that processing is performed in parallel with the imaging of an X-ray image. For example, here, two-dimensional X-ray images are sequentially captured, and in parallel with this, a process of generating a 3D roadmap image by superimposing 3D image data on the captured two-dimensional X-ray image is executed.

  The image data memory 25b stores image data such as an X-ray image, a 3D image, and a 3D roadmap image generated by the image operation circuit 25a.

  The region setting circuit 25c (region of interest setting unit) sets a region of interest in the X-ray image. For example, the region setting circuit 25c may set, as a region of interest, a region in which the pixel value in any one of the plurality of X-ray images is higher than the threshold value. Further, for example, the region setting circuit 25c may be capable of setting the region of interest by any one of the following methods (r1) to (r4).

  (R1) A method of setting a region of interest according to an operation of the input interface 23 by an operator. For example, the region setting circuit 25c may set a region of interest in a 3D image (3D volume image) in the 3D roadmap image by operating the input interface 23 by the operator. In this case, since the 3D roadmap image is aligned with the subject P, the region of interest can be set at an accurate position.

  (R2) A method of setting a region where the pixel value exceeds a threshold value as a region of interest in the entire X-ray image before or after the switching of the tube voltage. Note that "switching of the tube voltage" may be called "kV switching".

  (R3) For example, as shown in FIG. 2, an area where the pixel value exceeds the threshold value in a specified area (hereinafter, also referred to as a specified area) 31 in the X-ray image 30 before or after the tube voltage is switched. A method of setting 32 as a region of interest. Here, the designated area 31 may be designated based on anatomical information regarding an imaging target portion of the X-ray image, or may be designated according to an operation of the input interface 23 by an operator. The anatomical information may include information on the imaging target site and information on the geometric arrangement of the X-ray tube 3a and the X-ray detector 5. That is, the region setting circuit 25c, for example, based on the information of the imaging target part in the inspection protocol acquired from the system control unit 22 and the angle and position of the C-arm 9 acquired from the system control unit 22, the field of view position It is also possible to estimate and designate the designated area 31 from the position of the visual field. The designated area 31 may be set to a wider area (than the area that can be designated by the operator), for example, the central area (or upper area) of the X-ray image. In addition, the area setting circuit 25c includes information on the geometric arrangement of the X-ray tube 3a and the X-ray detector 5, the position of the bed 7, SID (source-image distance), and FOV. The designated area 31 may be designated using (field of view: field of view), subject information (height / weight), subject position information, and the like.

  (R4) For example, as shown in FIG. 3, a difference between the X-ray image 30a immediately before switching of the tube voltage and the X-ray image 30b one to several frames before the X-ray image 30a is obtained, and the difference is a threshold. A method of setting the region exceeding the area as a region of interest.

  The switching timing acquisition circuit 25d (timing acquisition unit) acquires information on the switching timing of the tube voltage in a plurality of X-ray images that are taken in time series with the switching of the tube voltage. Specifically, for example, the switching timing acquisition circuit 25d acquires information on the switching timing of the tube voltage from the system control unit 22. As the information regarding the switching timing of the tube voltage, for example, a switching signal indicating the switching timing of the tube voltage can be used.

  The display data generation circuit 25e generates display data based on the X-ray image generated by the image calculation circuit 25a, and sends the display data to the display 24. Here, the display data generation circuit 25e includes a pixel value correction circuit 25f (pixel value correction unit) and a color image generation circuit 25g (color image generation unit). Note that the pixel value correction circuit 25f or the color image creation circuit 25g is not essential and may be omitted. When the pixel value correction circuit 25f is omitted, a window width changing circuit described later may be used in addition to the color image creation circuit 25g.

  The pixel value correction circuit 25f executes the correction of the pixel value in at least one of the plurality of first X-ray images before the switching timing in the plurality of X-ray images and the plurality of second X-ray images after the switching timing. I do. For example, as shown in FIGS. 4 and 5, the pixel value correction circuit 25f outputs a pixel value in a plurality of second X-ray images after the switching timing T_sw acquired by the switching timing acquisition circuit 25d among the plurality of X-ray images. Is performed. Note that the pixel value correction circuit 25f may execute correction on the plurality of second X-ray images during the capturing of the plurality of X-ray images, and may perform the correction on the plurality of second X-ray images after the capturing of the plurality of X-ray images. The correction may be performed on the image. When the correction is performed during the capturing of the plurality of X-ray images, the correction of the pixel values in the plurality of first X-ray images before the switching timing among the plurality of X-ray images is not performed. When the correction is performed after capturing the plurality of X-ray images, the correction of the pixel values in the plurality of first X-ray images before the switching timing may be performed, and the plurality of second X-ray images after the switching timing may be performed. May be performed, or the pixel values of both images may be corrected. The case where the correction is performed after capturing a plurality of X-ray images will be described later. In other words, the correction processing can be executed in real time or after imaging. The pixel value to be corrected may be one or both of before and after the switching of the tube voltage. However, when performing the correction processing in real time, the pixel value to be corrected can be applied only after the tube voltage is switched. In the first embodiment, a case will be described in which correction processing is performed after switching of the tube voltage. Further, the pixel value correction circuit 25f may determine a parameter value used for correction based on a pixel value in the region of interest.

Here, the pixel value correction circuit 25f determines the pixel value L _Before of the first X-ray image immediately before the switching timing T_sw of the plurality of first X-ray images, and immediately after the switching timing T_sw of the plurality of second X-ray images. The parameter value C _After used for the correction may be determined based on the pixel value L _After of the second X-ray image. Note that the pixel value correction circuit 25f may determine a parameter value used for correction based on at least one of the plurality of first X-ray images and at least one of the plurality of second X-ray images. Alternatively, the pixel value correction circuit 25f may determine a parameter value used for correction based on two or more of the plurality of first X-ray images and two or more of the plurality of second X-ray images. Here, two or more of the plurality of first X-ray images may include the first X-ray image immediately before the switching timing T_sw of the plurality of first X-ray images, and may include the first X-ray image of the plurality of second X-ray images. The two or more may include the second X-ray image immediately after the switching timing T_sw among the plurality of second X-ray images. In these cases, L _Before may be, for example, an average pixel value in the region of interest in one or more frames immediately before the switching timing of the tube voltage. Similarly, L _After may be, for example, an average pixel value in the region of interest in one or more frames immediately after the switching timing of the tube voltage. C _After is a parameter value used for correcting the pixel values of the plurality of second X-ray images after the switching timing of the tube voltage, and may be determined as shown in the following equation, for example.

C _After = L _Before -L _After
The pixel value correction circuit 25f corrects the pixel values in the plurality of second X-ray images after the switching timing T_sw based on the determined parameter value. For example, the pixel value correction circuit 25f may correct the pixel value by adding the parameter value C _After to the pixel values in the plurality of second X-ray images after the switching timing T_sw. In this example, the negative parameter value C _After is added. However, the present invention is not limited to this. When C _After is obtained as L _After -L _Before , the positive parameter value C _After is subtracted. (However, L _Before <L _After ).

  The color image creation circuit 25g creates a time density curve for each pixel based on the pixel value corrected by the pixel value correction circuit 25f, calculates a blood flow information parameter based on the time density curve, and responds to the blood flow information parameter. A color image is created by assigning the colors to each pixel. The blood flow information parameters include TTP (Time To Peak), PH (Peak Height), TTA (Time To Arrival), WIDTH, MTT (Mean Transit Time), AUC (Area Under Curve), and the like. In the time density curve, the horizontal axis represents time, and the vertical axis represents contrast agent concentration, and is a curve representing a temporal change in contrast agent concentration (pixel value). Here, TTP indicates a time until the contrast agent concentration reaches a peak. PH indicates the peak value of the contrast agent concentration. AUC indicates a time integrated value of the contrast agent concentration from the first time phase to the last time phase. AUC corresponds to the area of the region surrounded by the time density curve and the horizontal axis (time axis). TTA is a phase (time) when the contrast agent concentration first exceeds the threshold value TH in the time-density curve, and indicates the arrival time of the contrast agent. As the threshold value TH, for example, any value within the range of 30 to 60% of the peak value can be used. WIDTH is a period (time width) in which the contrast agent concentration exceeds the threshold value TH, and may be called a half width when the threshold value TH is 50% of the peak value. MTT indicates the average transit time of the contrast agent. The color image creation circuit 25g creates a time-density curve for each pixel based on the pixel values before and after the correction, and calculates a blood flow information parameter based on the time-density curve. A color image may be created by assigning a color corresponding to the blood flow information parameter to each pixel. Specifically, for example, the color image creation circuit 25g uses a table in which the value of the blood flow information parameter is associated with the color information for each blood flow information parameter in advance, and the value of the blood flow information parameter is By associating the information with the information, a color image (parametric image) representing the value of the blood flow information parameter for each pixel in color is created. Such a color image, for example, when the value of the peak arrival time (TTP) of each pixel becomes longer as t1, t2, t3, t4, t5 from the upstream side to the downstream side of the blood vessel in the DSA image, the TTP The pixels are created by coloring each pixel according to the value, such as red (t1), yellow (t2), yellow-green (t3), light blue (t4), and blue (t5). The display data including the created color image is displayed on the display 24. Here, as the table, for example, a table for TTP, a table for PH, a table for TTA, a table for WIDTH, a table for MTT, a table for AUC, and the like are prepared in advance. Accordingly, as a color image, for example, an image in which the TTP value is color-coded for each pixel, an image in which the PH value is color-coded for each pixel, an image in which the TTA value is color-coded for each pixel, An image in which the WIDTH value is color-coded, an image in which the MTT value is color-coded for each pixel, and the like can be appropriately created. As such a color image creation circuit 25g, for example, a technique called parametric imaging (PI) can be used. The PI calculates the value of the blood flow information parameter such as the arrival time and the average transit time of the contrast agent from the time density curve for each pixel at the time of angiography, and converts the value of the blood flow information parameter into an image using a color scale or a gray scale. This is a technology for displaying in the form of an image. The color scale defines the color of a color image (eg, a gradation that continuously changes from red to blue, through yellow, green, and light blue) for each value of the blood flow information parameter. The gray scale defines, for each value of the blood flow information parameter, the gradation of a black-and-white image (for example, a gradation that continuously changes from black to white via gray with different shades). In this specification, the PI is described by taking a case where an image is formed by a color scale as an example.

  As shown in FIG. 6, the X-ray diagnostic apparatus 1 configured as described above has a system control function 271 and an image data processing function equivalent to individual hardware circuits such as a system control unit 22 and an image data processing unit 25. The function 272 may be realized by the processing circuit 27. The processing circuit 27 reads and executes a program in the memory 26 to realize a system control function 271 corresponding to the system control unit 22 and an image data processing function 272 corresponding to the image data processing unit 25. The image data processing function 272 includes an image calculation function 272a, an area setting function 272c, a switching timing acquisition function 272d, and a display data generation function 272e. The display data generation function 272e includes a pixel value correction function 272f and a color image creation function 272g. The image calculation function 272a, the area setting function 272c, the switching timing acquisition function 272d, the display data generation function 272e, the pixel value correction function 272f, and the color image creation function 272g respectively include the image calculation circuit 25a, the area setting circuit 25c, and the switching timing acquisition. It corresponds to the circuit 25d, the display data generation circuit 25e, the pixel value correction circuit 25f, and the color image creation circuit 25g. As this type of program, for example, information processing for causing a computer to realize a system control function 271, an image calculation function 272a, an area setting function 272c, a switching timing acquisition function 272d, a pixel value correction function 272f, and a color image creation function 272g. The program is ready for use. Alternatively, a control program for causing a computer to realize the system control function 271 and a computer for realizing an image calculation function 272a, an area setting function 272c, a switching timing acquisition function 272d, a pixel value correction function 272f, and a color image creation function 272g. Of medical image processing programs can be used. Note that the medical image processing program may be divided into several medical image processing programs. For example, a first medical image processing program for causing a computer to implement the image calculation function 272a, a second medical image processing program for causing a computer to implement the area setting function 272c, a switching timing acquisition function 272d, and pixel value correction A third medical image processing program for causing the computer to realize the function 272f, a fourth medical image processing program for causing the computer to realize the color image creation function 272g, and the like may be used. Further, the respective medical image processing programs may be appropriately combined. For example, the third medical image processing program may appropriately include at least one of the second and fourth medical image processing programs. The memory 26 stores information stored in the position data memory 21 and the image data memory 25b, and further stores a program. The memory 26, the input interface 23, the display 24, and the processing circuit 27 are connected to each other via a bus, and are provided in the console device 20. The memory 26, the input interface 23, the display 24, the area setting function 272c in the processing circuit 27, the switching timing acquisition function 272d, the display data generation function 272e, the pixel value correction function 272f, and the color image creation function 272g are provided by the medical image processing apparatus 200. Is composed. Note that the medical image processing apparatus 200 may be provided as a separate apparatus from the X-ray diagnostic apparatus 1 as described later.

  The memory 26 includes a memory body for recording electrical information such as a ROM (Read Only Memory), a RAM (Random Access Memory), a HDD (Hardware Disk Drive), and an image memory, and a memory controller and a memory interface attached to the memory body. Peripheral circuits. The memory 26 stores, for example, a program to be executed by the processing circuit 27, an X-ray image generated by the processing circuit 27, data used for processing by the processing circuit 27, data in the middle of processing, data after processing, and the like. Is done. The data used for the processing of the processing circuit 27 may include anatomical information regarding the imaging target site of the X-ray image. The memory 26 may store a 3D image and a 3D roadmap image.

  The input interface 23 and the display 24 have the same configuration as described above.

  The processing circuit 27 is a processor that reads out and executes a program stored in the memory 26 to realize a system control function 271 and an image data processing function 272 corresponding to the program. Here, the term “processor” refers to, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable device). It means a circuit such as a logic device (Simple Programmable Logic Device: SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). May be configured to directly incorporate the program into the circuit of the processor instead of storing the program.In this case, the processor realizes the function by reading and executing the program incorporated in the circuit. Single in In the processing circuit 27, a system control function 271, an image data processing function 272 (image calculation function 272a, area setting function 272c, switching timing acquisition function 272d, display data generation function 272e (pixel value correction function 272f and color image creation function 272g) However, the present invention is not limited to this, but a plurality of independent processors may be combined to form a processing circuit, and each processor may execute a program to realize each function. The same applies to the following embodiments and their modifications.

  In the following description, the configuration shown in FIG. 1 among the configurations shown in FIGS. 1 and 6 will be described as a representative example. The system control unit 22 and the image data processing unit 25 described as representative examples execute the same operations as the system control function 271 and the image data processing function 272 shown in FIG. Therefore, the description of such a representative example can be applied to the description of the operation of the processing circuit 27 shown in FIG. 6 by appropriately replacing the component names and reference symbols. This is the same in the following embodiments and modifications.

  Next, the operation of the X-ray diagnostic apparatus configured as described above will be described with reference to the flowchart of FIG. In the following description, among a plurality of X-ray images obtained by imaging, an X-ray image obtained before the switching timing of the tube voltage is also referred to as a first X-ray image and obtained after the switching timing of the tube voltage. The X-ray image is also called a second X-ray image.

  First, after confirming information on the subject P (patient name, imaging target site, etc.), the position of the bed 7 on which the subject P is mounted, and the angle and position of the C arm 9 such as the geometrical position. The placement is adjusted. Information on the geometric arrangement of the bed 7 and the C-arm 9 is stored in the position data memory 21. Further, an appropriate irradiation condition (tube voltage, tube current, irradiation rate, etc.) is input to the subject P via the input interface 23 by an operator such as a doctor or a technician. When capturing a mask image for each irradiation condition before the injection of the contrast agent, one of the irradiation conditions to be switched and used is input.

  Next, under the control of the system control unit 22, the subject P placed on the bed 7 is irradiated with X-rays from the X-ray tube 3a via the X-ray controller 11 and the high-voltage generator 13.

  Next, an X-ray image is generated and displayed based on the X-ray transmitted through the subject P. That is, the X-ray detector 5 detects the X-ray transmitted through the subject P and converts it into an electric signal. This conversion may be a direct conversion for converting X-rays into an electric signal or an indirect conversion for converting X-rays into an electric signal via light. The electrical signals collected by the X-ray detector 5 are output to the image data processing unit 25 after undergoing a predetermined conversion process. The image calculation circuit 25a of the image data processing unit 25 generates an X-ray image based on the output of the X-ray detector 5, and sends the X-ray image to the display data generation circuit 25e and the image data memory 25b. The display data generation circuit 25e generates display data including the X-ray image, and displays the display data on the display 24. The image data memory 25b stores the X-ray image as a mask image. Similarly, another irradiation condition is input, and a mask image corresponding to the other irradiation condition is captured. As a result, a mask image of the imaging target site before the injection of the contrast agent is captured for each irradiation condition to be switched and used. For example, a mask image including a high tube voltage in the irradiation condition and a mask image including a low tube voltage in the irradiation condition are captured. Each mask image is stored in the image data memory 25b. After capturing the mask image, irradiation conditions including a high tube voltage are input, a contrast agent is injected into the subject P, and a contrast image (X-ray image for each injection time) is captured.

  Next, in steps ST1 and ST2, the image calculation circuit 25a subtracts the contrast images of the second and subsequent frames after the injection of the contrast agent from the mask image of the first frame before the injection of the contrast agent, and determines the inflow blood vessel of the contrast agent. A first X-ray image (DSA image) to be represented is generated. The generated first X-ray image is input to the area setting circuit 25c, the display data generation circuit 25e, and the image data memory 25b. Hereinafter, unless otherwise specified, the X-ray image generated by the image calculation circuit 25a is a DSA image, is displayed on the display 24 via the display data generation circuit 25e, and is stored in the image data memory 25b. Note that the first X-ray image, which is a frame along a time series, is displayed as a moving image. Further, instead of the first X-ray image, a color image (parametric image) created from the first X-ray image by the color image creation circuit 25g may be displayed on the display 24.

  After step ST2, in step ST3, the switching timing acquisition circuit 25d determines whether or not the switching signal indicating the switching timing of the tube voltage has been output from the system control unit 22 to the X-ray controller 11 to determine whether or not the switching voltage has been output. It is determined whether or not it is the switching timing. If the result of the determination is that it is not the switching timing of the tube voltage, the processing of steps ST1 and ST2 is repeated and executed. If the result of determination in step ST3 is that the tube voltage is to be switched, the process proceeds to step ST4.

  In step ST4, the X-ray controller 11 controls the high voltage generator 13 so as to switch the current high tube voltage to the low tube voltage in accordance with the switching signal from the system control unit 22. Thereby, the tube voltage of the X-ray tube 3a is switched.

  After step ST4, in step ST5, the X-ray diagnostic apparatus 1 causes the X-ray tube 3a to generate X-rays at the switched tube voltage, and irradiates the subject with the X-rays. The X-ray detector 5 detects an X-ray that has passed through the subject and outputs an electric signal. The image calculation circuit 25a generates a second X-ray image based on the output of the X-ray detector.

  After step ST5, in step ST6, the region setting circuit 25c sets the region of interest in the first X-ray image immediately before the switching timing of the tube voltage or the second X-ray image immediately after the switching timing. As the operation of setting the region of interest, any of the methods (r1) to (r4) described above may be used. Here, the case where the method (r3) is used will be described as an example. For example, as illustrated in FIG. 2, the region setting circuit 25c determines whether or not the region setting circuit 25c has the second X-ray image 30 based on the anatomical information about the imaging target site of the second X-ray image 30 immediately after the switching timing. Is designated. Thereafter, the region setting circuit 25c sets, as the region of interest, a region 32 of the designated region 31 where the pixel value exceeds the threshold.

  After step ST6, in step ST7, the pixel value correction circuit 25f acquires a pixel value in the region of interest of the second X-ray image immediately after the switching timing of the tube voltage. Similarly, the pixel value correction circuit 25f acquires a pixel value in the region of interest of the first X-ray image immediately before the switching timing of the tube voltage.

After step ST7, in step ST8, the pixel value correction circuit 25f averages the pixel values acquired from the region of interest of the second X-ray image in step ST7 to obtain an average pixel value L _After . Similarly, the pixel value correction circuit 25f averages the pixel values acquired from the region of interest of the first X-ray image in step ST7, and obtains an average pixel value L _Before . Thereby, the pixel value correction circuit 25f determines the parameter value C _After (= L _Before -L _After ) used for correcting the pixel values of the plurality of second X-ray images after the switching timing of the tube voltage.

After step ST8, in steps ST9 to ST10, the pixel value correction circuit 25f executes correction of the pixel values in the plurality of second X-ray images after the switching timing based on the determined parameter value. For example, the pixel value correction circuit 25f executes the correction of the pixel value by adding the parameter value C _After to the pixel values in the plurality of second X-ray images after the switching timing. Thus, a corrected second X-ray image is obtained. The corrected second X-ray image is input to the image data memory 25b. Hereinafter, unless otherwise specified, the X-ray image corrected by the pixel value correction circuit 25f is a DSA image, which is displayed on the display 24 via the display data generation circuit 25e and stored in the image data memory 25b. . Note that the second X-ray image, which is a frame along a time series, is displayed as a moving image. Instead of the second X-ray image, a color image (parametric image) created from the second X-ray image by the color image creation circuit 25g may be displayed on the display 24.

  After step ST10, in step ST11, the image calculation circuit 25a determines whether or not to end imaging according to whether or not a signal indicating the end of imaging has been received from the system control unit 22. If the result of determination is that imaging has not ended, processing transfers to step ST12. If the result of determination in step ST11 is that imaging has ended, the processing ends.

  After step ST11, in step ST12, in the image calculation circuit 25a, the X-ray diagnostic apparatus 1 causes the X-ray tube 3a to generate X-rays and irradiate the subject with the X-rays. The X-ray detector 5 detects an X-ray that has passed through the subject and outputs an electric signal. The image calculation circuit 25a generates a second X-ray image based on the output of the X-ray detector. Thereafter, the process proceeds to step ST9. Hereinafter, the processing of steps ST9 to ST12 is repeatedly executed until it is determined in step ST11 that the imaging ends.

  As described above, according to the first embodiment, information on the switching timing of the tube voltage in a plurality of X-ray images that are taken in time series with the switching of the tube voltage is acquired. In addition, among the plurality of first X-ray images before the switching timing in the plurality of X-ray images and the plurality of second X-ray images after the switching timing, the correction of the pixel values in the plurality of second X-ray images is performed. I do.

  As described above, by performing the correction of the pixel values in the plurality of second X-ray images after the switching timing, it is possible to prevent a sharp change in the contrast of the image before and after the switching of the tube voltage and to make the image easy to see. it can. Therefore, it is possible to secure the contrast of the X-ray image and prevent a rapid change in the pixel value.

  Subsequently, the effect of the first embodiment will be supplementarily described by using a related technique called polyphase DSA as a comparative example. The multi-phase DSA is known as a technique for suppressing exposure while securing the contrast of the entire moving image. In the multi-phase DSA, imaging is performed at a high tube voltage at the start of imaging, and the tube voltage is switched to a low tube voltage when the contrast agent reaches the peripheral blood vessel. In the case of multi-phase DSA, it is necessary to prepare a mask image for each tube voltage.

  Such a multi-phase DSA usually has no problem, but according to the study of the present inventors, there is room for improvement in that an image becomes difficult to see due to a sharp change in contrast before and after switching of the tube voltage.

  On the other hand, the effect of the above-described first embodiment is superior to such a polyphase DSA in that a rapid change in the contrast of an image is prevented and the image is easily viewed.

  Further, according to the first embodiment, the pixel value of the first X-ray image immediately before the switching timing of the plurality of first X-ray images and the second X-ray image immediately after the switching timing of the plurality of second X-ray images are changed. A parameter value used for correction is determined based on the pixel value of the line image. Supplementally, parameters used for correction are determined from changes in pixel values (blood vessel contrast) before and after switching of the tube voltage, using the inter-frame continuity of the contrast agent concentration. As described above, the number of X-ray images used to determine the parameter values used for correction is two, which is just before and immediately after the switching of the tube voltage, and is therefore smaller than when three or more X-ray images are used. The parameter value can be determined by the calculation load.

  Further, according to the first embodiment, a region in which the pixel value in any one of the plurality of X-ray images is higher than the threshold is set as a region of interest, and based on the pixel value in the region of interest, Determine the parameter value. Therefore, before and after the switching of the tube voltage, a sharp change in the contrast of the region of interest in the image can be prevented, and the region of interest can be easily seen.

  Further, according to the first embodiment, the correction is performed on the plurality of second X-ray images during the imaging of the plurality of X-ray images. Thereby, a sharp change in the contrast of the image before and after the switching of the tube voltage during the inspection can be prevented, and the image can be easily viewed.

  According to the first embodiment, a time-density curve is created for each pixel based on the corrected pixel value, and a blood flow information parameter based on the time-density curve is calculated. A color image is created by assigning the colors to each pixel. Therefore, even if the pixel value (blood vessel contrast) changes due to the switching of the tube voltage, a sharp change in the time density curve can be prevented by correcting the pixel value, and the peak (TTP, PH) and area of the time density curve can be prevented. Blood flow information parameters such as (AUC) can be calculated correctly.

  Supplementally, the first time density curve at each pixel of an image taken at a high tube voltage and the second time density curve at each pixel of an image taken at a low tube voltage are similar to each other when the density is on a normal scale. When the density is on a logarithmic scale, there is a relationship in which the shapes are parallel to each other. For example, when the density on the vertical axis is a normal scale, a second time density curve is obtained by expanding the first time density curve similarly. When the concentration on the vertical axis is a logarithmic scale, a second time concentration curve is obtained by translating the first time concentration curve upward. In any case, if the pixel value is not corrected by switching the tube voltage, a third time density curve having a shape connecting the first time density curve and the second time density curve is obtained at the switching timing. Can be Such a third time-density curve does not represent a correct time-density curve in which the contrast agent concentration changes continuously, and discontinuity occurs in the contrast agent concentration before and after the switching timing. Specifically, in the third time density curve, the pixel value immediately after the switching timing sharply rises and exceeds the peak value before the switching timing. Therefore, the third time concentration curve has a problem that blood flow information parameters such as peak height (PH), peak arrival time (TTP), and area (AUC) cannot be calculated correctly. On the other hand, according to the first embodiment, even if the pixel value (blood vessel contrast) changes due to the switching of the tube voltage, a correct time-density curve can be created by correcting the pixel value. , The correct blood flow information parameter can be calculated. The blood vessel contrast is an image level difference in a difference image between a contrast region and a non-contrast region, and is also called a blood vessel density or a blood vessel contrast density.

[First Modification of First Embodiment]
Subsequently, a first modification of the first embodiment will be described.

  In the first modification of the first embodiment, instead of the correction shown in FIG. 4, as shown in FIG. 8, by extrapolating the pixel values of a plurality of first X-ray images immediately before the switching timing, This is a configuration for determining a parameter value used for correction.

For example, the pixel value correction circuit 25f includes a pixel value of a plurality of first X-ray images immediately before the switching timing T_sw of the plurality of first X-ray images, and a pixel value L _After of the second X-ray image immediately after the switching timing T_sw. , A parameter value C _After used for correction is determined.

Specifically, the pixel value correction circuit 25f extrapolates an approximate curve Cv that approximately connects the pixel values of the plurality of first X-ray images immediately before the switching timing T_sw of the plurality of first X-ray images, and performs switching timing. The pixel value L _Predic of the first X-ray image of one to several frames immediately after _{T_sw} is predicted. Thereafter, the pixel value correction circuit 25f calculates the parameter value C _After used for correction based on the predicted pixel value L _Predic of the first X-ray image and the pixel value L _After of the second X-ray image immediately after the switching timing T_sw. To determine. Note that the pixel values L _Predic and L _After may be average pixel values in the region of interest in one frame as described above. C _After is a parameter value used for correcting the pixel values of the plurality of second X-ray images after the switching timing of the tube voltage, and may be determined as shown in the following equation, for example.

C _After = L _After -L _Predic
Other configurations are the same as those of the first embodiment.

  According to the above configuration, as shown in FIG. 9, steps ST1 to ST3 are executed in the same manner as in the first embodiment. However, if the result of determination in step ST3 is that the tube voltage is to be switched, the process proceeds to step ST6A.

  In step ST6A, the region setting circuit 25c sets a region of interest in the first X-ray image immediately before the switching timing of the tube voltage.

  After step ST6A, in step ST7A, the pixel value correction circuit 25f acquires the pixel values in the regions of interest of the plurality of first X-ray images immediately before the switching timing of the tube voltage, and obtains the pixel values for each region of interest of each first X-ray image. Then, the obtained pixel values are averaged to obtain an average pixel value.

After step ST7A, in step ST8A, the pixel value correction circuit 25f extrapolates the approximate curve Cv that approximately connects each of the average pixel values, and calculates the pixel value L _Predic of the first X-ray image immediately after the switching timing T_sw. Predict.

  Thereafter, the X-ray controller 11 controls the high voltage generator 13 according to the switching signal from the system control unit 22 so as to switch the current high tube voltage to the low tube voltage. Thereby, the tube voltage of the X-ray tube 3a is switched.

  In the X-ray diagnostic apparatus 1, the X-ray tube 3a generates X-rays at the switched tube voltage, and irradiates the subject with the X-rays. The X-ray detector 5 detects an X-ray that has passed through the subject and outputs an electric signal. The image calculation circuit 25a generates a second X-ray image based on the output of the X-ray detector.

The pixel value correction circuit 25f averages the pixel values acquired from the region of interest of the generated second X-ray image to obtain an average pixel value L _After . Accordingly, the pixel value correction circuit 25f determines the parameter value C _After (= L _After −L _Predic ) used for correcting the pixel values of the plurality of second X-ray images after the switching timing of the tube voltage.

  After step ST8A, the processes after step ST9 are executed as described above.

  As described above, according to the first modification of the first embodiment, the pixel values of the plurality of first X-ray images immediately before the switching timing among the plurality of first X-ray images and the second X-ray image immediately after the switching timing are changed. A parameter value used for correction is determined based on the pixel value of the line image. Thereby, even when extrapolating the pixel values of the plurality of first X-ray images immediately before the switching timing, similar to the first embodiment, it is possible to prevent a sharp change in the image contrast before and after the switching of the tube voltage. The image can be easily viewed.

[Second Modification of First Embodiment]
Subsequently, a second modification of the first embodiment will be described.

The second modification of the first embodiment has a configuration in which the way of displaying pixel values is changed as shown in FIG. 10 instead of correcting the pixel values shown in FIG. As a display method, for example, a method of changing the window width WW can be used. Here, the window width WW indicates a distribution range of pixel values of the X-ray image when the pixel values of the X-ray image are displayed in gray scale. The gray scale is the gradation of a display image that displays a DA image or a DSA image (eg, a gradation that changes continuously from black to white via gray with different shades) for each pixel value of the DA image or the DSA image. ). Similarly, in the example shown in FIG. 10, gradation that continuously changes between black and white is used as the gradation of the display image. Supplementally, from the viewpoint of eliminating the difficulty of viewing before and after the switching of the tube voltage, instead of correcting the pixel value of the X-ray image, the window width WW for converting the pixel value of the X-ray image into the pixel value of the display image is changed. Has been corrected. Specifically, for example, a window related to a gray scale is set so that the gray density indicating the pixel value L _Before immediately before the switching timing T_sw is the same as the gray density indicating the pixel value L _After immediately after the T_sw. The width WW is switched. The “gray scale” may be called “display gradation” or “display image gradation”.

  Accordingly, as shown in FIG. 11, the display data generation circuit 25e includes an image generation circuit 25i (image generation unit) and a window width change circuit instead of the above-described pixel value correction circuit 25f and color image generation circuit 25g. 25h (window width changing unit).

  The image creation circuit 25i creates a plurality of display images by converting the pixel values of the plurality of X-ray images for each pixel in accordance with the grayscale window width. The “display image” may be called a “black and white image” or a “shade image”.

  The window width changing circuit 25h changes the window width for creating a plurality of second display images after the switching timing among the plurality of display images.

  Other configurations are the same as those of the first embodiment.

  In the second modification of the first embodiment, as shown in FIG. 12, the pixel value correction function 272f and the color image creation function 272g described above are omitted, and are equivalent to the image creation circuit 25i and the window width change circuit 25h. The image forming function 272i and the window width changing function 272h of the processing circuit 27 may be realized by the processing circuit 27. In this case, the processing circuit 27 reads out and executes a program in the memory 26 to realize an image creation function 272i corresponding to the image creation circuit 25i and a window width change function 272h corresponding to the window width change circuit 25h. . Other configurations are the same as those of the first embodiment.

  In the following description, the configuration shown in FIG. 11 among the configurations shown in FIGS. 11 and 12 will be described as a representative example. The image creation circuit 25i and the window width change circuit 25h given as representative examples execute the same operations as the image creation function 272i and the window width change function 272h shown in FIG. Therefore, the description of such a representative example can be applied to the description of the operation of the processing circuit 27 shown in FIG. 12 by appropriately replacing the component names and reference symbols. This is the same in the following embodiments and modifications.

  According to the above configuration, as shown in FIG. 13, steps ST1 to ST7 are executed in the same manner as in the first embodiment. However, in step ST2, the first display image created by converting the pixel values of the first X-ray image by the image creation circuit 25i for each pixel according to the window width related to the gray scale is displayed on the display 24. In other words, the first display image representing the first X-ray image is displayed corresponding to the window width WW.

After step ST7, in step ST8B, the window width changing circuit 25h changes the window width for creating a plurality of second display images after the switching timing among the plurality of display images. For example, the window width changing circuit 25h averages the pixel values acquired from the region of interest of the second X-ray image in step ST7, and obtains an average pixel value L _After . Similarly, the window width changing circuit 25h averages the pixel values acquired from the region of interest of the first X-ray image in step ST7 to obtain an average pixel value L _Before . As a result, the window width changing circuit 25h changes the window width WW for creating a plurality of second display images after the tube voltage switching timing T_sw. For example, the window width changing circuit 25h is as before, the parameter value C _{the After} - determines (= L _After L _Before), to change the window width WW only the parameter values C _{the After.} Specifically, when the upper limit of the pixel value in the window width WW before the switching timing T_sw of the tube voltage is L1 and the lower limit is L2, the upper limit of the pixel value in the window width WW after the switching timing T_sw of the tube voltage is L1. The window width WW is changed such that −C _After is set and the lower limit of the pixel value is set to L2-C _After .

  After step ST8B, in step ST10B, the display 24 displays the second display image representing the second X-ray image corresponding to the changed window width WW. More specifically, the image creation circuit 25i creates a second display image from the second X-ray image using the changed window width WW. This second display image is displayed on the display 24.

  After step ST10B, the processes after step ST11 are executed as described above. However, the return destination of step ST12 is step ST10B.

  As described above, according to the second modification of the first embodiment, a plurality of display images are created by converting pixel values of a plurality of X-ray images for each pixel according to a window width related to a gray scale. I do. A window width for creating a plurality of second display images after the switching timing among the plurality of display images is changed.

  As described above, even if the pixel value is converted in accordance with the window width for each pixel to create a display image and the window width is changed after the switching timing, the configuration is changed to the same as in the first embodiment. In addition, a sharp change in the contrast of the image before and after the switching of the tube voltage can be prevented, and the image can be easily viewed.

<Second embodiment>
Next, a second embodiment will be described.
The second embodiment is different from the first embodiment in which the X-ray diagnostic apparatus 1 performs correction, and as shown in FIG. 14, a medical image processing apparatus capable of communicating with the X-ray diagnostic apparatus 1 via a network. 40 is configured to execute the correction. Accordingly, it is possible to correct even the first X-ray image before the switching timing of the tube voltage. Specifically, the second embodiment can correct a plurality of first X-ray images before the tube voltage switching timing, a plurality of second X-ray images after the tube voltage switching timing, or both X-ray images. And

  Here, the configuration of the X-ray diagnostic apparatus 1 is the same as that of the first embodiment. However, in the X-ray diagnostic apparatus 1, the configuration for executing the above-described correction (the switching timing acquisition circuit 25d and the pixel value correction circuit 25f) may be omitted.

  The medical image processing apparatus 40 includes an input interface 43, a display 44, a memory 46, a processing circuit 47, and a network interface 48 connected to each other via a bus. Note that the medical image processing device 40 corresponds to the medical image processing device 200 described above. Therefore, the medical image processing apparatus 40 can be provided as a part of the X-ray diagnostic apparatus 1. When the medical image processing apparatus 40 is provided as a part of the X-ray diagnostic apparatus 1, the description of the medical image processing apparatus 40 may be replaced with the description of the medical image processing apparatus 200 in the X-ray diagnostic apparatus 1. This is the same in the following embodiments and modifications.

  The input interface 43 inputs various information, sets various conditions, inputs various command signals, and the like. The input interface 23 includes, for example, a trackball for performing input and setting, a switch button, a mouse, a keyboard, a touchpad for performing an input operation by touching an operation surface, and an integrated display screen and touchpad. This is realized by a touch panel display or the like. The input interface 43 is connected to the processing circuit 47, converts an input operation received from the operator into an electric signal, and outputs the electric signal to the processing circuit 47. Note that, in the present specification, the input interface 43 is not limited to one having physical operation components such as a mouse and a keyboard. For example, an example of the input interface 43 includes an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the device and outputs the electric signal to the processing circuit 47. .

  The display 44 includes a display main body for displaying medical images and the like, an internal circuit for supplying a display signal to the display main body, and peripheral circuits such as connectors and cables connecting the display main body and the internal circuit. The internal circuit performs D / A conversion and TV format conversion on the display data supplied from the processing circuit 47 and displays the data on the display body.

  The memory 46 includes a memory main body for recording electrical information such as a ROM, a RAM, an HDD, and an image memory, and peripheral circuits such as a memory controller and a memory interface attached to the memory main body. The memory 46 stores, for example, a program to be executed by the processing circuit 47, data used for processing by the processing circuit 47, data in the middle of processing, data after processing, and the like. The data used for the processing of the processing circuit 47 is mainly an X-ray image, and may include anatomical information regarding the imaging target site of the X-ray image. The memory 46 may store a 3D image and a 3D roadmap image.

  The processing circuit 47 is a processor that reads out and executes the program stored in the memory 46, thereby realizing an area setting function 472c, a switching timing acquisition function 472d, and a display data generation function 472e corresponding to the program. The display data generation function 472e includes a pixel value correction function 472f and a color image creation function 472g. As this type of program, for example, a medical image processing program for causing a computer (medical image processing apparatus 40) to realize a switching timing acquisition function 472d and a pixel value correction function 472f can be used. The medical image processing program may further cause the computer to appropriately implement an area setting function 472c, a color image creation function 472g, and the like. The area setting function 472c, the switching timing acquisition function 472d, the display data generation function 472e, the pixel value correction function 472f, and the color image creation function 472g include the above-described area setting function 272c, switching timing acquisition function 272d, and display data generation function 272e. , And a function similar to the pixel value correction function 272f and the color image creation function 272g. However, the switching timing acquisition function 472d and the pixel value correction function 472f perform slightly different operations with respect to the operation after the X-ray image is captured, as compared with the first embodiment that operates during the X-ray image capture.

  For example, the switching timing acquisition function 472d (timing acquisition unit) acquires information related to the switching timing of the tube voltage in a plurality of X-ray images that are taken in time series with the switching of the tube voltage. Specifically, for example, the switching timing obtaining function 472d obtains information on the switching timing of the tube voltage from the supplementary information of the X-ray image in the memory 46. As the information on the switching timing of the tube voltage, for example, time information indicating the switching timing of the tube voltage, a frame number, and the like can be used. Alternatively, the switching timing obtaining function 472d may detect a change in contrast from a plurality of X-ray images in the memory 46, and obtain information on the switching timing of the tube voltage from the detection result.

  The display data generation function 472 e generates display data based on the X-ray image in the memory 46 and sends the display data to the display 44. Here, the display data generation function 472e includes a pixel value correction function 472f (pixel value correction unit) and a color image generation function 472g (color image generation unit). Note that the pixel value correction function 472f and / or the color image creation function 472g are not essential and may be omitted. When at least the pixel value correction function 472f is omitted, an image creation function and a window width changing function described later may be used.

  The pixel value correction function 472f executes correction of a pixel value in at least one of the plurality of first X-ray images before the switching timing in the plurality of X-ray images and the plurality of second X-ray images after the switching timing. I do. Supplementally, when switching the tube voltage, a pixel value at any one of the tube voltages is used as a reference or a target pixel value is used as a reference. This is the same even when the tube voltage is switched a plurality of times. Here, a case where the tube voltage is switched once will be described as a representative example. For example, as illustrated in FIGS. 4 and 5, the pixel values in the plurality of second X-ray images after the switching timing T_sw acquired by the switching timing acquisition function 472d are executed. Further, for example, as shown in FIGS. 15 and 16, correction of pixel values in a plurality of first X-ray images before the switching timing T_sw acquired by the switching timing acquisition function 472d is executed. Alternatively, for example, as illustrated in FIG. 17, the correction of the pixel value is performed for both the plurality of first X-ray images before the switching timing T_sw and the plurality of second X-ray images after the switching timing T_sw. Note that the pixel value correction function 472f executes correction of a pixel value after capturing a plurality of X-ray images. Further, the pixel value correction function 472f may determine a parameter value used for correction based on a pixel value in the region of interest.

Here, when correcting the plurality of second X-ray images after the switching timing T_sw, the pixel value correction function 472f may determine the parameter value C _After to be used for the correction as described above. When correcting a plurality of first X-ray images before the switching timing T_sw, the pixel value correction function 472f may determine a parameter value C _Before used for correction as described below. That is, as described above, the pixel value L _Before of the first X-ray image immediately before the switching timing T_sw of the plurality of first X-ray images and the second X-ray immediately after the switching timing T_sw of the plurality of second X-ray images The image pixel value L _After is obtained. Note that the pixel value correction function 472f may determine a parameter value used for correction based on at least one of the plurality of first X-ray images and at least one of the plurality of second X-ray images. In this case, L _Before may be, for example, an average pixel value in the region of interest in one frame immediately before the switching timing of the tube voltage. Similarly, L _After may be, for example, an average pixel value in the region of interest in one frame immediately after the switching timing of the tube voltage. At this time, C _Before may be determined as shown in the following equation, for example.

C _Before = L _After -L _Before
Further, in the case where the correction of both the plurality of first X-ray images before the switching timing T_sw and the plurality of second X-ray images after the switching timing T_sw is performed, the parameter value C used for the correction is set as follows. _Before and C _After may be determined. That is, as described above, the pixel value L _Before of the first X-ray image immediately before the switching timing T_sw of the plurality of first X-ray images and the second X-ray immediately after the switching timing T_sw of the plurality of second X-ray images The image pixel value L _After is obtained. Further, a target pixel value L _Target between both pixel values is obtained. L _Target may be calculated, for example, as shown in the following equation.

L _Target = (L _Before + L _After ) / 2
At this time, C _Before may be determined, for example, as described below.

C _Before = L _Target -L _Before
C _After = L _Target -L _After
In this example, the parameter value C _After having a negative value is calculated. However, the present invention is not limited to this, and the parameter value C _After having a positive value may be calculated by setting C _After = L _After −L _Target (however, , L _Target <L _After ).

The pixel value correction function 472f is configured to determine, based on the determined parameter value, at least one of the plurality of first X-ray images before the switching timing in the plurality of X-ray images and the plurality of second X-ray images after the switching timing. One of the pixel values is corrected. For example, when correcting a plurality of second X-ray images after the switching timing T_sw, the parameter value C _After is added (or subtracted) to the pixel values in the plurality of second X-ray images in the same manner as described above. Pixel value correction may be performed. Further, for example, when correcting a plurality of first X-ray images before the switching timing T_sw, the correction of the pixel values may be performed by adding the parameter value C _Before to the pixel values in the plurality of first X-ray images. Good. Further, for example, when both the plurality of first X-ray images before the switching timing T_sw and the plurality of second X-ray images after the switching timing T_sw are to be corrected, the respective corrections may be similarly performed. . That is, by adding the parameter value C _Before to the pixel values in the plurality of first X-ray images and adding (or subtracting) the parameter value C _After to the pixel values in the plurality of second X-ray images, Correction may be performed.

  The color image creation function 472g has the same functions as the above-described color image creation circuit 25g and color image creation function 272g. That is, the color image creation function 472g creates a time density curve for each pixel based on the pixel value corrected by the pixel value correction function 472f, calculates a blood flow information parameter based on the time density curve, A color image (parametric image) is created by assigning a color corresponding to the color to each pixel. The blood flow information parameters are as described above. Similarly, the color image creation function 472g creates a time-density curve for each pixel based on the pixel values before and after the correction, and calculates a blood flow information parameter based on the time-density curve. Then, a color image (parametric image) may be created by assigning a color corresponding to the blood flow information parameter to each pixel.

  The network interface 48 is a circuit for connecting the medical image processing device 40 to the network Nw and communicating with another device such as the X-ray diagnostic device 1. As the network interface 48, for example, a network interface card (NIC) can be used. In the following description, the description that the network interface 48 is interposed in communication with another device is omitted.

  Next, the operation of the X-ray diagnostic apparatus and the medical image processing apparatus configured as described above will be described with reference to the flowchart of FIG.

  Now, the X-ray diagnostic apparatus 1 captures a plurality of first X-ray images, which are frames in a time series, under a high tube voltage at the start of imaging, and switches the high tube voltage to a low tube voltage. It is assumed that a plurality of second X-ray images, which are frames along the sequence, have been captured. The X-ray diagnostic apparatus 1 transmits a plurality of X-ray images including the plurality of first X-ray images and the plurality of second X-ray images to the medical image processing device 40. It is assumed that the medical image processing apparatus 40 has received a plurality of X-ray images from the medical image processing apparatus 40 and stored the plurality of X-ray images in the memory 46.

  In step ST21, the processing circuit 47 of the medical image processing apparatus 40 acquires information on the switching timing of the tube voltage in a plurality of X-ray images that are imaged in chronological order with the switching of the tube voltage. For example, the switching timing obtaining function 472d obtains information about the switching timing of the tube voltage from the supplementary information of the X-ray image in the memory 46.

  After step ST21, in step ST22, the processing circuit 47 extracts the first X-ray image immediately before the tube voltage switching timing T_sw and the first X-ray image immediately after the tube voltage switching timing T_sw from the plurality of X-ray images in the memory 46. Acquire a 2X-ray image.

  After step ST22, in step ST23, the processing circuit 47 sets a region of interest in the obtained first X-ray image or second X-ray image. As the operation of setting the region of interest, any of the methods (r1) to (r4) described above may be used.

  After step ST23, in step ST24, the processing circuit 47 determines the pixel value in the region of interest of the first X-ray image immediately before the switching timing T_sw of the tube voltage and the region of interest of the second X-ray image immediately after the switching timing T_sw. Get the pixel values in

After step ST24, in step ST25, the processing circuit 47 averages the pixel values acquired from the region of interest of the second X-ray image in step ST24 to obtain an average pixel value L _After . Similarly, the processing circuit 47 averages the pixel values acquired from the region of interest of the first X-ray image in step ST24 to obtain an average pixel value L _Before . When correcting the X-ray images before and after the switching, the processing circuit 47 further calculates a value between both the pixel values L _Before and L _After as a target pixel value L _Target . Thereafter, the processing circuit 47 determines a parameter value used for correcting the pixel values of the plurality of X-ray images based on both the pixel values L _Before and L _After .

Here, a case where the X-ray images before and after the switching are corrected will be described as an example. That is, the processing circuit 47 determines the parameter values C _Before and C _After used for correction as described below.

C _Before = L _Target -L _Before
C _After = L _Target -L _After
After step ST25, in step ST26, the processing circuit 47 acquires an X-ray image before correction for each of one or more sheets.

After step ST26, in step ST27, the processing circuit 47 corrects the pixel value of the X-ray image acquired in step ST26. Here, when correcting the pixel value of the first X-ray image before the switching timing T_sw, the correction of the pixel value is performed by adding the parameter value C _Before to the pixel value of the first X-ray image. . When correcting the pixel value of the second X-ray image after the switching timing T_sw, the correction of the pixel value is performed by adding the parameter value C _After to the pixel value of the second X-ray image.

  After step ST27, in step ST28, the processing circuit 47 displays the corrected X-ray image on the display 44. Note that the processing circuit 47 may display a color image (parametric image) created from the corrected X-ray image on the display 44 instead of the corrected X-ray image.

  After step ST28, in step ST29, the processing circuit 47 determines whether or not to end the correction based on the presence or absence of the uncorrected X-ray image among the X-ray images to be corrected. If the result of determination is that correction has not been completed, the operation moves to step ST26. Hereinafter, the processing of steps ST26 to ST29 is repeatedly executed until it is determined in step ST29 that the correction has been completed. If the result of determination in step ST29 is that correction has been completed, the process ends.

  As described above, according to the second embodiment, information on the switching timing of the tube voltage in a plurality of X-ray images taken in chronological order with the switching of the tube voltage is acquired. The pixel values of at least one of the plurality of first X-ray images before the switching timing in the plurality of X-ray images and the plurality of second X-ray images after the switching timing are executed. Therefore, a sharp change in the contrast of the image before and after the switching of the tube voltage can be prevented, and the image can be easily viewed.

  According to the second embodiment, a parameter value used for correction is determined based on at least one of the plurality of first X-ray images and at least one of the plurality of second X-ray images. For this reason, in the minimum case, the parameter value can be determined using two X-ray images, so that the parameter value can be determined with a smaller calculation load as compared with the case where three or more X-ray images are used.

  According to the second embodiment, the pixel value of the first X-ray image immediately before the switching timing of the plurality of first X-ray images and the second X-ray image immediately after the switching timing of the plurality of second X-ray images are changed. A parameter value used for correction is determined based on the pixel value of the line image. For this reason, compared with the case where an X-ray image which is not immediately before and immediately after the switching timing is used, a change in the pixel value after correction before and after the switching timing can be further reduced.

  Further, according to the second embodiment, a region where the pixel value in any one of the plurality of X-ray images is higher than the threshold value is set as a region of interest, and based on the pixel value in the region of interest, Determine the parameter value. Therefore, before and after the switching of the tube voltage, a sharp change in the contrast of the region of interest in the image can be prevented, and the region of interest can be easily seen.

  According to the second embodiment, after capturing a plurality of X-ray images, correction is performed on at least one of the plurality of first X-ray images and the plurality of second X-ray images. This prevents a sharp change in the contrast of the image before and after the switching of the tube voltage after the inspection, and makes it easier to see the image.

  According to the second embodiment, when a color image that is a parametric image is created, even if the pixel value changes at the time of switching the tube voltage, the pixel value is corrected, as in the first embodiment, as in the first embodiment. It is possible to correctly calculate a blood flow information parameter based on the time density curve.

[First Modification of Second Embodiment]
Subsequently, a first modification of the second embodiment will be described.

  In the first modification of the second embodiment, instead of the correction shown in FIG. 15, as shown in FIGS. 19 and 20, a curve Cv1 indicating a temporal change of a pixel value in a region of interest (ROI) is obtained. , And a curve Cv2 indicating a temporal change of a pixel value in a peripheral portion of the region of interest. Supplementally, the two curves Cv1 and Cv2 are compared, and at least one pixel value of the first X-ray image and the second X-ray image is set such that the curve Cv1 in the region of interest matches or is similar to the curve Cv2 in the peripheral portion. This is a configuration for correcting. The following description will be mainly given of an example in which the pixel values of a plurality of first X-ray images before the switching timing T_sw are corrected.

  Here, the region setting function 472c has a function of setting a peripheral portion of the region of interest in addition to the function of setting the region of interest described above. The function of setting the peripheral portion may be realized, for example, by following a blood vessel in the region of interest to the upstream side, or may be realized by an operation of the operator.

The pixel value correction function 472f performs correction based on two or more of the plurality of first X-ray images before the switching timing T_sw and two or more of the second X-ray images after the switching timing T_sw. Determine the parameter values to be used. Here, two or more of the plurality of first X-ray images may include the first X-ray image immediately before the switching timing T_sw of the plurality of first X-ray images. Similarly, two or more of the plurality of second X-ray images may include the second X-ray image immediately after the switching timing T_sw of the plurality of second X-ray images. For example, the pixel value correction function 472f creates a curve Cv1 connecting the pixel values of the plurality of first X-ray images in the region of interest and the pixel values of the plurality of second X-ray images. Further, a curve Cv2 connecting the pixel values of the plurality of first X-ray images before the switching timing T_sw is created. For example, the difference between the time t1 of the peak value of the pixel value of the region of interest before T_sw and the time t2 of the peak value of the pixel value of the peripheral portion before T_sw is Δt (= t1−t2), and the curve Cv1, The period of Cv2 is defined as Tcv. At this time, the curve Cv1 may be created by connecting the pixel values of the region of interest within the period Tcv ending at the time when the difference Δt has elapsed from the switching timing t_sw. Further, for example, the curve Cv2 may be created by connecting pixel values of peripheral portions in a period Tcv ending at the switching timing t_sw. However, the period Tcv of the curve Cv1 is not limited to the same period as the period Tcv of the curve Cv2, and may be different. Here, the pixel value correction function 472f corrects the pixel value in the region of interest so that the shape of the curve Cv1 for the region of interest matches or resembles the shape of the curve Cv2 for the periphery. In this example, switching the immediately preceding pixel value L _Cv2 timing t_sw switching in the curve Cv2 superimposed portions to curve Cv1 after timing t_sw, pixel values on the curve Cv1 corresponding to the pixel value L _Cv2 L _Cv1 , The parameter value C _Before used for correction is determined.

C _Before = L _Cv2 -L _Cv1
When correcting the pixel values of the plurality of first X-ray images in the region of interest before the switching timing T_sw, the pixel value correction function 472f adds the parameter value C _Before to the pixel values of the first X-ray image. Accordingly, the pixel value is corrected.

  Other configurations are the same as in the second embodiment.

  According to the above configuration, as shown in FIG. 18, steps ST21 to ST22 are executed in the same manner as in the second embodiment.

  After step ST22, in step ST23, the processing circuit 47 sets a region of interest and a peripheral portion of the region of interest in the obtained first X-ray image or second X-ray image.

  After step ST23, in step ST24, the processing circuit 47 determines the pixel values of the plurality of first X-ray images in the region of interest before the tube voltage switching timing T_sw and the plurality of first X-rays in the peripheral portion before the T_sw. Obtain the pixel value of the image. Further, the processing circuit 47 acquires the pixel value in the region of interest of the second X-ray image immediately after the switching timing T_sw.

  After step ST24, in step ST25, the processing circuit 47 averages the pixel values acquired from the region of interest of the second X-ray image in step ST24 to obtain an average pixel value.

Further, the processing circuit 47 averages the pixel values obtained from the regions of interest of the plurality of first X-ray images in step ST24 for each first X-ray image, and obtains the pixel values obtained from the regions of interest of the plurality of second X-ray images in the first region. Averaging is performed for each 2X-ray image, and a curve Cv1 is obtained by connecting these average pixel values. Similarly, the processing circuit 47 averages the pixel values obtained from the peripheral portions of the plurality of first X-ray images in step ST24 for each first X-ray image, and connects the average pixel values of the peripheral portions for each first X-ray image. Obtains a curve Cv2. The processing circuit 47 compares the two curves Cv1 and Cv2, and a pixel value L _Cv2 immediately before the switching timing T_sw in the curve Cv2 obtained by partially overlapping the curve Cv1 after the switching timing T_sw, and the pixel value L _Cv2 And the pixel value L _Cv1 on the curve Cv1 corresponding to Thereafter, the processing circuit 47 determines a parameter value C _Before used for correction based on the pixel values L _Cv2 and L _Cv1 .

C _Before = L _Cv2 -L _Cv1
After step ST25, the processes after step ST26 are similarly performed. However, in this example, in step ST27, the processing circuit 47 performs the correction of the pixel value by adding the parameter value C _Before to the pixel value in the region of interest of the first X-ray image acquired in step ST26. .

  As described above, according to the first modification of the second embodiment, correction is performed based on two or more of the multiple first X-ray images and two or more of the multiple second X-ray images. Determine the parameter value. Note that two or more of the plurality of first X-ray images may include the first X-ray image immediately before the switching timing among the plurality of first X-ray images. Further, two or more of the plurality of second X-ray images may include the second X-ray image immediately after the switching timing among the plurality of second X-ray images. Supplementally, a parameter used for correction is determined from changes in pixel values (blood vessel contrast) of several frames before and after the switching of the tube voltage using the inter-frame continuity of the contrast agent concentration. For example, a curve Cv1 connecting the pixel values of the plurality of first X-ray images and the pixel values of the plurality of second X-ray images in the region of interest is created. Further, a curve Cv2 connecting the pixel values of the plurality of first X-ray images before the switching timing T_sw is created. A parameter value used for correcting at least one pixel value of the first X-ray image and the second X-ray image is determined so that the shape of the curve Cv1 for the region of interest matches or is similar to the shape of the curve Cv2 for the peripheral portion. . Even in this case, the same effect as in the second embodiment can be obtained.

[Second Modification of Second Embodiment]
Subsequently, a second modification of the second embodiment will be described.

  As shown in FIG. 8, FIG. 21, or FIG. 22, the second modification of the second embodiment extrapolates the pixel values of a plurality of first X-ray images immediately before the switching timing to obtain a parameter used for correction. This is a configuration for determining a value. Note that the correction shown in FIG. 8 can be executed in the same manner as described above. Therefore, the following description mainly describes the correction shown in FIG. 21 or FIG.

The pixel value correction function 472f converts the pixel values of the plurality of first X-ray images immediately before the switching timing T_sw of the plurality of first X-ray images and the pixel value L _After of the second X-ray image immediately after the switching timing T_sw. Based on this, the parameter value C _Before used for the correction may be determined.

Specifically, the pixel value correction function 472f extrapolates an approximate curve Cv that approximately connects the pixel values of the plurality of first X-ray images immediately before the switching timing T_sw of the plurality of first X-ray images, and performs the switching timing. The pixel value L _Predic of the first X-ray image immediately after _{T_sw} is predicted. Thereafter, the pixel value correction function 472f determines the parameter value C _Before used for correction based on the predicted pixel value L _Predic of the first X-ray image and the pixel value L _After of the second X-ray image immediately after the switching timing T_sw. To determine. Note that the pixel value L _After may be an average pixel value in the region of interest in one or more frames, as described above. C _Before is a parameter value used for correcting the pixel values of the plurality of first X-ray images before the switching timing of the tube voltage, and may be determined as shown in the following equation, as described above.

C _Before = L _After -L _Predic
Further, when performing both the correction of the plurality of first X-ray images before the switching timing T_sw and the correction of the plurality of second X-ray images after the T_sw, as described above, the target pixel value L _Target , The parameter values C _Before and C _After used for the correction may be determined.

L _Target = (L _Predic + L _After ) / 2
At this time, C _Before may be determined, for example, as described below.

C _Before = L _Target -L _Predic
C _After = L _Target -L _After
In this example, the parameter value C _After having a negative value is calculated. However, the invention is not limited _thereto, and the parameter value C _After having a positive value may be calculated as described above.

  Other configurations are the same as in the second embodiment.

  According to the above configuration, as shown in FIG. 18, steps ST21 to ST23 are executed in the same manner as in the second embodiment.

  After step S23, in step ST24, the processing circuit 47 acquires the pixel values in the region of interest of the plurality of first X-ray images immediately before the tube voltage switching timing T_sw. Further, the processing circuit 47 acquires a pixel value in the region of interest of the second X-ray image immediately after the T_sw.

After step ST24, in step ST25, the processing circuit 47 averages the pixel values acquired from the regions of interest of the plurality of first X-ray images in step ST24 for each region of interest to obtain an average pixel value. Further, the processing circuit 47 extrapolates an approximate curve Cv that approximately connects each of the obtained average pixel values, and predicts the pixel value L _Predic of the first X-ray image immediately after the switching timing T_sw. Further, the processing circuit 47 averages the pixel values acquired from the region of interest of the second X-ray image in step ST24 to obtain an average pixel value L _After . Accordingly, the processing circuit 47 determines a parameter value C _Before (= L _After −L _Predic ) used for correcting the pixel values of the plurality of first X-ray images before the switching timing of the tube voltage. Alternatively, when performing both the correction of the plurality of first X-ray images before the switching timing T_sw and the correction of the plurality of second X-ray images after the T_sw, similarly to the above, the target pixel value L _Target , The parameter values C _Before and C _After used for the correction may be determined.

  After step ST25, the processes after step ST26 are executed as described above.

  As described above, according to the second modified example of the second embodiment, the pixel values of the plurality of first X-ray images immediately before the switching timing among the plurality of first X-ray images and the second X-ray image immediately after the switching timing are changed. A parameter value used for correction is determined based on the pixel value of the line image. As a result, even when extrapolating the pixel values of the plurality of first X-ray images immediately before the switching timing, similar to the second embodiment, a sharp change in the image contrast is prevented before and after the switching of the tube voltage. The image can be easily viewed.

[Third Modification of Second Embodiment]
Subsequently, a third modification of the second embodiment will be described.

A third modification of the second embodiment has a configuration in which the window width WW is changed, for example, as shown in FIG. 10, instead of the correction of the pixel values shown in FIG. Although not shown, the window width WW may be changed in place of the correction of the pixel values shown in FIGS. In any case, the third modification of the second embodiment is a method in which the gray density indicating the pixel value L _Before immediately before the switching timing T_sw and the gray density indicating the pixel value L _After immediately after the T_sw are changed. The window width WW relating to the gray scale is switched so as to be the same.

  Accordingly, as shown in FIG. 23, the display data generation function 472e of the processing circuit 47 includes an image creation function 472i and a window width change function 472h instead of the pixel value correction function 472f and the color image creation function 472g described above. (Window width changing unit).

  The color image creation function 472g creates a plurality of display images by converting the pixel values of the plurality of X-ray images for each pixel in accordance with the grayscale window width.

  The window width changing function 472h is a window width for creating at least one of a plurality of first display images before the switching timing and a plurality of second display images after the switching timing among the plurality of display images. To change.

  Other configurations are the same as those of the second embodiment.

  According to the above configuration, as shown in FIG. 24, steps ST21 to ST24 are executed in the same manner as in the second embodiment.

After step ST24, in step ST25C, the window width changing function 472h determines a window width WW for creating a plurality of second display images after the switching timing among the plurality of display images. For example, the window width changing function 472h averages the pixel values acquired from the region of interest of the second X-ray image in step ST24, and obtains an average pixel value L _After . Similarly, the window width changing circuit 25h averages the pixel values acquired from the region of interest of the first X-ray image in step ST24 to obtain an average pixel value L _Before . Thus, the window width changing function 472h determines the window width WW for creating a plurality of second display images after the tube voltage switching timing T_sw. For example, the window width changing function 472h determines the parameter value C _After (= L _Before −L _After ) as described above, and determines to move the window width WW by the parameter value C _After . Specifically, when the upper limit of the pixel value in the window width WW before the switching timing T_sw of the tube voltage is L1 and the lower limit is L2, the upper limit of the pixel value in the window width WW after the switching timing T_sw of the tube voltage is L1. The window width WW is determined so that −C _After is set and the lower limit of the pixel value is set to L2-C _After . Not limited to this, the window width changing function 472h determines the parameter value C _Before (= L _After −L _Before ) and creates a plurality of first display images before the switching timing T_sw of the tube voltage. The window width WW may be determined to be moved by C _Before . Alternatively, to calculate a pixel value L _Target target, the pixel value L _Target, L _{the Before,} on the basis of the L _{the After,} and the window width WW of the previous the t_sw, may determine the window width WW after the t_sw .

  After step ST25C, in step ST26C, the processing circuit 47 acquires one or more X-ray images.

  After step ST26C, in step ST27C-1, the processing circuit 47 determines whether to change the window width WW corresponding to the X-ray image acquired in step ST26C based on the information on the switching timing acquired in step ST21. judge. As a result of the determination, if it is to be changed, in step ST27-2, the processing circuit 47 changes the current window width WW to the window width WW determined in step ST25C. On the other hand, when the result of determination in step ST27C-1 is negative, processing circuit 47 proceeds to step ST28C.

  In step ST28C, the processing circuit 47 creates a display image corresponding to the window width from the X-ray image acquired in step ST26C using the latest window width WW, and causes the display 24 to display the display image.

  After step ST28C, the processes after step ST29 are executed as described above. However, the return destination of step ST29 is step ST26C.

  As described above, according to the third modification of the second embodiment, information on the switching timing of the tube voltage in a plurality of X-ray images that are taken in time series with the switching of the tube voltage is acquired. A plurality of display images are created by converting the pixel values of the plurality of X-ray images for each pixel according to the window width related to gray scale. The window width for creating at least one of the plurality of first display images before the switching timing and the plurality of second display images after the switching timing among the plurality of display images is changed.

  As described above, even if the pixel value is converted for each pixel according to the window width to create a display image and the window width is changed before and after the switching timing, the configuration is changed to the same as in the second embodiment. A sharp change in the contrast of the image before and after the switching of the tube voltage can be prevented, and the image can be easily viewed.

<Third embodiment>
Next, a third embodiment will be described.
The third embodiment is a modification of the first embodiment. Unlike the first embodiment in which a parameter value used for correction is determined based on a pixel value of an X-ray image, an X-ray of a contrast agent is different from the first embodiment. This is a configuration for determining a parameter value used for correction based on the attenuation coefficient. Accordingly, the plurality of X-ray images need to be images obtained by imaging using a contrast agent injected into a blood vessel of a subject.

Here, the pixel value correction circuit 25f calculates the X-ray attenuation coefficient μ _Before of the contrast agent at the tube voltage before the switching timing T_sw and the X-ray attenuation coefficient μ _After of the contrast agent at the tube voltage after the switching timing T_sw. Based on the difference, a parameter value C _After used for correction is determined.

C _After = μ _Before -μ _After
The parameter value C _After is not limited to this equation, and may be determined from another equation.

Further, the pixel value correction circuit 25f uses the determined parameter value C _After to correct the pixel values of the plurality of second X-ray images after the switching timing.

  Supplementally, the X-ray attenuation coefficient μ of the contrast agent depends on the tube voltage kV.

μ = f (kV)
Therefore, the X-ray attenuation coefficient of the contrast agent is acquired in advance for each tube voltage, and the pixel value after the switching is corrected using the difference between the attenuation coefficients before and after the switching timing of the tube voltage as a correction coefficient.

  The X-ray attenuation coefficient can be obtained, for example, by the following method (a) or (b).

  (A) The X-ray attenuation coefficient μ at each tube voltage kV for each contrast agent is measured in advance.

(B) from the X-ray attenuation coefficient mu _i of each content component i of the contrast agent, to calculate the X-ray attenuation coefficient for each tube voltage kV contrast agent mu.

μ = g (μ _i )
μ _i = f _i (kV)
Other configurations are the same as those of the first embodiment.

According to the above configuration, as shown in FIG. 25, in step ST0, the pixel value correction circuit 25f receives the contrast agent used for the inspection and the plurality of tube voltages from the system control unit 22. The pixel value correction circuit 25f is based on the difference between the X-ray attenuation coefficient μ _Before of the contrast agent at the tube voltage before the switching timing T_sw and the X-ray attenuation coefficient μ _After of the contrast agent at the tube voltage after the T_sw. , A parameter value C _After used for correction is determined. Note that step ST0 is not limited to being performed before capturing the first X-ray image, and may be performed in parallel with capturing the first X-ray image.

  After step ST0, steps ST1 to ST5 are executed as described above.

After step ST5, in steps ST9D to ST10, the pixel value correction circuit 25f executes correction of the pixel values in the plurality of second X-ray images after the switching timing based on the parameter value C _After determined in step ST0. . Thus, a corrected second X-ray image is obtained. The corrected second X-ray image is displayed on the display 24 via the display data generation circuit 25e, and is stored in the image data memory 25b. Note that the second X-ray image, which is a frame along a time series, is displayed as a moving image. Further, instead of the second X-ray image, a color image created from the second X-ray image by the color image creation circuit 25g may be displayed on the display 24. Further, the pixel value to be corrected may be limited to the pixel value in the region of interest.

  Hereinafter, the processes after step ST11 are executed in the same manner as described above. That is, hereafter, the processing of steps ST9D to ST12 is repeatedly executed until it is determined in step ST11 that the imaging ends.

  As described above, according to the third embodiment, the plurality of X-ray images are images obtained by imaging using the contrast agent injected into the blood vessel of the subject. The pixel value correction unit is used for correction based on a difference between the X-ray attenuation coefficient of the contrast agent at the tube voltage before the switching timing and the X-ray attenuation coefficient of the contrast agent at the tube voltage after the switching timing. Determine the parameter value. Supplementally, the parameter value used for correction is determined from the difference between the X-ray attenuation coefficients before and after the switching of the tube voltage using the tube voltage dependence of the X-ray attenuation coefficient of the contrast agent.

  Therefore, in addition to the effect of the first embodiment, it is possible to determine a parameter value used for correction before capturing a plurality of X-ray images. That is, the parameter value used for the correction can be determined without using the pixel values of the plurality of X-ray images. Along with this, it is possible to omit the setting of the region of interest for obtaining the pixel value used for determining the parameter value.

[First Modification of Third Embodiment]
Next, a first modification of the third embodiment will be described.

  A first modified example of the third embodiment is different from the second embodiment in which the medical image processing apparatus 40 performs the correction, in which the parameter value is determined based on the X-ray attenuation coefficient of the contrast agent. Is applied. As described above, the plurality of X-ray images need to be images obtained by imaging using the contrast agent injected into the blood vessel of the subject.

Here, the pixel value correction function 472f of the processing circuit 47 corresponds to the pixel value correction circuit 25f in the third embodiment. That is, the pixel value correction function 472f calculates the difference between the X-ray attenuation coefficient μ _Before of the contrast agent at the tube voltage before the switching timing T_sw and the X-ray attenuation coefficient μ _After of the contrast agent at the tube voltage after the switching timing T_sw. Is used to determine a parameter value to be used for correction. The parameter value may be determined as shown in the following (i), (ii) or (iii) according to the X-ray image to be corrected.

(I) When correcting pixel values of a plurality of first X-ray images before the switching timing T_sw, a parameter value C _Before used for correction is determined, for example, as shown in the following equation.

C _Before = μ _After -μ _Before
(Ii) When correcting the pixel values of the plurality of second X-ray images after the switching timing T_sw, for example, the parameter value C _After used for the correction is determined as described above.

C _After = μ _Before -μ _After
(Iii) When the correction of the pixel values of the plurality of first X-ray images before the switching timing T_sw and the correction of the pixel values of the plurality of second X-ray images after the T_sw are executed, for example, the target is set. The X-ray attenuation coefficient μ _Target is determined. Thereafter, the parameter values C _Before and C _After used for the correction are determined.

C _Before = μ _Target -μ _Before
C _After = μ _Target -μ _After
Note that the parameter values C _Before and C _After are not limited to the above four equations, and may be determined from other equations. The method of acquiring the X-ray attenuation coefficient is as described above.

Similarly, the pixel value correction function 472f uses the determined parameter value C _After to correct the pixel values of the plurality of second X-ray images after the switching timing.

  Other configurations are the same as in the second embodiment.

  According to the above configuration, as shown in FIG. 26, step ST21 is executed in the same manner as described above.

After step ST21, in step ST25E, the processing circuit 47 reads, for example, the contrast agent used for the examination and the plurality of tube voltages from the incidental information of the X-ray image. The processing circuit 47 corrects based on the difference between the X-ray attenuation coefficient μ _Before of the contrast agent at the tube voltage before the switching timing T_sw and the X-ray attenuation coefficient μ _After of the contrast agent at the tube voltage after the T_sw. Determine the parameter values used for The parameter value may be any of the above (A) to (C), but here, the case of the above (A) will be described as an example. That is, the processing circuit 47, X-rays attenuation coefficient of the contrast agent mu _{the Before,} on the basis of the difference between the mu _{the After,} the parameter value C _Before = _{μ After} use in correction - determining the mu _{the Before.} Step ST25E may be executed before step ST21.

  After step ST25E, step ST26 is executed as described above.

After step ST26, in steps ST27E to ST28, the processing circuit 47 corrects the pixel values in the plurality of first X-ray images before the switching timing based on the parameter value C _Before determined in step ST25E. Thus, a corrected first X-ray image is obtained. The corrected first X-ray image is displayed on the display 44 and stored in the memory 46. Note that the first X-ray image, which is a frame along a time series, is displayed as a moving image. Instead of the first X-ray image, a color image (parametric image) created from the first X-ray image by the color image creation function 472g may be displayed on the display 44. Further, the pixel value to be corrected may be limited to the pixel value in the region of interest.

  Hereinafter, the processes after step ST29 are executed in the same manner as described above. That is, hereinafter, the processing of steps ST9D to ST12 is repeatedly executed until it is determined in step ST29 that the correction has been completed.

  As described above, according to the first modification of the third embodiment, the plurality of X-ray images are images obtained by imaging using a contrast agent injected into a blood vessel of a subject. The pixel value correction unit is used for correction based on a difference between the X-ray attenuation coefficient of the contrast agent at the tube voltage before the switching timing and the X-ray attenuation coefficient of the contrast agent at the tube voltage after the switching timing. Determine the parameter value. Therefore, in addition to the effects of the second embodiment, it is possible to determine a parameter value used for correction before capturing a plurality of X-ray images. That is, the parameter value used for the correction can be determined without using the pixel values of the plurality of X-ray images. Along with this, it is possible to omit the setting of the region of interest for obtaining the pixel value used for determining the parameter value.

  According to at least one embodiment described above, information on the switching timing of the tube voltage in a plurality of X-ray images that are taken in time series with the switching of the tube voltage is acquired. The pixel values of at least one of the plurality of first X-ray images before the switching timing in the plurality of X-ray images and the plurality of second X-ray images after the switching timing are executed. Therefore, a sharp change in the contrast of the image before and after the switching of the tube voltage can be prevented, and the image can be easily viewed.

  Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1 X-ray diagnostic apparatus 3 X-ray generator 3a X-ray tube 3b X-ray restrictor 5 X-ray detector 7 Couch 9 C arm 11 X-ray controller 13 High voltage generator 13a X-ray controller 13b High voltage generator 15 C Arm / bed mechanism control unit 20 Console device 21 Position data memory 22 System control unit 23, 43 Input interface 24, 44 Display 25 Image data processing unit 25a Image operation circuit 25b Image data memory 25c Area setting circuit 25d Switching timing acquisition circuit 25e Display Data generation circuit 25f Pixel value correction circuit 25g Color image creation circuit 25h Window width change circuit 25i Image creation circuit 26, 46 Memory 27, 47 Processing circuit 271 System control function 272 Image data processing function 272a Image calculation function 272c, 472c Area setting function 272d, 472d Switching timing acquisition function 272e, 472e Display data generation function 272f, 472f Pixel value correction function 272g, 472g Color image creation function 272h, 472h Window width change function 272i, 472i Image creation function 40 Medical image processing device 48 Network Interface Nw Network

Claims (19)

A timing acquisition unit that acquires information about the switching timing of the tube voltage in a plurality of X-ray images that are imaged in chronological order with the switching of the tube voltage;
Pixel value correction for performing a pixel value correction on at least one of a plurality of first X-ray images of the plurality of X-ray images before the switching timing and a plurality of second X-ray images after the switching timing. A medical image processing apparatus comprising:   The pixel value correction unit according to claim 1, wherein the parameter value used for the correction is determined based on at least one of the plurality of first X-ray images and at least one of the plurality of second X-ray images. Medical image processing apparatus.   The pixel value correction unit includes a pixel value of a first X-ray image of the plurality of first X-ray images immediately before the switching timing and a second X-ray image of the plurality of second X-ray images immediately after the switching timing. The medical image processing apparatus according to claim 2, wherein the parameter value is determined based on a pixel value of a line image.   The said pixel value correction part determines the parameter value used for the said correction | amendment based on two or more of the some 1st X-ray images and two or more of a some 2nd X-ray image. 3. The medical image processing apparatus according to 2. Two or more of the plurality of first X-ray images include a first X-ray image immediately before the switching timing of the plurality of first X-ray images,
The medical image processing apparatus according to claim 4, wherein two or more of the plurality of second X-ray images include a second X-ray image immediately after the switching timing among the plurality of second X-ray images. A region-of-interest setting unit that sets a region in which the pixel value in any one of the plurality of X-ray images is higher than a threshold value as a region of interest;
The medical image processing device according to claim 2, wherein the pixel value correction unit determines the parameter value based on a pixel value in the region of interest.   The medical image processing according to any one of claims 1 to 6, wherein the pixel value correction unit performs the correction on the plurality of second X-ray images while capturing the plurality of X-ray images. apparatus.   The medical image processing apparatus according to claim 1, wherein the pixel value correction unit performs the correction after capturing the plurality of X-ray images. The plurality of X-ray images are images obtained by imaging using a contrast agent injected into a blood vessel of a subject,
The pixel value correction unit, based on the difference between the X-ray attenuation coefficient of the contrast agent at the tube voltage before the switching timing and the X-ray attenuation coefficient of the contrast agent at the tube voltage after the switching timing, The medical image processing apparatus according to claim 1, wherein a parameter value used for the correction is determined.   A time density curve is created for each pixel based on the pixel value corrected by the pixel value correction unit, a blood flow information parameter based on the time density curve is calculated, and a color corresponding to the blood flow information parameter is calculated for each pixel. The medical image processing apparatus according to claim 1, further comprising a color image creation unit that creates a color image by assigning the color image to a color image. A timing acquisition unit that acquires information about the switching timing of the tube voltage in a plurality of X-ray images that are imaged in chronological order with the switching of the tube voltage;
An image creating unit that creates a plurality of display images by converting pixel values of the plurality of X-ray images for each pixel according to a window width related to gray scale;
A window for changing the window width for creating at least one of a plurality of first display images before the switching timing and a plurality of second display images after the switching timing among the plurality of display images. The medical image processing apparatus according to claim 1, further comprising: a width changing unit. A timing acquisition unit that acquires information about the switching timing of the tube voltage in a plurality of X-ray images that are imaged in chronological order with the switching of the tube voltage;
Pixel value correction for performing a pixel value correction on at least one of a plurality of first X-ray images of the plurality of X-ray images before the switching timing and a plurality of second X-ray images after the switching timing. An X-ray diagnostic apparatus comprising:   The pixel value correction unit includes a pixel value of a first X-ray image of the plurality of first X-ray images immediately before the switching timing and a second X-ray image of the plurality of second X-ray images immediately after the switching timing. The X-ray diagnostic apparatus according to claim 12, wherein a parameter value used for the correction is determined based on a pixel value of the line image.   The X-ray diagnostic apparatus according to claim 12, wherein the pixel value correction unit determines a parameter value used for the correction based on the plurality of first X-ray images and the plurality of second X-ray images. A region-of-interest setting unit that sets a region in which the pixel value in any one of the plurality of X-ray images is higher than a threshold value as a region of interest;
The X-ray diagnostic apparatus according to claim 13, wherein the pixel value correction unit determines the parameter value based on a pixel value in the region of interest.   The X-ray diagnosis according to any one of claims 12 to 15, wherein the pixel value correction unit performs the correction on the plurality of second X-ray images while capturing the plurality of X-ray images. apparatus.   The X-ray diagnostic apparatus according to any one of claims 12 to 15, wherein the pixel value correction unit performs the correction after capturing the plurality of X-ray images. The plurality of X-ray images are images obtained by imaging using a contrast agent injected into a blood vessel of a subject,
The pixel value correction unit, based on the difference between the X-ray attenuation coefficient of the contrast agent at the tube voltage before the switching timing and the X-ray attenuation coefficient of the contrast agent at the tube voltage after the switching timing, The X-ray diagnostic apparatus according to claim 12, wherein a parameter value used for the correction is determined. A timing acquisition function of acquiring information on the switching timing of the tube voltage in a plurality of X-ray images captured in time series with switching of the tube voltage;
Pixel value correction for executing pixel value correction in at least one of the plurality of first X-ray images before the switching timing and the plurality of second X-ray images after the switching timing among the plurality of X-ray images. function,
Medical image processing program for causing a computer to realize.