JP2017104329A - X-ray diagnostic apparatus and X-ray CT apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray diagnostic apparatus and an X-ray CT apparatus, each capable of easily identifying a defective pixel.SOLUTION: The X-ray diagnostic apparatus of the embodiment comprises an X-ray tube, an X-ray detector, an image generation part and an image processing part. The X-ray tube emits X-ray to a subject from a plurality of positions. The X-ray detector detects the emitted X-ray. The image generation part generates a plurality of projection data corresponding to the plurality of positions on the basis of the X-ray detected by the X-ray detector. The image processing part subjects the projection data to image processing, obtains noise-uniformized data acquired by subjecting each of the plurality of projection data to noise-uniformization processing, subjects image data based on the noise-uniformized data to threshold processing to extract a defective pixel.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an X-ray diagnostic apparatus and an X-ray CT apparatus.

  In the X-ray diagnostic apparatus, X-rays emitted from an X-ray tube are detected by an X-ray detector, and projection data is output. The projection data may have defective pixels due to, for example, malfunction of the elements of the X-ray detector. If this defective pixel is not appropriately processed, artifacts appear in the X-ray image. Artifacts appearing in the X-ray image interfere with interpretation, and therefore it is necessary to suppress the occurrence or correct the X-ray image.

  In the conventional X-ray diagnostic apparatus, in the pixel value of the projection data, a pixel whose pixel value is extremely different from the surrounding pixel value is identified as a defective pixel, and the pixel is obtained using the surrounding pixel value. It was replaced with a pixel value.

Japanese Patent No. 5526062

  The problem to be solved by the present invention is to provide an X-ray diagnostic apparatus and an X-ray CT apparatus that can easily identify defective pixels.

  In order to solve the above problems, an X-ray diagnostic apparatus according to the present embodiment includes an X-ray tube, an X-ray detector, an image generation unit, and an image processing unit. The X-ray tube irradiates the subject with X-rays from a plurality of positions. The X-ray detector detects the irradiated X-rays. The image generation unit generates a plurality of projection data corresponding to a plurality of positions based on the X-rays detected by the X-ray detector. The image processing unit performs image processing on the projection data, obtains noise uniformity data obtained by performing noise uniformity processing on each of the plurality of projection data, and performs threshold processing on the image data based on the noise uniformity data To extract defective pixels.

  An X-ray CT apparatus according to a modification of the present embodiment includes an X-ray tube, an X-ray detector, an image generation unit, and an image processing unit. The X-ray tube irradiates the subject with X-rays from a plurality of positions. The X-ray detector detects the irradiated X-rays. The data collection unit generates a plurality of projection data corresponding to a plurality of positions based on the X-rays detected by the X-ray detector. The image processing unit performs image processing on the projection data, obtains noise uniformity data obtained by performing noise uniformity processing on each of the plurality of projection data, and performs threshold processing on the image data based on the noise uniformity data To extract defective pixels.

The figure which shows the structure of the X-ray diagnostic apparatus based on embodiment. The figure which shows a mode that the X-ray tube which concerns on embodiment changes the position which irradiates an X-ray, and image | photographs a subject. The figure which shows the relationship between the input pixel value and output pixel value in the noise equalization function based on Embodiment. The figure which shows the projection data when the subject image | photographs by changing the position which the X-ray tube irradiates X-ray based on embodiment. The figure which shows the several difference image when the test subject is image | photographed from several different positions based on embodiment. The figure which shows the projection data before the correction function correct | amends a defective pixel, the projection data after the correction function correct | amends a defective pixel, and the simulation result based on embodiment. 6 is a flowchart showing a flow of extracting and correcting defective pixels included in projection data using a plurality of projection data obtained by irradiating a subject with X-rays at a plurality of different positions according to the embodiment. The figure which shows the structure of the X-ray CT apparatus based on the modification 2 of embodiment.

  Hereinafter, the X-ray diagnostic apparatus 1 and the X-ray CT apparatus 2 according to the embodiment will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given when necessary. In the description of the embodiment, an X-ray diagnostic apparatus will be described as a basis, and an X-ray CT apparatus will be referred to in a modification of the embodiment.

  FIG. 1 is a diagram showing a configuration of the X-ray diagnostic apparatus 1. The X-ray diagnostic apparatus 1 is, for example, a mammography apparatus that images a breast, an X-ray TV apparatus that immediately displays an X-ray image of a subject being imaged, or an X-ray angiography apparatus that observes a blood vessel region.

  Hereinafter, the X-ray diagnostic apparatus 1 will be specifically described by taking the configuration of a mammography apparatus as an example.

  The X-ray diagnostic apparatus 1 irradiates a subject with X-rays and detects X-rays transmitted through the subject with an X-ray detector. The X-ray diagnostic apparatus 1 includes an X-ray tube 7 that generates X-rays, a high-voltage generator 8 that supplies a high voltage necessary for the X-ray tube 7 to generate X-rays, and an X-ray that detects X-rays. A line detector 10. The X-ray tube 7 is supported by the X-ray tube support mechanism 4. The mounting table 9 is supported by the mounting table support mechanism 3.

  The X-ray diagnostic apparatus 1 also includes an input interface circuit 25 that accepts input from an operator, a storage circuit 26 that stores imaging conditions, captured X-ray images, and the like, a display 27 that displays X-ray images, and the like. And a network interface circuit 28 for exchanging information with an external device of the X-ray diagnostic apparatus 1.

  Further, the X-ray diagnostic apparatus 1 includes an X-ray control circuit 6 that controls high voltage generation by the high voltage generator 8, a drive control circuit 31 that controls the movement of the mounting table support mechanism 3 and the X-ray tube support mechanism 4, and And a processing circuit 40 that performs image generation and image processing. The X-ray control circuit 6 and the drive control circuit 31 control each control target based on imaging conditions given from the input interface circuit 25, the network interface circuit 28, and the like. The X-ray control circuit 6, the drive control circuit 31, the processing circuit 40, the image generation circuit 41, and the image processing circuit 42 are processors.

  “Processor” means, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device (Simple Programmable Logic) Device: SPLD), Complex Programmable Logic Device (CPLD), Field Programmable Gate Array (FPGA)) and other circuits. The processor realizes a function by reading and executing a program from a storage area or a storage circuit 26 incorporated in the circuit of the processor. Hereinafter, when the term “processor” is used in the description of the present embodiment and the modified examples, it is based on the same definition. Further, the circuit exemplified as the processor is not limited to being configured as a single circuit for each processor, and may be configured as a single processor by combining a plurality of independent circuits to realize the function. Shall.

  The X-ray detector 10 is, for example, an FPD (Flat Panel Detector) in which a large number of detection elements are two-dimensionally arranged. Each detection element of the X-ray detector 10 detects X-rays generated from the X-ray tube 7 and converts the detected X-rays into electric signals. The electric signal generated in each detection element is converted into digital data by an analog-digital converter (not shown). This digital data is sent to an image generation circuit 41 of the processing circuit 40 described later.

  The mounting table support mechanism 3 includes a support member for supporting the mounting table 9 on which the subject is mounted. The mounting table support mechanism 3 supports the mounting table 9 so as to be horizontal or inclined with respect to a horizontal plane.

  The X-ray tube support mechanism 4 is configured by a support member for supporting the X-ray tube 7 that emits X-rays. The X-ray tube support mechanism 4 is configured such that, for example, the X-ray tube support mechanism 4 can rotate around a rotation axis (not shown).

  The movement of the mounting table support mechanism 3 and the X-ray tube support mechanism 4 described above is controlled by the drive control circuit 31. The drive control circuit 31 has an X-ray tube support mechanism drive function 311 and a mounting table support mechanism drive function 312 as functions.

  The X-ray tube support mechanism drive function 311 of the drive control circuit 31 controls the movement of the X-ray tube support mechanism 4. For example, the X-ray tube support mechanism drive function 311 swings the X-ray tube support mechanism 4. At this time, the X-ray tube 7 supported by the X-ray tube support mechanism 4 moves along a circular orbit around the rotation axis. The position of the X-ray tube 7 with respect to the X-ray detector 10 is changed by the control by the X-ray tube support mechanism drive function 311. By changing the position of the X-ray tube 7 with respect to the X-ray detector 10, the position of the X-ray tube 7 with respect to the subject placed on the mounting table 9 changes. When the position of the X-ray with respect to the X-ray detector 10 is changed, the direction in which the X-ray enters the X-ray detector 10 changes. As a result, it is possible to irradiate the subject placed on the placement table 9 with X-rays from a plurality of different positions.

  The mounting table support mechanism drive function 312 of the drive control circuit 31 controls the movement of the mounting table support mechanism 3. For example, the mounting table support mechanism 3 moves up and down to change the height of the mounting table 9 or to tilt the mounting table 9.

  Information necessary for the X-ray tube support mechanism driving function 311 and the mounting table support mechanism driving function 312 to drive the X-ray tube support mechanism 4 and the mounting table support mechanism 3 includes, for example, the moving speed of the X-ray tube 7 and This is the position of the mounting table 9. These pieces of information are stored in advance in the storage circuit 26 and read out by an input operation by the operator via the input interface circuit 25. Alternatively, the input interface circuit 25 may directly receive input from the operator, and the received input information may be reflected in the X-ray tube support mechanism drive function 311 or the mounting table support mechanism drive function 312.

  The X-ray control circuit 6 controls the high voltage generator 8 to emit X-rays from the X-ray tube 7 at a predetermined timing. The X-ray control circuit 6 can execute X-ray irradiation by the X-ray tube 7 at a predetermined timing in conjunction with the drive control of the X-ray tube support mechanism 4 and the mounting table support mechanism 3 by the drive control circuit 31 described above. To control. For example, the X-ray control circuit 6 controls the number of X-ray irradiations per unit time. The number of projection data obtained by detecting the X-rays irradiated by the X-ray tube 7 by the X-ray detector 10 is determined by the moving speed of the X-ray tube 7 determined by the X-ray tube support mechanism drive function 311 and the X-ray control. It is determined by the number of X-ray irradiations per unit time determined by the circuit 6. The parameter used to determine the number of projection data that can be acquired is any parameter other than the combination of the moving speed of the X-ray tube 7 and the number of X-ray irradiations per unit time as described above. It's okay.

  As described above, one or both of the mounting table support mechanism 3 and the X-ray tube support mechanism 4 are driven, and the X-ray control circuit 6 emits X-rays from the X-ray tube 7 at a predetermined timing. Thus, the high voltage generator 8 is controlled. Thereby, the X-ray tube 7 can irradiate X-rays from a plurality of different positions with respect to the subject placed on the placing table 9. By imaging the subject from a plurality of different positions, it becomes possible to observe a region that cannot be observed in a single X-ray irradiation direction. It is also possible to create an X-ray image relating to an arbitrary cross section of the subject by performing image processing on a plurality of X-ray images obtained by imaging the subject from different positions. Such a photographing method in the mammography apparatus is called tomosynthesis.

  The processing circuit 40 includes an image generation circuit 41 and an image processing circuit 42.

  The image generation circuit 41 generates projection data based on the digital data output from the X-ray detector 10. The projection data is, for example, image data of an X-ray image in which each pixel has one pixel value. Each pixel value of the projection data reflects the X-ray transmittance of the imaging region of the subject. The image generation circuit 41 is an example of an image generation unit in the claims.

  2 and 4 are diagrams for explaining the relationship between the position at which the X-ray tube 7 irradiates the subject with X-rays and the projection data.

  FIG. 2 shows a state in which the X-ray tube 7 changes the position at three locations T1, T2, and T3 and images the subject. For the sake of explanation, the right direction is taken as the x axis, and the front side of the drawing is taken as the y axis. The asterisk marked inside the subject is a site of interest inside the subject. When X-rays are irradiated from the X-ray tube 7 to the region of interest at three locations T1, T2, and T3, the projection images corresponding to the region of interest are respectively X-ray detectors 10. Appear at each of the positions P1, P2, and P3.

  FIG. 4 shows an example of projection data obtained when the X-ray tube 7 changes the position at three positions T1, T2, and T3 shown in FIG. This projection data is image data having a total of 25 pixels in 5 rows and 5 columns. Corresponding to FIG. 2, the row direction is defined as the x-axis and the column direction is defined as the y-axis. The numbers attached to the projection data diagrams shown in a lattice form indicate the values of the coordinates of the x-axis and the y-axis. The projection image P1 of the region of interest obtained by irradiating X-rays with the X-ray tube 7 at the position T1 is located at coordinates (4, 3) as shown in FIG. The projection image P2 of the region of interest obtained by irradiating the X-ray with the X-ray tube 7 at the position T2 is located at the coordinates (3, 3) as shown in FIG. 4B. The projection image P3 of the region of interest obtained by irradiating the X-ray with the X-ray tube 7 at the position T3 is located at the coordinates (2, 3) as shown in FIG. Thus, when the position where the X-ray tube 7 irradiates the X-ray is changed, the coordinates corresponding to the projected image of the projected image of the site inside the subject change. Note that the projection data shown in FIG. 4 is merely an example, and an arbitrary configuration may be adopted for the number of pixels.

  The projection data generated by the image generation circuit 41 may include defect data different from data originally obtained by irradiating the subject with X-rays. Here, a pixel in which defective data appears as a pixel value is referred to as a defective pixel. The defective pixel is generated due to, for example, a malfunction of the detection element of the X-ray detector 10. For example, a minute calcified tissue generated in the breast may be erroneously recognized as a defective pixel. If it is mistakenly recognized as a defective pixel, for example, the pixel value of the pixel in the projection data obtained due to the calcified tissue is rewritten based on the surrounding pixel values, and the information of the calcified tissue is lost. It will be. As a result, it becomes impossible to distinguish a lesion tissue and defective pixels, which are clinically useful information.

  The projection image corresponding to the part existing inside the subject basically changes in position (coordinates) on the projection data when the position where the X-ray tube 7 emits X-rays changes. For example, when a calcified tissue having a high X-ray absorption rate is present inside the subject, the coordinates of the pixel of the projection image corresponding to the calcified tissue change with a change in the position where the X-ray tube 7 irradiates X-rays. Will change. On the other hand, the defective pixel appears at the same coordinates on the projection data regardless of the position where the X-ray tube 7 emits X-rays.

  When the projection data generated by the image generation circuit 41 includes defective pixels, the image processing circuit 42 has a function of correcting the defective pixels by distinguishing them from a lesion tissue or the like existing inside the subject. The image processing circuit 42 is an example of an image processing unit in the claims.

  The image processing circuit 42 has a noise equalization function 421, a filter function 422, a defective pixel extraction function 423, and a correction function 424 as functions.

  The noise equalization function 421 equalizes noise for each pixel included in the projection data generated by the image generation circuit 41. In the X-ray detector 10, the magnitude of noise varies depending on the detected dose. Since the noise included in the original projection data varies in size for each pixel value, the noise equalization function 421 makes the influence of the noise constant regardless of the pixel value so that the effect is improved in threshold processing described later. Perform noise leveling.

  The noise leveling function 421 performs conversion in which noise that changes depending on the pixel value becomes substantially the same noise at any pixel value. FIG. 3 is a diagram illustrating the relationship between the input pixel value and the output pixel value. It is assumed that the pixel value I1 has a fluctuation range a1 due to the influence of noise. It is assumed that the pixel value I2 has a fluctuation range a2 due to the influence of noise. This difference in the fluctuation range is the difference in noise magnitude. In FIG. 3, a2 is larger than a1. That is, the noise level of the pixel value I2 is larger than the pixel value I1.

  In FIG. 3, the noise leveling function 421 converts a pixel value I1 into a pixel value O1 and a pixel value I2 into a pixel value O2. In the pixel value O1, the fluctuation range due to the influence of noise is b1. In the pixel value O2, the fluctuation range due to the influence of noise is b2. b1 is equal to b2. That is, the fluctuation range of the pixel value that differs for each input pixel value due to noise is equal in the output pixel value. It should be noted that the fluctuation range of the pixel value for each output pixel value does not need to be completely coincident, and some error may be allowed.

  The conversion process performed on each pixel by the noise equalization function 421 can be realized by, for example, storing a lookup table that associates an input pixel value and an output pixel value in the storage circuit 26 and referring to it appropriately. . Alternatively, the noise leveling function 421 may be configured to sequentially calculate the input / output relationship of pixel values. Note that the noise leveling function 421 can be executed by changing the conversion process in the noise leveling process for each acquisition mode of the X-ray detector 10. Here, the collection mode is a mode determined by, for example, a combination of the number of pixels collected as one pixel, sensitivity setting, and the like. For example, the noise leveling function 421 performs the noise leveling process by determining the collection mode based on information such as fluoroscopy or photographing, field size, and image resolution setting.

  Image data that is generated by the noise leveling function 421 using projection data and in which the influence of noise is substantially equal in all pixel values is referred to as noise leveling data. The coordinate of the pixel which each of projection data and noise equalization data has corresponds.

  The filter function 422 removes pixels that can be defective pixel candidates included in the noise uniformization data by filtering. The filter function 422 uses, for example, a median filter in order to perform filter processing. The median filter performs a process of replacing the pixel value of the target pixel with the median value of the pixel value of the target pixel and the pixel group existing in the vicinity of the target pixel. For example, if the filter size is a median filter of 3 pixels × 3 pixels, the pixel value of the pixel of interest is replaced with the median value of the pixel values of a total of 9 pixels of the pixel of interest and 8 pixels adjacent to the pixel of interest. The filter function 422 is not limited to the median filter, and may be configured to execute other filter methods. For example, filter processing using morphological operations is also possible. Morphological operation is a dilation process that replaces the pixel value of the target pixel with the maximum value of the pixel group in the vicinity of the target pixel, and the minimum value of the pixel value of the pixel group in the vicinity of the target pixel. It consists of shrinking treatment to replace. Filter processing using a morphological operation can be realized by a combination of expansion processing and contraction processing. Further, for example, the filter function 422 may perform filter processing using a low-pass filter. The low-pass filter has a function of removing high-frequency components of the image. Since noise is included in the high-frequency component of the image, it is filtered by a low-pass filter. Image data that has been subjected to filter processing on pixels that can be defective pixel candidates by the filter function 422 will be referred to as filtered data. Note that the pixel coordinates of the noise uniformization data and the filtered data correspond to each other.

  The defective pixel extraction function 423 extracts defective pixels from the projection data. First, the defective pixel extraction function 423 creates a difference image between the noise uniformization data and the filtered data. This difference image is image data including pixels that can be defective pixel candidates removed by the filter function 422. Next, the defective pixel extraction function 423 compares the threshold value with the pixel value of each pixel of the difference image, and selects a pixel having a pixel value outside the range defined by the threshold value in the difference image as a defective pixel candidate. And This threshold value can be determined based on imaging conditions such as a tube voltage, a tube current, a product of tube current and imaging time, and a mAs value representing an X-ray dose. Further, the threshold value may be changed every time the photographing condition changes. For example, by setting only one threshold value, a pixel having a pixel value that exceeds or falls below the threshold value can be set as a defective pixel candidate. Further, for example, an upper limit threshold and a lower limit threshold are set, and a pixel having a pixel value exceeding the upper limit threshold and a pixel value lower than the lower limit threshold can be set as a defective pixel candidate. For example, the threshold value may be stored in the storage circuit 26 in advance, or may be set when the input interface circuit 25 receives an input from the operator. Further, for example, it is not necessary to set a threshold value for extracting a pixel having an extremely high or extremely low pixel value in the original projection data. The pixel value threshold is extracted from the difference image pixels that have a pixel value change between the noise uniformization data and the filtered data that exceeds the fluctuation of the pixel value that can occur during normal X-ray imaging. Set as much as possible.

  As described above, the X-ray diagnostic apparatus 1 can image a subject from a plurality of different positions. Here, it is assumed that N pieces of projection data have been acquired. The N pieces of projection data are image data obtained by imaging the subject from a plurality of different positions.

  The defective pixel extraction function 423 creates a difference image between the noise uniformization data and the filtered data for each of the N pieces of projection data, and selects a pixel as a defective pixel candidate. Then, when a pixel that is a candidate for a defective pixel appears at the same coordinate in a predetermined M or more differential images among N differential images, the pixel at that coordinate is extracted as a defective pixel. In order to specifically describe the procedure by which the defective pixel extraction function 423 extracts defective pixels, FIG. 5 shows a plurality of difference images obtained when a subject is imaged from a plurality of different positions. In FIG. 5, description will be made assuming that the number N of all the difference images is 3, and the number M of the predetermined difference images for determining whether to extract as a defective pixel is 3. Each difference image of (a), (b), and (c) of FIG. 5 is obtained by irradiating X-rays from the X-ray tube 7 at, for example, three locations T1, T2, and T3 shown in FIG. Image data based on projection data. In FIG. 5, the hatched pixels and the blacked out pixels are pixels selected as defective pixel candidates by the defective pixel extraction function 423. In FIG. 5A, the pixels at coordinates (2, 2), (2, 3), and (3, 3) are defective pixel candidates. In FIG. 5B, pixels with coordinates (2, 2) and (2, 3) are candidates for defective pixels. In FIG. 5C, the pixels at coordinates (2, 2), (3,4), (4, 2) are defective pixel candidates. In the three difference images shown in FIGS. 5A, 5B, and 5C, when the number of times of being listed as a defective pixel candidate for each coordinate is counted, the coordinate (2, 2) is twice and the coordinate (2, 3), 3 times for coordinates (3, 3), 1 time for coordinates (3, 4), and 1 time for coordinates (4, 2). Now, since the value of the number M of the predetermined difference images for determining whether or not to extract as a defective pixel is determined to be 3, a pixel that is a defective pixel candidate is extracted as a defective pixel with coordinates ( 2 and 3). The defective pixel extraction function 423 stores the coordinate information of the extracted defective pixels in an external device via the storage circuit 26 or the network interface circuit 28.

  Note that the values of N and M determined for explanation in FIG. 5 are merely examples, and arbitrary values may be set. The values of N and M may be stored in advance in an external device via the storage circuit 26 or the network interface circuit 28, or may be set directly by an operator via the input interface circuit 25. Good. Further, the value of M is not limited to a fixed value, and may be set to a value that changes according to the number N of projection data. For example, the value of M is set as a percentage with respect to N.

  The correction function 424 corrects the defective pixel with respect to the original projection data generated by the image generation circuit 41 based on the coordinate information of the defective pixel extracted by the defective pixel extraction function 423. The correction function 424 replaces the pixel value of the defective pixel in the projection data with the average value of the pixel values of the four pixels adjacent to the defective pixel in the vertical and horizontal directions. Thereby, the correction of the defective pixel is completed. Projection data on which defective pixels have been corrected will be referred to as correction data. The coordinates of the pixels included in the projection data and the correction data correspond to each other. Note that the method of correcting the defective pixel of the projection data by the correction function 424 is not limited to replacing with the average value of the pixel values of four pixels adjacent in the vertical and horizontal directions of the defective pixel. For example, the defective pixel may be corrected using a bicubic method.

  FIG. 6 shows a simulation of projection data before the correction function 424 corrects the defective pixel (FIG. 6A) and projection data after the correction function 424 corrects the defective pixel (FIG. 6B). The results obtained are shown below. The projection data shown in FIG. 6 is data obtained by superimposing a plurality of image data taken while the X-ray tube 7 moves in the horizontal direction. In the projection data before correction in FIG. 6A, several horizontal lines appear at the bottom. This is an artifact that appears when detection elements in a column with FPD output defective pixels at a time. Further, another artifact having a point sequence exists near the center of the projection data. This artifact appears when one detection element with an FPD outputs a defective pixel. As shown in FIG. 6B, there is no artifact in the correction data obtained by correction by the correction function 424, and there is nothing that prevents interpretation.

  In the above description, it has been described that the defective pixel extraction function 423 stores the coordinate information of the extracted defective pixels in the external device via the storage circuit 26 or the network interface circuit 28. The stored coordinate information of defective pixels can be read, for example, when a new X-ray imaging is performed. For example, when using the X-ray detector 10 in which the coordinate information of the defective pixel has already been extracted at the time of X-ray imaging, the correction function 424 immediately performs the step of extracting the defective pixel by the defective pixel extraction function 423. It is possible to correct defective pixels.

  When a predetermined period has elapsed since the acquisition of the defective pixel coordinate information by the defective pixel extraction function 423, for example, a message prompting to acquire the defective pixel coordinate information again is displayed on the display 27 described later. Also good. Thereby, it is possible to cope with the case where the coordinates and number of defective pixels change with time. In addition, the operator can recognize that the coordinate information of the defective pixel needs to be updated.

  When a predetermined period has elapsed since the defective pixel extraction function 423 acquired coordinate information of the defective pixel, for example, when X-ray imaging is performed from a plurality of different positions on the subject, the defect is automatically detected. You may make it update the coordinate information of a pixel. Thereby, it is possible to cope with the case where the coordinates and number of defective pixels change over time without the operator being conscious.

  The display 27 is configured by, for example, a liquid crystal display or an LED (Light Emitting Diode) display. The display 27 displays image data such as projection data and correction data, for example. The display 27 can also be configured as a touch panel, and can also have the configuration of the input interface circuit 25. The display 27 is an example of a display unit in the claims.

  The display 27 may display information on defective pixels. The defective pixel information is, for example, coordinate information of defective pixels extracted by the defective pixel extraction function 423. The coordinate information of the defective pixel may be displayed superimposed on the original projection data or correction data. The coordinate information of the defective pixel may be indicated by a numerical value, for example, or may be indicated by a figure on the image data. The display 27 may be configured to display a message when a defective pixel is included in the projection data. For example, three messages of “caution”, “warning”, and “unusable” are stored in the storage circuit 26 in association with the number of defective pixels. For example, threshold values TH1 and TH2 for the number of defective pixels are provided. However, 0 <TH1 <TH2. Until the number of defective pixels exceeds TH1, a “caution” message is displayed to allow the operator to recognize that there is a defective pixel on the projection data. When the number of defective pixels exceeds TH1 and is equal to or less than TH2, a “warning” message is displayed to warn the operator that the reliability of projection data is low due to defective pixels. Further, when the number of defective pixels exceeds TH2, a message “unusable” is displayed to alert the user that it is necessary to check whether there is any abnormality in FPD replacement or other circuits. The message and the threshold value setting method for the number of defective pixels described above are merely examples, and it is arbitrary to reduce or increase the number of message and threshold levels.

  The input interface circuit 25 includes, for example, a mouse, a keyboard, a touch panel, a touch pad, a trackball, a joystick, a push button, a dial, and the like. The input interface circuit 25 receives an input operation by an operator. The input information received based on the input operation is, for example, instructions for starting and ending X-ray imaging and imaging conditions. The imaging condition is, for example, the number of times X-rays are irradiated from the X-ray tube 7 within a predetermined angle range when the X-ray tube support mechanism 4 is rotationally driven. Further, the imaging condition may be, for example, information on a predetermined angle range when the X-ray tube support mechanism 4 is rotationally driven, or information on the frequency with which X-rays are emitted from the X-ray tube 7 each time the X-ray tube support mechanism 4 is rotationally driven. . Further, the imaging condition may be, for example, an X-ray condition such as a tube voltage or a tube current supplied from the high voltage generator 8 to the X-ray tube 7 or an imaging position. For example, the input information may be stored in the storage circuit 26 or may be directly passed to each component of the X-ray diagnostic apparatus 1 as information necessary for processing in each component.

  The storage circuit 26 includes a magnetic disk (for example, a hard disk), a flash memory (for example, a solid state drive, a USB memory, and a memory card), and a circuit that reads and writes information from and to an optical disk (for example, a CD and a DVD). The The storage circuit 26 may take an external form connected via a USB port (not shown) or the network interface circuit 28, regardless of the form connected by the internal circuit.

  The network interface circuit 28 is used for acquiring, for example, imaging conditions from a hospital information system (HIS), a radiology information system (RIS), or the like (not shown) via the network. In addition, X-ray images taken with the X-ray diagnostic apparatus 1 can be stored in a picture archiving and communication system (PACS) or used to acquire image data from the PACS. is there.

  FIG. 7 is a flowchart showing a flow of extracting and correcting defective pixels included in projection data using a plurality of projection data obtained by irradiating the subject with X-rays at a plurality of different positions.

  [Step S1] The X-ray diagnostic apparatus 1 accepts an instruction to start imaging of the subject placed on the placement table 9 via the input interface circuit 25.

  [Step S2] The X-ray tube support mechanism drive function 311 and the mounting table support mechanism drive function 312 of the drive control circuit 31 drive the X-ray tube support mechanism 4 and the mounting table support mechanism 3 based on the imaging conditions. The X-ray tube 7 is in a state where X-rays can be irradiated from a predetermined position to the subject. The shooting conditions are received via the input interface circuit 25 and the network interface circuit 28, and information stored in advance in the storage circuit 26 is read and set.

  [Step S3] The X-ray control circuit 6 controls the high voltage generator 8 based on the imaging conditions, and supplies a tube voltage and a tube current to the X-ray tube 7. The X-ray tube 7 emits X-rays toward the subject.

  [Step S4] The X-ray detector 10 detects X-rays, converts the detected electrical signal into digital data, and outputs the digital data. Based on the output digital data, the image generation circuit 41 generates projection data.

  [Step S5] If X-ray irradiation has been completed at all positions where the X-ray tube 7 emits X-rays given as imaging conditions, the process proceeds to step S6. On the other hand, when the position where the X-ray tube 7 does not irradiate X-rays still remains, the process returns to step S2.

  [Step S6] The noise leveling function 421 of the image processing circuit 42 equalizes the noise included in the projection data and generates noise leveling data.

  [Step S7] The filter function 422 of the image processing circuit 42 removes pixels that can be defective pixel candidates included in the noise uniformization data by filtering, and generates filtered data.

  [Step S8] The defective pixel extraction function 423 of the image processing circuit 42 creates a difference image between the noise uniformization data and the filtered data.

  [Step S <b> 9] The defective pixel extraction function 423 performs threshold processing on the difference image to select pixels that are candidates for defective pixels.

  [Step S10] The defective pixel extraction function 423 extracts defective pixels from pixels that are candidates for defective pixels. When a pixel that is a candidate for a defective pixel appears at the same coordinate in a predetermined number or more of differential images taken at a plurality of different positions, the defective pixel extraction function 423 causes the pixel at that coordinate to be displayed. Are extracted as defective pixels.

  [Step S11] If a defective pixel is extracted by the defective pixel extraction function 423, the process proceeds to step S12. If not extracted, the flow ends.

  [Step S12] The defective pixel extraction function 423 stores the coordinate information of the extracted defective pixels in the storage circuit 26. In the case where the coordinate information of the extracted defective pixel or a message for calling attention is displayed on the display 27, it is displayed in this step.

  [Step S13] The correction function 424 of the image processing circuit 42 reads the coordinate information of the defective pixel from the storage circuit 26, and corrects the defective pixel in the projection data. Thus, the defective pixel correction flow is completed.

  As described above, according to the X-ray diagnostic apparatus 1 according to the present embodiment, noise caused by defective pixels is included from a plurality of projection data obtained by irradiating a subject with X-rays from a plurality of different positions. A difference image having various noise components is acquired. And when the pixel value of the same coordinate deviates from a predetermined threshold value over a predetermined number of difference images, the pixel located at the coordinate is extracted as a defective pixel. Based on the coordinate information of the extracted defective pixel, the defective pixel of the projection data is corrected.

  By using a plurality of projection data, the characteristics of defective pixels appearing at the same coordinates on the projection data can be used regardless of the position where the X-ray tube 7 irradiates X-rays. Like a tissue, there is no possibility that a pixel having a relatively high pixel value compared to surrounding pixels is erroneously identified as a defective pixel.

  In addition, when a defective pixel does not show an extremely high pixel value or an extremely low pixel value, the threshold processing is performed on each pixel value of the projection data as in the conventional method to extract defective pixels. Not valid. On the other hand, the X-ray diagnostic apparatus 1 according to the present embodiment creates a difference image having pixels that can be defective pixel candidates using noise uniformization data and filtered data generated based on projection data. doing. In addition, the threshold value of the pixel value when the threshold value processing is performed on the difference image is more than the fluctuation of the pixel value that may occur in normal X-ray image capturing, and the pixel value between the noise uniformization data and the filtered data The pixels where the change is seen are set to such an extent that they can be extracted from the difference image. Therefore, even if the defective pixel does not show an extremely high pixel value or an extremely low pixel value on the projection data, the defective pixel can be easily identified.

  Furthermore, according to the X-ray diagnostic apparatus 1 according to the present embodiment, the display 27 displays the coordinate information of the defective pixel extracted by the defective pixel extraction function 423. Thereby, for example, when an operator interprets an X-ray image, it is possible to easily grasp where defective pixels having low reliability are distributed. Further, the display 27 can display a message for caution and warning according to the number of defective pixels. As a result, the operator can easily grasp the necessity of replacement of the FPD or repair of the apparatus, for example.

  In the above description, a mammography apparatus has been described as an example of the X-ray diagnostic apparatus 1. However, an X-ray angiography apparatus or an X-ray TV apparatus may be used. In the X-ray angiography apparatus and the X-ray TV apparatus, the same configuration as that of the present embodiment can be obtained by replacing the mounting table 9 in the mammography apparatus with a bed. Further, the X-ray tube 7 in the mammography apparatus is supported by the X-ray tube support mechanism 4 and swings around the rotation axis. However, in the X-ray TV, the X-ray tube 7 is used as a bed or a subject. On the other hand, it becomes a structure which acquires the projection data in a several different position by moving in parallel.

  Next, a modification of this embodiment will be described. In the following description, components having substantially the same functions as those of the present embodiment are denoted by the same reference numerals, and redundant description is provided only when necessary.

(Modification 1)
As in the above-described embodiment, the defective pixel extraction function 423 is a defective pixel that a candidate pixel of a defective pixel appears at the same coordinate in a predetermined M or more difference images among N difference images. It was a judgment criterion. On the other hand, the defective pixel extraction function 423 according to the modification 1 determines whether the pixel is a defective pixel by using an addition image obtained by adding the pixel values of the N difference images at each pixel.

  First, the defective pixel extraction function 423 adds the pixel values of the N difference images obtained using the noise uniformization data and the filtered data, and creates an added image. Next, the defective pixel extraction function 423 performs threshold processing on the pixel value of each pixel of the added image. Similar to the above-described embodiment, the threshold setting method can be determined based on imaging conditions such as a tube voltage, a tube current, and a product of tube current and imaging time, such as a mAs value representing an X-ray dose. Further, the threshold value may be changed every time the photographing condition changes. Then, the defective pixel extraction function 423 determines that the pixel determined to correspond to the defective pixel by the threshold processing is the defective pixel. Since the coordinate position of the defective pixel does not change, the value of the added pixel value is larger in the added image than the pixel that is not the defective pixel. Therefore, defective pixels can be extracted by threshold processing for the pixel values of the added image. The defective pixel extraction function 423 stores the coordinate information of the extracted defective pixels in an external device via the storage circuit 26 or the network interface circuit 28.

  According to the X-ray diagnostic apparatus 1 according to the first modification, the defective pixel extraction function 423 creates an addition image obtained by adding pixel values of a plurality of difference images for each pixel. Then, threshold processing is performed on the added image to extract defective pixels. Thereby, it is possible to extract defective pixels at a time on the added image without extracting defective pixel candidates from individual difference images.

(Modification 2)
As described above, in the X-ray diagnostic apparatus 1, the coordinates on the projection data corresponding to the projection image of the site existing inside the subject change as the position where the X-ray tube 7 irradiates X-rays changes. We used the characteristic of being. However, for example, when the X-ray tube 7 is supported by the X-ray tube support mechanism 4 and is rotationally driven, if the part to be imaged is positioned at the rotational center of the rotational drive, the part existing inside the subject is detected. The coordinates on the projection data of the corresponding projection image may not change. When placing the subject on the placement table 9, it is preferable to set the position of the subject so as to avoid the center of rotation, but the pixel of the projection image of the part of the subject located near the center of rotation is It is also possible to reduce erroneous extraction as defective pixels.

  The defective pixel extraction function 423 of the image processing circuit 42 of the X-ray diagnostic apparatus 1 according to the modification 2 changes the threshold setting when selecting a candidate pixel of a defective pixel from the difference image according to the coordinates. For example, consider a case where the subject is located at the rotation center of the X-ray tube 7. At this time, the projected image of the part existing inside the subject is projected on the approximate center of the X-ray detector 10. Therefore, the pixel of the projection data corresponding to the detection element near the center of the X-ray detector 10 is highly likely to be erroneously recognized as a defective pixel.

  The defective pixel extraction function 423 sets a stricter criterion for selecting a defective pixel candidate for a pixel of coordinates corresponding to a detection element near the center of the X-ray detector 10 than a peripheral pixel for the difference image. To do. Strictly setting the reference means, for example, setting the upper limit of the pixel value threshold higher or setting the lower limit of the pixel value threshold lower. When the pixel value threshold value is made different for each coordinate, for example, the pixel value threshold value is set so that the criterion for selecting a defective pixel candidate is relaxed as the distance from the coordinate corresponding to the center of the X-ray detector 10 increases. Is possible. In addition, for example, the criteria for selecting candidates for defective pixels are strict only for pixels corresponding to coordinates near the center of the X-ray detector 10, and uniform pixels are used for pixels having other peripheral coordinates. A threshold value may be set.

  According to the X-ray diagnostic apparatus 1 according to the modified example 2, when the defective pixel extraction function 423 extracts a defective pixel candidate pixel from the difference image, the object positioned near the rotation center of the X-ray tube 7 is detected. The threshold value of the pixel value of the coordinates corresponding to the projected image of the part is set to be stricter than the surroundings. Thereby, it can reduce that the pixel corresponding to the projection image of the site | part of a to-be-examined object is extracted accidentally as a defective pixel on a difference image.

  Subsequently, another modification of the present embodiment will be described.

(Modification 3)
In the above-described embodiment and the modifications 1 and 2, the X-ray diagnostic apparatus 1 has been described. However, the function of extracting and correcting defective pixels is not limited to the X-ray diagnostic apparatus 1, and X-ray CT images are generated by reconstructing projection data obtained by irradiating X-rays around the subject. It can also be realized in the line CT apparatus 2.

  FIG. 8 is a diagram illustrating a configuration of the X-ray CT apparatus 2 according to the third modification. A configuration different from the X-ray diagnostic apparatus 1 in the above-described embodiment will be described below.

  The X-ray tube support mechanism 4 is a support member that supports the X-ray tube 7 and the X-ray detector 10. Further, the X-ray tube support mechanism 4 is configured to be rotatable around the mounting table 9, and the rotation speed is set by the control by the X-ray tube support mechanism drive function 311 of the drive control circuit 31. The rotation speed is received through the input interface circuit 25 or the network interface circuit 28 as a shooting condition, for example, and is set by reading information stored in the storage circuit 26 in advance.

  The mounting table support mechanism 3 moves the mounting table 9 in the horizontal direction in order to move it vertically, for example, to insert the annular X-ray tube support mechanism 4 into the cavity, and to remove it from the cavity. It is possible to move.

  Based on the digital data output from the X-ray detector 10, the data acquisition circuit 44 generates projection data for each view in which X-ray rays irradiated in a certain angle direction are bundled. The data collection circuit 44 is an example of a data collection unit in the claims. The projection data is, for example, data in which CT values associated with the respective detection elements of the X-ray detector 10 are assigned to pixels. In the X-ray diagnostic apparatus 1 already described, the image generation circuit 41 generates projection data in step S4 of FIG. 7, but in the X-ray CT apparatus 2, the data acquisition circuit 44 generates projection data. The projection data in the X-ray CT apparatus 2 is data in which X-ray intensity data received by each detection element of the X-ray detector 10 is associated with the position of each detection element and arranged two-dimensionally. An image processing circuit 42 (to be described later) in the X-ray CT apparatus 2 performs noise equalization processing on the projection data generated by the data acquisition circuit 44, and performs threshold processing on image data based on the generated noise equalization data. This makes it possible to extract defective pixels from the projection data.

  The image processing circuit 42 acquires projection data of a plurality of views, and extracts and corrects defective pixels included in the projection data, similarly to the X-ray diagnostic apparatus 1 in the above-described embodiment.

  The reconstruction circuit 43 of the processing circuit 40 performs image reconstruction using the projection data of a plurality of views output from the data collection circuit 44, and generates a reconstructed image. Here, the plurality of projection data includes an angle equal to or greater than an angle obtained by adding 180 degrees and the fan angle of the X-ray tube 7 in the rotation trajectory along the circumference of the X-ray tube support mechanism 4. This is data obtained by irradiating X-rays in a range. The reconstruction circuit 43 can generate a reconstruction image using the projection data in which the defective pixel is corrected by the image processing circuit 42.

  The display 27 displays the reconstructed image generated by the reconstructing circuit 43, for example.

  According to the X-ray CT apparatus 2 according to the modified example 2, the defective pixels included in the projection data can be extracted and corrected in the same manner as the X-ray diagnostic apparatus 1. Thereby, the reconstruction circuit 43 can generate a reconstruction image based on the projection data in which the influence of the defective pixel is reduced. A reconstructed image generated based on projection data in which the influence of defective pixels is reduced is an image in which the occurrence of artifacts is reduced.

  In the X-ray CT apparatus 2 according to the modification example 3, the configuration described in the modification examples 1 and 2 can be applied.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 X-ray diagnostic apparatus 2 X-ray CT apparatus 6 X-ray control circuit 7 X-ray tube 8 High voltage generator 9 Mounting stand 10 X-ray detector
DESCRIPTION OF SYMBOLS 31 Drive control circuit 311 X-ray tube support mechanism drive function 312 Mounting stand support mechanism drive function 40 Processing circuit 41 Image generation circuit 42 Image processing circuit 43 Reconfiguration circuit 44 Data acquisition circuit

Claims (10)

An X-ray tube that irradiates the subject with X-rays from a plurality of positions;
An X-ray detector for detecting the irradiated X-ray;
An image generation unit that generates a plurality of projection data corresponding to the plurality of positions based on the X-rays detected by the X-ray detector;
Image processing is performed on the projection data, noise uniformity data obtained by performing noise uniformity processing on each of the plurality of projection data is obtained, and threshold processing is performed on the image data based on the noise uniformity data. An image processing unit for extracting defective pixels.
X-ray diagnostic equipment. When the pixel value of the same coordinate deviates from the threshold value in the threshold processing over the image data based on a plurality of the noise uniformization data of a predetermined number or more, the image processing unit defectively identifies the pixel located at the coordinate Extract as pixels,
The X-ray diagnostic apparatus according to claim 1. The image processing unit creates an addition image obtained by adding pixel values of image data based on a plurality of the noise uniformization data for each pixel, and when the pixel value of the addition image deviates from a threshold value in the threshold processing, Extracting a pixel on the projection data corresponding to the coordinates of the addition image having a pixel value outside the threshold in the threshold processing as a defective pixel;
The X-ray diagnostic apparatus according to claim 1. The image processing unit obtains a difference image between the noise uniformized data and the filtered data obtained by filtering the noise uniformized data with respect to the image data based on the noise uniformized data. Generate,
The X-ray diagnostic apparatus according to any one of claims 1 to 3. The image processing unit corrects the defective pixel using a pixel value of a pixel located around the defective pixel;
The X-ray diagnostic apparatus according to any one of claims 1 to 3. A display unit for displaying image data;
The display unit displays coordinate information of the defective pixel;
The X-ray diagnostic apparatus according to any one of claims 1 to 3. A display unit for displaying image data;
The display unit displays a message according to the number of defective pixels.
The X-ray diagnostic apparatus according to any one of claims 1 to 3. The image processing unit sets a predetermined threshold value used for performing threshold processing on the image data based on the noise uniformization data by changing for each coordinate.
The X-ray diagnostic apparatus according to claim 1. A display unit for displaying image data;
The display unit displays projection data in which the defective pixel is corrected;
The X-ray diagnostic apparatus according to claim 5. An X-ray tube that irradiates the subject with X-rays from a plurality of positions;
An X-ray detector for detecting the irradiated X-ray;
A data collection unit that generates a plurality of projection data corresponding to the plurality of positions based on the X-rays detected by the X-ray detector;
Image processing is performed on the projection data, noise uniformity data obtained by performing noise uniformity processing on each of the plurality of projection data is obtained, and threshold processing is performed on the image data based on the noise uniformity data. An image processing unit for extracting defective pixels.
X-ray CT system.

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