JP2011067342A - X-ray diagnostic apparatus and x-ray diagnostic method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray diagnostic apparatus capable of displaying a subtraction image with fewer artifacts in the digital subtraction angiography (DSA) under natural respiration. <P>SOLUTION: The X-ray diagnostic apparatus includes: an image collecting part for radiographing a subject according to the respiratory cycle of the subject and collecting a group of mask images captured without a contrast agent and a group of contrast images captured by loading the contrast agent; a difference image generating part for generating a difference image between successive frames of the mask image group and contrast image group respectively; an arithmetic processing part for detecting the moving direction of the difference image varying according to the respiration of the subject, computing the respiration phase value of each frame of the mask image group and contrast image group, selecting a mask image and a contrast image with similar respiration phase values to be subtracted and generating a subtraction image; and a display part for displaying the subtraction image generated by the arithmetic processing part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray diagnostic apparatus and an X-ray diagnostic method for obtaining a subtraction image by subtracting mask image data captured under natural breathing and contrast image data captured with a contrast agent injected.

  Conventionally, there is an X-ray diagnostic apparatus as a medical image diagnostic apparatus. For example, in the examination of digestive organs and circulatory organs, in order to observe the fine state of blood vessels, mask image data taken before injecting a contrast agent into the blood vessels and contrast image data taken with the contrast agent injected There is a photographing method for subtracting (subtracting) and obtaining a subtraction image. This imaging method is generally called DSA (Digital Subtraction Angiography) imaging, and can display only contrasted blood vessels by obtaining a subtraction image.

By the way, in DSA imaging, when the subject moves, artifacts (false images) are generated without successfully erasing the background by subtraction, and the contrasted blood vessel image may not be clearly observed. In order to reduce artifacts, imaging is performed by instructing the subject not to move the body during angiography. Further, in the angiography of the abdomen, strong artifacts due to respiration occur, and the diagnostic ability is remarkably reduced. Therefore, it may be instructed not to breathe during contrast imaging.
However, angiography of the abdomen may take several tens of seconds depending on the site, and there is a problem that elderly people cannot stop breathing for a long time. This is called DSA imaging under spontaneous breathing). In this case, a mask image for one respiratory cycle is collected before contrasting, and subsequently necessary contrast images (contrast image group) are collected, and an image whose contrast image and background match in the post process is selected from the mask image group. Subtraction is performed by selecting (remasking) as a mask. This can reduce artifacts, but it is often used to create blood vessel images suitable for diagnosis and treatment because the mask image whose contrast image matches the background is selected manually from the mask image group. Takes time and effort.

  In Patent Document 1, in order to reduce labor in the post-process, a sensor or the like is attached to the body to monitor the respiratory state, and the X-ray irradiation timing is determined according to the respiratory phase specified based on information from the sensor. An X-ray diagnostic apparatus is disclosed in which a contrast image and a mask image are acquired with the same respiratory phase. However, in the example of Patent Document 1, a special instrument such as a respiration sensor is required when performing DSA imaging under natural breathing, and thus further improvement is required.

Japanese Patent Laid-Open No. 7-8479

  Conventionally, in order to reduce artifacts in the subtraction image, an image in which the contrast image and the background coincide with each other is selected from the mask image group. However, since this selection is performed manually, blood vessels suitable for diagnosis and treatment are selected. There was a problem that it took a lot of time and effort to create an image. Further, there is an example in which DSA imaging is performed under natural breathing as in Patent Document 1, but since a special instrument such as a breathing sensor is required, further improvement is required.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an X-ray diagnostic apparatus and an X-ray diagnostic method capable of displaying a subtraction image with few artifacts in DSA imaging under natural breathing. .

  The X-ray diagnostic apparatus according to claim 1 of the present invention includes an imaging unit including an X-ray generation unit that irradiates a subject with X-rays and an X-ray detection unit that detects X-rays transmitted through the subject; A mask image group obtained by photographing the subject in accordance with the breathing cycle of the subject and photographed without a contrast agent, an image collection unit for collecting a contrast image group photographed by introducing a contrast agent, and the mask image A difference image generation unit that generates a difference image of images of frames before and after each of the group and the contrast image group, and a moving direction of the difference image that varies depending on respiration of the subject, and the mask image group and the contrast image group An arithmetic processing unit that calculates a respiratory phase value of each frame, selects the mask image and the contrast image that approximate the respiratory phase value, and performs subtraction processing to generate a subtraction image; and And a display unit for displaying the subtraction image generated by the processing unit.

  The X-ray diagnostic method of the present invention according to claim 6 includes an X-ray generator that irradiates a subject with X-rays and an X-ray detector that detects X-rays transmitted through the subject. The subject is imaged in accordance with the respiratory cycle of the subject, a mask image group photographed without a contrast agent, and a contrast image group photographed by introducing a contrast agent are collected, and the mask image group and A difference image between frames of the contrast image group before and after each is generated, a moving direction of the difference image that varies due to respiration of the subject is detected, and a respiratory phase of each frame of the mask image group and the contrast image group Calculating a value, generating a subtraction image by subtracting the mask image and the contrast image that approximate the respiratory phase value, and displaying the subtraction image on a display unit And features.

  The X-ray diagnostic apparatus of the present invention can automatically display a subtraction image with few artifacts by DSA imaging under natural breathing. Moreover, since it is not necessary to repeat complicated remasking processing, the diagnostic efficiency can be improved.

The block diagram which shows the structure of the X-ray diagnostic apparatus which concerns on one Embodiment of this invention. 1 is a perspective view showing an external appearance of an X-ray diagnostic apparatus according to an embodiment. Explanatory drawing which shows the acquisition method of the difference image in one Embodiment. Explanatory drawing which shows an example of the profile curve extracted based on the difference image. Explanatory drawing which shows a respiratory phase and a respiratory phase value (%). Explanatory drawing which shows the production | generation process of a subtraction image. Explanatory drawing which shows the other example of calculation of a respiratory phase. The flowchart explaining operation | movement of a respiration phase image calculating part.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of an X-ray diagnostic apparatus (for example, an angio apparatus) of the present invention. In FIG. 1, an X-ray diagnostic apparatus 100 two-dimensionally detects an X-ray generator 10 for generating X-rays with respect to a subject P, and X-rays that have passed through the subject P, and generates a detection result. An X-ray detection unit 20 that generates X-ray projection data based on the X-ray projection data is provided.

  The X-ray generation unit 10 includes an X-ray irradiation unit 13 including an X-ray tube 11 and an X-ray restrictor 12, and a high voltage generator 14. The X-ray tube 11 is a vacuum tube that generates X-rays, and accelerates electrons emitted from a cathode (filament) by a high voltage to collide with a tungsten anode to generate X-rays. The X-ray diaphragm 12 is provided for the purpose of reducing the exposure dose to the subject P and improving the image quality by irradiating only the region to be imaged with X-rays. As a result, the X-ray detector 21 described later can detect an X-ray image of X-rays that has passed through the opening formed by the X-ray diaphragm 12 and transmitted through the region of interest of the subject P.

  The X-ray detection unit 20 includes an X-ray detector (FPD) 21 and a data conversion unit 22. The X-ray detector 21 converts and accumulates X-rays that have passed through the region of interest of the subject P into electric charges, and two-dimensionally detects minute detection elements that detect X-rays in the column direction and the line direction. It is configured by arranging. The data converter 22 includes an A / D converter and a parallel / serial converter, and generates X-ray projection data based on the charges read from the X-ray detector 21.

  The X-rays incident on the X-ray detection unit 20 are converted into digital data in synchronization with the X-ray pulse irradiation by the data conversion unit 22, and one frame of digital data (X-ray projection data) is generated for one pulse. Is done. The digital data is processed by an image processing unit 34 described later.

  The X-ray generation unit 10 and the X-ray detection unit 20 are supported by a C arm 41 (support device), and the C arm 41 is movable in the body axis direction of the subject P, for example. Furthermore, the X-ray diagnostic apparatus 100 has a computer system 30. The computer system 30 includes a system control unit 31, an operation unit 32, a user interface 33, an image processing unit 34, and a display unit 39. The image processing unit 34 includes a storage unit 35, a respiratory phase image calculation unit 36, an image data processing unit 37, and a D / A converter 38.

  The system control unit 31 includes a CPU 311 and the like, and comprehensively controls each unit of the X-ray diagnostic apparatus 100 to process and display image data. The operation unit 32 is operated by a user such as a doctor and includes an X-ray irradiation switch 321. An operation signal from the operation unit 32 is supplied to the system control unit 31 via the user interface 33 and processed by the CPU 311, and the high voltage control unit 40, the X-ray diaphragm 12, and the top plate 45 on which the subject P is placed. Control the position. The system control unit 31 also controls the X-ray detector 21 and the data conversion unit 22.

  The high voltage generator 14 generates a high voltage to be applied between the anode and the cathode in order to accelerate the thermoelectrons generated from the cathode of the X-ray tube 11. Based on the X-ray irradiation conditions input from 32, the tube current / tube voltage of the high voltage generator 14, the irradiation time, the irradiation repetition period, and the like are controlled.

  FIG. 2 is a perspective view showing an appearance of the X-ray diagnostic apparatus 100 (angio apparatus). In FIG. 2, the X-ray generation unit 10 and the X-ray detection unit 20 are supported to be opposed to a C arm 41, and the C arm 41 is supported by a stand 43 via an arm support unit 42. The portion including the X-ray generation unit 10 and the X-ray detection unit 20 constitutes an imaging unit.

  A couch 44 is disposed with respect to the C arm 41, and a subject (not shown) is placed on the couch 45 of the couch 44, and the position and height of the couch 45 can be controlled. . As a result, the C-arm 41 is relatively movable along the body axis direction of the subject, and is rotatable in the direction of arrow a along the periphery of the subject. The imaging unit (X-ray generation unit 10 and X-ray detection unit 20) can be slid in the direction of arrow b.

  The X-ray projection data generated by the imaging unit is processed by an image processing unit 34 (details will be described later), and the image data is displayed on the display unit 39. The display unit 39 is attached to, for example, a ceiling part and includes a plurality of monitors.

  An operation handle 46 is attached to the bed 44. By operating the operation handle 46, the height position of the top plate 45, the movement / rotation control of the C-arm 41, and the X-ray irradiation range can be controlled. Various controls such as adjustment and display control of the display unit 39 can be performed. In addition, although the C arm 41 has shown the example supported by the stand 43 set | placed on the floor surface, the X-ray diagnostic apparatus 100 of the type which installed the C arm 41 to the ceiling part so that a movement was possible may be sufficient. .

  Next, the image processing unit 34 that is a feature of the present invention will be described. The present invention is characterized by a DSA (Digital Subtraction Angiography) imaging method. DSA imaging means an imaging method in which only the contrasted blood vessels are displayed by subtracting the background before contrast enhancement from the angiographic image by digital image processing.

  First, the basic operation of X-ray imaging will be described. When a fluoroscopy or radiographing start operation is performed by the X-ray irradiation switch 321 of the operation unit 32, X-rays start to be emitted intermittently in a pulse form from the X-ray generation unit 10. The X-ray generated in the X-ray tube 11 can limit the irradiation field by the X-ray restrictor 12, and the irradiated X-ray passes through the subject P and enters the X-ray detection unit 20. X-rays incident on the X-ray detection unit 20 are converted into digital data in synchronization with X-ray pulse irradiation, and one frame of digital data is generated for one pulse. Here, the CPU 131 also controls the X-ray detector 21 and the data conversion unit 22 in synchronization with the X-ray generation control.

  Next, the operation of the image processing unit 34 will be described with reference to FIGS. In FIGS. 3 to 6, various symbols (A to G) are attached, but the same items are described with the same symbols.

  In DSA imaging, a subtraction image is obtained by subtracting (subtracting) the mask image data imaged before injecting the contrast agent into the blood vessel and the contrast image data imaged with the contrast agent injected. When photographing is performed in a sequence that can collect a mask image including one respiratory cycle, a contrast image group (contrast image group) is generated following the mask image group and recorded in the storage unit 35. The number of frames of the mask image group and the number of frames of the contrast image group are stored in an accompanying information storage memory (not shown). The X-ray detection unit 20 and the storage unit 35 constitute an image collection unit that collects a mask image group and a contrast image group.

  The respiratory phase image calculation unit 36 includes a difference image generation unit 361 and a subtraction calculation processing unit 362. The difference image generation unit 361 calculates the respiratory phase of each frame of the mask image group and the contrast image group from the digital data in the storage unit 35. The subtraction calculation processing unit 362 selects a mask image having a respiratory phase that most closely approximates a respiratory phase included in a certain contrast image in the contrast image group from the mask image group, and performs subtraction processing to generate a subtraction image.

  The subtracted data is subjected to image processing such as a spatial filter, and then subjected to display gradation processing by the image data processing unit 37, converted into a video signal by the D / A converter 38, and real time to the display unit 39. Is displayed.

  As a means for specifying the respiratory phase of the mask image and the contrast image, for each of the mask image group and the contrast image group, a difference image between the image one frame before and the image after one frame of each image is obtained. The movement direction of organs, bones, etc. during one frame is detected from the profile curve of the image, the respiratory phase of each image frame is specified by the change of the movement direction, and the mask image corresponding to the contrast image is automatically determined. To do subtraction.

  FIG. 3 is an operation explanatory diagram illustrating a method for acquiring a difference image. For example, when the subject takes a breath and performs imaging at an image acquisition rate of about several frames per second, the diaphragm moves up and down, and the position and shape of the organ moves mainly up and down. Deform. FIG. 3A shows the breathing state of the subject, timings t0 to t1 on the horizontal axis show one cycle of breathing, and timings t1 to t2 show the next one cycle.

  In DSA imaging, as shown in FIG. 3B, an image of only the background (mask image) before injecting the contrast agent is imaged for one period of respiration, and a mask image group is collected, and then the contrast is contrasted. A contrast image (contrast image) is taken while injecting the agent and continuing to breathe, and a group of contrast images is collected.

  FIG. 3C shows an image of each frame in the mask image group. The difference image generation unit 361 subtracts the previous frame and the image after the first frame from the frames other than the top frame. To generate a difference image. FIG. 3D shows a difference image. The difference image is an image of the difference between the two frames, and the marginal part of the organ is mainly extracted as the part that has moved.

  FIG. 4 shows a profile curve extracted based on the difference image. The profile curve is obtained by plotting pixel values for pixel data on a line when a line is drawn on the image. That is, FIG. 4D shows an enlarged view of adjacent difference images D1 and D2 among the difference images in FIG. 3D, and linear ROI (L1 in the vertical direction) on the difference images D1 and D2. When the pixel values for the pixel data on the line are plotted, the profile curves indicated by E1 and E2 in FIG.

  The profile curves E1 and E2 are curves in which the portion corresponding to the peripheral portion of the organ has a positive or negative value depending on the moving direction. The profile curves E1 and E2 move in accordance with the vertical movement of the diaphragm as indicated by arrows. In addition, as with the mask image group, the contrast image group also obtains a difference image and obtains a profile curve (not shown).

  When the profile curve E is acquired from the difference image D for each frame of the mask image group and the contrast image group, the movement of the organ due to respiration can be determined from the change in the profile curve, and the respiration phase within one respiration cycle is specified. be able to. In addition, the respiratory phase can be indicated by the respiratory phase value (%) indicating the position in one respiratory cycle with the timing at which the organ is present in the upward direction as the base point (0%).

  FIG. 5 is an explanatory diagram showing a respiratory phase and a respiratory phase value (%). FIGS. 5A to 5D are similar to FIGS. 3A to 3D, but in FIG. 5F, the respiratory phase is indicated by arrows, and the organ is moving upward or downward by respiration. Show. A period without an arrow is a period in which the moving direction is reversed, and is a state in which the organ is at the top or bottom.

  FIG. 5G shows the respiratory phase value (%). Assuming that the timing when the organ is present in the most upward direction is 0% (100%), the numerical value gradually increases toward 100 during the period in which the respiratory phase F is indicated by the upward arrow. During the period in which the moving direction is reversed and the respiration phase F is indicated by a downward arrow, the numerical value gradually increases from zero starting from 0%. Moreover, when the timing when the organ exists in the lowest direction (48% in this example) is passed, it increases toward 100 again. Therefore, by attaching a respiratory phase value (%) to the frame of the collected image C, it is possible to know the image at which position the organ is.

  FIG. 6 is an explanatory diagram showing a subtraction image generation process. FIG. 6B shows the collected mask image and contrast image group, and G shows the respiratory phase value (%). As shown in FIG. 6, when a subtraction image is obtained, an image of a frame having the same respiratory phase value is selected from the mask image group and the contrast image group, and subtraction processing is performed by the subtraction calculation processing unit 362, thereby subtraction. An image can be obtained. A subtraction image with few artifacts can be automatically displayed by selecting and subtracting the mask image and contrast image that have the closest respiratory phase value.

  Conventionally, in the subtraction display, when the background does not disappear well due to body movement or the like, it has been necessary to reselect (remask) another image frame as a mask image. However, according to the embodiment of the present invention, it is complicated. Since it is not necessary to repeat the remask process, the diagnostic efficiency can be improved. In addition, a subtraction image with few artifacts can be automatically displayed by DSA imaging under natural breathing without using a special sensor or the like to detect the respiratory phase.

  Next, a modified example of the present invention will be described. In the above embodiment, based on the profile curve of the difference image between adjacent frames, the direction that changes with the advance of the frame is determined, and the respiratory phase value (%) is calculated. In the modification, the moving direction of the organ is detected by only one difference image based on the distribution of the positive and negative signs of the profile curve of the difference image. This will be specifically described with reference to FIG.

  FIG. 7C schematically shows an image of each frame in the mask image group, and a difference image (D) is generated by subtracting the previous frame and the image after the first frame. In FIG. 7, for example, a differential image D1 when the organ is moving upward and a differential image D2 when the organ is moving downward are enlarged as representative examples.

  When the vertical linear ROI (L1) is set in the difference images D1 and D2, when the pixel values for the pixel data on the line are plotted, profile curves indicated by E1 and E2 in FIG. 7 are obtained. Since the positive and negative characteristics of the profile curves E1 and E2 are reversed as the frame advances, the respiratory phase (F) is determined from the characteristics of the profile curves E1 and E2, and the respiratory phase value (%) is calculated.

  The respiratory phase value (%) is calculated in the same manner as in FIG. 5G, and the timing at which the organ is present in the most upward direction is set to 0% (100%), and the period in which the respiratory phase F is upward gradually increases toward 100. The numerical value increases, and during the period in which the respiratory phase F is downward, the numerical value gradually increases from zero starting from 0%. Thus, the respiratory phase value (%) can be easily calculated by determining the respiratory phase F from the positive / negative characteristics of the profile curves E1 and E2.

  As a method for setting a linear ROI for detecting a profile curve, a method in which an operator designates an appropriate place in a post process or a method in which a linear ROI is preset may be employed. In addition, a method for automatically setting a plurality of preset linear ROIs as imaging parameters and automatically setting the linear ROI according to the imaging region, and comparing processing results when using a plurality of preset linear ROIs are appropriate. You may employ | adopt the method of selecting a thing. Furthermore, a method of automatically determining a linear ROI by detecting a periodic motion portion of an image may be employed.

In the above description, the movement of the diaphragm due to breathing is the head-to-tail direction, and the detection of the movement direction is mainly considered as the vertical direction. Therefore, the linear ROI in the vertical direction is exemplified. The left and right movements may be detected by the ROI.
In this embodiment, an example in which the respiratory phase is specified in the post-process after DSA imaging has been described. However, after acquiring the mask image group, the respiratory phase of each mask image in the mask image group is specified, and the process proceeds to contrast image acquisition. For the contrast image, the respiratory phase may be specified in real time based on the difference image. This also enables application to real-time remasking during DSA imaging.

  FIG. 8 is a flowchart for explaining the operation of the respiratory phase image calculation unit 36. In step S1, a difference image D between adjacent frames is generated and stored for each of the mask image group and the contrast image group. In step S2, for example, a linear ROI is set, a profile curve E at the position of the ROI of the difference image is created, and the profile curve is stored as numerical information.

  In step S3, the moving direction is identified from the distribution of the stored profile curves, the distribution of adjacent profile curves, and the change in position, and the respiratory phase F is detected. In step S4, a frame whose moving direction is reversed based on the respiratory phase F is detected, a respiratory cycle is determined based on the frame, and a respiratory phase value% G of each frame is calculated.

  In step S5, a mask image and a contrast image having the most approximate respiratory phase value are selected from the mask image group and the contrast image group, the frames of both images to be used at the time of subtraction are specified, and the frame number H is stored in the frame table. store. In step S6, a mask image and a contrast image used for subtraction are extracted using the frame number H as an index, and subtraction processing is performed to obtain a subtraction image and display it on the display unit 39.

  As described above, the X-ray diagnostic apparatus of the present invention can automatically display a subtraction image with few artifacts by DSA imaging under natural breathing. Moreover, since it is not necessary to repeat complicated remasking processing, the diagnostic efficiency can be improved. Further, it is not necessary to use a special sensor or the like for detecting the respiratory phase.

  In the above description, the X-ray diagnostic apparatus (angio apparatus) using the C arm has been described as an example, but the present invention can also be applied to other X-ray diagnostic apparatuses such as an X-ray CT apparatus. Various modifications can be made without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 100 ... X-ray diagnostic apparatus 10 ... X-ray generation part 11 ... X-ray tube 20 ... X-ray detection part 21 ... X-ray detector 22 ... Data conversion part 30 ... Computer system 31 ... System control part 32 ... Operation part 33 ... User Interface 34 ... Image processing section 35 ... Storage section 36 ... Respiration phase image calculation section 361 ... Difference image generation section 362 ... Subtraction calculation processing section 37 ... Image data processing section 38 ... D / A conversion section 39 ... Display section 40 ... High voltage Control unit 41 ... C arm 45 ... top plate

Claims (6)

An imaging unit including an X-ray generation unit that irradiates the subject with X-rays and an X-ray detection unit that detects X-rays transmitted through the subject;
Imaging the subject in accordance with the respiratory cycle of the subject, a mask image group captured without a contrast agent, and an image collection unit that collects a contrast image group captured by introducing a contrast agent;
A difference image generation unit for generating a difference image of images of frames before and after each of the mask image group and the contrast image group;
The moving direction of the difference image that varies with the breathing of the subject is detected, the respiratory phase value of each frame of the mask image group and the contrast image group is calculated, and the mask image and the contrast that approximate the respiratory phase value An arithmetic processing unit that selects and subtracts an image to generate a subtraction image;
An X-ray diagnostic apparatus comprising: a display unit that displays a subtraction image generated by the arithmetic processing unit.   The arithmetic processing unit sets a linear ROI in the difference image generated by the difference image generation unit, acquires a profile curve from pixel data on the ROI line, and determines a moving direction of the difference image from the profile curve. The X-ray diagnostic apparatus according to claim 1, wherein the X-ray diagnostic apparatus is detected.   The X-ray diagnosis apparatus according to claim 2, wherein the arithmetic processing unit sets the linear ROI in a plurality of two-dimensional directions and detects a plurality of moving directions of the difference image.   The X-ray diagnosis apparatus according to claim 2, wherein the arithmetic processing unit detects a moving direction of the difference image using at least one linear ROI set in advance according to an imaging region.   The arithmetic processing unit attaches a frame number to each frame of the mask image group and the contrast image group starting from a period in which the moving direction of the difference image is reversed, and uses the frame number as an index to use the mask image for subtraction. The X-ray diagnostic apparatus according to claim 1, wherein a contrast image is extracted. An imaging unit including an X-ray generation unit that irradiates the subject with X-rays and an X-ray detection unit that detects X-rays transmitted through the subject;
Photographing the subject according to the respiratory cycle of the subject, collecting a mask image group photographed without a contrast agent, and a contrast image group photographed by introducing a contrast agent,
Generating difference images of images of frames before and after the mask image group and the contrast image group,
Detecting a moving direction of the difference image that varies depending on the breathing of the subject, and calculating a respiratory phase value of each frame of the mask image group and the contrast image group;
Subtracting the mask image and the contrast image that approximate the respiratory phase value to generate a subtraction image,
An X-ray diagnostic method, wherein the subtraction image is displayed on a display unit.

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