JP2015112293A - Medical image processor and x-ray diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medical image processor capable of removing unerased remains (artifact) other than a blood vessel due to a three-dimensional movement from a difference image even though the movement of a subject exists.SOLUTION: The medical image processor of this embodiment includes a difference image generation part for performing difference processing of a mask image picked up before inputting a contrast medium into a subject and a contrast image picked up after inputting the contrast medium to generate a difference image, a white and black pair determination part for determining whether a pair of a white part and a black part exists within the predetermined range of the difference image when a part in which a pixel value is higher than a prescribed first threshold is made to be the white part and a part in which a pixel value is lower than a prescribed second threshold is made to be the black part on the difference image, and a removal processing part for removing pixels of the white part from the difference image in the case that the pair of a white part and a black part exists.

Description

  The present embodiment as one aspect of the present invention relates to a medical image processing apparatus and an X-ray diagnostic apparatus.

  2. Description of the Related Art Conventionally, two or more images with different imaging timings are compared and read for the same subject, and the subject is inspected based on the difference between the two images (see, for example, Patent Document 1). .

  In the field of X-ray medical image diagnosis, imaging using a contrast agent is performed in order to diagnose the occlusion state or open state of a blood vessel of a subject. In this type of contrast agent imaging, there is a difference between an image captured before injection of the contrast agent (hereinafter referred to as a mask image) and an image captured after injection of the contrast agent (hereinafter referred to as a contrast image). A method of generating a difference image by performing processing is often used.

  In the difference image, the bone part and the substantial part where the luminance hardly changes before and after the injection of the contrast agent are erased, while the blood vessel part whose luminance changes before and after the injection of the contrast agent can be made conspicuous. For this reason, the difference image is very useful for observing the blood vessel after the contrast medium is introduced. A technique for obtaining a blood vessel image from the difference images before and after the contrast medium is introduced is called DSA (Digital Subtraction Angiography).

JP 2002-157593 A

  In order to completely erase the background such as the bone in the difference image, it is a precondition that the subject does not move at all when the mask image is captured and the contrast image is captured. However, in reality, there is some movement of the subject (patient) between when the mask image is captured and when the contrast image is captured, and this movement causes a positional shift between the mask image and the contrast image. When the position shift occurs, the background (part other than the blood vessel) such as a bone portion disappears in the difference image as much as the position shift occurs, and this disappearance becomes an artifact in the difference image.

  In order to reduce this artifact, a technique is used in which one of the mask image and the contrast image is moved in the vertical and horizontal directions, or is rotated and aligned. However, the movement of the subject is not only a movement in a direction parallel to the projection plane of the mask image or contrast image (a parallel movement or a rotational movement in a two-dimensional plane), but also a three-dimensional movement accompanied by a twist or the like. It is common. The mask image and the contrast image are images in which such a three-dimensional movement is projected in a two-dimensional plane. For this reason, it is not possible to completely eliminate the disappearance (artifact) due to the positional deviation simply by translating the mask image and the contrast image in the vertical and horizontal directions or by rotating the mask image.

  Therefore, there is a need for a medical image processing apparatus and an X-ray diagnostic apparatus that can remove unremoved artifacts (artifacts) other than blood vessels due to this movement from the difference image even if the subject has a three-dimensional movement. .

  The medical image processing apparatus according to the present embodiment generates a difference image by performing a difference process between a mask image captured before injection of a contrast agent into a subject and a contrast image acquired after injection of the contrast agent. And a portion of the difference image having a pixel value higher than a predetermined first threshold value as a white portion, and a portion having a pixel value lower than the predetermined second threshold value as a black portion. A black and white pair determination unit that determines whether or not the white portion and the black portion pair exist within a predetermined range, and a removal processing portion that removes the white portion pixel from the difference image when the black and white pair exists. It is characterized by having provided.

Schematic which shows the external appearance structure of the X-ray diagnostic apparatus of this embodiment. The figure which shows the more specific structural example of the X-ray diagnostic apparatus of the system which has only a floor-standing type C arm. The functional block diagram which shows the function structural example of a medical image processing apparatus. 6 is a flowchart showing an example of the operation of the medical image processing apparatus according to the present embodiment. The figure explaining the position alignment method in the conventional medical image processing apparatus. The figure explaining the problem of the alignment method in the conventional medical image processing apparatus. The figure explaining the setting of the virtual straight line of the 1st Embodiment of the medical image processing apparatus which concerns on this embodiment, and the white part and the black part. The figure explaining the determination method in the black-and-white pair determination part of 1st Embodiment of the medical image processing apparatus which concerns on this embodiment. The figure explaining the process of the removal process part of 1st Embodiment of the medical image processing apparatus which concerns on this embodiment. The figure explaining the example which sets the virtual straight line of several directions to a difference image in 1st Embodiment of the medical image processing apparatus which concerns on this embodiment. The figure explaining the setting of the virtual strip | belt-shaped area | region to the difference image of 2nd Embodiment of the medical image processing apparatus which concerns on this embodiment.

  A medical image processing apparatus and an X-ray diagnostic apparatus according to this embodiment will be described with reference to the accompanying drawings.

  FIG. 1 shows an external structure of an X-ray diagnostic apparatus 2 including a medical image processing apparatus 1 of the present embodiment. The X-ray diagnostic apparatus 2 shown in FIG. 1 is a so-called biplane type X-ray diagnostic apparatus 2 including an overhead traveling Ω arm and a floor-standing C arm.

  The X-ray diagnostic apparatus 2 includes a holding device 21 that holds a floor-mounted C-arm 20, a ceiling mechanism 24 that holds an overhead traveling Ω arm 23, an image monitor 25, a bed device 26, an operation control unit 27, and a medical image processing device. 1 (not shown in FIG. 1).

  The X-ray diagnostic apparatus 2 of the embodiment is not limited to the configuration of FIG. 1, and may be configured to include only the floor-standing C arm 20 or only the ceiling traveling type Ω arm 23.

  FIG. 2 is a diagram illustrating a more specific configuration example of the X-ray diagnostic apparatus 2 of a system having only the floor-standing C-arm 20. As shown in FIG. 2, an X-ray irradiation device 200 is provided below the C arm 20, and an X-ray detection device 210 is provided above the C arm 20.

  The X-ray irradiation apparatus 200 includes an X-ray tube (X-ray source) 201 and a movable diaphragm device 202. The X-ray tube 201 receives supply of high voltage power from the high voltage supply device 203 and generates X-rays according to the conditions of high voltage power. X-rays generated by the X-ray tube 201 pass through the subject S lying on the top plate 261 of the bed apparatus 26 and reach the X-ray detection apparatus 210 at the top of the C arm 20.

  The X-ray detection apparatus 210 includes an FPD (Flat Panel Detector) 211 and an A / D (analog to digital) conversion circuit 212. The X-ray detected by the FPD 211 is converted into an electric signal, further digitized by the A / D conversion circuit 212, and sent to the medical image processing apparatus 1.

  The operation control unit 27 drives the C arm 20 and the couch device 26 by a user operation via an operation panel (not shown) or in response to an instruction from the medical image processing apparatus 1, as well as the X-ray irradiation apparatus 200 and X The line detector 210 is controlled.

  Note that the X-ray diagnostic unit 3 is configured by a configuration obtained by removing the medical image processing apparatus 1 from the X-ray diagnostic apparatus 2.

  FIG. 3 is a functional block diagram illustrating a functional configuration example of the medical image processing apparatus 1. Each function shown in FIG. 3 can be realized by software processing by causing a processor included in the medical image processing apparatus 1 to execute a predetermined program. In addition, each function may be realized by hardware such as ASIC, or may be realized by combining hardware processing and software processing.

  As illustrated in FIG. 3, the medical image processing apparatus 1 includes an X-ray image generation unit 110, an X-ray image storage unit 120, a difference image generation unit 130, a pixel shift processing unit 140, a monochrome pair determination unit 150, and a removal processing unit 160. The function of the display unit 170 is provided.

  The X-ray image generation unit 110 generates an X-ray image based on the X-ray signal detected by the X-ray detection device 210 and digitized by the A / D conversion circuit 212. The X-ray image generated by the X-ray image generation unit 110 includes a mask image captured before injecting the contrast agent and a contrast image captured after injecting the contrast agent.

  The X-ray image storage unit 120 stores the mask image and contrast image generated by the X-ray image generation unit 110.

  The difference image generation unit 130 acquires a mask image and a contrast image from the X-ray image storage unit 120, and performs a difference process between the mask image and the contrast image to generate a difference image.

  The pixel shift processing unit 140 performs pixel shift processing for correcting a two-dimensional positional shift between the mask image and the contrast image when generating the difference image generation unit 130. The pixel shift process will be described later.

  When the artifact remains in the difference image processed by the pixel shift processing unit 140, the monochrome pair determination unit 150 performs monochrome pair determination for detecting the artifact. The monochrome pair determination will be described later.

  The removal processing unit 160 performs processing to remove the artifact detected by the black and white pair determination unit 150. Processing for removing artifacts based on the black and white pair determination will be described later.

  The display unit 170 includes a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, and is processed by the difference image generation unit 130, the pixel shift processing unit 140, and the removal processing unit 160. Each image is displayed.

  FIG. 4 is a flowchart showing an example of the operation of the medical image processing apparatus 1 according to the present embodiment.

  In S <b> 101, the X-ray image generation unit 110 generates a mask image that is an X-ray image before the contrast agent is input, and stores the mask image in the X-ray image storage unit 120.

  In step S <b> 103, the X-ray image generation unit 110 generates a contrast image that is an X-ray image after the contrast agent is charged and stores the contrast image in the X-ray image storage unit 120.

  In S <b> 105, the pixel shift processing unit 140 performs pixel shift processing that corrects the positional deviation between the mask image acquired from the X-ray image storage unit 120 and the contrast image. Artifacts caused by misalignment between the mask image and the contrast image are called misregistration artifacts (hereinafter abbreviated as misregistration artifacts). Misregistration artifacts occur in the contour portion of the portion where the positional deviation occurs between the mask image and the contrast image.

  In step S <b> 107, the difference image generation unit 130 generates a difference image by performing difference processing between the mask image and the contrast image, and displays the difference image on the display unit 170.

  FIG. 5 is a diagram for explaining an alignment method in a conventional medical image processing apparatus. FIG. 5 shows an example in which an X-ray image in which a bone part and a blood vessel part are projected is acquired. FIG. 5A shows a “mask image A” before contrast medium injection, and FIG. 5B shows a “contrast image B” after contrast medium injection. Since FIG. 5A is before the contrast medium is charged, the blood vessel portion is not projected onto the X-ray image as indicated by a broken line. On the other hand, since FIG. 5B is after the contrast medium is charged, the blood vessel part is projected on the X-ray image as shown by the solid line, and both the bone part and the blood vessel part are projected in black. In this way, the portion that is difficult to transmit X-rays is projected in black as a signal having a small pixel value. In the examination for contrasting blood vessels, in order to observe only the contrasted part, the image after contrast medium injection (contrast image) is subtracted from the image before contrast medium injection (mask image), and the part other than the blood vessel part (for example, bone part) ) Is removed.

  A certain time is required for the contrast agent to reach the imaging region. Therefore, there are cases where the imaging position is shifted due to the body movement of the subject S while acquiring each image. In FIG. 5B, in addition to the images of the bone and blood vessels in the “contrast image B” (both drawn in black), the “mask image A” and the “contrast image B” are imaged. In order to show that a positional shift has occurred between the two, the positions of the bone part and the blood vessel part in the “mask image A” are indicated by a broken line for reference (the broken line is actually displayed in the “contrast image B”). is not).

  In FIG. 5B, an example in which the subject S is translated along the projection plane in the direction indicated by the arrow X between the time of capturing the “mask image A” and the time of capturing the “contrast image B”. Is shown.

  FIG. 5C shows the difference processing between the “mask image A” in FIG. 5A and the “contrast image” in FIG. 5B in which the positional deviation has occurred without performing positional deviation correction or the like. The difference image (AB) generated in this way is shown.

  In the following description, it is assumed that a difference image (AB) is generated by subtracting the image after contrast medium injection (contrast image B) from the image before contrast medium injection (mask image A). Alternatively, the difference image (B-A) may be generated by subtracting the image (mask image A) before contrast medium injection from the image after contrast medium injection (contrast image B).

  When the mask image A in FIG. 5A is imaged, no contrast agent is introduced into the blood vessel, so that the pixel value of the mask image A is substantially equivalent to the background. For this reason, in the blood vessel portion of the difference image (AB), only the white portion image in which only the black portion (low pixel value) of the blood vessel portion drawn in the “contrast image B” is reflected. That is, even if there is a position shift, no misregistration artifact due to the position shift occurs in the blood vessel portion on the difference image (AB).

  In contrast, as shown in FIGS. 5 (a) and 5 (b), the bone portion is rendered as a black image (that is, an image having a low pixel value) both before and after the contrast medium is introduced. The For this reason, if a positional shift occurs between the “mask image A” and the “contrast image B”, a part of the bone portion is not removed in the difference image (AB). That is, as shown in FIG. 5C, a portion where the bone portion of the “mask image A” and the bone portion of the “contrast image B” do not overlap is displayed in white or black. As described above, when a portion that cannot be removed from the contrast image is generated due to the position shift caused by the body movement, white or black misregistration artifacts are mixed into the difference image. On the difference image, since the blood vessel portion is drawn in white, particularly when a white misregistration artifact exists, it becomes impossible to correctly determine the blood vessel portion to be observed at the time of interpretation.

  Therefore, when generating the difference image, the other image is translated in the vertical and horizontal directions or rotated in accordance with the position of one of the acquired contrast image and mask image, and two images are obtained. To perform geometric alignment. Such alignment processing is called pixel shift processing. In the example shown in FIG. 5C, the subject S moves in the direction of the arrow X between the “contrast image B” and the “mask image A”. A “contrast image B ′” that is translated by the same amount in the opposite direction to X is generated and superimposed on the “mask image A” to eliminate the positional deviation. As described above, the pixel shift processing can correct a two-dimensional image shift due to the body movement of the subject S by correcting the shift of the imaging position.

  The pixel shift process may be automatically performed by the apparatus using a known alignment technique, or the display unit 170 displays “mask image A” and “contrast image B”, and the user selects one image. Manual positioning may be performed by using a pointing device such as a mouse for parallel movement or rotational movement.

  FIG. 5D shows a difference image between “contrast image B ′” obtained by subjecting the contrast image B acquired in FIG. 5B to pixel mask processing according to the position of the mask image A and “mask image A”. Is shown. In FIG. 5D, it can be seen that the bone misregistration artifacts as observed in FIG. 5C are removed from the difference image.

  However, the body movement of the subject S is not only a movement in a direction parallel to the projection plane of the mask image or the contrast image (a parallel movement or a rotational movement in a two-dimensional plane) but also a three-dimensional movement accompanied by a twist or the like. It is common that.

  FIG. 6 is a diagram for explaining that misregistration artifacts caused by such three-dimensional movement cannot be removed only by the pixel shift process.

  FIG. 6A is a “mask image A” similar to FIG. FIG. 6B is a “contrast image B”. FIG. 6B shows the projection surface of the subject S on the left side (in the direction indicated by the arrow X) when the “contrast image B” is imaged, compared to the “mask image A” imaged in FIG. And the angle between the upper part and the lower part of the bone part spreads in the direction of arrow Y.

  FIG. 6C shows a difference image (“mask image A” in FIG. 6A in which the positional deviation has occurred and “contrast image B” in FIG. 6B generated without performing pixel shift processing. A-B). In the difference image in FIG. 6C, a larger misregistration artifact is observed in the lower part of the bone than in the difference image shown in FIG.

  On the other hand, FIG. 6D shows “mask image A” in FIG. 6A and “contrast image B ′” after pixel shift processing is applied to “contrast image B” in FIG. 6B. A difference image (AB ′) obtained by performing a difference process on “mask image A” in FIG. FIG. 6D is a difference image (A−B ′) using “contrast image B ′” obtained by performing pixel shift processing in which “contrast image B” is translated in the direction opposite to arrow X. Although the misregistration artifact in the upper part of the bone shown in the upper left of FIG. 6D has been eliminated by the pixel shift process, the misregistration artifact in the lower part of the bone shown in the lower left is not eliminated. As described above, the pixel shift process can remove misregistration artifacts caused by the positional shift caused by the movement parallel to the projection surface of the subject S, but the entire bone part caused by the rotation of the joint part of the bone or the like. Misregistration caused by position shift due to a change in shape of the image (change in angle of the joint) or a position shift caused by projection of a three-dimensional movement in a direction different from the direction along the projection plane onto the two-dimensional plane Artifacts cannot be removed.

  Returning to FIG. 4, in S <b> 109 of FIG. 4, it is determined whether or not to perform a miss registration artifact removal process. The difference image that has been subjected to the difference process after the pixel shift process is displayed on the display unit 170, the user determines the occurrence status of misregistration artifacts remaining in the difference image, and the execution command signal input by the user based on the determination result Based on the above, it is determined whether or not to perform the miss registration artifact removal process. When the misregistration artifact removal processing is performed, the processing after S111 is performed, and when the removal processing is not performed, the difference image after the removal processing of S123, that is, the difference image obtained by performing only the pixel shift processing is displayed on the display unit. 170.

  In S <b> 111, the black and white pair determination unit 150 determines whether or not a white and black part pair exists within a predetermined range of the difference image based on the pixel value on the difference image generated by the difference image generation unit 130. On the difference image, a part where the pixel value is higher than a predetermined threshold is set as a white part, and a part where the pixel value is lower than the predetermined threshold is set as a black part. In S111, when determining the white portion and the black portion, a plurality of virtual straight lines that cover the difference image densely are set on the difference image.

  FIG. 7 is a diagram for explaining the setting of the virtual straight line and the white portion and the black portion caused by the positional deviation of the bone portion of the first embodiment of the medical image processing apparatus 1 according to the present embodiment. FIG. 7A is a diagram illustrating the setting of a virtual straight line to the difference image. Among these, the difference image shown in FIG. 7A is the same as the difference image (A−B ′) subjected to the pixel shift process shown in FIG. In the black and white pair determination unit 150, a virtual straight line is set when the black and white pair is determined. A plurality of horizontal lines on the difference image shown in FIG. 7A are virtual straight lines. Thus, the virtual straight line is set as a group of parallel straight lines along one predetermined direction so as to cover the difference image. The white portion and the black portion are determined for each of the set virtual lines.

  The upper diagram in FIG. 7B is a graph of pixel values of the mask image A corresponding to one virtual straight line indicated by XX ′ in FIG. 7A, and the lower diagram in FIG. This figure shows a graph of pixel values of a contrast image B ′ subjected to pixel shift processing. In either case, the horizontal axis indicates the horizontal width of the difference image, and the vertical axis indicates the size of the pixel value. A portion where the pixel value shows a large value in the plus direction on the graph is displayed in white on the projected image, and a portion showing a large value in the minus direction is displayed in black. Further, the portion where the pixel value is zero is the background portion, and is displayed in gray as lightness between white and black.

  As shown in FIG. 6A, in the mask image A, the bone part is displayed in black and the blood vessel part is not displayed. Therefore, in the change of the pixel value of the mask image A shown in the upper part of FIG. 7B, there is a portion where the pixel value is negative in the portion corresponding to the bone portion, and the change of the pixel value is in the blood vessel portion. can not see.

  On the other hand, as shown in FIG. 6B, in the contrast image B, the bone part and the blood vessel part are displayed in black. Similarly, in the contrast image B ′ obtained by subjecting the contrast image B to pixel shift processing, both the bone part and the blood vessel part are displayed in black. Accordingly, in the change in the pixel value of the contrast image B ′ shown in the lower part of FIG. 7B, there is a portion where the pixel value is negative in the portion corresponding to the bone portion, and the pixel value is also negative in the blood vessel portion. There is a part that becomes.

  Further, the range of pixel values indicating the bone portion is such that the contrast image B ′ shown in the lower part of FIG. 7B is more left than the mask image A shown in the upper part of FIG. It is shifted to. Therefore, when a difference image (AB ′) between the mask image A shown in the upper part of FIG. 7B and the contrast image B ′ shown in the lower part of FIG. 7B is generated, the difference image (A−B ′) shown in FIG. As described above, the pixel value of the bone portion is a range indicating a positive pixel value and a range indicating a negative pixel value except for a portion where the pixel values overlap. On the other hand, since the pixel value of the blood vessel portion is almost zero in the mask image A, the sign of the positive pixel value of the contrast image B ′ is inverted and becomes positive.

  In S113 of FIG. 4, the black and white pair determination unit 150 determines the white portion and the black portion based on the size of the pixel value on the virtual straight line, and determines whether the white portion and the black portion are a pair in order to determine whether they are a pair. The region is expanded to a predetermined range in both directions on the virtual straight line, and an overlapping region is obtained.

  In S115, it is determined whether or not there is a white part in the overlapping area. If there is a white part in the overlapping area, the removal processing unit 160 removes misregistration artifacts in S117.

  On the other hand, if there is no white portion in the overlapping area, it is determined whether all virtual straight lines have been processed in S121. If all virtual straight lines have not been processed, the process moves to the next virtual straight line in S119, The same process is repeated from S113 until the process is completed for all virtual straight lines. If it is determined in S121 that all virtual straight lines have been processed, the difference image after the removal process is displayed on the display unit 170.

  FIG. 8 is a diagram illustrating a determination method in the monochrome pair determination unit 150 of the first embodiment of the medical image processing apparatus 1 according to the present embodiment. FIG. 8 (a) is substantially the same as FIG. 7 (c), and shows a graph of the pixel value of the bone in the difference image (AB ′) between the mask image A and the contrast image B ′. ing. FIG. 8A shows that a portion showing a positive pixel value is higher than a predetermined first threshold value. Therefore, it can be determined that the portion showing the positive pixel value shown in FIG. 8A is a white portion. Similarly, it is indicated that the portion showing a negative pixel value is lower than a predetermined second threshold value. Therefore, the part showing the negative pixel value shown in FIG. 8A can be determined as a black part.

  The black and white pair determination unit 150 determines a white part and a black part and then determines that they are a pair. FIGS. 8B to 8D are diagrams for explaining a method for determining a black and white pair. First, as shown in FIG. 8B, the white area is enlarged in both directions from the center thereof to a predetermined range along a virtual straight line. The predetermined range may be determined based on a range designated by the user for removing misregistration artifacts, or may be determined based on an anatomical size or the like of the bone portion. Similarly, the black area is enlarged in the same direction as the white area in both directions from the center to a predetermined range along the virtual straight line. The areas enlarged in this way are referred to as an enlarged white area and an enlarged black area, respectively. The black and white pair determination unit 150 detects an overlapping area where the respective enlarged areas overlap (S113 in FIG. 4).

  As shown in FIG. 8C, when the white portion and the black portion are enlarged, the white portion or the black portion is present in the overlapping region where the enlarged white portion region and the enlarged black portion region overlap. As shown in FIG. 8D, when a white portion (a portion indicated by a grid line) is present in the overlapping area indicated by diagonal lines, the black and white pair determination unit 150 sets a pair of white and black portions on the virtual straight line. (Yes in S115 in FIG. 4). On the other hand, the white portion that does not pair with the black portion on the virtual straight line is not determined to be a misregistration artifact (No in S115 in FIG. 4).

  The white portion existing in the overlapping region is the bone misregistration artifact shown in FIG. 7A, and is specified as the artifact to be removed. On the other hand, as described above, since the blood vessel part is drawn as only a white part on the difference image, there is no black and white pair around the blood vessel part on the virtual straight line. For this reason, the white image of the blood vessel part is not determined as a misregistration artifact. In this way, the black and white pair determination unit 150 determines the white portion and the black portion, and further determines that they are pairs that exist within a predetermined range, so that the white portion as a misregistration artifact, that is, Identify the white parts to be removed.

  FIG. 9 is a diagram for further explaining the processing of the removal processing unit 160 of the first embodiment of the medical image processing apparatus 1 according to the present embodiment. FIG. 9A shows the same diagram as FIG. 8D, and shows that a white part to be removed is included in the overlapping region. FIG. 9B shows the pixel values of the difference image (A−B ′) before removing the white part to be removed, as in FIG. 7C. FIG. 9D is a difference image (A−B ′) before removing the white part to be removed in FIG. As shown in FIG. 9D, before performing the removal process, a misregistration artifact displayed in white is mixed in the projection portion of the bone. In FIG. 9B, the part determined to be a white part is displayed white on the difference image (A-B ′), and the part determined to be a black part is displayed black. The background portion where the other pixel values are zero is displayed in gray. When the blood vessel part is contrasted, only the blood vessel part projected in white is set as an observation target. Therefore, if misregistration artifacts displayed in white are mixed, the interpretation of the projected image is hindered.

  Therefore, the removal processing unit 160 of the medical image processing apparatus 1 according to the present embodiment removes a portion corresponding to this misregistration artifact.

  FIG. 9C shows a case where the pixel value of the white portion to be removed is set to zero. In this way, by setting the pixel value of the white part to be removed to zero, it is possible to remove the misregistration artifact displayed in white at the projection part of the bone part as shown in FIG. 9 (e).

  In FIG. 9C, at the same time, the pixel value of the black portion is set to zero. The part determined to be a black part can be distinguished from the blood vessel part on the difference image, but it is preferably not present because it may be misidentified as another part having a high X-ray transmittance, such as air. Therefore, by setting the pixel value of the black part paired with the white part to be removed to zero, the bone part can be completely removed from the difference image (A-B ′).

  As described above, the medical image processing apparatus 1 according to the present embodiment identifies a white part and black part pair, sets the pixel values of the white part and black part as a pair to zero, and treats the same as the background part. Thus, the miss registration artifact is removed from the difference image. In this way, it is an object to be contrasted by removing misregistration artifacts caused by three-dimensional movements accompanied by changes in body angles and torsion caused by body movement that cannot be completely removed by pixel shift processing. It is possible to generate a better difference image that allows easy observation of the blood vessel portion.

  In the first embodiment described so far, the virtual straight line is set in only one direction. However, as a modification thereof, a plurality of parallel straight line groups along a plurality of directions may be set.

  FIG. 10 is a diagram illustrating an example in which virtual straight lines in a plurality of directions are set in the difference image in the first embodiment of the medical image processing apparatus 1 according to the present embodiment. In FIG. 10, the same difference image as the difference image (A−B ′) illustrated in FIG. 7A is displayed. The first virtual straight line group shown in FIG. 10 is the same as the virtual straight line group shown in FIG. On the other hand, the second virtual straight line group is set in a direction different from that of the first virtual straight line group. For example, it is set in a direction rotated by 45 degrees with respect to the first virtual straight line group.

  For example, when the direction of movement of the subject S and the direction of the first virtual straight line group are orthogonal, a white part and black part pair cannot be formed on the straight line of the first virtual straight line group. The registration artifact cannot be deleted. Therefore, as shown in FIG. 10, by setting a group of virtual straight lines in a plurality of directions and performing monochrome pair determination, it is possible to improve the detection accuracy of misregistration artifacts. FIG. 10 shows a virtual straight line group in two directions, but the optimal number of directions can be set according to the detection accuracy of misregistration artifacts and the performance of the black-and-white pair determination unit 150 for processing the misregistration artifacts. That's fine.

  Furthermore, as a second embodiment, the virtual straight line may be set as a band-like virtual belt-like region having a certain width.

  FIG. 11 is a diagram for explaining the setting of the virtual band-like area to the difference image in the second embodiment of the medical image processing apparatus 1 according to this embodiment. In FIG. 11, the same difference image as the difference image (A−B ′) shown in FIG. 7A is displayed. As shown in FIG. 11, a plurality of virtual band-like areas that densely cover the difference image are set, and the white part and the black part are determined on each virtual band-like area. Similarly to FIG. 8A, a portion where the pixel value is higher than the predetermined first threshold is set as a white portion, and a portion where the pixel value is lower than the predetermined second threshold is set as a black portion. Then, it is determined for each of the plurality of virtual strip regions whether or not there is a pair having a white portion and a black portion overlap region on the virtual strip region.

  As shown in FIG. 11, by setting a virtual belt-like region group instead of a virtual straight line group, the amount of processing performed by the black-and-white pair determination unit 150 is reduced, and the determination can be performed efficiently. In addition, when the modification example in which the virtual straight line group is set from a plurality of directions illustrated in FIG. 10 is applied to the virtual belt-like region group, the processing amount performed by the black and white pair determination unit 150 is reduced, A black and white pair determination can be performed by setting a virtual band-like region group.

  Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments 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 Medical image processing apparatus 2 X-ray diagnostic apparatus 20 Floor-standing C arm 25 Image monitor 26 Bed apparatus 27 Operation control part 110 X-ray image generation part 120 X-ray image memory | storage part 130 Difference image generation part 140 Pixel shift process part 150 Black and white Pair determination unit 160 Removal processing unit 170 Display unit 200 X-ray irradiation apparatus 201 X-ray tube (X-ray source)
202 Movable diaphragm device 203 High voltage supply device 211 FPD
212 A / D conversion circuit 261 Top plate

Claims (9)

A difference image generation unit that generates a difference image by performing a difference process between a mask image captured before injection of a contrast medium into a subject and a contrast image captured after injection of the contrast medium;
On the difference image, when a portion where the pixel value is higher than the predetermined first threshold is a white portion and a portion where the pixel value is lower than the predetermined second threshold is a black portion, the difference image is within a predetermined range. A black-and-white pair determination unit that determines whether or not a pair of the white part and the black part exists,
If the black and white pair exists, a removal processing unit for removing the white pixels from the difference image;
A medical image processing apparatus comprising: The black and white pair determination unit
Setting a plurality of virtual lines that cover the difference image densely, and determining whether or not a pair of the white part and the black part exists on the virtual line for each of the plurality of virtual lines;
The medical image processing apparatus according to claim 1. The black and white pair determination unit
The white area is enlarged in both directions from the center to the predetermined range along the virtual straight line, and the black area is enlarged in both directions from the center to the predetermined range along the virtual straight line. A pair of the white part and the black part exists on the virtual straight line when the white part exists in an overlapping area where the enlarged white part area and the enlarged black part area overlap. It is determined that
The medical image processing apparatus according to claim 2. The removal processing unit
Removing the white pixel by setting the white pixel value to a minimum value or zero;
The medical image processing apparatus according to claim 1, wherein the medical image processing apparatus is a medical image processing apparatus. The removal processing unit
When the pixel value of the black portion is not zero, the pixel value of the black portion is set to zero.
The medical image processing apparatus according to claim 4. The black and white pair determination unit
6. The medical image processing apparatus according to claim 2, wherein the plurality of virtual straight lines are set as one parallel straight line group along a predetermined direction. The black and white pair determination unit
6. The medical image processing apparatus according to claim 2, wherein the plurality of virtual straight lines are set as a plurality of parallel straight line groups respectively along a plurality of directions. The black and white pair determination unit
A plurality of virtual band-like areas that densely cover the difference image are set, and on each of the virtual band-like areas, a part having a pixel value higher than a predetermined first threshold is set as a white portion, and the pixel value is set to a predetermined second value. When a portion lower than the threshold value is a black portion, it is determined whether or not a pair of the white portion and the black portion exists on the virtual strip region, for each of the plurality of virtual strip regions,
The removal processing unit removes the white pixel on the virtual belt-like region when the black-and-white pair exists;
The medical image processing apparatus according to claim 1. An X-ray imaging unit that performs X-ray fluoroscopic imaging on a subject;
A difference image generation unit that generates a difference image by performing a difference process between a mask image obtained by fluoroscopic imaging before injection of a contrast agent into the subject and a contrast image obtained by fluoroscopic imaging after injection of the contrast agent;
On the difference image, when a portion where the pixel value is higher than the predetermined first threshold is a white portion and a portion where the pixel value is lower than the predetermined second threshold is a black portion, the difference image is within a predetermined range. A black-and-white pair determination unit that determines whether or not a pair of the white part and the black part exists,
If the black and white pair exists, a removal processing unit for removing the white pixels from the difference image;
An X-ray diagnostic apparatus comprising: