JP2003250087A - X-ray diagnosing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray diagnosing apparatus capable of displaying a sharp subtraction image by correcting position deviation of photographing between a mask image and a contrast image. <P>SOLUTION: The X-ray diagnosing apparatus includes: an X-ray generating section 2; an X-ray detection section 5; a mechanism control section 6 for moving them; a mechanism position detection section 7 and a position information storage circuit 35 for detecting and storing a movement position; a mask image storage circuit 28 for storing the mask image obtained from the X-ray detection section 5; a position information comparison circuit 36 for comparing photographing positions of the contrast image and the mask image obtained from the X-ray detection section 5; a pixel shift circuit 30 and a subtraction circuit 31 for correcting the image on the basis of the comparison result and obtaining the subtraction image; and a display section 11 for displaying the subtraction image. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray diagnostic apparatus for obtaining a subtraction image from a mask image and a contrast image.

[0002]

2. Description of the Related Art An X-ray diagnostic apparatus is an image diagnostic apparatus that emits X-rays into the body of a subject, detects the intensity of the X-rays transmitted through the body by a detector, and displays the amount of transmission as a grayscale image. In recent years, advances have been made mainly in the cardiovascular field with the development of catheter procedures.

An X-ray diagnostic apparatus for the purpose of cardiovascular diagnosis is intended for the diagnosis of arteriovenous system such as cardiovascular system, but the diagnosis of the arterial system is the main focus. The state is observed by an X-ray transmission image. The basic device configuration in this case is an X-ray generation unit, an X-ray detection unit, a holding mechanism for holding them, a catheter bed (top plate), and a signal processing unit. A C-arm is usually used as the holding mechanism, and by combining it with a cantilever type catheter bed, a fluoroscopic imaging at a free position and angle with respect to a subject (patient) is possible. Further, in the movement in the body axis direction, the same effect can be obtained by moving the top plate instead of the holding mechanism.

Further, the circulatory X-ray apparatus has a digital fluorography function typified by digital subtraction angiography (DSA), and the X-ray transmission image information is converted into a digital signal, which facilitates various image processing. Become. When diagnosing a stenosis site in a blood vessel, the contrast agent is injected by imaging the diagnosis site before and after injecting the contrast agent into the blood vessel and performing subtraction (subtraction) between the two obtained images. Only existing blood vessels can be displayed with high contrast resolution.

When a blood vessel DSA image in a wide area such as a lower limb is obtained by a current X-ray diagnostic apparatus for cardiovascular system, it is impossible to observe the whole area with one image, so that the C arm or the top plate is moved. While shooting. That is, the X-ray tube of the X-ray generation unit and the X-ray II (image intensifier) of the X-ray detection unit, which are attached to both ends of the holding mechanism, are moved in the body axis direction of the patient before the injection of the contrast agent. While taking the reference image (mask image) at multiple places,
After further injecting the contrast agent, an image containing the contrast agent (contrast image) is captured at the same position. Next, the mask image and the contrast image obtained at the same site are subtracted, and the DSA image is displayed on the monitor in real time.

[0006]

In order to obtain a clear DSA image by the X-ray diagnostic apparatus for the circulatory organ, it is necessary to accurately align the contrast image and the mask image. In capturing a contrast image, an X-ray tube and an X-ray I.D. I. Is moving together with the holding mechanism, a method of irradiating an X-ray to obtain a contrast image when the holding mechanism reaches the same position as the position where the mask image was captured is used. If this method is used when the moving direction of the holding mechanism at the time of photographing and the moving direction of the holding mechanism at the time of photographing the mask image are the same, the positional deviation between the respective images is small. The positional deviation in this case is determined by the detection accuracy of the holding mechanism position detector, and the error is usually 0.1 mm or less. Therefore, the positional deviation between the contrast image and the mask image in this case has little influence on the occurrence of artifacts on the DSA image.

On the other hand, when the flow velocity of the contrast medium is extremely slow due to stenosis in the blood vessel or the like, the movement of the holding mechanism precedes too much, and the contrast medium is returned to the position of the contrast medium or stopped to stop the contrast medium. Will have to wait until When the holding mechanism returns, the holding mechanism moves in the opposite directions when the contrast image is captured and when the mask image is captured, which may cause a non-negligible positional deviation between the images for the reason described below.

The position accuracy of the contrast image when stopped is 1 mm or more depending on the stop position accuracy of the holding mechanism. That is, the positional deviation between the contrast image obtained while the holding mechanism is stopped and the mask image obtained while moving at a predetermined constant speed in advance is 1 mm.
Moderately, this deviation results in the production of unacceptable artifacts on the DSA image.

According to the present invention, a clear DSA image can be continuously obtained even when the holding mechanism is stopped or when the moving direction of the holding mechanism is opposite between the contrast image photographing and the mask image photographing. It is an object of the present invention to provide a diagnostic device.

[0010]

In order to solve the above-mentioned problems, the X-ray diagnostic apparatus of the present invention detects the X-rays emitted by the X-ray generating means for emitting X-rays to the subject. X-ray detection means, mechanism part and mechanism control means for moving at least one of an image system mechanism part in which the X-ray generation part and the X-ray detection part are integrated, and a top plate mechanism part on which a subject is placed. And X obtained by the detection means
An image storage unit that stores a line image, and an image of the subject that does not contain a contrast agent from the image storage unit is taken out as a mask image, and the image of the subject that contains the contrast agent is also taken out from the image storage unit. Subtraction means for performing subtraction with the contrast image,
Pixel shift means for pixel-shifting at least one of the mask image and the contrast image to obtain a subtraction image between these images, and display means for displaying the subtraction image obtained by the subtraction means. Is characterized by.

Therefore, according to the present invention, it is possible to obtain a clear subtraction image even when a contrast image is captured under a condition different from that of the mask image capturing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of an X-ray diagnostic apparatus for displaying a subtraction image according to the present invention in real time will be described below with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram showing a first embodiment of the present invention. This X-ray diagnostic apparatus uses an X-ray for the subject 3
X-ray generation unit 2 for irradiating the X-ray, a high voltage generator 1 for supplying a high voltage thereto, an X-ray detection unit 5 for detecting X-rays transmitted through the subject 3, and an X-ray generation unit 2 And a mechanism control unit 6 that holds the X-ray detection unit 5 and controls the movement thereof. The X-ray generation unit 2, the X-ray detection unit 5, and the top plate 4 constitute a mechanical unit, and the mechanical position detection unit 7 detects the position of this mechanical unit. The detection signal of the X-ray detection unit 5 is the image storage / operation unit 1.
It is supplied to 0 and stored / calculated. Image storage / operation unit 1
The image information of 0 is displayed on the display unit 11. The system control circuit 8 controls the entire apparatus according to an instruction from the console 9.

The high voltage generator 1 is for converting a power supply voltage into a high voltage and supplying it to the X-ray tube, and has a large output capacity of 80 KW to 100 KW by an inverter system.

The X-ray generator 2 comprises an X-ray tube 21 for irradiating the subject 3 with X-rays, and an X-ray diaphragm 22 for collimating the X-rays emitted from the X-ray tube 21. There is.
This X-ray tube 21 is a vacuum tube that generates X-rays, and accelerates electrons by the high voltage supplied from the high voltage generator 1,
X-rays are generated by colliding with a tungsten target. The X-ray diaphragm 22 is located between the X-ray tube 21 and the subject 3 placed on the top plate 4, and narrows the X-ray beam emitted from the X-ray tube 21 to an image receiving size to obtain a clear image. It has a function.

The top plate 4 is a bed on which the subject 3 is placed during X-ray photography, and is made of a material which easily transmits X-rays.
The top plate 4 is arranged between the X-ray generator 2 and the X-ray detector 5 which are arranged at a predetermined interval by the holding mechanism (C arm) 23, and is used to image a predetermined part of the subject 3. It is possible to move in the axial direction (direction perpendicular to the drawing).

The X-ray detection unit 5 detects the X-ray I.D. I. 24 and an X-ray television camera 26. This X-ray I.D.
I. The X-ray image information is converted into visible light by means of 24 and further converted into an optical image having high sensitivity by multiplying the luminance in the process of light-electron-light conversion. X converted to an optical image
The line image information is converted into an electric signal (video signal) by the X-ray television camera 26. X-ray TV camera 2
A CCD image pickup device 6 is used. In the following, the X-ray generation unit 2 and the X-ray detection unit 5 are collectively referred to as a video system.

The mechanism control unit 6 is composed of a video system mechanism unit 38, a top plate mechanism unit 39, and a mechanism control circuit 40. The image system mechanism unit 38 is integrated with the holding mechanism 23 that supports the X-ray generation unit 2 and the X-ray detection unit 5, and has a mechanism for rotation around the top plate 4 and horizontal movement in the body axis direction. Has been. The top plate mechanism section 39 is a top plate 4 on which the subject 3 is placed.
And a mechanism for horizontally moving the top plate 4 in the axial direction of the body of the subject with the subject 3 placed thereon. The mechanism control circuit 40 is a circuit that controls the movement of the image mechanism unit 38 and the top mechanism unit 39 in each direction, and outputs a control signal to each mechanism unit. Further, from the control circuit 40, the X-ray generation unit 2, the X-ray detection unit 5 and the top plate 4 are
Emits an identification signal for identifying the movement state of the.

The mechanism position detector 7 comprises a position detector 37, a position information storage circuit 35, and a position information comparison circuit 36. The position detector 37 receives a position signal from an encoder (not shown) attached to a movable part of the image system mechanism part 38 or the top plate mechanism part 39 via the mechanism control circuit 40,
The positions of the X-ray generation unit 2, the X-ray detection unit 5, and the top plate 4 are detected. The mechanism position detection result at the time of collecting the mask images is stored in the position information storage circuit 35 in advance. Further, the mechanism position detection result at the time of collecting the contrast image is sent to the position information comparison circuit 36. The position information comparison circuit 36 is a position information storage circuit 35.
The position information of the mask image sent from the device and the position information of the contrast image sent directly from the position detector 37 are compared, and if the position information of both images match, a matching pulse is output.

The system control circuit 8 is a central control circuit for controlling acquisition of X-ray fluoroscopic image data, control for image processing of the acquired image data, and movement control of a video system, and mask image photographing at the time of displaying a DSA image. Controls the entire system, including control of the video system for capturing contrast images and subtraction control of mask images and contrast images.

The operation console 9 is equipped with various switches and buttons, a keyboard, a display panel, etc., and is used for operations such as starting inspection, stopping and releasing the mechanical section, switching the moving direction, and changing the moving speed. The operation is performed from the operation console 9 by the operator of the apparatus.

The image storage / calculation unit 10 includes an A / D converter 27.
A mask image storage circuit 28 and an address control circuit 30.
And a subtraction circuit 31. A /
The D converter 27 converts the video signal from the X-ray television camera 26 into a digital signal. The mask image storage circuit 28 stores the mask image information obtained at the time of collecting the mask images and the mask image position information detected by the mechanism position detection unit 7 in association with each other. That is, the mask image storage circuit 28 is configured to output the mask image obtained at that position by inputting the mask image position information.

The subtraction circuit 31 subtracts, for each pixel, the mask image information stored in the mask image storage circuit 28 and the contrast image information sent from the A / D converter 27 when the contrast image is collected. Further, the address control circuit 30 performs control for shifting the mask image with respect to the contrast image by a predetermined number of pixels when subtracting the contrast image and the mask image. Specifically, it can be realized by shifting the read address of the mask image storage circuit 28.

The display unit 11 comprises a D / A converter 32, a display circuit 33, and a monitor 34. The image output of the subtraction circuit 31 is converted into an analog signal by the D / A converter 32, and the display circuit 33 is displayed. After being converted into a television format signal at, it is displayed on the monitor 34.

FIG. 2 is a flow chart showing a photographing procedure in the first embodiment of the present invention, and FIGS.
Shows how to move the video system. The operation of the entire apparatus will be described with reference to these drawings.

In this embodiment, X-ray transmission image information is converted into digital data at high speed, and the image data is subjected to subtraction processing in real time to enhance the image. For example, arteries and veins are obtained by subtraction of a mask image and a contrast image. Its main purpose is to observe the vascular system.
In this imaging method, as described above, the image system integrated with the holding mechanism 23 to trace the flow of the contrast agent injected into the blood vessel in the body (that is, the X-ray generation unit 2 and the X-ray detection unit 5). Obtain a subtraction image while moving.

The femoral artery of the foot is the main target site for X-ray DSA diagnosis. In this diagnosis, a contrast medium is injected into the blood vessels of the inguinal region, and the state in which it flows to the peripheral part of the toes is observed under a fluoroscopic image. For this reason, it is necessary to perform the contrast image capturing along this flow, and the image system is also moved from the mouse cage to the distal end to perform image acquisition.
On the other hand, the moving direction of the video system at the time of photographing the mask image is not particularly determined.

The image system at the time of photographing the mask image in FIG. 3 shows the case where the image is moved from the mouse ridge to the end of the foot (that is, the same direction as at the time of photographing the contrast image). This method has the trouble of returning the video system to the mask image radiographing start position X1 when switching from the mask image radiographing to the contrast image radiographing, but there is a mechanical error of the video system mechanical unit 38 or an error due to an X-ray irradiation time described later. Accurate alignment is possible because there are few.

The operation of the X-ray diagnostic apparatus at this time will be described below in association with the flowchart of FIG.

In photographing a mask image, first, the image system mechanism section 38 and the mechanism control circuit 40 move the image system to the mask image photographing start position X1 (step S1).
The X-ray tube 2 of the X-ray generation unit 2 at the imaging start position X1
1 radiates X-rays toward the subject 3 and the X-rays I.I. I. An X-ray transmission image is obtained by 24. X-ray I.D. I. At 24, the X-ray image is converted into an optical image, and further converted by the X-ray television camera 26 into an electric signal (video signal). The video signal output from the X-ray television camera 26 is A / of the image storage / calculation unit 10.
The digital signal is converted by the D converter 27 and stored in the mask image storage circuit 28.

On the other hand, a holding mechanism 23 integrated with the image system
The output of the encoder provided in the
Is sent to the position detector 37 of the mechanism position detector 7. The position detector 37 detects the imaging start position X1 of the video system, and the value thereof is stored in the position information storage circuit 35 and also added to the mask image information stored in the mask image storage circuit 28. Next, the image pickup start position X1 is moved by .DELTA.X in the body axis direction (X direction in FIG. 3), and the same operation as at the image pickup start position X1 is performed. In this way, the movement of the video system is repeated up to XN at a predetermined interval (here, equal intervals ΔX) to obtain N
The mask image of the location is stored as an image together with the video system position information.
Sequentially stored in the mask image storage circuit 28 of the arithmetic unit 10,
The image system position information is also stored in the position information storage circuit 35 of the mechanism position detection unit 7 (steps S2 to S3).

When the photographing of N mask images is completed in the section from X1 to XN, the image system and the holding mechanism 2
3 is returned to the shooting start position X1 of the first mask image.
At the time when the image system is returned to X1, the contrast agent is injected into the inguinal aorta of the subject 3, and the imaging of the contrast image is started. (Steps S4 to S5). In FIG. 3, also in this case, the video system starts moving from X1 toward XN at the foot end, similarly to the mask image shooting (step S5). With the movement of the image system, its position is counted and detected by the position detector 37 of the mechanism position detector 7, and the value is sent to the position information comparison circuit 36.

On the other hand, the position information storage circuit 35 has already stored the shooting position information of N points recorded at the time of shooting the mask image, and this position information is also sent to the position information comparison circuit 36. Here, the position information of the video system at the time of photographing the contrast image is compared with the position information already obtained at the time of photographing the mask image, and when they match, the signal output is sent to the high voltage generator 1. That is, when the position of the image system at the time of photographing the contrast image and the photographing position of the mask image coincide with each other, a coincidence pulse is output from the position information comparison circuit 36, and the high voltage generator 1 is triggered by this coincidence pulse to generate an X-ray. X-rays are radiated from the generator 2 to collect a contrast image.

By the way, the speed of the blood flow in the blood vessel in the body is not uniform because it depends on the diameter of the blood vessel and the presence or absence of stenosis. Therefore, the moving speed of the image system needs to be controlled according to the flow rate of the contrast agent, but the operator of the device can switch the frequency of the drive signal sent from the mechanism control circuit 40 to the image system mechanism section 38 on the console 9. Can be controlled with.

As shown in FIG. 3, the moving direction of the image system at the time of photographing the contrast image is the same as that at the time of photographing the mask image, and if the movement is continuous, even if the moving speed is not uniform, According to the image capturing method described above, the image capturing positions of the contrast image and the mask image can be matched with high accuracy.

The X-ray radiated by the trigger signal from the position information comparison circuit 36 passes through the subject 3 and the X-ray I.D. I. Two
The X-ray fluoroscopic image (contrast image) is formed at 4. The contrast image is once converted into an optical image here, and then converted into an electric signal by the X-ray television camera 26 (step S7). The image signal from the X-ray television camera 26 is converted into a digital signal by the A / D converter 27 of the image storage / calculation unit 10 and sent to the subtraction circuit 31. Here, a subtraction image is generated between the contrast image and the mask image at the same position sent from the mask image storage circuit 28 (step S9), and is displayed on the display unit 11 in real time (step S1).
0).

In this case, since the positional accuracy of the mask image and the contrast image is good, the position correction between the images by the address control circuit 30 is unnecessary. In this way, the contrast image photographing position is repeated until it reaches XN, and the photographing result is recorded by a recording device (not shown) as necessary. (Steps S11 to S12) In the description so far, a case has been described in which the video system at the time of contrast image shooting moves continuously in the same direction as at the time of mask image shooting. A case of temporarily stopping will be described with reference to FIGS. 2 and 4.

FIG. 4 shows a moving method of the image system when the image system is temporarily stopped during the movement, and the mask image photographing method (steps S1 to S3) has already been described in FIG. Since it is the same as the one described above, its explanation is omitted.

When the photographing of N mask images X1 to XN is completed, a contrast agent is injected into the aorta of the inguinal region, and the contrast image photographing is started (step S
4).

Similar to the case of FIG. 3, the video system is returned to the mask image photographing start position X1 and the contrast image is photographed while moving toward the foot end portion XN. However, when it is observed on the display unit 11 that the moving speed of the contrast agent is remarkably slow in the process of moving toward the terminal end (XN) of the image system, the device operator presses the stop button provided on the operation console 9. The movement of the image system is temporarily stopped, and it is made to wait until the contrast agent reaches the imaging region. Here, it is assumed that the video system stops at X0.

The stop of the image system is executed by the operator of the apparatus judging from the state of the contrast agent in the subtraction image displayed in real time. In accordance with an instruction from the operator, the contrast system is photographed at a predetermined time interval while the video system is stopped, and the subtraction image obtained at this time is displayed on the monitor 34.

A method of capturing a contrast image when the video system is stopped will be described below. The image system is moved toward the terminal end of the foot by using the reference point X1 as the start point of the contrast image capturing, and until the image system reaches X0, the position of the image system is the mask image capturing as in the case of the continuous movement described above. At the time of coincidence with the position (for example, X1, X1 + ΔX, ...), the trigger signal from the position information comparison circuit 36 radiates X-rays from the X-ray generation unit 2 toward the subject 3,
The transmission image is detected by the X-ray detection unit 5.

The output signal of the X-ray detector 5 is an image storage /
After being A / D converted in the arithmetic unit 10, it is sent to the subtraction circuit 31, where a subtraction image is generated with the mask image at the same position sent from the mask image storage circuit 28 and displayed on the display unit 11. (Step S5). However, in this case, since the positional deviation between the mask image and the contrast image is small, the pixel shift by the address control circuit 30 is not performed.

When the operator presses the video system movement stop button on the console 9 at the time when the video system moves to X0 (step S6), X0 is, for example, the mask image photographing positions Xa and X.
If it exists between b, the video system continues moving to the mask image photographing position Xb near the foot end.

Next, at the moment when the position information of the image system detected by the position detector 37 matches the photographing position Xb of the mask image stored in the position information storage circuit 35, a coincidence pulse is output from the position information comparison circuit 36. Then, the high voltage generator 1 and the X-ray generator 2 are driven by this signal to capture a contrast image.

A command to stop the video system is issued from the console 9 via the system control circuit 8. However, the video system mechanical unit 38 cannot stop the video system suddenly due to inertial force, causing a positional shift by δX and stopping. Step S13). That is, the actual video system stop position is Xb + δX. At this time, a video system stop signal is sent from the mechanism control circuit 40 to the changeover switch 41.
The drive signal of the high voltage generator 1 sent from the position information comparison circuit 36 up to now is switched to the drive signal sent from the system control circuit 8 at a predetermined interval.

The high voltage generator 1 is driven by this new drive signal to radiate X-rays, and the contrast image obtained by these X-rays is the A / D of the image storage / calculation unit 10.
It is sent to the subtraction circuit 31 via the converter 27 (steps S14 to S15). In addition, the position detector 37
The video system position information Xb + δX detected by is sent to the position information comparison circuit 36.

The positional deviation δX generated at this time when the image system is stopped is compared with the measurement error of the position detector 37 itself.
It is more than an order of magnitude larger and is a major factor in the occurrence of artifacts when subtraction images are generated, so correction is necessary.

Next, the correction method will be described. In the position information Xb + δX of the video system measured by the position detector 37, a position deviation δX from the mask image photographing position Xb is detected by the position information comparison circuit 36, and the result is the system control circuit 8
Are sent (step S16).

As described above, the position information comparing circuit 36 during the contrast image photographing generates a coincidence pulse when the image system is moving and the position coincides with the contrast image photographing position, and causes the X-ray generator 2 to operate. It has a first function of driving, and has a second function of detecting a positional deviation between the stop position and the mask image photographing position when the video system is stopped.

By the way, the photographing conditions of the mask image and the contrast image are set by the system control circuit 8 before photographing. For example, the X-ray tube 21, the subject 3, the X-ray I.D. I.
The magnification of the X-ray image determined from the 24 positions, that is, the number of pixels per unit length of the image is predetermined. Therefore, the relationship between the positional deviation δX of the image system and the number of pixels on the X-ray image can be easily calculated from this magnification.

If the pixel conversion value of this positional deviation δX is β, a good match can be obtained by shifting the mask image obtained by Xb + δX by β pixels in the body axis direction and superimposing it on the contrast image at the photographing position Xb. It can be obtained (step S17).

FIG. 5 schematically shows the pixel shift. The image is simplified with one-dimensional pixels, and the contrast image shows a case where the pixel is displaced by 2 pixels (that is, β = 2) from the mask image. 5A is a mask image, FIG. 5B is a contrast image, and FIG. 5C is a subtraction image.
(1) to A (7) are output addresses of the pixels of the mask image storage circuit 28, B (1) to B (7) are output addresses of the X-ray television camera 26, and C (1) to C (5). Is an output address of the subtraction circuit 31.

The subtraction circuit 31 subtracts the n + 2th pixel B (n + 2) in the contrast image from the nth pixel A (n) in the mask image. That is, C (n) = B (n + 2) -A
The pixel C (n) of the subtraction image is calculated as (n). However, the actual pixel shift calculation is performed by the mask image storage circuit 28 which is input to the subtraction circuit 31.
This can be easily performed by controlling the read address of 1 by the address control circuit 30.

The value of the shift amount β calculated by the system control circuit 8 is sent to the address control circuit 30, and the mask image at the photographing position Xb is pixel-shifted by β by the control signal of the address control circuit 30 to shift the photographing position. Xb + δ
Subtract the X contrast image. By this pixel shift, a subtraction image with few artifacts can be displayed on the display unit 11 (step S18-).
S19).

The operator of the apparatus observes the monitor 34 of the display unit 11 and continues the photographing with the image system stopped until the contrast agent reaches the region being photographed, and then the image on the console 9 is displayed. The system stop release button (not shown) is pressed to move the image system again along the flow of the contrast agent. This operation repeats the processes of steps S7 to S11 until the video system reaches XN.

When a plurality of contrast images are photographed while the video system is stopped, the pixel shift amount detected when the first subtraction image is generated can be applied to the second and subsequent images as they are. The position shift detection of the video system in step S16 in the flowchart can be omitted.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 6 shows a moving method of the image system including a case where the blood flow velocity is extremely slow and therefore the blood vessel is returned to the direction of the mouse cage. FIG. 7 is a flowchart showing the photographing procedure.

The procedure for photographing the mask image is the same as that already shown in the flowchart of FIG. 2, and the video system is moved to the mask image photographing start position X1 (step S31).
An X-ray transmission image is obtained every time the object is moved in the body axis direction at a substantially constant speed with this point as a reference point and moved by a predetermined interval ΔX.

First, the X-ray image information obtained by the X-rays emitted from the X-ray generator 2 at the reference point is converted into an electric signal by the X-ray detector 5 and stored in the mask image storage circuit 28. On the other hand, the position information X1 of the video system is detected by the position detector 37 and stored in the position information storage circuit 35 and the mask image storage circuit 28. The same operation is repeated until the photographing end position XN of the mask image (steps S32 to S33).

Next, in the image system, the photographing start position X of the mask image
After that, the contrast agent is injected into the aorta of the inguinal region, and the imaging of the contrast image is started. (Step S34
(S35) Here, a method of moving the image system at the time of capturing a contrast image will be described with reference to FIG. The image system captures a contrast image while moving from X1 toward the foot end portion XN. However, the image system is temporarily stopped at X0 on the way to the end (XN), and then moved in the direction opposite to the mask image capturing direction, and this movement reaches XC where the front edge of the contrast agent becomes observable. Until it is done.

Next, the image system temporarily stops at XC, and then starts moving toward the distal end of the foot again at a speed substantially equal to the speed of the contrast medium. In this case, if the stop time at X0 and XC is longer than the update time of the subtraction image,
If the correction method in the first embodiment is applied, a clear subtraction image can be obtained when the video system is stopped.

On the other hand, when the stop at X0 and XC is extremely short, correction by pixel shift is unnecessary. Here, assuming that the moving direction of the image system can be instantaneously switched between X0 and XC, the position between images that occurs when the moving direction of the image system during contrast image shooting is opposite to the mask image shooting direction. The deviation will be described with reference to FIG.

FIG. 8 is a diagram showing the relationship between the X-ray exposure time and the deviation of the imaging position. An X-ray image is taken during a period δt from the start of the X-ray exposure to the end of the exposure. . Therefore, the photographing time can be represented by a time delayed by δt / 2 from the exposure start time. Therefore, if the moving direction of the image system when shooting the mask image is opposite to the moving direction when shooting the contrast image, the contrast image shooting is performed when the image system position at the time of shooting the contrast image matches the mask image shooting position. However, in actuality, this is equivalent to shooting with a time difference of approximately δt as shown in FIG.

The positional deviation δY at this time is represented by δY = δt · V, assuming that the image system moves at the velocity V. A shooting procedure for shooting a contrast image having such a positional deviation will be described below.

The image system is moved toward the end of the foot by using X ₁ as the start point of the contrast image capturing (step S3).
5), until the image system reaches X0, the position information comparison circuit 36 is provided at the time when the image system position coincides with the mask image photographing position.
Outputs a match signal from.

By this signal, X-rays are radiated from the X-ray generator 2 toward the subject 3 and the transmitted image is detected by the X-ray detector 5. The output signal of the X-ray detection unit 5 is A / D converted in the image storage / calculation unit 10 and then sent to the subtraction circuit 31 to be sent to the mask image at the same position sent from the mask image storage circuit 28. A subtraction image is generated and displayed on the display unit 11 (steps S37 to S40). However, in this case, since the positional deviation between the mask image and the contrast image is small, the pixel shift of the mask image by the address control circuit 30 is not necessary.

When the image system has moved to X0, the operator presses the image system moving direction switching button on the console 9 to change the moving direction of the image system and move in the direction opposite to the mask image photographing direction. To start. (Step S36,
S43) In the process of moving the image system, the position detector 37
At the moment when the position information detected by the position information coincides with the mask image photographing position stored in the position information storage circuit 35, the position information comparison circuit 36 outputs a coincidence pulse.

This signal causes the high voltage generators 1 and X to
The line generator 2 is driven to capture a contrast image (step S44). However, this contrast image has a positional shift of δY as compared with the mask image. The contrast image obtained by this X-ray radiation is sent to the subtraction circuit 31 via the A / D converter 27 of the image storage / calculation unit 10. (Step S45).

By the way, the X-ray exposure period δt is predetermined by the apparatus, and the image system speed V is an amount set by the operator of the apparatus. Therefore, the positional deviation δY can be calculated by the system control circuit 8. The imaging conditions of the mask image and the contrast image are set by the system control circuit 8 before imaging, and the magnification of the X-ray image, that is, the number of pixels per unit length of the image is also determined in advance. . Therefore, the system control circuit 8 can also pre-calculate the relationship between the positional deviation δY and the number of pixels on the X-ray image from this magnification.

If the pixel conversion value of this positional deviation δY is γ, a good match can be obtained by shifting the mask image by γ pixels by the address control circuit 30 and superimposing it on the contrast image. That is, the value of the shift amount γ calculated by the system control circuit 8 is sent to the address control circuit 30, and the mask image storage circuit 28 shifts the mask image at the photographing position Xb by γ according to the control signal from the address control circuit 30. Then, the subtraction with the contrast image is performed and the result is displayed on the display unit 11. (Steps S46 to S48) The device operator continues moving the image system until the contrast agent can be observed on the monitor 34 of the display unit 11, and then again moves the image system along the flow of the contrast agent by the image system movement switching button. It is moved in the same direction as the mask image shooting direction. This operation repeats the processes of steps S37 to S40 until the video system reaches XN.

According to the methods described in the first and second embodiments, the moving direction of the image system at the time of photographing the mask image is the same as that at the time of photographing the contrast image, so that accurate alignment is possible. However, this method has a drawback in that it is necessary to return the image system from the foot end portion XN to the groin portion X1 before capturing a contrast image, which lowers diagnostic efficiency.

FIG. 9 shows a third embodiment aiming at the improvement of such a point. The moving direction of the image system at the time of photographing a contrast image is relative to the moving direction of the image system at the time of photographing a mask image. It is a modification of the second embodiment in which the reverse direction is applied.

FIG. 9 shows a case where the image system at the time of photographing the mask image is moved in the direction from the terminal end of the foot to the groin area (that is, the direction opposite to that at the time of photographing the contrast image).
In this method, when switching from mask image capturing to contrast image capturing, the direction of the video system may be switched as it is, and therefore efficient switching is possible.

However, also in this case, since the photographing direction of the contrast image and the photographing direction of the mask image are different, the positional deviation δγ shown in FIG. 8 occurs. However, since the countermeasure method is the same as the case of the backward movement of the video system from X0 to XC in the second embodiment (however, the direction of pixel shift is opposite), detailed description thereof will be omitted.

Next, the effect of correcting the pixel shift in the present invention will be described with reference to FIG. 10 (a) is a mask image, and FIG. 10 (b) is a contrast image, which schematically shows the in-vivo tissue 51 not involved in the contrast agent, the blood vessel wall 52 before and after the injection of the contrast agent, and the contrast agent 53 in the blood vessel. is there. This contrast image has an error δX (β pixel) due to the shift of the stop position of the image system with respect to the mask image.

FIG. 10 (c) is an image obtained when the subtraction of each image is performed without pixel shift. In addition to the intravascular contrast agent image 53 which is emphasized by the contrast agent, the edge 54 of the in-vivo tissue 51 is shown. And the edge 55 of the blood vessel wall 52
Remains as an artifact. On the other hand, FIG. 10D is an image in which the error δX is corrected by the pixel shift and the subtraction is performed, and only the blood vessel in which the contrast agent is present is emphasized and displayed.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, but can be modified and used. For example, as a means for correcting the movement error of the video system, the image to be pixel-shifted is not limited to the mask image and may be a contrast image. However, in order to realize this, a contrast image storage circuit (not shown) is inserted between the A / D converter 27 and the subtraction circuit 31 in FIG. 1, and its output address is controlled by the address control circuit 30.

The movement of the image system has been described as a means for realizing relative movement of the image system and the subject when photographing a contrast image or a mask image. It may be moved. Further, the C-arm structure has been mentioned as a holding mechanism integrated with the video system, but the holding mechanism is not limited to this.

[0081]

As described above, according to the present invention, the artifacts on the subtraction image generated when the image system is stopped or when the moving directions of the image pickup system in the contrast image photographing and the mask image photographing are opposite to each other are reduced. Therefore, a clear DSA image can be observed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a flowchart of the first embodiment of the present invention.

FIG. 3 is a diagram showing a moving method of a video system when the video system is continuously moved.

FIG. 4 is a diagram showing a method of moving a video system according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a pixel shift calculation.

FIG. 6 is a diagram showing a moving method of a video system according to the second embodiment of the present invention.

FIG. 7 is a diagram showing a flowchart of a second embodiment of the present invention.

FIG. 8 is a diagram showing a displacement mechanism in the second embodiment of the invention.

FIG. 9 is a diagram showing a moving method of a video system according to the third embodiment of the present invention.

FIG. 10 is a diagram showing an effect of pixel shift correction according to the present invention.

[Explanation of symbols]

2 X-ray generation unit, 5 X-ray detection unit, 7 mechanism position detection unit, 11 display unit, 28 mask image storage circuit,
30 address control circuit, 31 subtraction circuit, 35 position information storage circuit, 36 position information comparison circuit, 38 video system mechanism part, 39 top plate mechanism part, 4
0 mechanism control circuit,

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4C093 AA16 AA24 BA07 BA09 CA08                       DA02 EB02 EC16 EC33 ED07                       EE02 FD01 FF12 FF34 FF37                       FH02                 5B057 AA08 BA03 BA24 BA26 CH08                       CH11 DA04 DA07 DA08 DA12                       DA16 DB02 DB09 DC33

Claims (9)

[Claims] 1. A plurality of X-ray images at different positions on a subject are collected as mask images, and a plurality of images at different positions on a subject injected with a contrast agent are collected as contrast images. In an X-ray diagnostic apparatus that creates and displays a subtraction image between a mask image and a contrast image at positions corresponding to each other, in the X-ray diagnostic apparatus, when the subtraction means shifts a corresponding position between the mask image and the contrast image. An X-ray diagnostic apparatus having a pixel shift unit that performs a pixel shift process so as to eliminate this deviation. 2. An X-ray generation means for emitting X-rays to an object, an X-ray detection means for detecting the emitted X-rays, and the X-ray generation means and the X-ray detection means are integrated. A mechanism unit and a mechanism control unit that moves at least one of the image system mechanism unit and the top plate mechanism unit on which the subject is placed; and an image storage unit that stores the X-ray image obtained by the detection unit, An image of the subject that does not contain a contrast agent is taken out from the image storage means as a mask image,
Similarly, after subtraction means for performing subtraction between the contrast image of the subject including the contrast agent extracted from the image storage means, and at least one of the mask image and the contrast image is pixel-shifted. An X-ray diagnostic apparatus comprising a pixel shift means for obtaining a subtraction image between these images and a display means for displaying the subtraction image obtained by the subtraction means. 3. The X-ray diagnostic apparatus according to claim 1, wherein the pixel shift means controls reading of an image from the image storage means. 4. The value of the pixel shift is determined based on a difference between a mechanical position when a mask image is photographed and a mechanical position when a contrast image is photographed, which is measured by a position detecting means. The X-ray diagnostic apparatus according to 2. 5. The X-ray diagnostic apparatus according to claim 2, wherein the pixel shift means starts its operation based on a mechanical stop signal from the mechanical control means. 6. The X-ray diagnostic apparatus according to claim 5, wherein the pixel shift means operates when a position when the mask image is acquired and a position when the contrast image is acquired are different from each other. . 7. The pixel shift means operates when the moving direction of the mechanical section when the mask image is photographed is opposite to the moving direction of the mechanical section when the contrast image is photographed. X-ray diagnostic device. 8. The X-ray diagnostic apparatus according to claim 7, wherein the pixel shift value is preset based on an X-ray exposure time. 9. The pixel shift means operates based on a signal from the mechanism position detection means indicating that the mechanism section is moving in the opposite direction during generation of the subtraction image. Item 7. The X-ray diagnostic apparatus according to Item 7.