JPS642372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital subtraction type X-ray apparatus for obtaining high-quality X-ray images with excellent contrast by eliminating the influence of scattered X-rays.

Computer Radiography
Radiography) scans the subject with a narrowly focused X-ray beam (fan beam or pencil beam), and processes the image produced by the narrow beam over the entire scan range.
It is known to remove the influence of scattered radiation and provide an X-ray image with good contrast.

However, this method is unsuitable for photographing moving parts because it takes a long time to scan the entire surface of the subject.

This invention incorporates the advantages of computer radiography into instantaneous imaging using ordinary area beams, and uses a digital subtractor based on a completely new idea to obtain sharper X-ray images without the influence of scattered radiation. The present invention aims to provide an X-ray system of the Shion type.

Note that in this specification, a finely focused X-ray beam means a directional X-ray beam that is usually called a Fan beam or a pencil beam.
Elijah beam refers to an X-ray beam with a radial spread used in ordinary X-ray photography.

Examples will be described below.

Figure 1 shows an example using a fan beam scan, in which 1 is an X-ray tube, 2, 3
is a slit made of a lead plate for obtaining the fan beam X, and is scan driven in the direction of the arrow at a constant speed by the scanning mechanism 4 during X-ray emission. Furthermore, the slits 2 and 3 are completely removed from the front of the subject during area beam irradiation, which will be described later. The transmitted X-ray image of the subject B by this fan beam is detected by the image tube 5, and the intensified output image is passed through the aperture 6 (in this case, fully open) to the image pickup tube 7 (TV
(camera) is extracted as a video signal.
This image pickup tube is driven by the camera control unit 8 in synchronization with X-ray exposure, and its output signal is applied as a composite video signal to the input terminal T of the image processing circuit shown in FIG.

In Fig. 2, the switch _S1 is used to switch between image processing using the fan beam and image processing using the area beam, which will be described later.When the switch is set to the contact a side, the slits 2 and 3 are placed in front of the subject B. , the scanning mechanism 4 is energized and moves in front of the subject at a constant speed, so that the subject is scan-irradiated with a fan beam. In this state, the output video signal of the image pickup tube 7 is converted into digital data via the log amplifier 9 and the A/D converter 10, and is integrated via the arithmetic unit 11 (which operates as an adder in this case), and the data is The image is taken into the image memory 12. In this case, in the present invention, the image signal of the object part (direct X-ray image) that is linearly irradiated by the fan beam is excluded from the output video signal of the image pickup tube, and the image of the entire surrounding area, that is, the scattered image, is excluded. One feature is that the video signals of the image portion formed by X-rays are integrated and stored on the image memory for each pixel.

For example, in the apparatus shown in Figure 1, if the field of view of the image tube used is 14 inches, the length of one side will be 355 mm. If the fan beam X scans the entire field of view in 4 seconds, the moving speed of the slits 2 and 3 will be 355 mm/4 seconds = 88.77 mm/sec. On the other hand 4
Since the frame rate of a TV camera is usually 30 frames per second, the number of image frames taken into the memory per second is 30 frames/second x 4 seconds = 120 frames. The number of scanning lines on a typical monitor TV is 525.
However, the number of frames that scan the effective field of view is about 480, so here we use 355 mm.
Consider that the effective field of view is covered by 480 scanning lines. Here, while importing one frame image (1/
30 seconds), the distance that the slit or fan beam moves is 88.75/30mm. cover this distance
The number of scanning lines of the TV camera is 480/355mm x 88.75/30mm = 4. That is, while capturing one frame of image data, the X-ray beam moves by four scanning lines of the TV camera. Therefore, the video signals on these four scanning lines become direct X-ray image signals from the fan beam. Therefore, if only the four signals are cut out when the image data signal is taken into the image memory, only the video signal due to the scattered X-rays other than the direct X-rays will be stored in the image memory.

However, in an actual device, a TV camera performs so-called interlaced scanning, so one field of image scanning takes 1/60 seconds, and one frame of image is obtained in two fields. This is shown on the camera's input screen as shown in Figure 3. In the figure, P is the camera input screen and the solid lines F ₁ , F ₃ ,
F ₅ ... is the trajectory of the scanning line in the first field,
Dotted lines F ₂ , F ₄ , F ₆ . . . are scanning line trajectories in the second field. As mentioned above, in one frame of image data, the data affected by the direct X-ray beam corresponds to four scanning lines, so the slit position is sequentially moved downward from the top position. If the start of the movement is completely synchronized with the start of X-ray exposure and the camera's imaging scan, the image signal of the first frame (first 1/30 second) during imaging will be equal to l ₁ in Figure 3. The signals on the four scanning lines shown are video data from the direct X-ray beam, and in the second frame (next 1/30 second), the four signals shown in l ₂ correspond to this, and in the third frame, This applies to l ₃ . However, due to the interlaced scanning, in reality, the scanning lines F ₁ and F ₈ correspond to this in the first field of the first frame, and the scanning lines F ₂ and F ₄ correspond to this in the second field of the same frame.
There will be two books.

Unit 1 calculates the output video signal of the TV camera.
In order to cut out the signals of four scanning lines (two in one field) that are affected by the direct beam when the signals are taken into the image memory 12 via the field 1, the following steps are taken in this embodiment.

A timing control circuit ₁₃ ' is provided in the control unit 13 which performs commands such as specifying the address of the image memory, reading and reading data, and controlling the operation of the arithmetic unit. A gate signal is generated at the time when image signals corresponding to the scanning lines l ₂ , l ₃ ... arrive,
This can be achieved by controlling the AND gate provided before the arithmetic unit and performing operations such as setting all the image signals to zero at this time.

As described above, while the fan beam is scanning, an image of the object due to scattered X-rays is captured and stored in the image memory 12. In this specification, this operation is referred to as a scattered X-ray image mask creation operation. This memory operation itself is not particularly different from the procedure of ordinary image processing, and the image data of each frame (excluding the cut portion) is accumulated and stored in sequence for each pixel. This operation is performed for 4 seconds in this embodiment.

Next, the operation of setting the switch _S1 in FIG. 2 to the contact point b side and performing area beam photography will be explained. S ₁
When enters the b side, the slit scanning mechanism 4 operates,
The slits 2 and 3 are automatically removed from the front of the subject, and the diaphragm 6 is inserted. (In the previous case, since a larger amount of X-rays were received, the aperture was set to adjust the brightness of the image plane.) At the same time, the arithmetic unit 11
The function changes from the previous function as an adder to the function as a subtracter.

When an X-ray exposure switch (not shown) is pressed in this state, an area X-ray beam irradiates the same subject for 1/30 seconds in accordance with a synchronization signal from the camera control unit 8. During this time, the transmitted X-ray image is taken out as a video signal by the TV camera 7 via the image tube 5 to the terminal T, A/D converted, and input to the arithmetic unit 11. In this arithmetic unit, the reproduced image signal based on the scattered X-ray image stored by the above operation is subtracted from the image signal based on the area X-ray. In this case, each scanning line is synchronized and image processing is performed accurately for each pixel. In the present invention, this process of subtracting both images is called a subtraction operation.

Next, the output signal of this subtraction operation is applied to the monitor TV via the D/A converter 14 as a luminance signal. At the same time, this subtraction output signal is stored in the image memory 12 and read out again. (No operation is performed and the image is output as is), the image can continue to be displayed even after the X-ray exposure is completed.

Note that when reading the reproduced signal of the scattered radiation image from the image memory and subtracting it from the area beam X-ray image, the former is 4 seconds of data, and the latter is 1/
Since this is 30 seconds of data, in order to match it, the calculation unit 11 is provided with a function to appropriately shift the contents of the reproduced image memory during subtraction calculation and subtract the contents as 1/120. .

By configuring as described above, an X-ray image in which the influence of scattered radiation is almost completely removed can be obtained.

In this case, the subject is exposed to X-rays for a relatively long time (such as about 4 seconds) to create a scattered radiation mask image, but this point is similar to conventional computer radiography, and the X-ray dose is Since it is a fan beam, it is extremely small and there is virtually no problem. On the other hand, computer radiography uses this to form images for diagnostic purposes, so it is not suitable for photographing moving objects, and since some movement of the human body is unavoidable, the influence of scattered radiation can be excluded. Even so, a completely sharp image cannot be obtained.

In contrast, in the present invention, the basic image is an area beam image, and the Huang beam image is just a scattered radiation image, not for diagnosis, and is only for subtraction from the basic image. Even if there is movement in Since the X-ray image is enhanced and the influence of scattered rays is removed, a high-quality X-ray image with higher contrast can be obtained.

In the present invention, the same effect can be obtained by using an image sensor or active array sensor in which scintillators or photomultipliers are arranged two-dimensionally in place of the image tube or TV camera. The same thing can be done with a pencil beam instead of a fan beam.

[Brief explanation of drawings]

1 and 2 are operation explanatory diagrams and circuit diagrams of the embodiment of the present invention, and FIG. 3 is a diagram explaining the operation of the scanning line of the TV camera. 1... X-ray tube, 2, 3... Moving slit, 5...
...Image tube, 6...Aperture, 7...Image tube (TV
camera), 8...camera control unit,
10... A/D converter, 11... Arithmetic unit,
12... Image memory, 13... Control unit, 1
4...D/A converter, 15...Monitor TV.

Claims (1)

[Claims] 1 The X-ray image of the subject is extracted as an image signal via a video detector and an imaging device, and this is transmitted to a CRT.
The apparatus shown above includes means for scanning an object with a narrowly focused X-ray beam, a video detector and an imaging device for converting the X-ray image obtained thereby into a digital image signal, and this image signal. an image memory device that integrates and stores the image signal components of the image portion of the X-ray image that receives the direct X-ray beam; 1. A digital subtraction type X-ray apparatus, comprising a calculation unit that performs a subtraction operation on a reproduced image signal from the apparatus, and displays an X-ray image based on the subtraction image signal from the calculation unit.