JPH0139782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tomography apparatus capable of simultaneously obtaining a plurality of tomographic images by performing a single tomography.

Conventional tomography methods, such as the rotational cross-sectional imaging method shown in FIG. 1 and the longitudinal tomography method shown in FIG.
are installed relative to each other, the X-ray tube 2 is moved on a circular orbit l1 in the rotational transverse imaging method, and the X-ray tube 2 is moved on an arcuate orbit m1 in the longitudinal tomography method, and incidentally, The film 3 also moves relative to each other on a circular orbit l2 and an arcuate orbit m2, respectively. In such a conventional imaging method, the above imaging method must be performed every time the desired imaging cross sections a and b within the subject 1 are changed for diagnostic purposes, which saves time and operation time. It requires a lot of effort,
Furthermore, for the subject 1, the X-ray exposure dose is forced to increase, causing a considerable problem.

The purpose of the present invention is to provide an X-ray tube that irradiates X-rays toward a subject, a high-voltage generator that supplies high voltage to the X-ray tube, and a high-voltage generator that can eliminate the above-mentioned drawbacks. The X-ray tube and irradiating X-rays from a direction intersecting the virtual axis at a predetermined inclination angle while moving a predetermined trajectory around an imaginary axis parallel to the longitudinal direction of the bed with a detector disposed facing the bed; In a tomography apparatus that obtains an image of a desired tomographic plane in a direction perpendicular to the virtual axis by detecting X-rays transmitted through the subject with the X-ray detector, A fluorescent device has an input surface large enough to detect X-rays emitted from any position of the fluorescent device, and converts an X-ray image detected by the input surface into a visible light image; an image pickup tube that converts an optical image into a video signal as a charge signal and stores it on the mesh surface; a first storage means that temporarily stores the video signal taken by the image pickup tube; means for calculating the radius and center of each annular locus drawn by each pixel point of the desired tomographic plane on the mesh surface of the image pickup tube; and calculating the coordinates of each point of each annular locus from the radius and center. and forming each pixel signal of the desired tomographic plane by selectively reading out and adding signals stored at storage positions corresponding to the coordinates from the first storage means for each of the annular trajectories. a second storage means for storing each pixel signal, and a means for reading each pixel signal from the second storage means and displaying the desired tomographic plane. It provides equipment.

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 3, 1 is the subject;
2 is an X-ray tube; 4 is a fluorescent plate that detects the amount of transmitted X-rays from the subject 1; 5 is an optical lens system; 6 is a television camera (imaging tube) that captures a visible light image formed on the fluorescent plate; Reference numeral 7 designates an image processing device which performs arithmetic processing on the basis of the output signal from the television camera 6 and sends an image signal of a desired cross section to a display device such as a television monitor which will be described later; 8 designates a display device.

The principle of tomography according to the present invention will be explained below.

In FIG. 4, the locus of the focal point of the X-ray tube 2 is assumed to be a circle with a radius R on the X-Y coordinate plane shown in the drawing.

The fluorescent surface of the fluorescent plate 4 is shown as an x-y coordinate plane.
Further, the distances from both coordinate planes to the desired photographed cross-section in the subject 1 are assumed to be D1 and D2, respectively.

The center of the cross-section to be photographed, that is, the intersection point 0 between the rotation center axis of the X-ray tube and the cross-section to be photographed, is
Create a circle with radius r on the coordinate plane.

The circle is expressed by the following formula.

x ² + y ² = r ² ... (1) where R: r = D1: D2 r = R x D2 / D1 ... (2) The phosphor on the fluorescent surface 4 is a very fine particle. The photoelectric conversion surface of the image pickup tube 6 that detects this light is a mesh surface divided into small blocks.

Therefore, when detecting the locus formed on the fluorescent surface 4 at point 0, it is not a continuous one, but one in which the light image formed on the mesh surface of the image pickup tube 6 and the elements on the mesh surface match. This results in the detection of only discontinuous signals.

If the function that converts a continuous trajectory on the fluorescent surface 4 to a discontinuous trajectory on the image pickup tube 6 is f(x, y), the signal at point 0 is ∫ ^r _-r ∫ ^r _-r f(x, y ) dxdy ...(3) Next, considering point B, which is on the same cross section as point 0 of object 1 and is located at a distance of b0 from point 0 in the Y-axis direction, on the x-y coordinate plane A circle with radius r is created, but it is translated by b in the y-axis direction from point 0.

The circle is expressed by the following formula.

x ² + (y-b) ² = r ² ...(4) where b0:b=D1:(D1+D2) b=b0・D1+D2/D1 ...(5) Therefore, the signal at point B is ∫ ^{r +b} _-r+b ∫ ^r _-r f{x, (y-b)}dxdy ...(6).

Next, in FIG. 5, if we consider point A located at a distance a0 in the It is translated by a in the x-axis direction from the time of 0.

The circle is expressed by the following formula.

(x-a) ² +y ² = r ² ...(7) Here a=a0・D1+D2/D1 ...(8) Therefore, the signal at point A is ∫ ^r _-r ∫ ^r+a _-r+a f{(x-a), y}dxdy...(9) In the end, the X-axis from the center on the X-Y coordinate plane of the photographed section,
The points located at a0 and b0 in the Y-axis direction are fluorescent plane x
On the −y coordinate plane, (x-a) ² + (y-b) ² = r ² ...(10) However, from (2), (5), and (8), a=a0・D1+D2/D1, b= It appears as a circle with the formula b0・D1+D2/D1 r=R・D2/D1.

This is as shown in FIG.

Therefore, the signals necessary to create a cross-sectional image at point (a0, b0) on the photographed cross-section X-Y are ∫ ^r+b _-r+b ∫ ^r+a _-r+a f{(x-a), (y-b)}dxdy
...(11) becomes. Also, according to Fig. 4, the X-rays emitted from the X-ray tube 2 reach the point 0 without passing through the point 0 at the locus x ² + y ² = r ² on the x-y coordinate plane. is the majority. In other words, for the X-rays that reach point β above x ² + y ² = r ² , only the X-rays emitted from point α of the X-ray tube cross point 0 of the object, and the X-rays emitted from points other than α are not exposed. The sample passes through a point other than the 0 point or directly reaches the β point.

Therefore, an extra dose of X-rays is superimposed on the integrated value of the X-ray dose taken out as the signal described above. However, this unnecessary X-ray detection signal is merely related to increasing the density on the image and does not cause any inconvenience.

In Figure 7, point 0 on the required photographic cross section
The locus on the fluorescent surface is circle 0, whereas point P or point Q on the same axis as point 0 and on the other cross section shown is circle P and circle Q, which is completely different from circle 0. It becomes another circular locus.

Furthermore, according to FIGS. 4 and 5, the trajectory of another point on the same cross section as point 0 intersects with circle 0 only at two points, resulting in a completely different trajectory.

If the signals on the mesh plane of these two intersecting points are integrated, they can be ignored.

Therefore, one point in the object has a unique locus unique to that point on the fluorescent surface, and therefore, the integral value of the charge signal of each element on the mesh surface of the image pickup tube for that point is It becomes an image signal.

Now, to add an explanation to f(x, y) in equation (3), FIG. It is projected onto. FIG. 9 shows an image in which the image in FIG. 8 coincides with each element on the mesh surface over 50% or more of the area. That is, f(x, y) can be considered as a conversion from the continuous figure shown in FIG. 8 to the discontinuous figure shown in FIG. The so-called figure 9 also approximates figure 8.

Next, the specific operation of the image processing device 7 shown in FIG. 3 will be explained with reference to the flowchart shown in FIG. 10.

During actual imaging, the X-ray tube 2, subject 1, fluorescent plate 4, optical lens system 5, and image pickup tube 6 are arranged as shown in Figure 3, and the X-ray tube 2 rotates once while emitting X-rays. let At this time, the image pickup tube 6 is powered on and only beam scanning is stopped so that the fluorescent signal on the fluorescent plate 4 is stored as a charge signal on the mesh surface of the image pickup tube 6.

Imaging is completed by one rotation of the X-ray tube 2, and then the image processing device 7 processes the charge signal on the mesh surface of the image pickup tube 6. In image processing, the signals stored on the mesh surface of the image pickup tube 6 are stored in a storage device. At that time, the digital signal is stored in the storage device via the A-D converter.

Signals from the image pickup tube 6 can be easily read out by beam scanning the image pickup tube 6.

Now, the required cross-sectional position of the patient must be determined.

Once a tomographic plane is set, the radius of the annular locus drawn by each pixel point of this tomographic plane on the mesh plane of the image pickup tube as the X-ray tube moves is calculated from the above-mentioned equation (2).
This radius remains unchanged during the processing of one image; the only thing that changes is the center of the annular trajectory for each point on the cross section.

Therefore, it is necessary to read out the center each time the cross section is processed point by point.

Now, once the center is determined, we must calculate the coordinates of the points shown in Figure 9, that is, the points of the locus on the mesh surface.

Once the pixel position on the mesh plane for one point on the photographed cross section is determined in this way, only the corresponding signal from among the signals previously stored in the storage device is read out.

The plurality of read signals are all added up and stored in the storage device again.

Next, the same calculations are repeated for other points on the photographed section and all are stored in the storage device as video signals. A tomographic image is displayed by sequentially reading out the signals of the desired tomographic plane and scanning the video tube.

Next, an image processing device for a tomography apparatus according to the present invention will be explained.

The parameter input device inputs information such as (1) the distance between the imaged cross section and the center of rotation of the X-ray tube, (2) the distance between the imaged cross section and the fluorescent surface, before or after the image is taken for data processing purposes.
(3) Input the X-ray tube rotation radius to the central processing control unit CPU. The video signal from the image pickup tube 6 is a decoded signal consisting of a synchronization signal and a video signal portion, and the synchronization signal is separated to form the base point of the digital address of the video signal. Further, the video signal component is sampled at the digital address, converted to a digital image through an AD converter, and stored in the memory by the CPU together with the digital address. The stored data is converted into coordinates on the tomographic plane by a data processing method described separately, and then displayed on the CRT 8, which is a display device.

In FIG. 11, a subject 1 is examined by an X-ray tube 2.
After the imaging of the desired tomographic plane in
0, generates a scanning start signal to the VTR 11. Through this scanning, the video signal output from the image pickup tube control device and the process amplifier 10 is recorded on the VTR 11.

The video signal recorded on the VTR 11 is transferred to the computer interface 12 and the central processing control unit CPU 1 according to a command from the parameter input device 9.
After being converted into a digital image via 3, it is recorded on a magnetic tape device 14.

The operation of the CPU 13 is to calculate the address corresponding to the digital image on the predetermined tomographic plane, add the images on the circumference, create a new tomographic digital image, and record it on the magnetic tape. Digital image can be input using parameter input device 9 as required.
is commanded and displayed on the CRT display device 8.

Next, the operations performed inside the computer interface 12 will be explained with reference to FIG.

The analog signal for one horizontal scanning period, which is a composite of the video signal and the synchronization signal from the VTR 11, is input to the synchronization separator 15, where it is separated into an analog signal portion and a synchronization signal. This separated synchronization signal provides an oscillation synchronization trigger to the oscillator 16. The clock signal output from the oscillator 16 is sent to the counter 17.
Count. The output of this counter 17 is decoded by a decoder 18, which opens and closes gates 19 to 21 for the analog video signal for one horizontal scanning period from the sync separator 15, and the video signal is sampled and held for a certain period of time. Here, devices 22-2 having a sampling function and a hold function
After the sampling and holding operations for one horizontal scanning period, which are in charge of 4, are completed, the sampling,
A hold end signal is output to the clock oscillator 16, thereby inhibiting the input of the clock from the oscillator 16 each time the sampling and holding operations for one horizontal scanning period are completed.

Further, the analog signal for the next horizontal scanning period from the VTR 11 is input to the synchronization separation section 15, and the separated synchronization signal supplies an oscillation synchronization trigger to the oscillator 16. As a result, the oscillator 16 whose clock output has been inhibited starts outputting a clock, and sampling and holding operations for the next horizontal scanning period are performed in the same manner as for the one horizontal scanning period.

Further, the output signal from the counter 17 serves as an oscillation start trigger signal for the clock oscillator 25. The clock signal from this clock oscillator 25 is counted by a clock counter 26, and the output signal from this counter 26 is used to sequentially gate the output signals of the devices 22 to 24 having both sampling and holding functions by a multiplexer 27 and gate A- An input signal to the D converter 28, ie, a video sample signal is provided. At the same time, the counter 26 outputs to the CPU 13 a signal representing the digital address on one horizontal scanning line of the video signal pixel to be sampled and held next.

A signal from the clock oscillator 25 is outputted to a pulse timing generation circuit 29, and from this circuit 29 is outputted to the A/D converter 28, and becomes an A/D conversion start signal. The output from this A-D converter 28 outputs a video digital signal to the CPU 13.

The output signal of the clock counter 26 is sent to the counter 3.
The counter 30 counts the number of horizontal scanning lines and supplies it to the CPU 13.
The address of the video signal pixel is specified by this number of horizontal scanning lines and the digital address of the previous video signal pixel, and is used when reading out the video signal of each pixel from the coordinate calculation results described above. The other output of the counter 30 means the end of A-D conversion of the video signal for one screen, and notifies the CPU of the end of required data collection.

Next, using FIGS. 13, 14, 15, and 16, the processing contents in the central processing unit and the process up to displaying the processed video on a display device such as a CRT will be explained.

The CPU 13 outputs a clock signal at the same time as the digital video signal at each address is output as a luminance density signal to the DA converter 31. This clock signal enters a counter 32 and is counted, and the count output passes through a DA converter 33 and is
Supply axis analog signal to CRT8.

The carry signal of the counter 32 becomes a clock input to the counter 34 and is counted by the counter 34.
The output signal of this counter 34 is sent to a D-A converter 35.
After passing through, the Y-axis analog signal is supplied to the CRT8.

The clock signal output from the CPU 13 is input to an unblank signal generator 36, and the video analog signal is input to an unblank gate 37, which is used to display a point on the CRT 8 with luminance modulation of the video signal. Provides axis analog signals. The output signal of the counter 34 is a count carry signal and also informs the CPU 13 that the display of one frame has ended.

Note that the X and Y axis signals here are the X and Y axis signals of the tomographic plane.
This is done in the program to correspond to the coordinates.

The method for selecting each element of the digitized image f(x,y) on the mesh surface of the image pickup tube 6 described above is as follows.
This can be easily done, for example, by coordinate transformation.

A circular figure x ² in the X-Y coordinate system as shown in Figure 14
By converting +y ² = a ² to the x-y coordinate system, it becomes a square shape as shown in Figure 15 where x ² = a ² where |y|≦a y ² =a ² where |x|≦a shall be converted.

In this way, by selecting an element at a digitized position that is approximately circular on the mesh surface as shown in FIG. 9, the signal of the element in the square area shown by diagonal lines in the matrix in FIG. 16 is extracted. It is the same as the above and can be selected very easily.

The sum of the signals, that is, the integral of the signals in the black portion of FIG. 9 can be expressed as follows.

ΣP (x, y) + ΣP (x, y) y=a y=-a -a→x→a -a→x-a +ΣP(x, y)+ΣP(x, y) x=-a x=a -a→y→a -a→y→a or ΣPmn+ΣPmn+ α→n→α+2a α→n→α+2a m=β m=β+2a ΣPmn+ΣPmn β→m→β+2a β→m→β+2a n=α n=α+2a As explained above As shown, by emitting radiation from the X-ray tube once, that is, by emitting radiation while moving on a single circular orbit, it is possible to image any cross section perpendicular to the central axis of rotation of the X-ray tube. This method has the advantage that it does not require much time or effort on the part of the operator, and the amount of X-rays to which the subject is exposed can be reduced.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining a conventional X-ray tomography method, FIG. 3 is a schematic configuration diagram of an embodiment of a tomography apparatus according to the present invention, and FIGS. 4 and 5.
Figures 6 and 7 are diagrams for explaining the principle of imaging by the tomography apparatus of the present invention, and Figure 8 is a schematic diagram showing the trajectory projected onto the mesh surface of the imaging tube at an arbitrary location inside the subject. Figure 9 is a figure obtained by converting the continuous locus displayed in Figure 8 into a discrete continuous display, Figure 10 is a flowchart showing specific operations of image processing, and Figure 11 is A schematic diagram showing the specific configuration of the data processing device of the present invention, FIG. 12 is a schematic configuration diagram for explaining analog image to digital image conversion in the computer interface and data collection to the storage device, and FIG. 13 is the center Images processed by a processing unit are transferred to a CRT
14, 15, and 16 are schematic configuration diagrams for explaining the method of displaying on a display device such as This is a diagram for 1... Subject, 2... X-ray tube, 4... Fluorescent plate, 5... Optical lens system, 6... Image pickup tube, 7...
Image processing device, 8...display device.

Claims (1)

[Claims] 1. An X-ray tube that irradiates X-rays toward a subject, a high-pressure generator that supplies high voltage to this X-ray tube, an X-ray control device that controls this high-pressure generator, and a device on which the subject is mounted. the bed, and an X-ray detector that detects X-rays that have passed through the subject placed on the bed; the X-ray tube and the X-rays are emitted from a direction intersecting the virtual axis at a predetermined angle of inclination while moving along a predetermined trajectory around a virtual axis parallel to the subject, and the X-rays transmitted through the subject are detected by the X-rays. In a tomography apparatus that obtains an image of a desired tomographic plane in a direction perpendicular to the virtual axis by detecting it with a device, X-rays emitted at any position on the trajectory of the X-ray tube are detected. A fluorescent device that has an input surface as wide as possible and converts an X-ray image detected on the input surface into a visible light image, and a mesh surface that converts the visible light image of this fluorescent device into a video signal as a charge signal. an image pickup tube stored above; a first storage means for temporarily storing image signals taken by the image pickup tube; means for calculating the radius and center of each circular locus drawn by pixel points; means for calculating the coordinates of each point on each circular locus from the radius and center; and calculating the coordinates from the first storage means. means for forming each pixel signal of the desired tomographic plane by selectively reading and adding signals stored in corresponding storage positions for each of the annular trajectories; and a second means for storing each pixel signal. A tomography apparatus comprising: storage means; and means for reading each pixel signal from the second storage means and displaying the desired tomographic plane.