JPS5832748A - Radioactive ray tomography apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation tomography apparatus capable of obtaining a tomographic image of only a specific region within a subject.

2. Description of the Related Art In recent years, radiation tomography apparatuses have appeared that use a method called a target scan, as shown in FIG. 1, to obtain a tomographic image of only a specific part of a subject. The reason for the emergence of such a method is to minimize the amount of radiation that a subject is exposed to and to improve the spatial resolution of a tomographic image of a specific part of the subject.

For example, a target scan type X-ray tomography apparatus, as shown in FIG. 1, has a wedge 6 disposed between a collimator 1 and a subject 2, and a specific region 4 (hereinafter referred to as target) within the subject 2. ) A predetermined portion of the wedge 3 is made thick so as to reduce the amount of X-rays to areas other than the target 4, and the arrangement density of the detection elements in the object area A is high, and it passes through the object other than the target 4. The arrangement density of the detection elements in the X-ray region B is small.

However, even though the wedges 3 are provided with different thicknesses, while the X-ray tube 5 rotates and scans along the tomographic plane of the object, various parts of the object 2 other than the target 4 (
X-rays continue to be irradiated (although the dose has been reduced). Therefore, the purpose of irradiating only the target 4 with the X-ray beam and minimizing the amount of X-rays to which the subject 2 is exposed has not been achieved. However, by increasing the arrangement density 11 of the detection elements in the X-ray region A in the detector 6, the spatial resolution of the tomographic image of the target 4 can be increased, but the increase in the number of detection elements means an increase in the number of electronic circuits. This results in increased complexity and makes the X-ray tomography apparatus extremely expensive.

Furthermore, in order to arrange the increasing number of detection elements on the detector B,
The distance between the X-ray tube 5 and the detector 6 must be increased], and in such a case, not only the X-ray tomography apparatus becomes larger, but also the rotation radius of the X-ray tube 5 becomes larger. This makes cable handling complicated.

The present invention has been made in view of the above circumstances, and provides a radiation tomography apparatus capable of scanning a target in a subject with the minimum necessary radiation dose and obtaining a target tomographic image with high spatial resolution. The purpose is to

Next, an X-ray tomography apparatus which is an embodiment of the present invention will be described with reference to the drawings.

2 to 5 are schematic explanatory diagrams for explaining the basic principle of the present invention.

First, in order to reduce xm* as much as possible to the parts of the subject other than the target to be observed, and to improve the spatial resolution of the tomographic image of the target, as shown in Figure 2, it is necessary to Narrow down the irradiation angle of the x5 fan beam so that only target 4 in specimen 2 is irradiated with X-rays, and detect a detection element with the same number of channels as the detection element in an X-ray tomography device that irradiates the entire specimen 2. It is necessary to arrange them in the container 6. However, as shown in Fig. 2, only target 4 per - time is
The X-ray tube 5 that emits rays rotates around the subject 2, and even if the tomographic image of the target 4 is reconstructed based on the X-ray transmission data obtained by irradiating X-rays at each predetermined rotation angle, the image quality is extremely high. It is very difficult to make an accurate diagnosis. This is because X'#Ii tomographic images consist of X-ray transmission data covering the entire tomographic plane of subject 2 for each X-ray irradiation and X-ray transmission data obtained by irradiating X-rays from all directions on the tomographic plane. This is because it is reconstructed based on the data.

By the way, as shown in FIG. 2, when only the target 4 is irradiated with X-rays per time, as shown in FIG. , the intensity at the time of emission is ■, the distance M of the object 2 through which the X-ray beam passes,
The distance of target 4 through which the a beam passes is R1, the X-ray absorption coefficient of target 4 is μ, and the object 2 excluding target 4 is
When the X-ray absorption coefficient of is μW, the X-ray transmission data NR is expressed by the equation (1) (%) (%) (1) Further modification of the equation (1) results in the equation 0.

NR-μwr, = (μmμW) R・・・・・・・・・(
Therefore, as shown in FIG. 4, if it is possible to obtain the X-ray transmission data NW for the sixth object 7 having the same shape and the same X1fJ absorption coefficient as the subject, the X-ray transmission data NW (G) Since it is shown by the formula, NW = An If/ioW 諭μW・L (G) The difference between the actual measurement data NR and NW is expressed as This corresponds to X-ray transmission data NX of a virtual object in which the ray beam passing distance is R and the X-ray absorption coefficient is μ-μW. Then, when reconstruction processing is performed based on this X-ray transmission data NX,
The obtained tomographic image does not show only the target 4 extracted from the subject 2.

Therefore, if phantoms of various sizes that approximate the subject are selected as the third object 7 and X-ray transmission data for the phantoms of various sizes are accumulated, the second
As shown in the figure, X11i! From the X-ray transmission data obtained by narrowing down the irradiation angle and irradiating only target 4, subtracting the X-ray transmission data for a phantom equivalent to the object size and performing reconstruction processing based on the gain/loss data, target 4 is obtained. It is possible to accurately obtain tomographic images of only

Next, an embodiment of an X-ray tomography apparatus for realizing the above basic principle will be described.

FIG. 6 is a block diagram showing an X-ray tomography apparatus which is an embodiment of the present invention, and FIGS. 7 to 9 are cross-sectional views showing a phantom serving as a subject model. The X-ray tube 10 and the detector 12 are arranged opposite to the detector 12 with the subject 11 in between.
The X-ray tube 10 synchronously rotates around the tomographic plane by a predetermined angle, for example, by 0.60, and the X-ray tube 10
It is designed to fire a line of fire. 13 is a collimator,
Reference numeral 14 denotes a wedge, which narrows down the irradiation angle of the emitted Xa so that only the target 15 within the subject 11 is irradiated with the X-ray fan beam. Note that the collimator 13 can be attached and detached in various sizes depending on the size of the target 15. The detector 12 has, for example, 512 channels of detection elements arranged therein, and is configured to output data regarding the detected X-ray intensity.

The data processing unit 16 is equipped with an A/D converter, various buffer memories, a divider, a logarithmic converter, etc., and receives 1 kA/D of data related to fc X-ray intensity input from the detector 12.
By converting it, it is detected as digital data
Digital data X0 regarding the intensity of blank X-rays that do not pass through the subject 11 is detected at the same time, and the digital data X0 regarding the subject 11 is converted into blank digital data X.
After dividing by 0, the result is logarithmically converted and the obtained X-ray transmission data NR is stored in the memory.

The phantom data storage section 17 is configured to store and output X-ray transmission data processing section for phantoms of various sizes. More specifically, since the phantom is to be used as a model of the tomographic plane of the subject 11, phantoms of various sizes having contours equivalent to the tomographic plane contour of the subject 11 are prepared. For example, since the tomographic contour of the abdomen of the subject 11 is approximately elliptical, a phantom 23A having an elliptical cross-sectional shape with a major axis of A and a minor axis of B as shown in FIG. Since the contour of the tomographic plane of the chest of
A phantom 23B having a cross-sectional shape as shown in the figure is prepared. Moreover, since the size of the tomographic plane of the subject 11 varies depending on whether it is an adult or a child, the phantoms 23A and 23B are of various sizes as shown in Table 1.

Table 1 And inside the phantoms 23A and 23B, the subject 11
It is filled with a substance, such as water or ethylene glycol, that has an X-ray absorption coefficient similar to that of . Furthermore, since the subject 11 includes various organs and cavities, the cross-sectional structure of the phantom 230 is made into two layers, and the phantom 24 is made into a cavity or filled with water, as shown in FIG. For example, the phantom 23C having a hollow 024 is suitable as a phantom for chest imaging. As mentioned above, for phantoms of various sizes, the phantom data storage section 17 is
The object size setting unit 18 stores and outputs the X-ray transmission data NW obtained by rotationally scanning with the X-ray irradiation beam. It is configured to be input to a comparison selector 19, which will be described later. The thickness and width of the subject 11 may be set by detecting the thickness and width with a photoelectric detection device installed on a gantry (not shown), converting the detected values into digital values, and then inputting the detected values to the comparison selector 19. Alternatively, the operator may input the thickness and width of the subject 11 obtained by measuring with a caliper, for example, using a keyboard. Recall the X-ray transmission data W for each size of phantom, compare the size (thickness and width) of the object inputted in the object size setting section 18 with the phantom size, and set the object size and a certain allowable range. X-ray transmission data NW of a phantom size that approximates the above is selected.

The calculation unit 20 inputs the X-ray transmission data NR of the subject 11 stored in the data processing unit 16, and also inputs the X-ray transmission data NW of the Siphantom from the comparison selector 19.
It is configured to subtract the X-ray transmission data NW of the selected seven antom from the X-ray transmission data NR of the subject 11 and output the result to the image composition section 21.

The image composition section 21 performs reconstruction processing based on the data output from the calculation section, and displays a tomographic image of only the target 15 on the display section 22.

Next, the operation of the X-ray tomography apparatus configured as described above will be described.

For example, when reconstructing a tomographic image of an organ in the subject 11, such as the liver, first measure the width and thickness of the abdomen of the subject 11 with, for example, calipers. The specimen size is input into the specimen size setting section 18 in advance. Next, the X-ray tube 10 is rotated, for example, by 0.6° around the tomographic plane of the subject 11, and an X-ray beam is irradiated at each rotation angle. X-ray tube 1
The detector 12, which rotates in synchronization with zero, detects the X-ray intensity of 512 channels for each irradiation, for example, and outputs the detected data to the data processing section 16. During one rotation of the X-ray tube 10, 9, for example, 600 X-ray irradiations are performed (
66010, 6), the detector 12 will sequentially output the detection data of 600 times to the data processing unit 16. The data processing unit 16 sequentially A/D converts the input detection data, detects it as digital data Then, digital data X regarding the subject 11 is divided by blank digital data XIO, and the result is logarithmically converted to obtain X-ray transmission data NR, which is stored in a memory. On the other hand, since the phantom data storage unit 17 irradiates the abdomen of the subject 11 with Xat, the phantom 23A having a substantially elliptical shape as shown in FIG. Then, the comparison selector 19 stores the X-ray transmission data NY for phantoms of various sizes obtained from the phantom data storage section 17. Call the NW, compare the phantom size with the subject size inputted in the subject size setting section 18, and select the phantom size X that approximates the subject size.
The line transmission data NW is selected and outputted to the calculation section 20. The arithmetic unit 20 subtracts the X-ray transmission data NY of the selected phantom size output from the comparison selector 19 from the X-ray transmission data NR of the subject 11 inputted from the data processing unit 16 (NR-NW). ) and outputs the result to the image reconstruction unit 21. After the image reconstruction unit 21 performs reconstruction processing based on the data obtained by subtraction, the display unit 2
At step 2, a tomographic image of only the target 15, for example, the liver, is displayed on the television.

Although one embodiment of the present invention has been described above in detail, it goes without saying that this invention is not limited to the above embodiment and includes various modifications within the scope of the gist of the invention. .

According to this invention, since only the target inside the subject is irradiated with radiation, the radiation exposure to the subject can be reduced, and even though only the target is irradiated with radiation and rotated scanned, only the target tomographic images can be obtained. Moreover, if the number of detection elements in the detector is made equal to the number of detection elements arranged in the detector in a normal radiation tomography system ft that irradiates the entire area of the subject, the electronic circuit will become complicated. It is possible to obtain tomographic images of only the target with high spatial resolution without increasing the size of the entire device.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a conventional target scanning method, FIGS. 2 to 5 are schematic explanatory diagrams for explaining all the basic principles of this invention, and FIG. 6 is an embodiment of this invention. A block diagram showing an X-ray tomography apparatus and FIGS. 7 to 9 are cross-sectional views showing a phantom serving as a subject model. 11... Subject, 15-... Target, 1
6... Data processing unit, 17... Phantom data storage unit, 18... Subject size setting unit, 19...
- Comparison selector, 20... Calculation unit, 21... Image reconstruction unit, 22... Display unit, 25A, 23B,
23C-...Phantom. (μ-μW) Figure 7 Figure 8 Figure 9

Claims (4)

[Claims] (1) In a radiation tomography system that scans the subject with a radiation beam at every predetermined rotation angle and reconstructs the radiographic data using a computer to obtain a tomographic image, a specific part of the subject is targeted. The radiographic data obtained by scanning a phantom with a radiation beam at each predetermined rotation angle is corrected with the radiographic data obtained by scanning a phantom of the same size as the subject at a predetermined rotation angle with a radiation beam. A radiation tomography apparatus characterized in that a reconstruction process is performed based on the obtained data to obtain only a tomographic image of a specific part of a subject. (2) The radiation tomography apparatus according to claim 1, wherein the shape of the phantom approximates the shape of the tomographic plane of the subject. (3) The radiation tomography apparatus according to claims 1 and 2, wherein the shape and filling material of each part of the phantom correspond to each part on a tomographic plane of the subject. (4) A radiation tomography apparatus according to any one of claims 1 to 3, characterized in that a hollow portion is provided within the phantom.