JPH0134058B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radiation tomography examination apparatus that is effective in obtaining a tomographic image of a subject using a high-energy radiation beam.

[Technical background of the invention and its problems]

This type of device is a CT (Computed
This device uses an X-ray beam and an image processing computer to accurately reproduce a two-dimensional tomography line in a three-dimensional object, and is widely used, especially in the medical field.

By the way, when obtaining a two-dimensional tomographic image, there is an It is necessary to drive the motor with a certain correlation, and there have been several methods of controlling the motion.

One of them is called the pencil beam method, in which a single X-ray generator 1 and a single detector 2 are translated in the direction of the arrow shown in FIG. After sampling the X-ray transmission data of the specimen 3 at each predetermined pitch and then rotating it by a predetermined angle in the direction of the arrow B in the figure, this time a translation operation is performed in the direction of the arrow C in the figure, which is the opposite direction to the arrow A in the figure. In this method, the X-ray transmission data of the subject 3 is similarly sampled at each predetermined pitch, and the X-ray transmission data of the subject 3 is collected while repeating this translational-rotational motion until the rotation angle reaches at least 180°. .

The other one is called the fan beam method, which consists of an X-ray generator 1' and, for example, about 256 to 512 detectors 4-1, 4-1, arranged in an arc, as shown in FIG. 2, X-ray detector group 4 with...
The radiation of the fan-shaped X-ray beam 5 from the X-ray generator 1' causes each detector 4-1, 4-
2, sequentially sample the X-ray transmission data of the subject 3 obtained from... in a predetermined order, and then
The detectors 4-1, 4-2,
. . . X-ray transmission data of the subject 3 taken out from the object 3 is sequentially sampled in a predetermined order, and the X-ray transmission data of the subject 3 is collected while repeating this rotational movement until the rotation angle reaches at least 180°. be. FIG. 3 is a timing chart when data obtained by the two drive control means described above is collected. In other words, in FIG. 3, the X-ray generators 1 and 1', the X-ray detector 2, and the detector group 4 are rotated by a predetermined angle at timing S1, and then the X-ray transmission data is sampled at timing S2. It shows that.

However, the above two drive control means have the following problems.

(1) Difficulty in installing high-voltage cables, etc.

High-voltage cables are introduced into the X-ray generators 1 and 1' to control the acceleration of electrons, and cooling pipes are introduced to avoid functional deterioration due to heat. If the Very difficult to install,
Another disadvantage is that there are many accidents that damage high-voltage cables.

(2) X-ray beam deviation.

Industrial X-ray generators 1 and 1' often have to generate a higher-energy X-ray beam than those for medical use from the perspective of inspecting industrial products, and for this reason they are generally larger. A heavy weight is used, and it is held by a holding frame to minimize displacement. However, as mentioned above, the X-ray generators 1 and 1' are
Since vibration is generated each time rotation, reverse translation, and rotational motion is repeated, a vibration absorbing material such as rubber is interposed between the X-ray generators 1, 1' and the holding frame to absorb the vibrations. Therefore, the X-ray generators 1, 1' themselves cannot be firmly fixed to the holding frame. As a result, the X-ray generators 1 and 1' and the holding frame tilt each time they are rotated to the right or left, making it impossible to emit an X-ray beam more accurately than the X-ray generators 1 and 1'. There is.

(3) In addition to the above-mentioned drawbacks, the fan-beam method also has the following drawbacks. In general, medical equipment has weak X-ray energy, so
Gas detectors are used as the detectors 4-1, 4-2, . . . . However, the gas detector
High-energy X-ray beams, such as those used in the inspection of industrial products, are unsuitable because of the problems of decreased sensitivity and nonuniformity of sensitivity. Therefore, in the case of a high-energy X-ray beam, the detector 4-
As 1, 4-2, . . . , solid state detectors such as scintillation detectors and semiconductor detectors are used. However, solid-state detectors have a larger external shape than gas detectors, so it is not possible to mount a large number of detectors 4-1, 4-2, etc. as shown in Fig. The disadvantage is that data cannot be collected with high precision.

[Purpose of the invention]

The present invention facilitates the introduction of high-voltage cables and cooling pipes into the X-ray generator, eliminates the problems of damage to the high-voltage cables and deviation of the radiation beam during scanning, and is effective for high-energy radiation beams. It is an object of the present invention to provide a radiation tomography inspection device that can be easily mounted and can reliably collect data even if it is a solid-state detector with a large external shape.

[Summary of the invention]

Although the radiation generator that emits the fan-shaped radiation beam is fixed, the present invention makes the subject to be irradiated with the radiation beam rotatable, and the radiation detector group having a plurality of detectors is relatively small. The configuration is such that the detector is rotated within a certain angle range, and data from each detector is sampled at every predetermined rotation angle while the subject is rotating once, and then, after the subject has rotated once, the radiation detector group is sampled. This is a radiation tomography examination apparatus that rotates the object by a small angle within the certain angular range, and then samples data while rotating the object.

[Embodiment of the Invention] Next, an embodiment of the present invention will be described with reference to FIGS. 4 to 10. FIG. 4 shows a radiation generator 11, a subject 12, and a radiation detector group 1.
It shows the arrangement relationship with 3. This radiation generator 11 emits a fan-shaped X-ray beam 14 with a fan angle α, and is fixedly installed at a predetermined position and direction. This fan-shaped X-ray beam 14 passes through a slit 15 to the subject 1.
2. Note that the radiation generator 11 may be one that emits radiation beams 14 other than X-rays depending on the properties of the subject 12. The subject 12 is placed on a turntable 16, as shown in FIG. 6, and is rotated by the rotation of the turntable 16. The radiation detector group 13 detects the radiation energy transmitted by the subject 12 and obtains radiation transmission data. Detector 13-1, 13-2,...13
-n, and these detectors 13-1, 1
3-2, . . . are arranged in an arc shape. Each detector 13-1, 13-2, . . . uses a solid-state scintillation detector as shown in FIG. This scintillation detector consists of a scintillator 13a, a photomultiplier 13b, and a preamplifier 13c, and can obtain radiation transmission data with high sensitivity and constant sensitivity even with a high-energy radiation beam 14. . In addition, each detector 13-1, 13-2,...
A gas detector may be used if the radiation energy is weak.

Next, FIG. 6 is a diagram showing a drive system for driving the turntable 16 and the radiation detector group 13.
In the figure, 21 is a table drive motor that rotates the turntable 16 via gears 22 and 23, 24 is an encoder that outputs an angle pulse via gears 23 and 25 every time the turntable 16 rotates by a predetermined angle, and 26 counts the angle pulses input from the encoder 24, and also counts the angle pulses inputted from the encoder 24, and also counts the n detectors 13-1, 13 for each angle pulse.
-2, .
This is a detector group driving motor that rotates the detector group by a predetermined angle within the range of n. Note that the radiation detector group 13
is the gear 2 connected to the detector group drive motor 27.
It is attached to an arcuate gear 29 which is rotated by meshing with the gear 8.

Next, FIG. 7 is a block diagram showing the overall configuration of the apparatus. In the figure, 31 is a radiation generator 11
This general control unit applies high voltage to the drive control unit 32 via high voltage cables, cooling pipes, etc., supplies a cooling medium, and performs controls such as turning on power to the drive control unit 32. The drive control section 32 is composed of elements 21 to 26 shown in FIG. 6, and the like. Reference numeral 33 denotes a detector group drive control section for driving the radiation detector group 13, and is constituted by, for example, elements 27 to 29 in FIG. 6. 34 is a scan detection unit that detects that the detector group 13 has rotated by a predetermined angle. Reference numeral 35 indicates a data collection unit, 36 indicates an image reconstruction device that converts the radiographic data collected by the data collection unit 35 into image data, and 37 indicates a CRT display.

Next, the operation of the apparatus configured as described above will be explained with reference to FIGS. 8 to 10.
For convenience of explanation, the number of detection channels is “8”.
The number of projections N for each channel is “320”
The explanation will be made assuming that the number of scans SN of the radiation detector group 13 is four. First, the table drive motor 21 is driven based on a start command signal. S11 in FIG. 9 shows the driving period T of the motor 21. When the table drive motor 21 rotates, the rotation is transmitted to the turntable 16 via gears 22 and 23. Here, the turntable 16 rotates at a constant speed, and the subject 1 on the table 16 is rotated at a constant speed.
2 is rotated as the table 16 rotates. At this time, the fan-shaped radiation beam 14 emitted from the radiation generator 11 passes through the subject 12 and enters each of the detectors 13-1 to 13-8. On the other hand, the encoder 24 detects the rotation angle of the turntable 16 via the gears 23 and 25, and outputs 320 angle pulses S12 with a pulse width t1 for one rotation of the turntable 16, as shown in FIG. ,
This is applied to the pulse generator 26. This pulse generator 26 counts the angular pulses S12, and for every angular pulse S12, S1 in FIG.
3', a timing signal S13 consisting of eight pulses is outputted to the data collection section 35.
give to The processing of the above pulses is performed by the data collection unit 3.
You can also do this with 5. When the data acquisition unit 35 receives eight pulses from the pulse generator 26, the first
Each detector 1 located in the A scanning area as shown in Figure 0
Radiographic data from 3-1 to 13-8 are collected sequentially. Subsequently, from the encoder 24, the second
When the third, fourth, ... angle pulse S12 is output, the pulse generator 2
As shown in FIG. 10, the data collection unit 35 moves through projections 2, 3, 4, and so on through the detectors 13-1 to 13-1 located in the A scanning area.
Collect radiographic data from 8. and,
Since 320 angle pulses S12 are output from the encoder 24 for one rotation of the turntable 16, the data collection section 35 collects the data indicated by diagonal lines in FIG.

In this way, the pulse generator 26 generates 320 angular pulses S for one rotation of the turntable 16.
After counting 12, a drive signal is given to the detector group drive motor 27. Then, the motor 27 rotates by a predetermined minute angle, which is then rotated by the gear 2.
8 and 29 to the radiation detector group 13. As a result, the radiation detector group 13 rotates by a minute angle Δα and moves to the B scanning area. For example, if the fan angle is α, the number of detectors is 8, and the scanning area is 4, this minute angle is (α/8)/4. After the radiation detector group 13 rotates by a minute angle, the turntable 16 rotates again and the encoder 24 outputs the angle pulse S12.
The data collection unit 35 collects data from each of the detectors 13-1 to 13-8 located in the B scanning area every 12 seconds. In this case as well, while the turntable 16 rotates once, data from each of the detectors 13-1 to 13-8 in the B scanning area is collected in 320 projections. When the turntable 16 rotates once, the radiation detector group 13 is moved to the C scanning area to collect data. Furthermore, turntable 16
After one revolution, it moves to the D scanning area and collects data according to the number of projections. After all the data has been collected by the scanning control as described above, the image reconstruction device 36 constructs an image based on software similar to the conventional fan beam method and displays it on the CRT display 37.

Therefore, with this configuration, although it is impossible to implement in the case of a large detector that is originally suitable for high energy, it is possible to reduce the number of detectors and perform scanning by moving minute angles at a time. Data can be collected just as reliably by arranging a large number of detectors.

Note that the present invention is not limited to the above embodiments. For example, although the radiation detector group 13 is rotated by a minute angle each time the turntable 16 rotates once, it may be rotated continuously within this minute angle range. In other words, data is collected while driving the subject 12 and the radiation detector group 13 in synchronization.

〔Effect of the invention〕

Since the present invention is configured as described above, it has the following effects.

(1) Since the radiation generator is fixed, it is particularly effective for those that are unsuitable for movement or have high energy.

(2) By making the radiation generator a fixed type,
The high-voltage cable and cooling system can be drawn in very easily to the line generator, and since the high-voltage cable does not move even during scan control, there is no chance of damage and accidents, and of course the high-voltage cable can be easily insulated. Furthermore, since the X-ray generator can be firmly fixed, it will not be displaced or tilted, and a fan-shaped radiation beam can be emitted accurately.
Moreover, it is a large volume, high energy radiation that is not suitable for transportation.

(3) Furthermore, when using high-energy radiation beams, such as in the inspection of industrial products, solid-state detectors are more advantageous than gas detectors due to the problems of decreased sensitivity and non-uniformity of sensitivity; With conventional methods, it is not possible to mount a solid-state detector with a relatively large external size. In this regard, this device moves a small number of detectors continuously or intermittently by a minute angle each time the subject rotates, so even large detectors can be installed and data can be collected reliably. High sensitivity and uniform sensitivity can be achieved even with an energetic radiation beam.

(4) Furthermore, not only can the number of detectors be reduced, but the rotation angle range is smaller than in conventional systems, which has the advantage of eliminating troubles such as breakdowns.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams explaining the conventional method;
Fig. 3 is a diagram showing the data collection timing in the conventional method, Figs. 5 is a configuration diagram of the scintillation detector, FIG. 6 is an example configuration diagram showing the drive system of the subject and the radiation detector group, and FIG. 8 is a block diagram showing the overall configuration of the device, FIG. 8 is a flowchart explaining the operation order, FIG. 9 is a timing diagram explaining the operation of the drive system in FIG. 6,
FIG. 10 is a diagram illustrating the data collection order. 11... Radiation generator, 12... Subject, 13
...Radiation detector group, 13-1 to 13-8...Detector, 16...Turntable, 21...27...
Motor, 22-25, 28, 29... Gear, 24
...Encoder, 26...Pulse generator, 35...
...Data collection unit, 36...Image reconstruction device, 37
...CRT display.

Claims (1)

[Claims] 1 A fixedly installed radiation detector that emits a fan-shaped radiation beam, and n detectors arranged equally within at least the fan angle α of the radiation beam emitted from this radiation generator and on the same plane. A group of radiation detectors arranged opposite to each other in an arc shape, a turntable provided between the group of radiation detectors and the radiation generator, on which a subject is placed and rotated, and this turntable rotates by a predetermined rotation angle. Each time the turntable rotates, n data collection timing signals are output to collect radiation transmission data from each of the detectors in a certain scanning area of the detector. data collection means for collecting radiation transmission data corresponding to the number of projections; 1. A radiation tomography examination apparatus comprising: a detector driving means that rotates the detector automatically or continuously to collect radiation transmission data in the next scanning area.