JPS60170748A - Tomographic inspecting device - Google Patents

Abstract

PURPOSE:To obtain a tomographic image of good quality by eliminating the error of the reconstituted tomographic image due to difference in sampling beam interval as to a CT device of the 2nd generation. CONSTITUTION:A subprocessor 19 has a counter which counts encoder pulses from a position detector 14A and outputs a value (m) proportional to the movement extent of a translation frame 2. The sampling number of a radiation detecting element with a number (n) is calculated from said (m), and a sampling pulse Ps is sent out to sample holding circuits 16-1-16-N of respective radiation detecting elements (n) every time -in varies by one. A reset pulse PR is sent out to integrators 15-1-15-N an extremely short time lag tau after said pulse Ps. Then, a data transfer timing signal ST is sent out to buffer memories 18-1-18-N according to a predetermined sequence. When said data is transferred, an address signal SA for discriminating the data is sent out to a system controller 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation tomography inspection apparatus that uses radiation to obtain a cross-sectional image of an object to be inspected and thereby inspect the object.

[Technical background of the invention]

2. Description of the Related Art There is a radiation tomography inspection device called a computer tomography scanner (hereinafter referred to as a CT parent device) as a device that can non-destructively and accurately measure internal defects, composition, structure, etc. of an object.

This device includes, for example, a radiation source that emits fan beam X-rays that spread in a flat fan shape, and is placed facing this radiation source through a subject, so that the fan beam X-rays spread in multiple directions. Using a detector equipped with a plurality of radiation detection elements, the radiation source and the detector are sequentially rotated in the same direction, for example, in 1 degree increments over a range of 180° to 360°, centering on the subject. After collecting X-ray absorption data from multiple directions, a computer etc. performs image reconstruction processing to reconstruct a tomographic image. Since the image can be reconstructed with a wide range of gradations, it is possible to understand the state of the tomographic plane in detail.

This is a so-called 3rd generation CT rack.In addition, an X-ray source that emits pencil beam X-rays and a detector are installed opposite to this X-ray source. is traverse scanned along the cross section of the object to be inspected, rotated by a predetermined angle every time one traverse scan is completed, and then subjected to the traverse scan and rotational scan using a detector having several detection elements. The so-called second generation, which can also be called an improved version of the first generation,
Using a detector with detection elements arranged around the entire circumference of the object to be inspected and an X-ray source that emits wide fan beam X-rays,
There are various types of OCT apparatuses such as the so-called fourth generation in which only the X-ray source is rotated and scanned.

By the way, among the various methods, the number of detection elements of the second generation CT rack equipment is smaller, the equipment configuration is simpler than the third and fourth generations, and the data collection is much faster than projection data collection using pencil beam X-rays. This method is suitable for measurement OCT devices because it takes a short time.

As shown in FIG. 1, this second-generation OCT device has a disc-shaped rotating frame 1 with a hole 1a formed in the center to serve as an imaging area.
An annular translation frame 2 is provided above the hole 1a. An X-ray tube 3 for irradiating fan beam X-rays FB with a width is fixedly provided on one of the opposing sides of the translating 7-frame 2, and the A plurality of radiation detection elements 4a, which have a minute spread of X-rays in the υ direction, are arranged in parallel at equal intervals to face the tube 3 to detect the
A detector 4 capable of detecting line intensity with spatial resolution is fixedly provided. Here, the X-ray path connecting the X-ray tube 3 and each radiation detection element is called an X-ray path, and each radiation detection element outputs a signal corresponding to the radiation intensity on this X-ray path. The translation frame 2 is configured to be linearly movable in a predetermined direction on the rotation frame 1, and this movement is performed by a translation drive unit 5 provided on the rotation frame 1.

A is an object to be inspected disposed in a hole la of the rotary frame 1, and the rotary frame 1 is rotated by the rotary drive unit 6 about the hole 1jL.

Reference numeral 7 denotes an X-ray controller that controls the tube current, tube voltage, and X-ray exposure of the X-ray source 2. Reference numeral 8 denotes a scanner controller, which drives and controls the translation drive unit 5 and rotation drive unit 7. Reference numeral 9 denotes a system controller, which is configured as a cptr and controls the entire system. 10 is a data collection device υ, and the radiation detector 4
It receives each radiation detection element output signal, performs ~Φ conversion, and outputs it as X-ray absorption data.

Reference numeral 11 is a high-speed arithmetic reconstruction circuit, which receives the absorption data for each glossy eye collected by the data collection device, and
For this, preprocessing such as logarithmic transformation, gain correction, and offset correction is performed, and the preprocessed data is condeluded, and the concollated data is then back-projected in the projection direction to create a tomographic image. It is something that is reconfigured. Reference numeral 12 denotes a magnetic disk sb for storing the data of this reconstructed image, and 13 indicates a black and white CT value (data as a value corresponding to the level of radiation absorption) in a desired range from the data stored in the magnetic disk 12. This is a CRT display that displays a grayscale image. Note that 14 is a position detector that detects the position of the translation frame 2.

In such a configuration, when an operator first operates a console (not shown) to start up the system and start imaging, the system controller 9 controls the scanner controller 8 to perform translational scanning of the translational frame 2, that is, traverse scanning. and controls the rotation of the rotating frame 1 in predetermined angle increments, and also controls the X-ray controller 77 to sequentially apply a predetermined tube current and tube voltage to the X-ray tube 3 for a predetermined time width in accordance with the traverse scan. give. From this, fan beam X-rays FB are sequentially emitted from the X-ray tube 3 in a pulsed manner.

An object to be inspected A is disposed at the rotational center position (photographing area) of the rotating frame 1), and an X-ray tube 3 and a detector 4 are placed facing each other in the translation frame 2 through the photographing area. Since the X-ray tube 3 is installed at
B will be exposed. The radiation transmission value of each X-ray path in this fan beam X-ray FB is detected by each radiation detection element of the radiation detector 4 and converted into an electrical signal.

This converted signal is collected by the data acquisition device 10, sent to the high-speed calculation reconstruction circuit 11, and subjected to logarithmic conversion, gain correction, offset correction, etc. for each Zorological Execution (1 shooting direction). The data (X-ray absorption data at each x-ray for each x-ray excursion) are further convolved and then back-projected to find the CT value of each pixel position, and this C
A tomographic image based on the T value is reconstructed. This reconfiguration circuit 11
The reconstructed image is stored in the magnetic disk 12, and by giving commands from the console, CT values in a desired range are displayed on the CRT display 13 as necessary at a gradation level corresponding to the CT values. As a result, the reconstructed image is displayed as a black and white grayscale image.

Now, if we look at the circuit configuration near the data collection device 10 in the above device, it is constructed as shown in FIG. That is, each radiation detection element 4al to 4 in the detector 3
an are connected to integrators 15-1 to 15-N, respectively, and each integrator 5-1 to 15-N is connected to a corresponding sample-and-hold circuit 16-1 to 16-N, respectively.
Every time X-rays are irradiated, the signal output from each radiation detection element is integrated, and its value is sampled. Each sample-and-hold circuit 16-1 to 16-N is connected to a multiplexer 17 that performs selection switching, and the signals sampled and held by these sample-and-hold circuits 16-1 to 16-N are sent to the multiplexer 17. υ
Sequentially selected and extracted to multiplexer 17(7)f
& stage AD converter 18. Then, it is converted into a digital signal. The output of each radiation detection element, which has been cidigitally converted by the AD converter 18, is sent to the high-speed reconstruction circuit 11.

The first digit of the translational frame 2 to the detector 14 have a sampling interval d as the translational frame 2 is translated (traversed).
The system controller 9. generates a response-like sampling signal for each translation of the system controller 9. Send to -1. The system controller 9 selects the predetermined translation values from the first position 1 to the detector 14, and 2
In response to the sampling signal output to the d-movement 4σ, the 1. This signal is then sent to the zangle-and-hold circuits 16-1 to 16-N and the integrators 15-1 to 15-N of the data acquisition device 10 to reset the integral value and sample/J1. - Rudo ('i go.

Here, the sampling signal and the reset signal are sent to the integrators 15 -
1 to 15-N and sample AND month; -old circuit 16-
1. It is the same signal for ~16-N. Therefore,
The following inconveniences occur. That is, second generation OCT
The device uses narrow fan beam X-rays;
Radiation detection element 4a1. ~4an are arranged in a straight line in the direction of spread of fan beam X-rays. Therefore, the radiation detection element on the central X-ray beam in the fan beam X-ray and the other X-rays) J? Due to the angular difference of X-ray i4 in the on-soot radiation detection element, if reset and sampling are performed at the same timing every time a translation of the sampling interval d is performed, the radiation in the center will be affected as shown in Figure 3. The distance between Xi' beams (hereinafter referred to as the sampling beam interval) at the next sampling timing differs between the detection element and the radiation detection element D' in the peripheral area.'j In other words, the radiation detection element D' The sampling beam interval dn of (An) is the set angle θ of the radiation detection element.

, when the sample interval is d, dn=dllIeCθ0...-(1), which differs depending on the position. In addition, S is the focal point of the X-ray tube 3,
Further, A indicates adjacent sampling beams of the radiation detection element j at the center, and B indicates adjacent sampling beams of the radiation detection element j at the periphery.

However, since the reconstruction circuit is constructed with equal sampling beam spacing for each detection element, errors occur in the reconstructed 1lli plane image due to the difference in sampling beam spacing. The error in this cross-sectional image is the set angle θ of the radiation detection element.

The wider the range, the larger the number of squares in the image, the sharper the image becomes.

[Purpose of the invention]

Kii 13 Akira was created in consideration of the above-mentioned belief, and is a radiation therapy that can eliminate errors in reconstructed tomographic images caused by differences in sampling beam intervals and obtain high-quality tomographic images in second-generation OCT equipment. The purpose is to provide a tomographic inspection device.

[Summary of the invention]

In order to achieve the above objective, the present invention uses a radiation source that emits fan beam radiation with a relatively narrow qV and a detector having dissipative radiation detection elements arranged at a predetermined pitch through the object to be inspected. The radiation source and the detector are arranged facing each other, and the radiation source and the detector are arranged to face each other. Translational scanning is performed along the surface, radiation detection is performed at predetermined translational intervals, and each time this translational scanning is completed, the radiation source and detector are rotated by a predetermined angle around the object to be inspected, and the translational scanning is repeated to detect the object to be inspected. In an apparatus that collects radiation absorption data from multiple directions of a body cross section and reconstructs the cross-sectional image of the object to be inspected based on the collected data, the radiation detection timing of the detector is arranged for each radiation detection element. The sampling beam interval error for each array position is compensated at each radiation detection timing for each predetermined sampling interval, which is caused by the difference in elevation angle with respect to the radiation source, which differs depending on the position of each radiation detection element. This makes it possible to obtain highly accurate reconstructed images.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the first page.

No. 41) is the data collection device 10A in the device of the present invention.
This is a professional diagram showing the 17/l configuration in the vicinity and is the same as that of other basic 11ζ or FIGS. 1 and 2. Therefore, the same parts as in FIGS. 1 and 2 will be given the same reference number and their explanation will be omitted.

The difference from the conventional example is the configuration of the data acquisition device 10 and the position detector J (A), and the signal from the position detector J4A is a much faster pulse than the conventional sampling signal. An address signal used to identify the data output from the point and data collection bag @ 10 A to the data node DB is given to the data collection device 10k instead of the conventional reset signal and sampling signal via is sent from the data collection device 10k to the system controller 9.The control line system is omitted for simplicity in FIG. 1-flZ.

The inside of the data collection device 10 includes a radiation detection element 4al,
~4nn corresponds to integrators 15-1°~15-N, respectively.
, sample and hold circuit 16-1° to 16-N,
AD converter 17-1. ~17-N.

buffer memories 18-1. ~18-N are connected to the sub-processor 19.

Also, the integrator 15-1. ~15-N, sample and hold circuit 16-1. ~16-N, AD converter 1
7-1. ~17-N, buffer memory 18-ha~18-
N is connected to the sub-processor 19. The encoder pulse output line PB and address signal line PA from the position detector 14k are connected to the sub-processor 19.

The subprocessor 19 consists of a microprocessor, memory, logic circuit, etc., and has the following functions: 01, counts the (D encode f/#) response from the position detector 14k, and is proportional to the amount of movement of the translation frame 2. value m
It has a counter that outputs .

2 From the above m, the sampling number of the radiation detection element with number n 〒n=INT(m -3cm θ1, -7 (L s
in θ. +ε)+I) ・−−・−・ Say (2)1
(described later), each time in changes by one, the sample-and-hold circuit 16-1 . ~16
- Send sampling signal P8 to N.

3. The reset pulse P8 is applied to the integrator 15-1 with a delay of a minute time τ from the sampling signal P8.
~15-N.

4. Data transfer timing signal ΔST is transferred to buffer memory 1B-1, ~ according to a predetermined sequence.
18-N.

5. When transferring the data, send an address signal SA for distinguishing the data to the system controller 9.

Next, the operation of this device having the above configuration will be explained.

First of all, referring to FIG. 1, during scanning, the rotary frame 1 is rotated in steps by the rotary drive unit 6, and when the step rotation is stopped, the translation frame 2 is translated, and the 7-am beam Xi beam FB is The X-ray intensity at that time when crossing the inspected object A is detected by each radiation detection element 4 of the detector 4.
It is measured by a. The scanning ends when the total angle of the step rotation is about half a turn or about one turn, and the X-ray intensity data obtained by this scanning is collected by the data acquisition device 10 through integration, sampling, and AD conversion, and is subjected to high-speed calculation. A reconstruction circuit 11 performs reconstruction processing to construct a cross-sectional image. The data of this reconstructed image is then stored on the magnetic disk 1.
2 and stored, and also displayed on the CRT display device 13. The system controller 91d manages scanning through the X-ray controller 7, scanner core 8, and also performs theta processing of the data acquisition device 10A1, the reconstruction circuit 1, the CRT display 13, the magnetic field, and the screen 12.

Looking at the operation of the data acquisition device 10 of the apparatus of the present invention with reference to FIG. 4, during scanning, X-rays from the X@ tube 3 enter the detector 4, and each radiation detection element (al, When an output current corresponding to the incident X-ray intensity is output from ~4an, the output box and current are integrated by the 411 dividers 1'5-1.~15-N, respectively.-Force, position detector during scanning 14k generates eight pulses every fixed scan-IIi and applies them to the ZAG processor and sensor 19.Then, this pulse PE is divided into reset pulses PR and sampling pulses P and P, which are different for each radiation detection element, by the pulse processor and sensor 19. .

This reset pulse PIt is applied to the corresponding seedling divider 15-1.
~15-N, respectively. (Reset) When receiving the y9 pulse PR, the 6-node dividers 15-1 to 15-N are reset, but just before that, the integrators 15-1. The output of ~15-N is the corresponding Zanzol-and-hold circuit ho17-1.
~17-NICJ: f) Sampled and held according to sampling number Ps. And the corresponding AD converter 23-1. ~23-N, it is converted into digital b1 and the corresponding buffer memory 1B-1,
~18-N. Then, due to the data transfer timing 5X@ST, the buffer memory 23-1. ~23
-N storage data is sent to the magnetic disk 12 or the high-speed reconfiguration circuit 11 via the system controller 9. Then, reconstruction processing is performed in the high-speed calculation reconstruction circuit 1.

Here, the above equation (2) will be explained with reference to FIG.

The concentric circles equally spaced around the center of rotation of the rotating arene, l (when viewed from the slice plane) are called sampling circles. Then, the X-ray dose from the position where the X-ray beam touches this sampling circle to the next tangent position is detected by each radiation detection element 4a1° to 4a11, and this detection output is integrated.

Here, ml-j sampling number (0 to 2N), d is the sampling interval, O is the rotation center of rotation frame 1, and S
i is the sampling circle of sampling number i, Bc is the beam group detected by the radiation detection element in the center, B8 is the beam group detected by the peripheral radiation detection element, ε is the deviation from the center of rotation, and ε/d is the sun sillage. Indicates a phase.

In order to explain FIG. 5 more clearly, with reference to FIG. 6 which shows the relationship between a certain radiation detection element Dn at a certain sample position, the X-ray beam BM, and the rotation center O, the detection of sampling AI and radiation detection number n Deriving the relationship between the element Dn and the count value m of encoder pulses output by the position detector JJA, the position 11 yen on the rotational frame at the time of the first 'insulation' by the radiation detection element Dn is expressed as Xn +
If it is 1! n, i =Ztanθ, +(d・(i−I)1ε
) secθn −−−−・・(3) Solve for the quantity and get S′ +””m′cosθn, sinθn7+I ・・−=
(4) Here, X is the position of the translation frame 2, the S radiation source, the set angle of the θnI′i radiograph aJ coordinate, and t is the distance 1′ between 8 and the translational locus tracing the rotation center O. :d-18' is the translational distance 1'J on the rotating frame corresponding to the encoder pulse interval! , m is the radius of the sampling circle expressed in the count value unit of the encoder pulse output to the position detector 14, and d is the sampling interval.

By setting υg', d, j, ε, and k as constants in the above equations (3) and (4), the above equation (2) can be derived.

In indicates the sampling plane l of the detector n, which is approximated by truncating p to the nearest whole number.

The error of in due to approximation is 8' smaller than d in s/d, that is, if the position detector J4A, which is much finer than d, is used, the error can be ignored.

According to this apparatus, (1) the sampling beam interval is equal for each radiation detection element, so errors in the reconstructed cross-sectional image are reduced and a higher quality image can be obtained.

(2) Also, the set angle θ of the detector. Since the distance between the radiation source and the detector can be increased, it is possible to shorten the distance between the radiation source and the detector, making it possible to realize a CT system that can accurately examine small objects. What was impossible because it was impossible becomes possible).

(3) This is particularly effective in the case of a highly accurate CT device with a large number of image matrices.

Benefits such as:

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, and can be modified as appropriate without changing the gist thereof. For example, in addition to X-rays, RI (radioisotope), etc. It can also be implemented using other radiation sources.

〔Effect of the invention〕

As described in detail above, the present invention involves a radiation source that emits relatively narrow fan beam radiation and a detector that includes a plurality of radiation detection elements arranged at a predetermined pitch, facing each other through an object to be inspected. At the same time, the radiation source and the detector are translated and scanned along the cross section of the object to be inspected, and radiation is detected at predetermined translational intervals. The source and detector are rotated by the angle of the knob and translation scanning is repeated to collect radiation absorption data from multiple directions of the cross section of the object to be inspected, and based on this collected data, the cross-sectional image of the object to be inspected is reconstructed. In the apparatus, the radiation detection timing of the detector is varied for each radiation detection element according to its arrangement position, and the above radiation detection timing is determined at a predetermined sampling interval caused by a difference in elevation angle with respect to a radiation source that differs depending on the position of each radiation detection element. To provide a radiation tomography examination apparatus having such characteristics that a highly accurate reconstructed image can be obtained by compensating the sampling beam interval error on the array position side at each radiation detection timing. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional device, FIG. 2 is a block diagram showing the main part configuration, FIG. 3 is a diagram for explaining the relationship of sampling beams in the conventional device, and FIG.
The figure is a block diagram showing an embodiment of the present invention.
6 are diagrams for explaining the relationship of sampling beams by the apparatus of the present invention. 1...Rotation frame, 2...Translation frame, 3...
・X mA tube, 4...detector, 4 a r 4 a
1 * ~ 4 an... Radiation detection element, 5...
Translation drive unit, 6... Rotation drive unit, 7... X IN controller, 8... Scanner controller, 9...
System controller, 10.1OA...Data collection device, 1..High-speed calculation reconfiguration circuit, 12..Magnetic disk, 13..CRT display device, 14.14k.
・・1st color horizontal instrument, 15-1. ~l ”5- N...
Integrator, 16-1. ~16-N... Sample and hold circuit, 17-1 17-N... AD converter, 1B-1, ~1B-N... Buffer memory, 19.
...Sub-processor. and 1 Hiroshi's representative and patent attorney Takehiko Suzue Figure 1 Figure 5 Figure 6

Claims (1)

[Claims] When a radiation source that emits a relatively wide fan beam radiation and a detector having a plurality of radiation detectors arranged at a predetermined pitch are placed facing each other with the object to be inspected in between, co-pregnancy with the radiation source described above can be achieved. The detector and the detector are translated and scanned along the cross section of the object to be inspected, radiation is detected at predetermined translational intervals, and each time this translational scan is completed, the radiation source and the detector are rotated by a predetermined angle around the object to be inspected. In an apparatus that repeatedly performs translational scanning to collect radiation absorption data from multiple directions of a cross section of an object to be inspected, and reconstructs a cross-sectional image of the object to be inspected based on the collected data, the radiation detection timing of the detector is 1. A radiation tomography examination apparatus characterized in that the radiation detecting elements differ according to their arrangement positions.