JPH04128679A - Positron ct device - Google Patents

Abstract

PURPOSE:To detect movement of an object to be detected to correct position information, and to reduce or prevent false information by providing a read-in circuit for inputting position information from a coincidence circuit into output signals, and a position correction circuit for converting inputted position variation information into reference coordinates of the object to be detected. CONSTITUTION:This position CT device is provided with distance measuring sensors 10a, 10b, 10c, a distance measuring circuit 11, a data read-in circuit 12, and a position correction circuit 13. The distance measuring sensors 10a - 10c are used for the purpose of measuring the distance from an object 14 to be detected situated in an opening part 15 of a detector-line 1, composed of a light emitting element for emitting a light toward the object 14, and a light receiving element for detecting a light which strikes the object 14 and is reflected from it, and mounted on the inside peripheral surface of the opening part 15, for example, in three directions crossing at right angles. Thus, the position of the object 14 in the opening part 15 can be determined by the distances x1, x2, x3 up to the object 14 in three directions measured by the three distance measuring sensors 10a, 10b, 10c.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to the use of positron-emitting nuclides (injected into a subject).
Regarding the positron 0 device that detects annihilation gamma rays emitted from (radioactive isotopes that undergo positron decay) and obtains tomographic images of the diagnostic site of the subject, it is particularly useful for detecting the movement of the subject during examination and collecting position information. The present invention relates to a positron CT device that can be corrected to reduce or prevent artifacts. [Conventional Technique] As shown in No. 3μ, a conventional positron CT apparatus of this type has a detector row 1 around an opening into which a subject is inserted; A simultaneous i-count circuit 2 which detects a coincidence event by inputting the emission signal of the radiation emitted from the subject by each of the above-mentioned detectors, and takes in the output from this coincidence circuit 2 and converts it into projection data. A data conversion Okiji 3, a memory circuit 4 as a storage device that stores this projection data, and an image reconstruction circuit 5 that performs a predetermined correction on the ship shadow data from this memory circuit 4 and then inverts the image. It also included an image display device 6 for displaying this reconstructed image. In FIG. 3, the reference numeral 7 indicates a main memory that directly exchanges data with the memory circuit 4 using the DMA method, and the reference numeral 8 indicates the correction of the detector sensitivity for the projection data read out from the main memory 7. and a data correction circuit that performs absorption correction and radiation data correction, and reference numeral 9 indicates a central processing unit (CPU) that controls the operation of each of the above components. In such positron CT apparatuses, little countermeasures have been taken to prevent deviations in tomographic images due to movement (body movement) of a subject during examination, that is, the occurrence of false images. Furthermore, in the case of re-examination of the same patient after a certain period of time after a certain examination, it is difficult to ensure reproducibility of the positioning of the diagnosed area, and it is difficult to ensure a comparative evaluation of the tomographic images obtained in both examinations. Sometimes I couldn't enable it. In contrast, conventionally, a specially made positioning mask is prepared for each patient to be examined, and this positioning mask is used to fix the patient's head, for example, to a bed. This prevents body movements of the subject to reduce or prevent the occurrence of false images, and reproduces the positioning of the diagnostic site of the subject in re-examination. [Problems to be Solved by the Invention] However, in such a conventional positron CT apparatus, in order to prevent the generation of false images in the obtained tomographic image, a special positioning mask is used to position the subject's head, for example. was fixed to the bed. The subject was to be fixed on a bed for, for example, several hours during the examination. Therefore. The subject was restrained for a long period of time, inflicting mental and physical pain. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a positron CT apparatus that can solve these problems, detect the movement of a subject under examination, correct position information, and reduce or prevent false images. shall be. [Means for Solving the Problem] In order to achieve the above object, the positron C according to the present invention
The T device inputs a detector row in which a plurality of detectors are arranged facing each other around an opening into which the subject is inserted, and a detection signal of radiation emitted from the subject by each of the detectors, and performs a coincidence event. A coincidence counting circuit for the hands, and a data conversion circuit that takes in the output signal from this coincidence counting circuit and converts it into projection data. A storage device that stores this projection data, an image reconstruction circuit that reconstructs an image after predetermined correction is performed on the projection data from this storage device, and an image display device that displays this reconstructed image. A positron CT apparatus having a plurality of distance measuring sensors for measuring the distance to the subject located within the opening of the detector array, and obtaining distance signals from these distance measuring sensors to determine the position of the subject. A distance measuring circuit that generates positional fluctuation information, a data reading circuit that reads this positional fluctuation information into the output signal from the coincidence counting circuit, and a position correction circuit that converts the read positional fluctuation information into reference coordinates of the subject. It is equipped with the following. Further, the distance measuring sensor is preferably attached to the inner circumferential surface of the opening of the detector array. Furthermore, the distance measurement sensor may be configured with a light emitting element that emits light toward the subject, and a light receiving element that detects the light that hits the subject and is reflected.

[For production]

The positron CT device configured in this way. A distance measurement sensor measures the distance to the object located within the opening of the detector array, and a distance measurement circuit takes in the distance signal from the distance measurement sensor to determine the position of the object and generates position fluctuation information. The data reading circuit reads the generated positional variation information into the output signal from the coincidence circuit, and further operates to convert the read positional variation information into the reference coordinates of the subject using the positional correction circuit. Due to this. The positional information is corrected by detecting the movement of the subject under examination, and as a result, artifacts can be reduced or prevented. [Example] Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a positron CT apparatus according to the present invention. This positron CT device detects annihilation gamma rays emitted from a positron-emitting nuclide introduced into a subject to obtain a tomographic image of the diagnostic site of the subject.As shown in the figure, a detector array 1 , a coincidence circuit 2, a data conversion circuit 3, a memory circuit 164, a single image reconstruction circuit 5, an image display device r6, a main memory 7, a data correction circuit 8, and a CPU 9. It includes distance measuring sensors 10a, 10b, and 10c, a distance measuring circuit 11, a data reading circuit 12, a position correction circuit 1-3, and the like. The detector row 1 detects annihilation gamma rays emitted from a positron-emitting nuclide injected into the subject.
As shown in FIG. 2, an opening 15 into which the subject 4 is inserted
A plurality of unit detectors are arranged around the subject 14 and facing each other, and are formed into a ring shape as a whole. The coincidence circuit 2 measures a coincidence event in which the two opposing unit detectors of the above-mentioned detector array simultaneously detect annihilation gamma rays. The device inputs signals that detect emitted annihilation gamma rays, generates output signals only when each input signal is input at intervals shorter than a specific decomposition time, and counts the output signals. The data conversion circuit 3 takes in the signal output from the coincidence circuit 2 and converts it into projection data. For example, the data conversion circuit 3 is a ROM (read-only memory). The memory circuit 4 serves as a storage device that sequentially stores projection data measured within a certain period of time and output from the data conversion circuit 3. The one-image reconstruction circuit 5 reconstructs an image after a predetermined correction is performed on the projection data read out from the memory circuit 4. Furthermore, the image display device t6 receives the image data reconstructed by the image reconstruction circuit 5 and displays it as an image. For example, it consists of a D/A converter and a television monitor. In FIG. 1, reference numeral 7 indicates a main memory that directly exchanges data with the memory circuit 4 using the DMA method, and reference numeral 8 indicates correction of the detector sensitivity for the projection data read out from the main memory 7. and a data correction circuit that performs absorption correction and radiation data correction,
Reference numeral 9 denotes a central processing unit [
(CPU) It is grainy. Here, in the present invention, the first
As shown in the figure, distance measuring sensors loa, 10b, 10c, a distance measuring circuit 11, a data reading circuit 12, and a position correction circuit 13 are added. The distance measuring sensors 10a to 10c measure the distance to the subject 14 located within the opening 15 of the detector row 1, and each includes a light emitting element that emits light toward the subject 14; As shown in FIG. Mounted in the direction. The object 1 measured from three directions with these three distance measuring sensors 10a, 10b, and 10c.
Distance to 4x1. The position of the subject 14 within the opening 15 can be determined from x, , x. Note that the above-mentioned light-emitting element is, for example, a light-emitting diode (
An infrared LED) or a laser diode is used, and a photodiode or the like is used as the light receiving element. The distance measurement circuit 11 includes the three distance measurement sensors 10a to 10c.
The position of the subject 14 is determined by taking in signals for the distances xt+xz+X output from the respective locations, and generates position fluctuation information due to the body movement of the subject 14.
A distance signal in each direction is generated based on the time difference between the emission start time of the light emitted from the light emitting element in each of the distance measuring sensors 10a, 10b, and 10c and the arrival time of the light arriving at the light receiving element. For example, by converting the voltage signal into a voltage signal using a time-to-wave height converter, and then converting this voltage signal into a digital signal using an A/D converter, positional fluctuation information with respect to the reference position of the subject 14 at the time of starting the test is generated. It looks like this. The data reading circuit 12 reads the positional variation information of the subject 14 generated by the distance measuring circuit 11 into the output signal from the coincidence counting circuit 2, and is configured to read the position fluctuation information of the subject 14 generated by the distance measuring circuit 11 into the output signal from the coincidence counting circuit 2. When the coincidence counting circuit 2 generates an output signal by inputting a detection signal from the position change information, the positional variation information is input and read. Furthermore, in the 1st position correction circuit jg13, the data reading circuit 12 reads the position fluctuation information from the ranging aperture jgll into the output signal from the coincidence circuit 2, and calculates the position of the projection data converted via the data conversion circuit 3. It converts the fluctuation information into the reference coordinates of the subject 14, and includes, for example, a ROM in which a conversion table for converting the positional fluctuation information of the subject 14 to the reference coordinates is written. Next, the operation of the positron CT apparatus of the present invention configured as described above will be explained. First, as shown in FIG. 2, the subject 14 is inserted into the opening 15 of the detector array 1 and the test is started. At this time. The three distance measuring sensors 10a to 10c provided on the inner peripheral surface of the opening 15 emit light toward the subject 14 and detect the reflected light to determine the distance from each direction! 4. X, , x, is measured and this distance signal is sent to the distance measuring circuit 11. Then, the distance measuring circuit 11 receives the distance signal and determines the position (xl, xg*X3) of the subject 14 within the opening 15. This becomes the position of the subject 14 at the start of the examination, and becomes the reference coordinate. Next, the position information from the distance measuring circuit 11 is input to the data reading circuit 12, and is read into the output data obtained by counting the annihilation gamma rays from within the subject detected by the detector array 1 by the coincidence counting circuit 2. And this data reading circuit 1
The data output from 2 is input to a data conversion circuit 3 and converted into projection data. This projection data is then stored in the memory circuit 4. Assume that in this state, a positional shift occurs due to the body movement of the subject 14, as shown by the broken line in the second @. Then, due to the operation of the distance measuring sensors 10a to 10c,
The distance from each direction of the subject 14 after the body movement is measured, and a new distance signal is sent to the distance measuring circuit 11. The m-distance circuit 11 takes in the new distance signal and determines the position of the subject 14 after the body movement, and also calculates the position IE at the time of the start of the test.
(X 1v
ΔX l l Δxi) is determined. Then, this positional fluctuation information is sent to the data reading circuit 12, and the coincidence counting circuit 2
Next, the output data from the data reading circuit 12 is converted into projection data via the data conversion circuit 3, and then input to the position correction circuit 13. In this position correction circuit 13, the position variation information (ΔX l t
Δx2. Δxa) is converted to the reference coordinates of the subject 14 in real time. Thereby, the positional deviation due to the body movement of the subject 14 is corrected. Through the subsequent image re-creation and image display operations, subject 1
Pseudo-images are reduced or prevented for the tomographic images of No. 4. Although the 1-position correction circuit 13 is shown as being separate from the data conversion circuit 3 in FIG. 1, the present invention is not limited to this, and when both are configured with ROM, the position correction circuit 13 is shown as being separate from the data conversion circuit 3. It may also be incorporated into the conversion circuit 3. [Effects of the Invention] Since the present invention is configured as described above, the distance measuring sensor lo
a to 10c, the distance from the subject 14 located within the opening 15 of the detector row 1 is taken aside, and the distance measurement circuit 11 captures the distance signals from the distance measurement sensors 10a to 10c to detect the subject 14. The position is determined and position fluctuation information is generated, the data reading circuit 12 reads the generated position fluctuation information into the output signal from the coincidence circuit 2, and the position correction circuit 1; 3 reads the position fluctuation information twice. The positional variation information can be converted into the reference coordinates of the subject 14. Thereby, the movement of the subject 14 under examination is detected and the position information is corrected, and as a result, it is possible to reduce or prevent false images in the tomographic image of the subject 14. Therefore, it is not necessary to use a specially made positioning mask to fix, for example, the head of the subject 14 on a bed as in the past.
The test can be easily performed without causing mental or physical pain to the subject 14. Furthermore, since multiple projection data obtained for the subject 14 can be converted to the reference coordinates of the subject 14, it is possible to accurately reproduce the positioning of the diagnostic region in the case of re-examination of the same patient. Comparative evaluation of tomographic images obtained in a single-vehicle examination can be effectively performed without the need for. Therefore, the diagnostic ability of the device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the positron CT apparatus according to the present invention, 2nd vfJ is an explanatory diagram showing the mounting state of the distance measuring sensor to the detector row and the measuring state of the positional deviation amount of the object, and FIG. FIG. 1 is a block diagram showing a conventional positron CT apparatus. ]...detector row, 2...coincidence circuit, 3...
・Data conversion circuit, 4...Memory circuit, 5...
・Image reconstruction circuit, 6...Image display device, 9...
・CPU,], Oa~10e... Distance sensor,
11... Distance measuring circuit, 12... Data reading circuit,
13... Position correction circuit, 14... Subject, 15.
··Aperture.

Claims (3)

[Claims] (1) A coincidence event is performed by inputting a detector row in which multiple detectors are arranged facing each other around the opening into which the subject is inserted, and the detection signal of the radiation emitted from the subject by each of the above detectors. A coincidence circuit for measuring, a data conversion circuit for capturing an output signal from this coincidence circuit and converting it into projection data, a storage device for storing this projection data, and a predetermined correction for the projection data from this storage device. Positron CT, which has an image reconstruction circuit that reconstructs an image after the image has been imaged, and an image display device that displays the reconstructed image.
The device includes a plurality of distance measuring sensors that measure the distance to the subject located within the opening of the detector array, and a system that captures distance signals from these distance measuring sensors to determine the position of the subject and obtains position fluctuation information. A distance measurement circuit that generates a distance measurement circuit, a data reading circuit that reads this position variation information into an output signal from the coincidence counting circuit, and a position correction circuit that converts this read position variation information into reference coordinates of the subject. A positron CT device characterized by: (2) The positron C according to claim 1, wherein the distance measuring sensor is attached to the inner peripheral surface of the opening of the detector row.
T device. (3) Claim 1 characterized in that the distance measuring sensor is constituted by a light emitting element that emits light toward the subject and a light receiving element that detects light that hits the subject and is reflected. or the positron CT apparatus described in 2.