JPH08304551A - Position ct equipment - Google Patents

Abstract

PURPOSE: To save time and labor for regulation of the sensitivity of a large number of sensors and to increase the accuracy in the regulation in a position CT equipment having a large number of two-dimensional radiation position detectors arranged in the shape of a ring. CONSTITUTION: CPU 53 reads out data collected in regard to a reference radiation source from a memory 52. Regulation of the sensitivity among two-dimensional radiation position detectors 10 is conducted by controlling variable gain amplifiers 41-44 for one detector 10 in common. Regulation of the sensitivity among photosensors 11, 21, 12 and 22 in each detector 10 is conducted by controlling the variable gain amplifiers 41-44 for each detector 10 discretely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic device used in the field of nuclear medicine, and more particularly to a positron CT device.

[0002]

2. Description of the Related Art A positron CT device administers RI (radioisotope) of a positron-emitting nuclide as a drug to a subject and reconstructs a tomographic image representing the distribution state in the body by calculation. is there. A large number of radiation detectors are arranged in a ring shape, a subject is inserted into the ring, radiation from the subject is detected, and coincidence count data is collected.

As this radiation detector, one having a structure as shown in FIG. 5 has been conventionally used. This is configured as a two-dimensional radiation position detector 10 that obtains the incident position when the radiation is incident on a two-dimensional plane.
That is, the two-dimensional radiation position detector 10 shown in FIG.
The four photosensors 11, 21, 12, and 22 detect which of the 48 scintillators 31 such as BGO, which is divided into 6 in the X direction and 8 in the Z direction, enters the radiation.
The optical sensors 11, 21, 12, 22 are usually PMTs.
(Photomultiplier) is used. The light receiving surfaces of the optical sensors 11, 21, 12, 22 are optically coupled to the light emitting surface of the scintillator 31 divided into 6 × 8 via the light guide 32.

48 scintillators 3 divided into 6 × 8
When the radiation enters any one of the 1, the light is emitted, and the light passes through the light guide 32 and the four optical sensors 11, 21,
Although the light enters 12 and 22, the closer to the light emitting point, the larger the incident light amount, and the output also increases in proportion thereto. Therefore, by calculating the ratio of the outputs of the optical sensors 11, 21, 12, and 22, it is possible to obtain a position signal indicating the light emitting point, that is, which divided scintillator 31 is incident.

In the positron CT apparatus, a large number of such two-dimensional radiation position detectors 10 are arranged in a ring shape as shown by a dotted line. When the ring-shaped array surface is the XY plane, the Z direction is a direction perpendicular to the XY plane. The subject is inserted in the Z-direction with respect to the ring-shaped array of the detector 10, and the cross section (XY) crossing the subject is taken.
A tomographic image of the surface is obtained. That is, as described above, each of the two-dimensional radiation position detectors 10 can detect that the radiation is incident on any of the six positions in the X direction for each of the eight positions in the Z direction. A tomographic image can be reconstructed for each slice position.

By using the two-dimensional radiation position detector 10 as described above, it becomes possible to simultaneously obtain positron tomographic images for a large number of slice planes. Therefore, it is possible to simultaneously obtain tomographic images of a large number of slice planes at different positions in the body axis direction of the subject without moving the subject.

By the way, in such a two-dimensional radiation position detector 10, an optical sensor 1 such as a photomultiplier is used.
It is unavoidable that the sensitivities of 1, 21, 12, and 22 vary or individually change. With such fluctuations,
The output varies among a large number of two-dimensional radiation position detectors 10, the position calculation in each two-dimensional radiation position detector 10 becomes inaccurate, and the spatial resolution and the sensitivity deteriorate. The constituent image cannot be obtained.

Therefore, it is necessary to adjust the gain among a large number of two-dimensional radiation position detectors 10, or to adjust the gain among a plurality of optical sensors in each two-dimensional radiation position detector 10. There is. Conventionally, such gain adjustment is performed manually.

[0009]

However, if the gain of each optical sensor of a large number of two-dimensional radiation position detectors is manually adjusted as in the prior art, the gain adjustment is performed by a large number of two-dimensional radiation position detectors. Since it has to be carried out between a plurality of photosensors in each two-dimensional radiation position detector, the operation is very complicated, time-consuming, and it is difficult to adjust with high accuracy. is there.

In view of the above, it is an object of the present invention to provide a positron CT apparatus improved so that complicated adjustment of the gain of an optical sensor can be automatically performed.

[0011]

In order to achieve the above-mentioned object, according to the present invention, the number of light beams is smaller than the number of two-dimensionally arranged scintillators and the number of scintillators optically coupled to them. A sensor, and a signal processing circuit that obtains a position signal of which of the scintillators the radiation has entered from the relationship between the outputs of the photosensors when the radiation of a predetermined energy enters the scintillator,
It is provided with a large number of two-dimensional radiation position detectors arranged in a ring shape, a coincidence counting circuit for performing coincidence counting between those position signals, and a memory for obtaining a count value for each of the coincidence counted position signals. In a positron CT apparatus, a gain adjustment circuit that adjusts the gain of each output of the above-mentioned many optical sensors, and a gain adjustment circuit that changes the gain for each individual two-dimensional radiation position detector and collects data from a reference line source. While determining the gain of the optical sensor of each two-dimensional radiation position detector using the total count value of the entire two-dimensional radiation position detector, and collecting data on the reference radiation source, each direction of the above-mentioned two-dimensional array of scintillators. And a control circuit that determines the gain of the optical sensor in each two-dimensional radiation position detector so that the total count value at the symmetrical positions of the two becomes equal. Rukoto has become a feature.

[0012]

The data of the reference radiation source is collected while changing the gain of the output of each of the plurality of photosensors for each individual two-dimensional radiation position detector, and the data is collected for each two-dimensional radiation position detector based on the data. The total count value of the whole is obtained, and the gain of the optical sensor of each two-dimensional radiation position detector is determined according to the total count value. This is automatically performed by the control circuit, so that variations in sensitivity among the two-dimensional radiation position detectors are eliminated. Further, while collecting data on the reference radiation source, the gain of the optical sensor in each two-dimensional radiation position detector is determined so that the total count value at the symmetrical position in each direction of the two-dimensional array of scintillators becomes equal. Is automatically performed by the control circuit, and thereby the variation in the sensitivity of the optical sensor in each two-dimensional radiation position detector is corrected.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a signal processing system of a positron CT apparatus according to an embodiment of the present invention. In FIG. 1, the outputs of the photosensors 11, 21, 12, 22 of the two-dimensional radiation position detector 10 are input to a signal processing circuit 40 to obtain a position signal. The two-dimensional radiation position detector 10 is configured as shown in FIG. The signal processing circuit 40 includes variable gain amplifiers 41, 42, 43 and 44 that amplify the outputs of the optical sensors 11, 21, 12, and 22, an energy calculation circuit 45, an energy discrimination circuit 46, and a position calculation circuit 47. And an address conversion circuit 48.

When the outputs of the optical sensors 11, 21, 12, and 22 are A, B, C, and D, the energy calculation circuit 4
5 adds these outputs (A + B + C + D) to obtain an output corresponding to the energy of the incident radiation. The energy discrimination circuit 46 determines whether or not the wave height of this energy signal is within a predetermined window. The position calculation circuit 47 calculates the position of which 6 × 8 scintillator 31 in FIG. 5 the radiation has entered, based on the ratio of the outputs A, B, C, D described above. That is, the X direction is (A +
C) / (A + B + C + D), the Z direction is (A + B)
The position is calculated by / (A + B + C + D). The position signal is converted into a position address signal by the address conversion circuit 48. The address conversion circuit 48 is controlled by the output of the energy discrimination circuit 46, and outputs the position address signal only when the energy signal enters a predetermined window.

Such a signal processing circuit 40 is provided in each of a number of two-dimensional radiation position detectors 10 arranged in a ring shape as shown in FIG. The position address signal is the coincidence counting circuit 5
Input to 1. The coincidence counting circuit 51 detects that two position address signals are input at the same time, and sends the position address signals to the memory 52 as an address designation signal. In the memory 52, +1 at the specified address
Is added.

When collecting data for normal image reconstruction,
This memory 52 collects data by adding +1 at one address designated by a set of two position address signals counted at the same time, and at the time of sensitivity adjustment, the simultaneous count is performed by the control of the CPU 53. The addition of +1 is performed at the two addresses designated by the two position address signals.

At the time of sensitivity adjustment, the CPU 53 controls the gain control circuit 54, and first, the variable gain amplifier 41 that amplifies the output of each of the photosensors 11, 21, 12, 22 for one two-dimensional radiation position detector 10. The gains of up to 44 are simultaneously changed sequentially, for example, every 30 seconds from a minimum value (or a value close thereto) to a maximum value (or a value close thereto). At this time, the two-dimensional radiation position detector 10
A reference radiation source for adjustment is arranged in the internal space of the ring-shaped arrangement of the
Under the control of U53, it is set to be sufficiently narrow in accordance with the emission energy of the radiation source.

The pulse waveform of the energy signal output from the energy calculation circuit 45 is as shown in FIG. 2. When the gains of the variable gain amplifiers 41 to 44 are low, the peak value is small, and when the gain is high, the peak value is increased. Grows larger. When the window of the energy discriminating circuit 46 is as shown by W, when the pulse crest value is in the W, a position address signal is generated from the address converting circuit 48 and addition is performed in the memory 52. Since this window W is determined in accordance with the radiation source that is actually used as described above, if as many pulse peak values as possible fall within this W, the variable gain amplifiers 41-41.
The gain of 44 is proper.

Therefore, the added value of the counts at all the positions (48 positions) to be detected by the one-dimensional radiation position detector 10 which is the object of adjustment is obtained. That is, the total of the count values at all the addresses of the memory 52 specified by the position address signal output from the address conversion circuit 48 of the signal processing circuit 40 connected to the one two-dimensional radiation position detector 10 is added. Calculate the count value. This total count value changes as the gain changes, as shown in FIG. 3, but the maximum gain is an appropriate gain as described above. As a result, the CPU 53 can control the gain control circuit 54 to set the gain of the variable gain amplifiers 41 to 44 connected to the one two-dimensional radiation position detector 10 to an appropriate gain. Two-dimensional radiation position detector 1
It means that the sensitivity of 0 is set to the maximum.

Under the control of the CPU 53, such adjustments are automatically performed in sequence for the other two-dimensional radiation position detectors 10, and the maximum sensitivity is obtained for all the two-dimensional radiation position detectors 10. The settings are made to be obtained, and variations among the two-dimensional radiation position detectors 10 are eliminated.

Next, a large number of two-dimensional radiation position detectors 1
Adjustments are made to eliminate variations among the photosensors 11, 21, 12, 22 in each of the 0s. Also at this time, similarly to the above, the reference radiation source is arranged in the ring-shaped array of the two-dimensional radiation position detector 10, and the window of the energy discriminating circuit 46 is set to be narrow according to the emission energy of the radiation source. Keep it. When data collection is performed for a certain time in this state, a count value is obtained for each position corresponding to each of the 48 scintillators 31 as shown in FIG. 4 for the one-dimensional radiation position detector 10 of interest. . Therefore, the total count values xa and xb of one row (8 positions) at both ends in the X direction are obtained, and the gains of the variable gain amplifiers 41 and 43 for the optical sensors 11 and 12 are set to the same value (xb / x).
a) · kx, and the gains of the variable gain amplifiers 42 and 44 for the optical sensors 21 and 22 are the same value (xa / xb).
・ Set to kx (kx is an experimentally determined correction coefficient). After that, data collection is similarly performed for a certain period of time, total count values xa and xb at both ends are obtained, and the gain is determined again in the same manner as described above.
Make a / xb close to 1. Then, the variation in sensitivity in the X direction, that is, the variation in sensitivity between the optical sensors 11 and 12 and the optical sensors 21 and 22 can be corrected.

Similarly, data is collected for a fixed time,
Total count value z of 1 row (6 positions) at both ends in Z direction
Find a and zb. Then, the gains of the variable gain amplifiers 41 and 42 for the optical sensors 11 and 21 are set to the same value (zb
/ Za) · kz, and the gains of the variable gain amplifiers 43 and 44 for the optical sensors 12 and 22 are set to the same value (za / z).
b) Determined as kz (kz is an experimentally obtained correction coefficient). After that, data is similarly collected for a certain period of time, the total count values za and zb at both ends are obtained, and the gain is determined again in the same manner as described above, so that za / zb approaches 1. As a result, variations in sensitivity in the Z direction, that is, the optical sensor 11,
It is possible to correct variations in sensitivity between the light sensor 21 and the optical sensors 12 and 22.

The operation of correcting the variation in sensitivity among the optical sensors in one two-dimensional radiation position detector 10 as described above is automatically performed for the other two-dimensional radiation position detectors 10 sequentially by the control of the CPU 53. Will be performed. In this way, for all the two-dimensional radiation position detectors 10, variations in sensitivity among the photosensors in each of them are corrected. Therefore, the position calculation in each of the many two-dimensional radiation position detectors 10 can be accurately performed, and the position resolution can be improved.

In the above description, the total count values xa, xb, za, z for one row at both ends in the X and Z directions.
Although the variation in sensitivity is corrected using b, the total count value of several rows or more can be used instead of one row.
For example, as shown in FIG. 4, it is possible to use half total count values xa ′ and xb ′ in the X direction and half total count values za ′ and zb ′ in the Z direction.
Also, various calculation methods for gain setting are conceivable, such as using a difference instead of using the ratio of the total count values as described above. Furthermore, instead of adjusting the gain of the output from the optical sensor with the variable gain amplifier, the gain of the optical sensor itself can be adjusted.

[0025]

As described above, according to the embodiment,
According to the present invention, a plurality of scintillators arranged two-dimensionally and a number of photosensors less than the number of scintillators optically coupled to the scintillators are provided. In a positron CT device in which a number of two-dimensional radiation position detectors that obtain a position signal indicating whether or not radiation is incident on a ring are arranged in a ring type, adjustment work is automatically performed to correct variations in the sensitivity of a large number of optical sensors as a whole. It becomes possible to perform with high accuracy. Therefore, the labor of the adjustment work can be significantly reduced, the adjustment time can be shortened, and the adjustment accuracy can be greatly improved. As a result, the positron CT is always in the optimum condition.
You can measure.

[Brief description of drawings]

FIG. 1 is a block diagram showing a signal processing system of a positron CT apparatus according to an embodiment of the present invention.

FIG. 2 is a time chart showing a relationship between a pulse waveform of an energy signal and a window.

FIG. 3 is a graph showing a relationship between a set gain and a total count value.

FIG. 4 is a diagram schematically showing detection positions in one two-dimensional radiation position detector.

FIG. 5 is a perspective view showing a two-dimensional radiation position detector.

[Explanation of symbols]

10
Two-dimensional radiation position detector 11, 21, 12, 22 Optical sensor 31
Scintillator 32
Light guide 40
Signal processing circuit 41, 42, 43, 44 Variable gain amplifier 45
Energy calculation circuit 46
Energy discrimination circuit 47
Position calculation circuit 48
Address conversion circuit 51
Simultaneous counting circuit 52
Memory 53
CPU 54
Gain control circuit

Claims (1)

[Claims] 1. A number of two-dimensionally arranged scintillators, a number of photosensors less than the number of scintillators optically coupled to them, and light of a predetermined energy incident on the scintillators. A number of two-dimensional radiation position detectors arranged in a ring shape, each of which includes a signal processing circuit that obtains a position signal indicating which of the scintillators the radiation is incident on, based on the relationship between the outputs of the sensors, and the position signals of those position signals. In a positron CT apparatus provided with a coincidence counting circuit for performing coincidence counting between the two and a memory for obtaining a count value for each of the coincidently counted position signals, a gain for adjusting the gain of each output of the above-mentioned multiple photosensors. The adjustment circuit and the data collected for the reference radiation source while changing this gain for each individual two-dimensional radiation position detector are used for each two-dimensional emission. The total count value of the entire radiation position detector is used to determine the gain of the optical sensor of each two-dimensional radiation position detector, and while collecting data for the reference radiation source, the two-dimensional symmetry of the scintillator is symmetrical in each direction. A positron CT apparatus comprising: a control circuit that determines a gain of an optical sensor in each two-dimensional radiation position detector so that the total count value at the position becomes equal.