JPH0933658A - Positron imaging equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity in the distribution of detection sensitivity in the area of a visual field by a method wherein the central point of a light- receiving face of a gammaray detector in the end of a detector array and the central point of the light-receiving face of an adjacent gamma-ray detector are disposed at a specified distance from each other. SOLUTION: In a detector array 210, the positions of the centers of the respective light-receiving faces of gamma-ray detectors 211 and 212 and 21n -1 , and 21n are disposed at a distance L from each other respectively. Besides, the positions of the centers of the respective light-receiving faces of gamma-ray detectors 21k and 21k+1 (k=2, 3...n-2) are disposed at a distance L' from each other. So with a detector array 220. In the detector arrays 210 and 220 wherein the light-receiving faces of the detectors 21k and 22k (k=1, 2, 3...n) in the direction of arrangement have a width W respectively, these detectors are so disposed as to satisfy the relationships of L<=2W and L<L'<=2L. When annihilation of an electron-positron pair occurs in a portion 110 of integration of a radioactive isotope in an object 100 of measurement, a pair of photons (gamma rays) are generated consequently and detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positron imaging device for measuring the internal substance distribution of an object to be measured.

[0002]

2. Description of the Related Art A substance labeled with a radioisotope (RI) that emits a positron is introduced as a tracer into a measurement target such as a human body or an animal body, and a positron emitted from the radioisotope and an electron in a normal substance are injected. Attention has been focused on a positron imaging device that measures a pair of photons (gamma rays) generated by the pair annihilation with and to measure the internal substance distribution of the measurement target and its change over time. In this case, the energy of the photon generated due to the annihilation of the electron-positron pair is almost the same as the mass energy of the positron or electron (5 llkeV). Also, the two photons are emitted in opposite directions. By measuring the characteristic photon pairs as described above and determining the frequency of electron-positron pair annihilation near each point in the measurement target, the distribution of the labeled substance in the measurement target is measured. In the measurement of individual photons of a photon pair, in consideration of the energy and the current measurement means, the photon is converted into scintillation light in the scintillator of the gamma ray detector, and a measurement system for detecting this scintillation light by the photodetector is used. It is common.

Although several types of positron imaging devices have been proposed, among them, a positron probe device (hereinafter referred to as TOF positron probe device) has been reported as a simple positron imaging device (for example, TOF positron probe device). USP471256
1, USP 4772791, JP-A-6-347550,
M. Yamamoto, et al .: IEEE Transactions on Nuclea
r Science, Vol.36, No.1,1989, pp.998-1002).

FIG. 7 is a block diagram of a TOF positron probe type positron imaging apparatus. FIG. 8 is a layout diagram of a conventional detector array. Note that in FIG. 8, each detector array is described as including four gamma ray detectors.

FIG. 7 (a) shows an apparatus configuration in the case where the measurement target is the human brain, and the detector array 210 and the detector array 220 are arranged with their light-receiving surfaces facing each other with the human head sandwiched. It FIG. 7B shows an apparatus configuration in the case where the measurement target is the heart of a human body, and the detector array 210 and the detector array 220 are arranged so that their light-receiving surfaces face each other with the human chest interposed therebetween. FIG. 7C shows a device configuration in the case where the measurement target is the whole body of the human body, and two detector arrays 210 and 220 arranged with their light receiving surfaces facing each other are moved to perform scan measurement. In either case, the detector array 210 and the detector array 22 of the TOF positron probe device are
Reference numeral 0 indicates an RI integrated region 110 located inside the measurement target 100, with the light receiving surfaces facing each other across the measurement target 100.
When photons emitted due to the annihilation of the electron-positron pair in and emitted in opposite directions are incident, the photons are detected.

In the detector array 210, the gamma ray detectors 21 ₁ to 21 ₄ are fixedly arranged in a line at an equal distance L between the light receiving surface center points, and in the detector array 220, the gamma ray detectors 22 ₁ to 22 ₄ are arranged. The light receiving surfaces are fixedly arranged in a line at equal intervals with a distance L between the center points. When a gamma ray enters _one gamma ray detector, for example, the gamma ray detector 21 ₁ , scintillation light is generated by the scintillator 21 ₁ a, and the scintillation light is detected by the photodetector 21 ₁ b to detect gamma ray incidence. To do.

One photon of the photon pair generated by the electron-positron pair annihilation is detected by one gamma ray detector in the detector array 210. The other photon is detected by one gamma ray detector in the other detector array 220. By utilizing the difference in the time of flight of photons obtained by measuring the difference between the photon detection times detected by these two gamma ray detectors, the annihilation position of the electron-positron pair on the straight line connecting these two gamma ray detectors is used. presume. Each time a photon pair is detected, a large number of estimated electron / positron pair annihilation positions are obtained and arithmetic processing is performed to measure the substance distribution in the measurement target. Therefore, the image reconstruction calculation processing, which was necessary in other types of positron imaging apparatuses, is not necessary.

[0008]

The TOF positron probe device of the conventional example described above has the following problems.

The photon pair generated by the annihilation of the electron-positron pair is detected by one gamma ray detector in the detector array 210.
The detection is performed in combination with one gamma ray detector in the detector array 220 that is arranged so as to face the measurement target 100. A line connecting the centers of the light receiving surfaces of these two gamma ray detectors is called a coincidence counting line. The coincidence counting line represents the center position (sampling position) of the area where the photon pair can be set to the same side by these two gamma ray detectors. For example, as shown in FIG. 8, if each detector array 210, 220 has four gamma ray detectors, there are 16 (= 4 × 4) coincidence lines. In the detector arrays 210 and 220 in which gamma ray detectors are arranged at equal intervals, the coincidence counting lines overlap on the center line C between the detector arrays 210 and 220. On this center line C, the sampling pitch is half the distance between the center points of the light receiving surfaces of the gamma ray detectors of the detector arrays 210 and 220, and the visual field area (area having detection sensitivity) of the detector arrays 210 and 220.
The sampling density is the coarsest.

Further, the field of view of the pair of gamma ray detectors whose light receiving surfaces face each other does not have a flat detection sensitivity. FIG. 9 is an explanatory diagram of a detection sensitivity distribution of a pair of gamma ray detectors facing each other. As shown in this figure,
A pair of gamma ray detectors 21 ₁ whose light-receiving surfaces face each other,
The field of view of 22 ₁ does not have a flat detection sensitivity. At the center between the gamma ray detector 21 ₁ and the gamma ray detector 22 ₁ , there is a triangular detection sensitivity distribution having the maximum detection sensitivity at the center, and a trapezoidal shape in the gamma ray detector 21 ₁ or a region near the gamma ray detector 22 _1. The detection sensitivity distribution is.

Then, two detector arrays 21 facing each other are provided.
The detection sensitivity distribution in the visual field region between 0 and the detector array 220 was calculated by simulation. FIG. 10 is an explanatory diagram of the detection sensitivity distribution of the conventional detector array. The width of the light receiving surface in the arrangement direction of the gamma ray detectors 21 ₁ to 21 ₄ and the gamma ray detectors 22 ₁ to 22 ₄ is 20 mm, and the scintillator is barium fluoride (BaF ₂ ) having a length of 25 mm. Gamma ray detectors are arrayed at a pitch of 35 mm and detector arrays 210, 2
20, the detector array 210 and the detector array 220 were subjected to a simulation calculation of the detection sensitivity distribution when the detector array 210 and the detector array 220 were faced with a distance of 400 mm. It can be seen that the detection sensitivity distribution in the center of the visual field area has the largest nonuniformity in the detection sensitivity within the visual field area. That is, in the conventional detector array, since the gamma ray detectors are arranged at equal intervals, there is a problem that the nonuniformity of the detection sensitivity is large in the center of the field of view of the detector arrays 210 and 220.

The field of view in the detector array direction (direction crossing the coincidence counting lines) is determined by the distance between the light receiving surface center points of the gamma ray detector, and the field of view expands as the light receiving surface center point distance increases. However, if the distance between the center points of the light receiving surfaces of the gamma ray detector is made too large, an insensitive portion occurs. FIG. 11 is an explanatory diagram of the visual field area of the detector array.

Even if a photon pair is generated, the size of the maximum field of view of the detector array obtained in a range having no dead part which cannot be detected as a pair is determined by the center of the light receiving surface of the gamma ray detector constituting the detector array. It depends on the distance between the points and the width of the light receiving surface.
When the distance between the center points of the light receiving surfaces of the gamma ray detector is L and the width of the light receiving surface of the gamma ray detector in the array direction is W, L> 2
In the case of W, the insensitive portion B is generated by being sandwiched by the sensitive portion A (hatched portion in the drawing) where the photon pair can be detected (FIG. 11).
(A)). In the case of L ≦ 2W, no dead part is generated (FIG. 11 (b)). In a detector array in which n gamma ray detectors are arranged at equal intervals, the size of the maximum field of view obtained without a dead part is such that the distance L between the light receiving surface center points of the gamma ray detector is This is when the width W of the surface is twice (L = 2W). That is, in the conventional detector array, since the gamma ray detectors are arranged at equal intervals, the size F of the visual field area of the detector array is narrow and F =
There is also a problem that it is limited to (2n-1) W.

The present invention has been made in order to solve the above problems, and is capable of improving the uniformity of the detection sensitivity distribution in the visual field region and making the visual field region wider than before. An object is to provide a device (TOF positron probe device).

[0015]

The positron imaging apparatus according to the present invention comprises (1) a first number of gamma ray detectors arranged in one direction, and
A first detector array that detects the first photon when a first photon of a photon pair generated due to annihilation of a positron pair is incident; and (2) the first detector array with the measurement target interposed therebetween. A second detector array which is arranged so as to face each other and is arranged in the one direction, and which comprises a second number of gamma ray detectors and detects the second photons when the second photon of the photon pair is incident. And (3) signal processing for calculating the position where the electron-positron pair annihilation occurs by inputting the signal output from the first detector array and the signal output from the second detector array. Means and a light receiving surface center point of the first gamma ray detector at the first end of the first detector array,
The light-receiving surface center point of the gamma-ray detector adjacent to the first gamma-ray detector is arranged at a first distance that is equal to or less than twice the width of the light-receiving surface in the one direction of the gamma-ray detector, The light receiving surface center point of the second gamma ray detector at the second end of the first detector array and the light receiving surface center point of the gamma ray detector adjacent to the second gamma ray detector are the gamma ray A light receiving surface of a third gamma ray detector at a first end of the second detector array, the light receiving surface being arranged at a second distance that is not more than twice the width of the light receiving surface in the one direction of the detector. The center point and the light receiving surface center point of the gamma ray detector adjacent to the third gamma ray detector are separated by a third distance that is not more than twice the width of the light receiving surface in the one direction of the gamma ray detector. And a fourth gamma ray at the second end of the second detector array. The light-receiving surface center point of the emitter and the light-receiving surface center point of the gamma-ray detector adjacent to the fourth gamma-ray detector are not more than twice the width of the light-receiving surface in the one direction of the gamma-ray detector. Placed at a distance of 4,
The distance between the light receiving surface center points of two adjacent gamma ray detectors other than the first to fourth gamma ray detectors is not less than the maximum distance of the first to fourth distances, In addition, it is less than or equal to twice the minimum distance of the first to fourth distances.

Since the present invention is configured as described above, it operates as follows.

When electron-positron pair annihilation occurs in the object to be measured, a photon pair is generated and two photons of the photon pair are emitted in opposite directions. A first detector array consisting of a first number of gamma ray detectors arranged in one direction and a second detector array consisting of a second number of gamma ray detectors arranged in the same direction as the first detector array. The detector arrays are arranged so as to face each other with the measurement target interposed therebetween, and the first detector array is the first photon pair.
Of the photon of the photon is incident on the second detector array, and the second detector array detects the photon of the second photon of the photon pair upon incidence. The signal processing means inputs the signal output from the first detector array and the signal output from the second detector array, and calculates the position where electron-positron pair annihilation occurs.

In this measurement, the gamma ray detector is arranged as follows. The distance L1 between the light-receiving surface center points of the gamma ray detector at the first end of the first detector array and the gamma ray detector next to it, and the gamma ray detector at the second end of the first detector array And the distance L2 between the light-receiving surface center points of the gamma-ray detectors adjacent thereto and L2, and the distance between the light-receiving surface center points of the gamma-ray detectors at the first end of the second detector array and the adjacent gamma-ray detectors L3, and the distance L4 between the light receiving surface center points of the gamma ray detector at the second end of the second detector array and the gamma ray detector adjacent to the second detector array are the widths of the light receiving surfaces in the arrangement direction of the gamma ray detectors. Is less than twice. Any one of the gamma ray detectors other than the gamma ray detectors at the ends of the first detector array and the gamma ray detectors other than the gamma ray detectors at the ends of the second detector array are adjacent to each other. The distance L between the light-receiving surface center points of the two gamma-ray detectors satisfies the conditional expression Lmax <L ≦ 2Lmin. However, Lmax is the maximum value of L1 to L4, and Lmin is the minimum value of L1 to L4. By arranging the gamma ray detectors constituting the first and second detector arrays satisfying the above conditions, the occurrence of electron-positron pair annihilation is measured in a wide field of view, and there is no dead part. The uniformity of the measurement sensitivity distribution is improved.

Further, in the positron imaging apparatus according to the present invention, the first to fourth distances may all be the same, or two adjacent neighbors except for the first to fourth gamma ray detectors. The distances between the light receiving surface center points of the two gamma ray detectors may all be the same, or the first number and the second number may be the same number. In these cases,
Not only the same operation as described above can be obtained, but also the detector array can be easily designed and manufactured, and the signal processing in the signal processing means can be facilitated.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, a first embodiment of the present invention will be described. FIG. 1 is a configuration diagram of a positron imaging apparatus according to the first embodiment of the present invention.

The detector array 210 includes n gamma ray detectors 21 ₁ , 21 ₂ ,. . . , 21 _n are arranged one-dimensionally in this order, and each gamma ray detector 21 ₁ , 21
₂ ,. . . , 21 _n face the measurement object 100. Similarly, the detector array 220 includes n gamma ray detectors 22 ₁ , 22 ₂ ,. . . , 22 _n are arranged one-dimensionally in this order, and each gamma ray detector 22 ₁ ,
22 ₂ ,. . . , 22 _n face the measurement object 100. The detector arrays 210 and 220 are arranged to face each other with the measurement target 110 interposed therebetween.

In the detector array 210, gamma ray detectors 21 ₁ and 21 ₂ and gamma ray detector 21 _n-1
And 21 _n are arranged such that the center positions of their light receiving surfaces are separated by a distance L, and gamma ray detectors 21 _k and 21 _{k + 1} (k = 2,
3, ..., n-2), the center position of each light receiving surface is distance L '
Are arranged at intervals. In the detector array 220, the gamma ray detectors 22 ₁ and 22 ₂ and the gamma ray detectors 22 _n-1 and 22 _n are arranged such that the center positions of their light receiving surfaces are separated by a distance L, and the gamma ray detector 22 _k And 22 _{k + 1} (k = 2,3, ..., n-2) are arranged such that the center positions of the respective light receiving surfaces are separated by a distance L '. Further, the width of the light receiving surface of the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n) in the array direction is W. Detector array 210 according to the present invention
And 220, the relationship of L ≦ 2W, L <L ′ ≦ 2L (1) is satisfied, and each gamma ray detector 2
1 _k and 22 _k (k = 1,2,3, ..., n) are arranged.

Gamma ray detectors 21 _k and 22 _k (k = 1,2,
Each of 3, ..., n) consists of a scintillator and a photodetector. For example, the gamma ray detector 21 ₁ includes a scintillator 21 ₁ a and a photodetector 21 ₁ b. Each scintillator is formed of, for example, barium fluoride (BaF ₂ ) or cesium fluoride (CsF). As each of the photodetectors, for example, a photomultiplier tube capable of detecting photons with high sensitivity is used. In one gamma ray detector, the scintillator and the photodetector are optically coupled by, for example, silicon grease or silicon RTV rubber, and the surface other than the coupling surface of the scintillator with the photodetector is, for example, Teflon tape. , A reflection agent such as barium sulfate, aluminum oxide, or titanium oxide is applied.

When the electron-positron pair annihilation occurs in the RI integrated region 110 in the measurement object 100, a pair of photons (gamma rays) is generated accordingly, and the respective photons are emitted in the opposite directions. When one photon of a photon pair is incident on a gamma ray detector in detector array 210, that gamma ray detector detects that photon. When the other photon of the photon pair strikes one gamma ray detector in detector array 220, that gamma ray detector detects that photon. In the gamma ray detector where the photon is incident, the scintillator generates scintillation light in an amount corresponding to the energy of the incident photon, and the photodetector generates an electric pulse signal having a wave height corresponding to the light amount of this scintillation light. An electric pulse signal is output. The electric pulse signals output from the respective gamma ray detectors are input to the pair annihilation occurrence estimation unit 300 and the flight time difference measurement unit 400.

The pair annihilation occurrence estimator 300 includes a discriminator 31 for inputting the electric pulse signals output from the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n).
_k , 32 _k (k = 1,2,3, ..., n) and discriminator 3
The simultaneous counting circuit 330 receives the signals output from 1 _k and 32 _k (k = 1,2,3, ..., n).

Discriminators 31 _k and 32 _k (k = 1,
2,3, ..., n) are connected to the gamma ray detector 2
The output terminals of 1 _k and 22 _k (k = 1,2,3, ..., n) are connected in a one-to-one correspondence. For example, the electrical pulse signal output from the gamma ray detector 21 _{1 is} transmitted to the discriminator 31
Entered into ₁ .

Discriminators 31 _k and 32 _k (k = 1,
(2,3, ..., n) each has a threshold value set near 511 keV, which is the photon energy of the gamma rays generated by electron-positron pair annihilation, and compares the input electric pulse signal with this threshold value. To do. As a result, it is determined whether the photons incident on the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n) have undergone the scattering process, and the scattering process is performed. Only photons that do not pass through are adopted as the true signal. This is because the true electron-positron annihilation cannot be detected even if the scattered photons are detected. Each of the discriminators 31 _k and 32 _k (k = 1,2,3, ..., n) outputs light receiving detector information indicating the position information of the gamma detector that detected the gamma ray incidence.

The coincidence counting circuit 330 receives the photodetector information output from the discriminator 31 _k (k = 1,2,3, ..., n) and the discriminator 32 _k (k = 1,2). , 3, ..., n) and the received light detector information output. A photon detected by one gamma ray detector in the detector array 210 and a photon detected by one gamma ray detector in the detector array 220 are detected by the detector array 210 and the detector array 220.
Considering whether or not each photon is a photon of a photon pair due to the annihilation of an electron-positron pair generated between the photon detection time, the distance between two photon detection detectors, and the speed of light. And judge. The result is output as pair annihilation occurrence notification information.

The pair annihilation occurrence estimation unit 300 estimates that electron-positron pair annihilation has occurred from the above two judgments, and the fact (pair annihilation occurrence notification information) and all discriminators 31 _k and 32 _k ( The output signal (light receiving detector information) from k = 1,2,3, ..., n) is output to the data collection processing unit 500.

The time difference of flight measuring section 400 is a pre-amplifier 4 for inputting and amplifying the electric pulse signals output from the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n).
1 _k , 42 _k (k = 1,2,3, ..., n) and pre-amplifier 41 _k
A constant fraction discriminator (hereinafter referred to as CFD) 430 for inputting a signal obtained by bundling the signals output from (k = 1,2,3, ..., n), and a pre-stage amplifier 42 _k
(k = 1,2,3, ..., n) CFD440 which inputs the signal which bundled the signal output, and the delay circuit 450 which inputs the signal output from CFD430 and delays for a fixed time,
A time-to-peak converter that inputs a signal output from the delay circuit 450 and a signal output from the CFD 440 and outputs a pulse signal having a peak value according to the time difference between them.
Amplitude Converter; hereafter referred to as TAC) 460
And an analog-digital converter (hereinafter referred to as ADC) 470 that digitally converts the peak value of the pulse signal output from the TAC 460.

Pre-stage amplifiers 41 _k , 42 _k (k = 1,2,3, ...,
n) each input terminal is a gamma ray detector 21 _k , 2
The output terminals of 2 _k (k = 1,2,3, ..., n) are connected in a one-to-one correspondence. For example, the electrical pulse signals output from the gamma ray detector 21 ₁ is input to the preamplifier 41 _1.
Each of the pre-stage amplifiers 41 _k and 42 _k (k = 1,2,3, ..., n) amplifies the inputted electric pulse signal.

The CFD 430 is a pre-stage amplifier 41 _k (k = 1,2,
The signals output from (3, ..., n) are bundled and input, the input signal group is converted into one high-speed timing, and the delay circuit 4
Output to 50. The CFD 440 has a pre-stage amplifier 42 _k (k =
The signals output from (1,2,3, ..., n) are bundled and input, and the input signal group is converted into one high-speed timing, and TAC
Output to 460. The delay circuit 450 receives the signal output from the CFD 430 and delays it for a fixed time.
Output to TAC460.

The TAC 460 inputs the signal output from the delay circuit 450 and the signal output from the CFD 440, converts the signal into a pulse signal having a peak value according to the time difference between both timing signals, and outputs the pulse signal to the ADC 470. .
The ADC 470 digitally converts the peak value of the pulse signal output from the TAC 460, and outputs this digital signal (time-of-flight difference information) to the data collection processing unit 500.

The data collection processing unit 500 includes a signal output from the pair annihilation occurrence estimation unit 300 and the flight time difference measurement unit 40.
From the data collection processing device 510 for accumulating and processing the signal output from 0, the image display device 520 for displaying the calculation result in the data collection processing device 510, and the image printing device 530 for printing out the calculation result. Become.

Upon receiving the pair annihilation occurrence notification information (information indicating that electron-positron pair annihilation has occurred) output from the pair annihilation occurrence estimation unit 300, the data collection processing device 510 outputs it from the flight time difference measurement unit 400. The flight time difference information (time difference when two photons are detected) and the light receiving detector information (position information of the two gamma ray detectors detecting the photon pair) output from the pair annihilation occurrence estimating unit 300 are input.
In this way, the data collection processing device 510 sequentially collects and accumulates the light receiving detector information and the flight time difference information measured with the electron-positron pair annihilation.

The data collection processing device 510 performs processing in the following procedure on the basis of the photodetector information and the flight time difference information relating to the individual annihilation of electron / positron pairs accumulated during or after the measurement, until the electron / positron is detected. An image showing the pair annihilation occurrence position distribution is constructed. First, based on the accumulated light-receiving detector information corresponding to one electron-positron pair annihilation, the centers of the light-receiving surfaces of the two gamma-ray detectors that detected the photon pair are connected to each other, and the electron-positron pair annihilation occurs. Calculate a straight line through the position. Next, the position where electron-positron pair annihilation occurs on this straight line is calculated based on the corresponding flight time difference information. If the position where electron-positron pair annihilation occurs is calculated by the above procedure for all the accumulated light-receiving detector information and time-of-flight difference information, an image showing the electron-positron pair annihilation occurrence position distribution can be obtained. The data collection processing device 510 sends this image to the image display device 520 and the image printing device 530.

The image display device 520 displays an image representing the electron-positron pair annihilation occurrence position distribution calculated by the data collection processing device 510. Image printing device 530
Prints an image representing the electron / positron pair annihilation occurrence position distribution calculated by the data collection processing device 510.

Next, the arrangement and operation of the gamma ray detectors in the detector array according to the present invention will be described in more detail. FIG. 2 is a layout of a detector array according to the present invention.

For simplicity of explanation, the detector array 21
Each of 0 and 220 will be described as including four gamma ray detectors.

The detector array 210 consists of four gamma ray detectors 21 ₁ to 21 ₄ , and the detector array 220 consists of four gamma ray detectors 22 ₁ to 22 ₄ . Further, gamma ray detectors 21 ₁ and 22 ₁ , gamma ray detectors 21 ₂ and 22 ₂ , gamma ray detectors 21 ₃ and 2
2 ₃ and the gamma ray detectors 21 ₄ and 22 ₄ are assumed to have light receiving surfaces facing each other.

Gamma ray detectors 21 ₁ and 21 ₂ , gamma ray detectors 21 ₃ and 21 ₄ , gamma ray detectors 22 ₁ and 2
2 ₂ and the gamma ray detectors 22 ₃ and 22 ₄ are arranged such that the center points of their light receiving surfaces are separated by a distance L.
Gamma ray detectors 21 ₂ and 21 ₃ , gamma ray detector 22 ₂
And 22 ₃ are arranged such that the center points of the respective light receiving surfaces are separated by a distance L ′. The width of the light receiving surface of the gamma ray detector in the array direction is W.

A straight line connecting the centers of the light receiving surfaces of one gamma ray detector in the detector array 210 and one gamma ray detector in the detector array 220 represents a coincidence counting line. The coincidence line represents the central position (sampling position) of the area where the photon pair can be clocked by these two gamma ray detectors. The center line C between the detector array 210 and the detector array 220 is indicated by a dashed line.

In FIG. 2A, L and L'have a relationship of L≤2W, L <L '<2L (2). The coincidence counting line in this case is
This is compared with the case where the gamma ray detectors are arranged at equal intervals in the conventional detector array (FIG. 8). Gamma ray detector 21
Coincidence line between ₁ and 22 ₃ , gamma ray detector 2
_Three coincidence counting lines between 1 ₂ and 22 ₂ and gamma ray detectors 21 ₃ and 22 ₁ intersect at one point on the center line C in the conventional example, In FIG. 2A, it is separated into two points. Similarly, the coincidence counting line between the gamma ray detectors 21 ₂ and 22 ₄ , the coincidence counting line between the gamma ray detectors 21 ₃ and 22 ₃ , and
Three coincidence lines between the gamma ray detectors 21 ₄ and 22 ₂ intersect at one point on the center line C in the conventional example, but are separated into two points in FIG. 2A (see FIG. 2). (Indicated by a symbol D). Therefore, the detection sensitivity distribution near the center line C can be expected to be more uniform than in the conventional example.

In FIG. 2B, L and L'have a relationship of L≤2W, L <L '= 2L (3). In this case, the intersections of the coincidence counting lines on the center line C between the detector array 210 and the detector array 220 are evenly spaced, and further uniform detection sensitivity distribution can be expected.

The size of the visual field area of the detectors 210 and 220 will be compared with that in the conventional example. When the gamma ray detectors are arranged at equal intervals in the conventional detector array (FIG. 8), the width F ′ of the field of view is F ′ = 3L + W (4), while the detector array according to the present invention has The width F of the visual field is F = 4L + W (5), and the visual field in the present invention is larger by L than the visual field in the conventional example.

Next, the detection sensitivity distribution of the detector array according to the present invention will be described. FIG. 3 is an explanatory diagram of the detection sensitivity distribution of the detector array according to the present invention.

The detection sensitivity distribution was obtained by simulation calculation. In the simulation calculation, L = 35 mm (6a) L '= 70 mm (6b) W = 20 mm (6c). These values satisfy the expression (3).
Further, the distance between the light-receiving surfaces of the detector array 210 and the detector array 220 is 400 mm. It can be seen that the detection sensitivity distribution near the center of the visual field area is smoother than the detection sensitivity distribution (FIG. 10) in the case of the evenly-spaced array in the conventional detector array. It can also be seen that the field of view is enlarged.

Next, another arrangement of the gamma ray detector according to the present invention will be described. FIG. 4 is a layout of the gamma ray detector according to the present invention.

The detector array 210 consists of seven gamma ray detectors 21 ₁ to 21 ₇ , and the detector array 220
Consists of seven gamma ray detectors 22 ₁ to 22 ₇ .

Gamma ray detectors 21 ₁ and 21 ₂ , gamma ray detectors 21 ₆ and 21 ₇ , gamma ray detectors 22 ₁ and 2
2 ₂ and the gamma ray detectors 22 ₆ and 22 ₇ are arranged such that the center points of their light receiving surfaces are separated by a distance L. Gamma ray detectors 21 _k and 21 _{k + 1} , gamma ray detectors 22 _k and 22
_{k + 1} (k = 2,3,4,5) are arranged such that the center points of the respective light receiving surfaces are separated by a distance L '. Also shown are 49 (= 7 × 7) coincidence lines.

Also in this case, as compared with the conventional example, the overlap of the coincidence counting lines on the center line C is solved, and therefore, the uniformity of the detection sensitivity distribution can be obtained.

Next, the case where each detector array according to the present invention is generally composed of n gamma ray detectors will be described.

Detector array 210 and detector array 220
In each, n gamma ray detectors 21 ₁ to 21 _n and n gamma ray detectors 22 ₁ to 22
_It is assumed that _n are arranged at intervals as described in the description of FIG.

Also in this case, the overlapping of n ² coincidence lines on the center line C between the detector array 210 and the detector array 220 can be dispersed to make the detection sensitivity distribution uniform. Further, the field of view of the detector arrays 210 and 220 can be expanded. The width F ′ of the field of view when the gamma ray detectors of the conventional example are arranged at equal intervals is F ′ = L (n−1) + W (7), whereas the gamma ray according to the present invention is In the arrangement of the detectors, the width F of the field of view is F = 2L (n-2) + W (8). That is, when each of the detector arrays 210 and 220 is composed of n gamma ray detectors, the expansion ratio of the visual field region of the present invention with respect to the conventional example is F / F '= (2L (n-2) + W) / (L (n-1) + W)… (9), which is enlarged.

Next, a second embodiment of the present invention will be described. FIG. 5 is a configuration diagram of a positron imaging apparatus according to the second embodiment of the present invention.

In this embodiment, the positions of the _n gamma ray detectors 21 ₁ to 21 _n forming the detector array 210 are set and the information on these positions is set in addition to the configuration of the _first embodiment. Position setting device 230 for sending the data to the data collection processing unit 510, and the positions of the n gamma ray detectors 22 ₁ to 22 _n forming the detector array 220 are set, and information of these positions is set in the data collection processing unit. A detector positioner 240 is added to 510. The data collection processing unit 510 constructs an image representing the electron-positron pair annihilation occurrence position distribution in consideration of the position information of each gamma ray detector. The other components perform the same operations as in the first embodiment.

Gamma ray detectors 21 _k and 22 _k (k = 1,2,
3, ..., n) has a structure in which its position is not fixed and can be freely set.

The detector position setting device 230 sets the position of each gamma ray detector 21 _k (k = 1,2,3, ..., n),
Information on the position of the gamma ray detector 21 _k (k = 1,2,3, ..., n) (detector position information) is sent to the data collection processing unit 510.
Similarly, the detector position setting device 240 sets the position of each of the gamma ray detectors 22 _k (k = 1,2,3, ..., n), and the gamma ray detector 22 _k (k = 1,2, n). 3, ..., n) position information (detector position information) is sent to the data collection processing unit 510. However,
The position of each gamma ray detector is limited to the range satisfying the condition of the equation (1) described in the first embodiment.

As in the case of the first embodiment, the pair annihilation occurrence estimation unit 300 indicates that electron-positron pair annihilation has occurred (pair annihilation occurrence notification information) and two gamma ray detectors that have detected photon pairs. And the position information (light receiving detector information) of the above are output to the data collection processing unit 500.

As in the case of the first embodiment, the time-of-flight difference measuring unit 400 calculates the difference in the photon detection times of two gamma ray detectors that have detected a photon pair or their photon detection times (flight time difference information). Output to.

The data collection processing unit 510 detects in addition to the pair annihilation occurrence notification information and the light receiving detector information output from the pair annihilation occurrence estimation unit 300, and the flight time difference information output from the flight time difference measurement unit 400. Position setting device 23
The detector position information sent from 0 and 240 is also input, and an image showing the electron-positron pair annihilation occurrence position distribution is constructed based on these information.

The positron imaging apparatus according to this embodiment is used as follows. First, the visual field region is expanded by widening the interval between the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n), and a wide measurement region of the measurement target 100 is measured. Next, gamma ray detectors 21 _k and 2
By narrowing the interval of 2 _k (k = 1,2,3, ..., n), the visual field area is narrowed and the detection sensitivity is enhanced, and only the vicinity of the specific RI integrated region 110 found by the previous measurement is measured. . By gradually narrowing the interval between the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n), the field of view may be further narrowed and the detection sensitivity may be increased.

The electron / positron pair annihilation position distribution is measured with the highest sensitivity when the interval between the gamma ray detectors 21 _k and 22 _k (k = 1,2,3, ..., n) is minimized. be able to. FIG. 6 is an explanatory diagram of the detection sensitivity distribution of the detector array according to the present invention.

In this figure, the detector array 210 is composed of four gamma ray detectors 21 ₁ to 21 ₄ , and the four gamma ray detectors 21 ₁ to 21 ₄ are arranged adjacent to each other. Similarly, the detector array 220 includes four gamma ray detectors 22 ₁ to 22 ₄ , and the four gamma ray detectors 22 ₁ to 22 ₄ are arranged adjacent to each other.

Detector array 210 and detector array 220
FIG. 6 shows the result of simulation calculation of the detection sensitivity distributions of the detector arrays 210 and 220 under the condition of L = L '= W = 20 mm (10) with the distance between the respective light receiving surfaces set to 400 mm. It should be noted that this condition satisfies the expression (1).

Comparing this figure with FIG. 3, when the gamma ray detectors adjacent to each other in the detector arrays 210 and 220 are arranged with a narrow interval, the field of view becomes narrower, but the detection sensitivity becomes higher and the detection is performed. It can be seen that the sensitivity distribution is smooth.

As described above, in each of the detectors 210 and 220, the gamma ray detector can be arranged at an arbitrary position, and in the data acquisition processing section 500, the detector position information of each gamma ray detector is also taken into consideration. The position of the RI integrated region 110 can be detected quickly by constructing an image showing the positron pair annihilation occurrence position distribution and gradually narrowing the interval of the gamma ray detectors, and performing RI measurement. It is possible to measure the distribution of electron-positron pair annihilation position near the accumulation region 110 with high sensitivity.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the distance between the gamma ray detector at one end of the detector array and the adjacent gamma ray detector and the distance between the gamma ray detector at the other end and the adjacent gamma ray detector are May be different. The gamma ray detectors except for both ends of the detector array may not be evenly spaced. The arrangement interval of the gamma ray detectors forming one detector array and the arrangement interval of the gamma ray detectors forming the other detector array may be different. The number of gamma ray detectors constituting one detector array may be different from the number of gamma ray detectors constituting the other detector array.

[0070]

As described above in detail, according to the present invention, with respect to the gamma ray detectors forming the two detector arrays that are arranged to face each other with the object to be measured sandwiched therebetween, each end of the detector array is detected. The distance L between the light-receiving surface center points between the gamma-ray detector in and
Regarding the distance L ′ between the center points of the light-receiving surfaces between two adjacent gamma-ray detectors excluding the gamma-ray detectors at both ends of the detector array, the width W of the light-receiving surface of the gamma-ray detectors in the array direction is not more than twice. , L <L ′ ≦ 2L, the electron / positron pair annihilation position distribution in the measurement target can be measured with a uniform sensitivity distribution and a wider field of view than in the conventional example.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a positron imaging apparatus according to a first embodiment of the present invention.

FIG. 2 is a layout of a detector array according to the present invention.

FIG. 3 is an explanatory diagram of a detection sensitivity distribution of the detector array according to the present invention.

FIG. 4 is a layout view of a gamma ray detector according to the present invention.

FIG. 5 is a configuration diagram of a positron imaging device according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a detection sensitivity distribution of the detector array according to the present invention.

FIG. 7 is a configuration diagram of a positron imaging device.

FIG. 8 is a layout view of a conventional detector array.

FIG. 9 is an explanatory diagram of a detection sensitivity distribution of a pair of gamma ray detectors facing each other.

FIG. 10 is an explanatory diagram of a detection sensitivity distribution of a conventional detector array.

FIG. 11 is an explanatory diagram of a field of view of a detector array.

[Explanation of symbols]

100 ... Measurement target, 110 ... RI accumulation site, 210, 2
20 ... Detector array, 21 ₁ , 21 ₂ ,. . . , 2
2 ₁ , 22 ₂ ,. . . ... Gamma ray detector, 230, 24
0 ... Detector position setting device, 300 ... Pair annihilation occurrence estimation unit,
31 ₁ , 31 ₂ ,. . . , 32 ₁ , 32 ₂ ,. . . ... Discriminator, 330 ... Simultaneous counting circuit, 400 ... Flight time difference measuring section, 41 ₁ , 41 ₂ ,. . . , 42 ₁ , 4
2 ₂ ,. . . ... Pre-amplifier, 430, 440 ... Constant fraction discriminator (CFD),
450 ... Delay circuit, 460 ... Time-to-peak converter (TA
C), 470 ... Analog-to-digital converter (AD
C), 500 ... Data collection processing unit, 510 ... Data collection processing device, 520 ... Image display device, 530 ... Image printing device.

Claims (4)

[Claims] 1. A first number of gamma ray detectors arranged in one direction, wherein the first photon of a photon pair generated upon annihilation of an electron-positron pair in a measurement target is incident. A first detector array for detecting, and a second number of the gamma ray detectors arranged opposite to the first detector array with the measurement target interposed therebetween and arranged in the one direction, A second detector array that detects the second photon when the second photon of the photon pair is incident; a signal output from the first detector array;
And a signal processing means for calculating a position where electron-positron pair annihilation occurs by inputting a signal output from the detector array of the first detector array of the first detector array. The light receiving surface center point of the first gamma ray detector at the end and the light receiving surface center point of the gamma ray detector adjacent to the first gamma ray detector are the width of the light receiving surface in the one direction of the gamma ray detector. And a second gamma ray detector disposed at a first distance that is less than or equal to 2 times, and the light receiving surface center point of the second gamma ray detector at the second end of the first detector array. And a light receiving surface center point of the gamma ray detector next to the gamma ray detector are arranged at a second distance which is equal to or less than twice the width of the light receiving surface in the one direction of the gamma ray detector, and the second detector array. A third gamma ray detector at the first end of the The plane center point and the light receiving plane center point of the gamma ray detector adjacent to the third gamma ray detector have a third distance which is not more than twice the width of the light receiving plane in the one direction of the gamma ray detector. A light receiving surface center point of a fourth gamma ray detector located at a second end of the second detector array and a light receiving surface center point of a gamma ray detector adjacent to the fourth gamma ray detector. Is arranged at a fourth distance which is equal to or less than twice the width of the light receiving surface in the one direction of the gamma ray detector, and is adjacent to each other except for the first to fourth gamma ray detectors. The distance between the light-receiving surface center points of the two gamma ray detectors is larger than the maximum distance of the first to fourth distances and is twice the minimum distance of the first to fourth distances. A positron imaging device characterized by the following: 2. The positron imaging apparatus according to claim 1, wherein the first to fourth distances are all equal. 3. The positron imaging according to claim 1, wherein the distances between the light-receiving surface center points of any two adjacent gamma ray detectors except the first to fourth gamma ray detectors are equal. apparatus. 4. The positron imaging apparatus according to claim 1, wherein the first number and the second number are the same number.