JPS60188868A - Positron ct device - Google Patents

Abstract

PURPOSE:To detect gamma-ray with noise reduced by grouping gamma-ray detectors unequally, combining groups of detectors to make the shape of effective visual field to necessary ranges and making its fan fraction small. CONSTITUTION:Detectors (black circles) arranged on the circumference of a gamma-ray detecting device are grouped unequally, for instance, 13 in the first group, 15 in the second group, 15 in the third group 3-13 in the ninth group. Opposite groups, for instance, the 4-7th groups are selected for the first group, and the shape of pseudo ellipse of effective visual field 31 of good resolution is obtained. The fan fraction, a ratio of a simultaneous count detector and a total detector is made small by combining the detector groups properly. Accordingly, even if the fan fraction is small and the effective visual field is pseudo ellipse, detection can be made conformable to the shape of a subject and little noise as cephalic section the thoracic section are elliptic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field III of the Invention] The present invention relates to a positron CT apparatus, and more particularly to a positron CT apparatus that is capable of reducing noise generated by coincidental coincidence, which is a noise component of a regroove image. Concerning the device π.

[Background of the invention]

A positron CT device is a device that displays the concentration distribution of a positron emitting isotope (hereinafter referred to as an "r-ray source") administered into a living body on a plane substantially perpendicular to the body axis. Here, the positional information of the radiation source is determined by a large number of gamma ray detectors (hereinafter referred to as "detectors" in II+) surrounding the living body in a ring or polygon shape, when 41 positrons are destroyed. It can be obtained by multiplying a pair of generated annihilation gamma rays by the same nhn1 number.

In positron CT equipment, the detector group is divided into multiple groups to simplify the hardware.

A method is being used in which the a1 number is taken simultaneously between one group and a plurality of groups facing this A. For this, °C is 1. For example, N, Δ, Mu1. Idni, (!1
．． +13゜IEEENS -26(2), 2
See 703-2706 (1!370).

A typical circuit scheme for H1 measurement of coincidence is as follows. The outputs of the plurality of detectors are each input into 1) a processing circuit, and the preprocessing circuit outputs a timing pulse. The outputs of preprocessing circuits that belong to the same group are input to the same address encoder circuit. An address encoder circuit encodes the address of the detector into a binary number. Further, the timing signals of all the detectors belonging to the same group are ORed and input to the subsequent coincidence counting circuit. In any coincidence counting circuit, when the timing signals are ANDed between two groups, that is, simultaneous i! When t fi occurs, the simultaneous n1 between both groups
Output the number as an event 1-flag. When an event occurs, the address signal of the detector related to the simultaneous a1 number among the detectors in both groups is latched to a pulse width appropriate for later signal processing and transmitted to the output circuit.

In a conventional positive I-ron CT device, a group of detectors arranged on the circumference is divided "equally" into several groups, and for any group, one The number of groups connected via several circuits (hereinafter referred to as "number of opposing groups") was also constant. For this reason, in the above-mentioned apparatus, the number of detectors arranged on the circumference must be a multiple of the total number of groups, which is a constraint on f& appropriate design.

That is, preferably, the detector width should be determined independently from the target and the proportion of scattered radiation noise, and the number of detectors should be determined by the following: ``detector width and detector ring'' After the diameter is determined, the target sensitivity should be determined. However, as described above, in the past, there were constraints on the number of detectors, so it was often necessary to change the detector width and detector ring diameter from the original 31-pixel value.

Furthermore, in the above-mentioned apparatus, the method is determined for how many groups the entire group of detectors arranged around the circumference should be divided into, how many opposing groups and how many M1 numbers should be taken simultaneously. There is also the problem that characteristics such as effective field of view and coincidence fan fraction are uniquely determined, and there is no degree of freedom in adjustment.

Here, the effective field of view refers to a range in which sampling characteristics are flat and performance such as resolution and sensitivity can be guaranteed. In addition, simultaneous 31 number fan flux (hereinafter simply "
``Fan fraction'') is the ratio (,n,/n, ), and in order to widen the effective field of view, it is necessary to make the fan fraction human, but coincidental coincidence noise, which has a negative effect on the image, increases in proportion to the fan fraction (S , E, L) arc
ny, o.

+: til: J, Nuc], Mad, IG (2)
IIGG-1173 (1075)) Therefore, in order to cover the required effective field diameter and to keep the coincidence rate as low as possible, the fan fraction must have an optimal value. .

However, in the conventional method, the fan fraction is equal to the ratio of the number of opposing groups to the total number of groups, and the total number of groups is about 10 at most, so the fan fraction is (
There was also the problem that Moe could only take a limited value.

Therefore, in general, there was no choice but to leave the situation as follows.

As a result, by making the effective field of view larger than necessary, coincidental coincidence noise increases in proportion to the product of the number of loops and the number of opposing groups, so it is not practical to significantly increase the total number of groups. isn't it.

Note that the shape of the effective field of view is limited to the conventional method, which is approximately circular (actually, a regular polygon). The purpose of this is to solve the above-mentioned problems in conventional positron equipment, increase the degree of whiteness in the shape and size of the effective field of view, and avoid unnecessary expansion of the effective field of view, thereby eliminating accidental simultaneous n1 number noise. It is possible to reduce the positive 1
- To provide a Ron CT device.

[Summary of the Invention] The main point of the present invention is to divide the detector group into uneven groups,
By appropriately selecting the arrangement order of the groups, the shape of the effective field of view is made into a pseudo-elliptical polygon, ensuring a wide effective field of view in the required direction. The point is that by limiting the effective field of view, it is possible to keep the effective fan fraction at a low value.

In addition, by using an arbitrary number of detectors and dividing the field as closely as possible, the shape of the field of view can be made into a pseudo polygon, and the necessary effective field of view diameter can be obtained without unnecessarily increasing the fan fraction. In this case, by reducing the fan fraction, it becomes possible to reduce the random coincidence noise by the same ratio.

[Embodiments of the invention]

EMBODIMENT OF THE INVENTION Hereinafter, after a detailed description of the present invention, embodiments will be described based on the drawings.

First, the relationship between the grouping method and the shape of the effective view 5f will be described. FIG. 1 is an explanatory diagram thereof, showing the boundaries of the effective field of view determined by the i-th group. The opposing group that is counted simultaneously with the first group is J+ +Jz
There are E groups of +...+ IE r + JE.

The boundary line 11 is a straight line connecting the one with the smallest detector number among the detectors belonging to the i-th group and the one with the largest detector number among the detectors belonging to the JE-1th group. The boundary line 12 is a straight line connecting the detector with the highest number among the detectors belonging to the i-th group and the detector with the lowest detector number among the detectors belonging to the first group.

The effective field of view determined by the i-th group is the area between the straight lines 11 and 12. because.

In the area outside the boundary line, there are no sunblinks parallel to the line 11, ie the two detectors coupled via the simultaneous a1 number circuit, and in the area outside the boundary line 12 there are no sunblinks parallel to the line 11; This is because parallel sampling does not exist.

Therefore, for all groups, the effective i+
If you look at field a, the common areas will be the effective field of view for grouping. By using this relationship, it is possible to calculate the effective field of view for arbitrary grouping, and as a result, the shape and size of the effective field of view obtained by changing the method of grouping the detectors can be adjusted. It became possible to do so.

The present invention will be explained in detail below.

FIG. 2 schematically shows a +1'4 configuration of a positron device, which is an embodiment of the present invention. In the figure, 2
1a-2In is a detector, 22a 22n is a preprocessing circuit, 23a to 2'3n is an address encoder, 24
shows a coincidence circuit. Further, FIG. 3 is a diagram showing the arrangement of the detectors in the above device.

In this example, 128 gamma ray detectors have a diameter of 5
They are arranged at equal intervals on the circumference of /Icm. As a detector, a B 14G c 30□2 single crystal coupled to a photomultiplier tube is used.

The detectors are arranged in a counterclockwise direction starting from the one located vertically above.
They are numbered from I to D13, and 1]
The first group consists of 13 detectors from 1 to D13,
15 pieces from D14 to D28 are placed in the second group, D
15 pieces from 29 to D43 are in the third group, 15 pieces from D44 to D58 are in the fourth group, D59 to D7
The 12 pieces up to ゜ are in the 5th group, the 15 pieces from D7□ to D85 are in the 6th group, the 15 pieces from D86 to DloO are in the 7th group, the 15 pieces from DIol to D1□5 are in the 8th group, D116 The 13 pieces from D128 to D128 are assigned to the 9th group. For each of the nine detector groups described above, the number of opposing groups is set to 4, h, and therefore the coincidence circuit consists of 18 circuits.

FIG. 4 is a block diagram showing the input and output of the address encoder circuit and some of the coincidence counting circuits described above. In the figure, 101 to 109 indicate address encoder circuits of the first to ninth groups, and 201 to 204 indicate coincidence circuits in which the first group is involved. Note that the groups opposite to the first group are the fourth to seventh groups, and the coincidence circuits that do not involve the first group are omitted.

The outputs of the 128 detectors are each input to a preprocessing circuit, and the outputs shown as PI-P128 in FIG. 4 are input to the address encoder circuits 101-109. The address encoder circuits 101 to 100-6
Connected to the V power supply.

The address encoder circuits 101 to 109 encode the detector address into a 4-bit binary number, and
As mentioned above, it has the S function of pulse-shaping the OR signal of the timing signals of all the detectors belonging to the same group and outputting it as the timing signal TI-T9.

Output as A4.

The effective visual field shape is a polygon close to an ellipse, and there is a problem with nine human bodies. On the other hand, in the case of the five embodiments, Plan B,
With a smaller number of simultaneous ni circuits than Plan C, the effective field of view and fan fraction characteristics comparable to Plan C can be achieved, resulting in high economic efficiency.

In another embodiment of the invention, the detectors are grouped unevenly, and the number of opposing groups for at least one group is configured to be different from the number of opposing groups for another group.

In the conventional method of changing only the number of opposing groups compared to nine detector groups that are evenly grouped, the effective field of view shape is limited to a specific shape, but as mentioned above, it is possible to make the grouping uneven. As a result, the first conspicuousness of the effective field of view shape is further expanded.6 Note that in the description of the above embodiment, the case where the detectors are arranged on the circumference has been described, but other detector arrangements, such as It is also possible to improve the effective field shape and size of a polygonal detector array according to the present invention.

Furthermore, the present invention is not limited to the device that performs the i-bring scan as shown in the above embodiments, but also the device that uses the hinge-type scan (for example, S, E, Derenzo, e-stain 1.:
I EEE NS-28(1)81-89.1981
), devices using Daiko 1 to Mink scanning (e.g.
Z, H, Cho, atal, : I EEE N
S-28(1) 94-98, 11) 8]).

Non-scanning devices (e.g. S, E, Derenz
o, et al.: IEEE NS-24(1)54
4-558.1977), etc., and similar effects can be obtained.

Furthermore, it goes without saying that the present invention can be applied not only to a single-layer Posi-1-C' device, but also to a device that simultaneously collects data from multiple layers.

〔Effect of the invention〕

As described above, according to the present invention, in a positron CT apparatus configured to divide a detector group into a plurality of groups and take coincidence counts between each group, at least one group among the plurality of groups Since the configuration is configured such that the number of detectors belonging to one group is different from the number of detectors belonging to other groups, it is possible to group the detector groups for any number of detectors, which is useful for optimal system design. It has the effect of being extremely effective. Another advantageous effect is that it becomes easy to set the shape of the effective field of view to a shape other than a circle that matches the shape of the object to be photographed. Note 1
When carrying out the present invention, the number of parts such as an address encoder and a coincidence circuit, and the amount of wiring are almost the same as in the prior art, and there is no problem at all in terms of economy.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the grouping of detectors and the effective field of view, and Fig. 2 is a diagram showing the relationship between the grouping of detectors and the effective field of view.
A schematic configuration diagram of the device, Figure 3 is a diagram showing the arrangement of the detector, which is the main part, and the shape of the effective field of view, No. 1121 is F
The connection diagram of the 81-way block, FIG. 5, is a diagram showing the arrangement of the detectors and the shape of the effective field of view in another embodiment of the present invention. 21a 21n: Detector, 22a-22n: Preprocessing circuit, 23a-, 23n, 101-109 Near address encoder, 24, 20J to 204: Simultaneous ri
F number circuit, PI to P128: Output of preprocessing circuit. Special A'1 Applicant: Hitachi, Ltd. (1 person) Representative Patent Attorney Masatoshi Isomura 1 Figure 2 Figure 3 Figure 4 Inside the Center

Claims (1)

[Claims] (1) The detector 11T is divided into a plurality of groups and the positives 1 to 1 are configured to take coincidence counts between each group.
In the RON CT apparatus, the number of detectors belonging to at least one of the plurality of groups is different from the number of detectors belonging to other groups. Device 1゜