JPS59122984A - Scintillation camera - Google Patents

Abstract

PURPOSE:To contrive to enlarge an effective visual field, by determining a light emitting display position, by performing operation for satisfying a predetermined condition based on the outputs of four adjacent rectangular or square photoelectronic multipliers arranged in a grating configuration. CONSTITUTION:Four rectangular or square photoelectronic multipliers P1-P4 are arranged in a grating configuration so as to position the photoelectronic multipliers P1, P3 and P2, P4 on diagonal lines. When predetermined two outputs S1, S2 and S3, S4 among outputs S1-S4 due to light emission and reception from the scintillators of these multipliers are respectively added and treated with operation amplifiers 3, 4 and a dividing device 7, a light emitting display position X is determined by operation for satisfying the condition of the formula I . Similarily, light emitting display position Y for satisfying the condition of the formula II is determined. By these operations, the effective visual field in light emitting display is not a region determined at the center of the multipliers P1-P4 but comes to the region externally contacted with said region and the enlargement of the effective visual field is attained. Moreover, it is similar when many photoelectronic multipliers are used as units each comprising four.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an arrangement of photomultiplier tubes for enlarging the effective field of view of a scintillation camera and a method of calculating the output thereof.

Conventionally, the method widely used in scintillation cameras to calculate the display position on the display device with respect to the incident position of gamma rays (hereinafter referred to as position calculation circuit) is called the resistance matrix method. Photomultiplier tube (hereinafter referred to as PMT) Pl, P21..., PM
output +11.112+...18N and these X
Direction position coordinates kl, k2. ..., kN, and the y-direction position coordinates 1+, +2, ..., lN, it is calculated based on the display position on the display device with respect to the incidence of γ-rays. In this method, the area that becomes the image (hereinafter referred to as the effective field of view) is narrow compared to the arrangement area of the PMT.
For example, when a hexagonal PMT with a diameter of 501111 is arranged, a circular area with a diameter of 350H is required for the arrangement, but the effective field of view is at most a diameter of 260fi.

To explain the cause of this, consider the case of two PMTs in the − dimension. Figure 1 shows a one-dimensional scintillator camera with two PMT Ps, P2, and the incident γ-ray becomes fluorescent light in the scintillator (1) and passes through the light guide (2) to PMT P+, P2. Signal 81
, 82. Figure 2 shows the wave height of the signal sl I B2 with respect to the incident position X of r'7 * kl *
k2 is the position of PMT Pl, P2 in the X direction. In the conventional calculation method.

The display position X on the display device is determined by the formula (1).When the r-ray incident position X changes, the display position X changes as shown by the curve gs in Fig. To,
When the display position is between 2 and 2, the display position
However, when it is not between 1 and 2, the change in display position X is small. This means that when the incident position is not between This means that the change cannot be discerned on the display device, and the effective field of view is eventually limited to between kl and 2.

The present invention provides an arithmetic method different from the resistance matrix method described above for the purpose of expanding the effective field of view, and uses the linear equation (3
).

x = -! ! −'−１ ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
(3) The change in display position X when the γ-ray incident position X changes is as shown by curve g2 in Figure 3, and the change in display position X when the incident position X changes is 0 song A! Unlike igt. It is also large when the incident position X is not between 1 and 2,
The range in which a change in the incident position X can be identified as a change in the display position 1i1X is approximately equal between the left and right outer ends of the PMT arrangement. Therefore, the effective field of view is expanded approximately twice as compared to the conventional method.

The above is a one-dimensional example, and the scintillation camera actually used is a two-dimensional detector, but the situation is exactly the same. A case where four PMTs are arranged in a square shape will be described below. FIG. 4 is a diagram of the detector viewed from the scintillator side.

The position of PMT in each direction is P M T P+ ,
For P2- PsP4, the X direction is kl * k2
* Given by tcs l k4・Y direction is b, +
2, given by 13.14. From the square arrangement,
kx= kz, ki=4.11==14+ h=1g
There is a relationship between The one-dimensional calculation method (formula (3)) described above can be extended to a nine-dimensional equation in the case of two dimensions.

8+ +112 11I +84X=~
”=L-Bianichi ・・・・・・・・・・・・・・・(4)
811 1114 An example of an arithmetic circuit that realizes the calculation of x and Y in the above equation is shown in the fifth section.
As shown in the figure. Figure 5(a) is an arithmetic circuit for X, and P
The output of M T Pl, P2 at e 82 is resistor R
P M T
The outputs 83 and 114 of Ps and P4 are added by the operational amplifier (4) through the resistor R, and the outputs of the operational amplifiers (3) and (4) become the inputs of the divider (7), and the outputs of the operational amplifier (3) The output is divided by the output of the operational amplifier (4),
The result is output as a display position signal X. Figure 5 (b
) is an arithmetic circuit for the display position signal Y, and its operation is the fifth
It is similar to the figure (IL).

PMT signal that is input to the arithmetic circuit @11 I121
The only difference is that the input position of sl 184 is different from that in FIG. 5(a).

The circuit configuration is exactly the same.

Next, we will discuss the case where a large number of PMTs are included. In such a case, an arithmetic circuit can be constructed by regarding the PMT array as a set of four small parts. As an example. As shown in Figure 6.

1.7 When a total of 16 PMTs are arranged in a square grid with 4 rows in each direction, they are considered to be a collection of 4 small parts of 1 set of 4, and the display position x for the gamma particle incident position 1i x, y
, Y can be performed, for example, in the following two steps.

Calculate which of the four small parts the light has entered.

(B) Calculate equation (4) within the incident small portion.

Display position ii X, Y are determined.

This calculation will be described in detail below. FIG. 6 is a diagram of the detector viewed from the scintillator side.

The four small parts are &, Ez, Ea, E4, and the X-direction position coordinate of the center position of each small part is nil.
+ 1112 + ulB, 1114.

The position coordinates in 7 directions are each 01 * B2 + n11 @
Let it be lI4. From that arrangement, 1111:012
e ull"in41111""I141 There is a relationship of J=mu8. The small part Bi (i represents one of 1.2.3.4) is P M T Pix , Pl2.
It is composed of Pis, Pl4, and the center position of those PMTs has the X coordinates kil, kiz, kis,
ki4y zasek is lil, fiz, l1i1i4
and kit = ki2. kis=ki4.
lit = li4.

There is a relationship fiz == li3. FIG. 7 is an example of an arithmetic circuit for determining the display position. When gamma rays are incident.

PMT signal of small part E1 81'l m g+2 + 8
18 m 814 is the resistance Rf! : are added by the operational amplifier (9) to become the signal Ul. Ul is the signal U2 from the small parts of the pond E2, E4, hE4,
U3, Ua and comparator 101, (111, (6)
The output of each comparator becomes the input of the AND gate 13. When the γ rays are incident on the small portion E1, the signal Ul becomes larger than any of the other signals U2°Ua and U4, so the comparator uO).

αu, (all outputs of 12+ are high level,
The output FNl of the AND gate 13 becomes high level. On the other hand, gamma rays or small part E! If the input signal is input to a source other than Ea, device 1 becomes low level.A similar circuit is constructed using the subsection E2
In DE4, the X and Y signals are each calculated by a circuit similar to that shown in FIG. The X signal of each subsection 0, for example E, is.

The adder adds it to the constant voltage signal VXI. VXI is a voltage signal having a value proportional to the center position coordinate mlK of the predetermined small part E+, and this means that when the γ-ray incident position X or the right end of the small part E4 changes to the small part E1, the 9 display coordinates are continuous. It is determined by a trial test conducted in advance so that it changes smoothly.

The output X1 of the adder passes through the gate (141. Gate 0
4) Output Xl of AND gate [131 output F, N
When l is /% low level, it is equal to X, and when EN is low level, it becomes zero. Similarly, small part E2
+ E3 * For Ei4.

Signal heart, X3. The first order X+ , X2 ,
Xs and X4 are added by an adder 116) to generate a position signal X' on one display device. The 6th place 1a signal Y' is obtained in exactly the same manner.

The nonlinearity that is generally a problem with detectors like the present invention is 1
For example, a position correction circuit as shown in FIG.
This problem can be solved by providing K at the stage before the adder ti41 shown in the figure. To explain the correction circuit in FIG. 8, the X and Y signals are ti
l. A decoy A/D converter (for example, each with 8-bit accuracy) converts it into a digital value.

This value specifies the memory address. Memory (1!ll
The correct positions of x and Y (that is, the incident positions x and y) are recorded at the specified address. This has been previously recorded by measurements using point sources and the like. This correct position signal is output from memory 091. Since non-linearity is corrected in this way, it does not pose a problem in the present invention.

Next, the effects of the present invention will be described. In the case of d PMTs, in the conventional calculation method, the effective field of view is a rectangle connecting the center positions of the PMTs, or almost an effective field of view, whereas in the present invention, the effective field of view is a rectangle circumscribing the PMTs, so the area of the effective field of view is approximately It becomes 4 times. Also.

When there are more than four PMTs, for example 16, conventionally the rectangle connecting the centers of the outermost PMTs was the effective field of view, but in the present invention the circumscribed rectangle becomes the effective field of view. One area is approximately 1.8 times (16/9 times).

As detailed above, the present invention can provide an excellent scintillation camera with a wide effective field of view.

[Brief explanation of drawings]

Figure 1 shows a one-dimensional scintillation temporary camera with two photomultiplier tubes, Figure 2 shows the output distribution of the two photomultipliers relative to the r-ray incident position XK, and Figure 3 shows the gamma-ray incident position xK. Graph of display position X against. Figure 4 is a layout diagram of a scintillation camera with four photomultiplier tubes, Figure 5 is an example of a position calculation circuit in the case of Figure 4, and Figure 6 is a scintillation camera with 16 photomultiplier tubes. 7 shows an example of the position calculation circuit in the case of FIG. 6, and FIG. 8 shows an example of the nonlinearity correction circuit. (υ...Scintillator (2)...Light guide (3), (4J, <5), (6)...Operation amplifier R...Resistor (7), (8)...
Divider (9)...Operation amplifier (101, U1)
, α... comparator [131... and gate circle...
・Adder α5...Gate (161...Adder surface, 0 stage...A/D converter Hit...Memo! J(
ROM) Y1 Figure 2 Figure 40 (ku) Shaku (1)) Figure 5 Inasu Otsu Figure Inasa 7 Concave

Claims (1)

[Claims] In a device that detects light emitted by radiation incident on a scintillator as an electrical signal with a number of photomultiplier tubes and displays it on a display device in accordance with the incident position of the radiation, the photomultiplier tube etc. Four adjacent photomultiplier tubes Pl are arranged in a square or rectangular grid and form a square or rectangle. P2, P3. Each output of P4 81 * 82
Based on + s3 + 84. Equipped with a calculation circuit that calculates the position where the light emission is displayed. A scintillator camera, characterized in that the Mayuko calculation circuit performs the following calculation. X=(81+82)/(sa+s4)Y=(8
1+84)/(lIz+!1g) However, photomultiplier tubes P1 and P3 * P2 and P4 are located diagonally,
In addition, it is assumed that the photomultiplier tubes are point symmetrical with respect to the array center of each photomultiplier tube.