JPH0452418B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in scintillation cameras.

A scintillation camera is equipped with a scintillator, a number of photoelectric converters arranged on the back of the scintillator, and a position calculation circuit that calculates the position of scintillation (light emission) in the scintillator using the outputs of these photoelectric converters. Ori,
The light emitting position (that is, the radiation incident position) is calculated using the principle that the farther the light emitting point is, the smaller the output of the photoelectric converter is. By the way, if even a small output of the photoelectric converter is used for this position calculation, the small output contains many noise components, which deteriorates the accuracy of the position calculation and actually reduces the spatial resolution.

An object of the present invention is to provide a scintillation camera in which noise is removed and spatial resolution is improved by electrically processing the small output of a photoelectric converter so that it is not used for position calculations. shall be.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a large number of photomultipliers (PMTs), which are photoelectric converters, are connected to the back of a scintillator 11 via a light guide 12.
13 are arranged, and each output of the PMT 13 passes through a preamplifier 14, and is first added for each row and each column in an adding circuit 15 for each row and each column. For example, the PMT13 is arranged as shown in Figure 2, and the sum signal of each row is output as the addition result.
X1 to X13 and summation signals Y1 to Y7 of each column are obtained.
Furthermore, each output of the PMT 13 after passing through the preamplifier 14 is inputted to each of the noise component extraction amplifiers 16 and introduced into the energy calculation circuit 19. The circuit for one signal of the noise component extraction amplifier 16 consists of an OP amplifier 31 and a clamping diode 34 as shown in FIG. 3, for example, and when a signal smaller than a predetermined voltage V is input as shown in FIG. It has the characteristic of amplifying at a predetermined amplification degree and saturating the output with voltage V when a signal larger than this voltage V is input, that is, it has input/output characteristics as shown in the input/output characteristics in Figure 5. There is. Therefore, by passing this noise extraction amplifier 16, PMT
Thirteen small outputs, that is, outputs with many noise components, are extracted. Each of these noise components is added to the adder circuit 17.
are added row by row and column by column. Then, in the subtraction circuit 18, the sum signal of each row is
The sum signal of the noise components of each corresponding row is subtracted from X1 to X13, and the sum signal of each column Y1 to
The sum signal of the noise component of each corresponding column is subtracted from Y7. A concrete example of the noise component addition circuit 17 and subtraction circuit 18 is shown in FIG. In FIG. 6, only one row or one column is shown. The noise component addition circuit is
A resistor 41 to which each noise component of the PMT 13 is added,
42, 43, 44..., an OP amplifier 51, and a resistor 52, and the subtraction circuit is composed of an OP amplifier 6.
1 and resistors 62 to 65. Since the sum signal of each row and each column outputted from the subtraction circuit 18 in this way has noise components removed by subtracting the noise components extracted by the noise component extraction amplifier 16,
This signal is sent to the position calculation circuit 20 to perform position calculation, and is normalized by dividing by the energy signal Z output from the energy calculation circuit 19, resulting in position signals X and Y. It has a high spatial resolution. This position signal X, Y
is sent to the display device 22, and when the unranked signal obtained by passing the energy signal Z through the pulse height analyzer 21 is sent to the display device 22, it specifies the position of the point to be displayed. A high radioisotope distribution image can be obtained.

Note that the noise component extraction amplifier 16 of the above embodiment
As shown in Fig. 5, the input/output characteristics of the input/output characteristics consist of a part (a) with a predetermined amplification degree in a region where the input is small and a part (b) with a predetermined amplification degree in a region where the input is large.
In part A, the characteristic curve does not have to be linear,
In addition, in partial B, by having a small amplification factor close to zero instead of being completely saturated at a certain voltage, substantially the same effect can be obtained even if the characteristic slopes gently upward to the right. .

Moreover, instead of using two OP amplifiers as shown in FIG. 6, the noise component addition circuit 17 and subtraction circuit 18 are replaced with one OP amplifier 71 as shown in FIG.
One adder circuit may be used, which is constituted by a resistor 72, a resistor 73 for inputting the summation signal of each row or column, and resistors 74, 75, . . . for inputting noise components of the PMT 13.

Furthermore, as shown in FIG.
The noise component may be subtracted after weighted addition is performed in . i.e. OP
In an adder circuit consisting of an amplifier 81 and resistors 82, 83, 84, etc., the summation signals of each row or each column are weighted and added by mutually changing the values of the resistors 83, 84, and so on. ，
93, 94, . . . , each added signal of the noise component as a result of addition for each row or each column is weighted and added by mutually changing the values of the resistors 93, 94, . these
Subtraction may be performed using a differential amplifier circuit including an OP amplifier 101 and resistors 102 to 105.

In the above description, the case where addition is performed for each row and column has been explained, but it is equally effective when addition is performed according to all other possible addition rules.

As described in the embodiments above, according to the present invention, the corresponding addition result of the extracted noise component is subtracted from the output of the photoelectric converter that is added according to a certain rule. Spatial resolution can be improved compared to conventional ones.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a schematic diagram showing a PMT arrangement, Fig. 3 is a circuit diagram of a noise component extraction amplifier, Fig. 4 is a time chart of PMT output, and Fig. 5 is a graph showing the input/output characteristics of the noise component extraction amplifier shown in Fig. 3, Fig. 6 is a circuit diagram showing a part of the specific example of Fig. 1, and Figs. 7 and 8 are circuit diagrams of modified examples, respectively. be. 11...Scintillator, 12...Light guide, 13...PMT, 14...Preamplifier, 15
... Signal addition circuit for each row and each column, 16 ... Noise component extraction amplifier, 17 ... Noise component addition circuit for each row and each column, 18 ... Subtraction circuit for each row and each column, 19 ... Energy calculation circuit , 20... Position calculation circuit, 21... Wave height analyzer, 22... Display device.

Claims (1)

[Claims] 1 A scintillator that generates scintillation in response to incident radiation, a number of photoelectric converters that are arranged on the back side of this scintillator and convert the scintillation light guided to each into an electrical signal, and each photoelectric converter In a scintillation camera consisting of a position calculation circuit that calculates the scintillation position by , and a display position that displays a point at a display position defined by the position determined by this position calculation circuit, the outputs of each of the photoelectric converters are input. is,
A noise component extraction amplifier that has a predetermined amplification degree for small inputs and has a function of saturating to approximately the constant value for inputs larger than a certain value, and the output of the noise component extraction amplifier is added according to a certain rule. a first addition circuit that obtains a noise component addition signal; and a second addition circuit that obtains an addition signal by adding the outputs of the photoelectric converters according to the same fixed rules as above at a stage before the position calculation circuit. and a subtraction circuit that subtracts corresponding outputs of the first adder circuit from the outputs of the second adder circuit.