JPS593377A - Scintillation camera - Google Patents

Abstract

PURPOSE:To improve space resolving power, by subtracting the result of addition corresponding to the noise components extracted from the outputs of photoelectric transducers added according to a certain specified rule. CONSTITUTION:PMTs 13 which are many photoelectric transducers are arranged behind a scintillator 11 via a light guide 12. The respective outputs of the PMTs 13 are introduced respectively through a preamplifier 14 to an adder 15, an amplifier 16 for extracting noise components and a calculation circuit 19 for energy. The outputs contg. many noise components of the PMTs 13 are extracted by passing the outputs through the amplifier 16. The respective noise components are added for each row and column in an adder 17. The added signals of the noise components in the respective rows and columns are subtracted respectively in a subtractor 18. The signals are fed to a calculation circuit 20 for position which calculates the position and devides the same by the energy signal Z outputted from the circuit 19 thereby normallizing the same.

Description

[Detailed description of the invention] This invention relates to improvements in scintillation cameras.

The 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. The light emission position (that is, the radiation incident position) is calculated using the principle that the farther the light emission 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 accuracy of the position calculation will deteriorate because this small output will have many noise components, and the spatial resolution will deteriorate on the contrary.

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 a small output of a photoelectric converter so that it is not used for position calculation.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a large number of photoelectric converters P
MTs (photomultipliers) 13 are arranged, and each output of the 2MTs 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. The PMTl 3 are arranged as shown in FIG. 2, for example, and the summation signals X1 to X13 . and obtain summation signals Y1 to Y7 for each column. Furthermore, each output of the PMT 13 that has passed through the preamplifier 14 is input to each of the noise component extraction amplifiers 16 and is also introduced into the energy calculation circuit 19. For example, the circuit for one signal of the noise component extraction amplifier f16 is O as shown in Figure 3.
It consists of an amplifier 31 and a clamping diode 34, and as shown in Fig. 4, when a signal smaller than a predetermined voltage is input, it is amplified with a predetermined amplification degree, and a signal larger than this voltage is amplified. It has the characteristic of saturating the output with voltage ■ when it is input, and has the input/output characteristic as shown in the input/output characteristic of FIG. 5. Therefore, by passing the signal through the noise extraction amplifier 16, the small output of the PMTl 3, that is, the output containing many noise components, is extracted. These noise components are added for each row and each column in the adding circuit 17. Then, in the subtraction circuit 18, the summation signal of the noise component of each corresponding row is subtracted from the summation signal X1-X13 of each row, and the summation signal Y1-X13 of each column is subtracted.
The sum signal of the noise components of each corresponding column is subtracted from Y7.

A specific 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 includes a resistor 41 to which each noise component of PMTl 3 is added.
42, 43° 44..., OF angle 51, and resistor 5
2, and the subtraction circuit is composed of a differential amplifier circuit composed of an OP anzoro 1 and resistors 62 to 65. In this way, the sum signal of each row and each column outputted from the subtraction circuit 18 is a signal from which the noise component has been removed by subtracting the noise component extracted by the noise component extraction amplifier 16. When divided by the energy signal Z output from the energy calculation circuit 19, the position signals X and Y obtained by normalization are obtained with high spatial resolution. ing. These position signals X and Y are 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 radioisotope distribution image with high resolution can be obtained on the display device 22.

The input/output characteristics of the noise component extraction amplifier 16 of the above embodiment are as shown in FIG. It consists of part (b), but in part (a) the characteristic curve does not have to be linear, and in part (b) it does not completely saturate at a certain voltage but has a small amplification degree close to zero. By holding it, substantially the same effect can be obtained even if the characteristic is gently sloped toward the upper right.

In addition, instead of using two OP angles as shown in FIG. 6, the noise component addition circuit 17 and subtraction circuit 18 are replaced with one OP angle 1, a resistor 72, and each row or each row as shown in FIG. A resistor 73 for inputting the column summation signal and 2MT13
It is also possible to use one adding circuit constituted by the respective noise component input resistors 74, 75, . . . .

Furthermore, as shown in FIG. 8, the weighting may be performed in the position calculation circuit 20 by performing addition and then subtracting the noise component. In other words, the OP amplifier 81 and the resistor 82
．． In an adder circuit consisting of 83, 84..., the weighting is added by mutually changing the values of the resistors 83, 84... and the summation signals of each row or each column, and on the other hand, the OP angle 91 and the resistors 92, 93... In an adder circuit consisting of .94..., weighting is performed by mutually changing the values of the resistors 93, 94... and the added signals of the noise components as a result of addition for each row or each column. They may be added and then subtracted by a differential amplifier circuit composed of a plurality of OP amplifiers 7'' and 101° 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 photoelectric converter output added according to a certain rule. It is possible to improve the spatial resolution more than anything else.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention. Figure 2 is a schematic diagram showing the PMT array, Figure 3 is a circuit diagram of the noise component extraction amplifier, Figure 4 is a time chart of PMT output, and Figure 5 shows the input/output characteristics of the noise component extraction amplifier in Figure 3. A graph to represent. FIG. 6 is a circuit diagram showing a part of the specific example shown in FIG. 7 and 8 are circuit diagrams of modified examples, respectively. 11...Scintillator 12...Light guide 1
3...PMT 14...Preamplifier 15
...Signal addition circuit 16 for each row and each column...Noise component extraction amplifier 17...Noise component addition circuit 18 for each row and each column...
- Subtraction circuit 19 for each row and each column...Energy calculation circuit 20...Position measurement circuit 21...Curve height analyzer 22
...Display device applicant Shimadzu Corporation $2 Drama screen: Figure 3

Claims (1)

[Claims] (1) A scintillator that generates scintillation in response to incident radiation; a large number of photoelectric converters arranged on the back of this scintillator that convert the scintillation light guided to each into electrical signals; a position calculation circuit that calculates a scintillation position based on the converter output;
In a scintillation camera that outputs a point from a display device that displays a point at a display position determined by the position calculated by the position calculation circuit, the output of each photoelectric converter is adjusted to a predetermined amplification degree for small inputs. For large inputs, the noise components are extracted through noise component extraction amplifiers with zero or small amplification, and these are added according to a certain rule to obtain a noise component addition signal. A scintillation camera characterized in that the noise component addition signal is subtracted from the signal obtained by adding the outputs of the photoelectric converters according to a certain rule.