JPS5920879A - scintillation camera - Google Patents

Abstract

PURPOSE:To output a digital value of the number of bit necessary for obtaining a specified spatial resolution irrelevant to energy by using a voltage corresponding to energy of radiation as reference voltage in the A/D conversion of a photoelectric conversion output. CONSTITUTION:A scintillation light detection signal through a photoelectric converter forming a photomultiplier is inputted into a corresponding sequential comparison type A/D converter 71. In the sequential comparision processing with the converter 71, a digital output of a sequential bit from MSB of a register 19 and a voltage proportional to radiation energy based on the output of the photomultiplier as reference voltage are inputted into a D/A converter 18 and converted into analog from digital with a comparison reference voltage applied to a comparator 17 varying according to the radiation energy. The number of bit of the digital data thus processed lessens as the radiation energy becomes larger and thus, a digital value of the number of bit required to obtain a specified spacial resolution is outputted. This simplifies the construction of the A/D converter/position computing circuit of a scintillation camera.

Description

DETAILED DESCRIPTION OF THE INVENTION 1' Knee This invention relates to a type of scintillation camera that performs digital end position calculation processing.

This type of scintillation camera is provided with an AD converter for AD converting each output of a large number of photoelectric converters, respectively, and the position calculation circuit has a digital-like configuration. In this case, the resolution of the image depends on the number of bits of the digital position information. However, the output of the photoelectric converter increases as the energy of the incident radiation increases.

Therefore, if the number of focuses of the AD converter and position calculation circuit is determined so as to obtain the necessary spatial resolution at high energy, the number of binotos of data is insufficient at low energy, and the necessary spatial resolution cannot be obtained. Therefore, in the past, the AI) converter and position calculation circuit were designed to obtain y bits of data such as 9 even with low energy, knowing that the number of bits was too large due to high energy and wasted. The number of bits has been increased, which inevitably leads to higher prices.

This invention achieves A
1] An object of the present invention is to provide a scintillation camera which is designed to reduce the cost by reducing the number of bits of a converter and a position calculation circuit compared to conventional ones.

Hereinafter, an M5 example of the present invention will be described with reference to the drawings. In FIG. 1, a scintillator 1 generates lentils in response to incident radiation, and is made of, for example, NaI (Tt) crystal. The light of this zonal beam is guided by the id 2 to a large number of photomultiglares 3, where it is converted into an electrical signal. The outputs of these photomultiglares 3 pass through each of the preamplifiers 4, are integrated by the corresponding integration circuits 5, and are then taken into each of the Zanglebold circuits 6 and held, and are input to each A.D. The signal is input to a converter 7. Each preamplifier 4
All outputs d of are added by an adder circuit 8, then integrated by an integrator circuit 9, and further passed through a sample hold circuit 10 to obtain an energy signal Z. This energy signal Z is sent to the pulse height analyzer 11, and when the energy signal 2 is within the window set according to the energy of the nuclide used by the window setting device 20, the brightness signal UNBLAN is output.
K is generated from the pulse height analyzer 11. This energy signal Z is also sent to an amplifier circuit 12, and from this amplifier circuit 12 a voltage proportional to the energy signal Z is supplied to each of the AI converters 7 as a reference voltage VREF.

The dinotal outputs of each AJ) converter 7 are multiplied by weights according to the coordinates of the corresponding photomultiglare 3 in X and Y weighted integration circuits 13.14, and then added together in addition circuits 15.16. Then, input the digital position signals X and Y. To simplify the explanation, the timing control of each circuit such as the integrating circuit, non-glue hold circuit, AI converter, etc. is omitted, but it is assumed that the timing of each circuit is controlled by an appropriate signal.

AI) The converter 7 may be of any type, but
Here, a description will be given assuming that a successive approximation type AI) converter 71 shown in FIG. 2 is used. Input VIN is controller 17
It is compared with the output vou'r of the I)A converter 18, and the comparison output is sent to the successive approximation processing renostator 19. This renostar 19 initially outputs an output DIN in which only the MSB (largest bit) is "1" and all others are "0", and the corresponding analog output voUT is compared by the comparator 17, and the M
The SB is determined, and then a similar comparison and determination is made for the second bit from the MSB, 7), and this is converted into L S B (
Repeat flft' with the minimum bit) size, and M S B
All bits from to LSB are determined to obtain the dinotal output 1) OUT. AD converter 71 with here
is n pits, the code of J)IN is (bn
-1+bn-2+0'+bITbo). At this time, VOUT = k-VagF-(bn-1-2°+bn
−2゛2−1−1−°−,・,+b, ,2−(n−2
) +bo・2−(n−1)) (where k is a proportionality constant), and after the AD conversion is completed, VOUT′=−VIN DOUT=DIN. However, VREF "Z. Therefore, if the energy signal Z is large, the reference voltage VRE
Since F also becomes large, it is possible to always obtain data with the same number of focus regardless of the energy, and standardization using the energy signal Z is also performed at the same time. Therefore, due to the standardization using the energy signal "Z", there is no need for the division circuit that was required in the past. And this reference voltage, voltage VRT
Since f is changed each time the radiation is incident in accordance with the energy of the incident radiation, it can be applied even to the measurement of multiplex vectors or multiple nuclides.

It should be noted that AD converters of other types than the successive approximation type (for example, parallel comparison type) can also be used for the same reason because the relationship with respect to the reference voltage and voltage is exactly the same.

Furthermore, in the circuit shown in FIG. 1, a configuration is adopted in which each output of the preamplifier 4 has an integral characteristic, and a configuration in which a peak hold circuit is used instead of the integral circuit 5.9 and the sample hold circuit 6.10. You can also do that.

Furthermore, in order to improve the count rate characteristics by supplying the reference voltage VREF before the input of the AI) converter 7, the integration circuit 5
It is also burdensome to insert a delay circuit on the input or output side.

In the above embodiment, the reference voltage and voltage VREF of the AD converter 7 are changed every time radiation is incident, but the window setting device 20
A window setting signal given to the pulse height analyzer 11 from the pulse height analyzer 11 may be given to the amplifier circuit 12 instead of the energy signal Z as shown by the dotted line, so that the reference voltage VREF corresponds to the set window. This does not mean that a reference voltage VREF proportional to the energy signal Z for each incident radiation is given, so a division circuit for standardization by energy is required, but the reference voltage VREF of the AD converter 7
Since EF is proportional to the energy setting window, it is possible to always obtain the same number of bits of data regardless of whether it is high energy or low energy, which makes it possible to obtain data with the same number of bits regardless of whether the energy is high or low. There is no need to use a converter or position calculation circuit. In this case, it is still possible to measure multiple spectra and multiple nuclides by setting the reference voltage VREF to the highest of multiple set energy windows, although the accuracy will deteriorate for low-engineering systems. be.

As described above with respect to the embodiments, according to the present invention, the bit precision can be made the same regardless of the energy within the range of precision required to obtain the necessary spatial resolution. can be reduced and the price can be lowered.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of this invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
l) It is a block diagram showing an example of the configuration of a converter. ■...Scintillator 2...Light is ID 3.
...Fut multiplier 4...Preamplifier 5,9...Integrator circuit 6.
10... Sample hold circuit 7... AI) Converter 8, 15, 16... Repair circuit 11... Pulse height analyzer 12... Amplifier circuit 13.
14... Weight accumulator 17... Controller 18... I) A converter] 9... Successive approximation processor 20... Window setter 71... Successive approximation type AD converter

Claims (3)

[Claims] (1) A scintillator that generates scintillation in response to incident radiation, a number of photoelectric converters to which scintillation light is guided and generates electrical signals, and an AD converter into which the output of each of these photoelectric converters is input, respectively. In the scintillation camera, the scintillation camera is equipped with a position calculation circuit that receives digital outputs of these AD converters, and generates a voltage proportional to the energy of the radiation, and supplies this voltage as a reference voltage to the AD converters. A cinderella camera characterized by having a reference voltage supply circuit. (2) The reference voltage supply circuit is composed of an adder circuit that adds all the outputs of the multiple photoelectric converters, and a voltage converter circuit that generates a voltage proportional to the output of the adder circuit. A scintillation camera according to claim 1, characterized in that: (3) The reference voltage supply circuit is constituted by a voltage generation circuit that generates a voltage according to a window setting signal applied to a pulse height analyzer for analyzing the pulse height of the energy signal. The scintillation camera according to item 1.