JPH0668545B2 - Digital scintillation camera - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a radioisotope (hereinafter referred to as R
The present invention relates to a digital scintillation camera in which RI (which is referred to as I) is injected, the position of RI that selectively gathers in a specific organ or diseased part is detected by a scintillation detector, and then visualized as an integrated image for functional diagnosis of a living body.

[Technical background of the invention and its problems]

The scintillation camera has a structure in which a plurality of photomultiplier tubes are arranged in a matrix, and a preamplifier is connected to each photomultiplier tube (hereinafter also referred to as a photomultiplier) to amplify and output a signal.

By the way, each photomultiplier tube has its own gain and characteristics due to manufacturing reasons, etc.
Calibration is required at the time of shipment and installation. Further, even after the calibration is carried out at the time of shipping or installation, the characteristics of the above-mentioned photomulch will fluctuate due to a change with time during use, so that the calibration becomes necessary again.

Conventionally, the calibration data used first is used again for the next calibration, or a reference photogenerator is built into each of the matrix-type photomultiplier tubes and the There is a method such as making data to calibrate the fluctuation amount at that time by observing the output of the corresponding photomultiplier tube based on light emission, and feeding back this data to the gains of all the preamplifiers to successively control the preamplifier gains to a constant value. Was used.

However, the next calibration method using the fixed calibration data cannot perform accurate calibration due to the change of the photomultiplier with time, etc. There is a problem that the reference light emitter must be provided for each tube and that the calibration means does not use γ-rays, so that accurate correction cannot be performed.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a digital scintillation camera capable of accurately calibrating fluctuations in a photomultiplier tube while having a simple and inexpensive structure.

[Outline of Invention]

In order to achieve the above-mentioned object, the present invention is a digital scintillation camera that detects radiation from a radiation source administered into a subject and obtains a radiation source distribution image, and the scintillation light is arranged in a matrix. A plurality of photomultiplier tubes for converting and amplifying signals, a plurality of preamplifiers for respectively amplifying the outputs of the photomultiplier tubes, and a calibration radiation source placed at a predetermined position of each of the photomultiplier tubes,
Preamplifier output distribution S _i connected to the photomultiplier tube
And the energy distribution matrix part that stores the output distribution W _ij of other preamplifiers, and the preamplifier output distributions S _i and W _ij stored in this correction matrix part and the preamplifier output distribution S _i ′ when actually detected. An arithmetic processing unit for obtaining a variation of the amplification factor of the photomultiplier tube, and a gain control unit for adjusting the gain of the preamplifier according to the variation obtained by the arithmetic processing unit. Is.

Example of Invention

 The present invention will be specifically described below with reference to examples.

FIG. 1 is a block diagram showing an embodiment of the device according to the present invention. 1a~1n are arranged in a matrix, a photomultiplier tube that amplifies and converts the scintillation light into an electric signal (hereinafter photomultipliers, also referred to as PMT), the output _S 1 to S _n of each photomultiplier 1a~1n Are output to the preamplifiers 2a to 2n, respectively. The outputs S _{11 to} S _1n of the preamplifiers 2a to 2n are input to the position signal generating circuit 4. From the position signal generating circuit 4, X, Y signals (coordinate address signals), Z signals (energy corresponding signals)
And UNB (unblank) signals are output. Reference numeral 5 denotes an A / D converter for converting each of the above signals into a digital signal. Of the digitized signals, the XY signal is input to the linearity correction matrix circuit 6 in the subsequent stage, and the Z signal is energy correction which will be described in detail. Matrix circuit 10
And output to the wave height analyzer 11. The linearity correction matrix circuit 6 stores data for correcting the linearity distortion of the characteristics of the X and Y signals, and the linearity correction (calibration) is performed here. X, Y signals and U after such correction is performed
The NB signal is input to the CPU (central processing control circuit).
The energy correction matrix circuit 10 is a circuit for arranging and storing a reference spatial energy distribution created based on the data collected at the time of shipping or installation of the device in a matrix form, and the wave height is constantly kept during use of the device. It can be input to and output from the CPU 7 via the analyzer 12. A real-time (real-time) spatial energy distribution matrix circuit 13 is provided on the output side of the wave height analyzer 11 which inputs the Z signal. The real-time spatial energy distribution matrix circuit 13 stores the spatial energy distribution, which is created based on the data collected at the time of periodical adjustment or clinical use when the device is used, arranged and stored in a matrix, and controls the CPU 7. Based on this, it is possible to input and output sequentially. The CPU 7 sequentially compares the output from the energy correction matrix circuit 10 in which the reference spatial energy distribution is stored with the output from the real-time spatial energy distribution matrix circuit 13 stored each time the device is used, and the energy curves of both are stored. Is calculated, and when the arithmetic circuit built in the CPU itself cannot keep up, the external high speed arithmetic processing unit 14 is used to perform the arithmetic operation. Reference numeral 9 in the drawing is a gain control circuit, which inputs the energy fluctuation amount of each photomultiplier calculated by the CPU 7, and outputs a control signal for switching the analog switches 3a to 3n according to the fluctuation amount. Wherein each gain adjustment resistor _VR 1 to VR _n and the respective preamplifiers 2 a to 2 n, and the analog switch 3a~3n is built for switching each resistance value, the analog switches 3a~3n is from the gain control circuit 9 Switching is controlled by a signal.

Next, the operation of the above device will be described.

First, at the time of shipment or installation of the apparatus, preliminary data Wij that is a basis for obtaining a gain adjustment signal to be applied to the gain control circuit 9 is obtained and stored in a memory circuit (not shown) connected to the CPU 7, for example. The preliminary data Wij is obtained as follows.

FIG. 2 shows a plurality of photomultiplier tubes (photomultipliers) 1a to 1n.
Are arranged in a matrix, and the point source is sequentially positioned and narrowed down just above each Photomul arranged in this way, and the spectrum of the energy output of each Photomul at this time is taken into the CPU 7. Find each peak value. The scanning of the point source at this time may be performed, for example, by attaching a calibration radiation source to the X and Y plotters, automatically moving to the center of each photomultiplier, and interlocking with it to capture the output of each preamplifier. Here, the method of collecting the spectrum will be described in detail. For example, the output distribution Wij from the preamplifier of the i-th photomul when the point source is narrowed down to the j-th photomul is obtained. However, it is normalized as the ratio when Wii = 1.

Further, when the apparatus is shipped or installed, the energy correction matrix circuit 10 obtains the reference spatial energy distribution data E ₁ as shown in FIG.

Next, the spatial energy distribution E ₂ based on the output signal from each photomultiplier at the clinical time is obtained by simple calibration performed in a short cycle, and stored in the real-time spatial energy distribution matrix circuit.

The reference spatial energy distribution E ₁ and the real-time energy distribution E ₂ thus obtained are loaded into the CPU 7, the difference between the two is obtained, and the gain variation can be calculated based on the difference and by referring to the preliminary data Wij. it can.

Next, a calculation example of the gain variation will be described.

First, the definition of each symbol will be described.

The output of the center position of the i-th Photomul in the reference spatial energy distribution is Si, and the output of the center position of the i-th Photomul in the real-time spatial energy distribution is S
If i'is defined and Vi is defined as Si'-Si, the spatial energy distribution is Gain change GV of the i-th photomultiplier when changing to
i is represented by the following matrix calculation formula.

That is, the gain variation of each photomul is calculated from the reference spatial energy distribution and the real-time spatial energy distribution, for example, by using the high-speed arithmetic processing unit 14 based on the above equation (1).

Here, regarding the method of determining the center point of each Photomul,
For example, in a system provided with both energy and linearity correction, position coordinates and addresses in memory correspond one-to-one, so mutual conversion is possible, and the center point in this case can be easily obtained.

Here, in consideration of statistical fluctuations at the time of clinical derivation of the spatial energy distribution obtained by simple calibration, when adding the energy signal to the address on the memory corresponding to each position coordinate, A threshold is set by the count number, and only the position coordinates that have reached the count number higher than that are sequentially corrected by the first equation. The problem at this time is the processing of addresses that have not reached the threshold count number, which is replaced by the oldest and newest energy signal. This problem can be solved, for example, by collecting a spatial energy distribution for calibration every morning (this collection can be done in a very short time compared to the data collection for linearity correction) (ie the threshold count is reached at all addresses). You can continue to collect until).

Further, it is the timing of the sequential correction at the clinical time, for example, when each clinical end or when the threshold count number of each address reaches a certain number.

Further, regarding concrete gain control of the preamplifier, for example, an analog switch with an attenuator for fine gain adjustment as shown in FIG. 4 is used as a GVi represented by the formula (1).
This can be easily realized by controlling with an analog switch control signal so that the gain becomes a reciprocal multiple of the gain fluctuation. Of course, it goes without saying that the gain control circuit is inserted before the position signal system and the energy signal system at the relatively first stage of the preamplifier are separated.

Next, as a means to warn that the spatial energy distribution has changed too much from the time of installation, etc., the spatial energy distribution obtained at the clinical time or by simple calibration as shown in FIG. Is detected within the range of theoretically correctable thresholds U and L, and is notified by monitor or voice synthesis, and the gain of the analog switch in FIG. 4 corresponds to the intermediate gain of the attenuator. It is initialized to prompt the tuning of the detector.

〔The invention's effect〕

As described above, according to the present invention, the preamplifier output distribution (real-time spatial energy distribution) at the present time is compared with the preamplifier output distribution (reference spatial energy distribution) collected for calibration, so that the time-dependent photomul It is possible to calibrate a change in the amplification factor.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a plan view showing the arrangement of photomultiplier tubes used therein, and FIG. 3 is a characteristic diagram for explaining the operation of the embodiment, FIG. 4 is a block diagram showing the configuration of the gain adjusting section of the above embodiment, and FIG. 5 is a characteristic diagram for explaining another embodiment of the present invention. 1a to 1n ... Photomultiplier tube, 2a to 2n ... Preamplifier, 3a to 3n ... Analog switch, 4 ... Position signal generating circuit, 7 ... CPU, 9 ... Gain control circuit, 10 ... Energy correction Matrix, 13 ... Real-time spatial energy distribution matrix.

Claims (1)

[Claims] 1. A digital scintillation camera for detecting radiation from a radiation source administered to a subject and obtaining a distribution image of this radiation source, arranged in a matrix and converting scintillation light into an electric signal for amplification. A plurality of photomultiplier tubes, a plurality of preamplifiers for amplifying the outputs of the photomultiplier tubes, and a photomultiplier tube when a calibration radiation source is placed at a predetermined position of each of the photomultiplier tubes. energy correction matrix unit that stores the output distribution W _ij of the preamplifier output distribution S _i and another preamplifier is, the preamplifier of the preamplifier output distribution stored in the correction matrix section S _i, when actually detected and W _ij An arithmetic processing unit for obtaining a variation of the amplification factor of the photomultiplier tube from the output distribution S _i ′, and a variation obtained by the arithmetic processing unit. And a gain control unit for adjusting the gain of the preamplifier.