JPH01138485A - Radiation image device - Google Patents

Abstract

PURPOSE:To correct an array of many sensors with high accuracy by adding a circuit which functions to make individual sensor output signal pulses constant in pulse width correspondingly to the individual sensors of the sensor array. CONSTITUTION:The circuit 5 which makes the pulse width constant is added to the device behind a crest discriminating circuit 4 to make the pulse width constant. A radiation quantum signal from the sensor array 1, e.g., individual elements 2 formed by arraying CdTe semiconductor sensors linearly is amplified by a pulse amplifier 3 and separated from noises and separated into a digital signal corresponding to radiation energy by the circuit 4. The output signal of the circuit 4 is inputted to the circuit 5 to make the pulse width constant. The output of this circuit 5 is counted by a counter 6, corrected by a CPU 7 according to a specific expression, and stored in a memory 8. Thus, the array of many sensors is corrected with high accuracy.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a radiation imaging apparatus for medical or industrial use.

As a conventional radiation image receiving method, a semiconductor detector array is used.
A method has been developed to display an image by detecting the number of radiation quantum signals and using the count value of the signal as the pixel density (
(Japanese Unexamined Patent Publication No. 100885/1985). According to this method, energy information about the number of radiation quanta can be detected by using, for example, a pulse height discrimination circuit. For this reason, if applied to an X-ray CT device, for example, it will be possible to eliminate the effects of It enables distribution measurement, etc., and is revolutionary in radiation image measurement.

However, with the development of pulse detection technology, semiconductor materials, and improvements in electronic circuit technology, it has reached a practical level, but it is difficult to correct linearity due to missed counts at high counting rates. , it was difficult to apply to high-precision images with high contrast characteristics.

Conventionally, nonlinear elements and the like have been used to correct the linearity of individual sensors, but with the development of computers, calculation-based correction has begun to be put into practical use in recent years.

However, in the case of high-precision image sensor arrays, the number of sensors is large, and the individual sensors have different sensitivities and linearities, so there is currently no practical means.

Problems to be Solved by the Invention The present invention provides means for correcting the linearity of a semiconductor sensor array individually and with high precision for each sensor.

Means for Solving the Problem Corresponding to the circuit of each sensor of a sensor array for detecting radiation quanta as a number of pulse signals, at least one
By adding a circuit that has the function of making more than one pulse width constant, linearity in a high count rate field is corrected.

In active pulse counting, it is known that for a sensor with paralysis time τ(SEC), if the measured counting rate is N (CPS), the true counting rate N o (CPS) is expressed by the following formula. It is being

No=N/1-Nτ (1) For example, in a semiconductor sensor, the pulse generation inside the semiconductor is said to be very fast, less than l -10n5ec, but the actual pulse output detected is The pulse width output from the pulse height discrimination circuit varies from approximately 10 nSeC to 100 n5ec due to differences in the response characteristics of the pulse amplifiers, or variations in the response characteristics of the pulse height discrimination circuit. Therefore, as is, it is necessary to provide each sensor with an individual correction coefficient. Therefore, by providing each sensor with a circuit that makes the pulse width constant, eliminating variations in the output pulse width (τ), it is possible to correct the linearity of each sensor with just one coefficient. .

Embodiment FIG. 1 shows an embodiment of the present invention. A pulse amplifier 3 amplifies radiation quantum signals from a sensor array 1, for example, individual elements 2 in which CdTe semiconductor sensors are arranged in a line. The amplified signal is processed by the pulse height discrimination circuit 4,
It is separated into digital signals corresponding to noise and radiation energy.

For boat fishing, the wave height discrimination circuit 4 is composed of a comparator 21 having a comparison voltage source 22, as shown in FIG.

The pulse width (τ) of the output signal of the comparator 21 depends on the pulse width of the output signal from the pulse amplifier 3 and the response speed of the comparator 21. Now, the time tlV for which the output signal Vin from the pulse amplifier 3 exceeds the reference voltage Vd is tlV.
After in becomes below Vd, the comparator 21 turns OF.
Assuming that the time when the signal becomes F is t2, the pulse width t3 of the output signal of the comparator 21 is as follows: t3=t, 1+t2 (2). However, as shown in FIG. 4, tl changes greatly depending on the height of Vd. In addition, the response speed of the comparator and the variation between individual sensors are around ±50%, so
It is difficult to make τ constant for all elements.

Therefore, in the present invention, a pulse width constant circuit 5 is provided after the pulse height discrimination circuit 4 to stabilize the pulse width. FIG. 3 shows an embodiment of the pulse width constant circuit. A monostable multivibrator 31 is used as the circuit element, and a pulse signal is output using the rising edge of the comparator output signal as a trigger. The pulse width of the pulse width stabilization circuit 5 has a pulse width determined by a time constant of a capacitor C31 and a resistor R33 which are attached to the outside of the monostable multivibrator 21. The relationship with the pulse amplifier output is shown in FIG. Regarding the pulse width stabilization method, in this embodiment, a pulse width stabilization circuit 5 is provided after the pulse height discrimination circuit 4, but it is also possible to provide the same function in the pulse height discrimination circuit 4. The output of the pulse width constantization circuit 5 is counted by a counter 6, and the output is counted by a calculation device (CPU) 7.
is stored in a storage device (memory) 8. The counted data is corrected using equation (1) above.

The correction factor rJIr is determined by the time constant of the multivibrator. It can also be easily determined by actual measurement. In FIG. 4, it is expressed as τ>r3, but it can also be set as τ≦τ3 by combining it with the high-speed drive circuit of the comparator. An example of a high-speed drive circuit is shown in FIG.

τ city is stored in the storage device 8 and can be read out during calculation.

Since there is no need to read T for each individual element, high-speed processing is possible. Furthermore, since the coefficients are constant, it is also possible to add an independent calculation @path and calculate the true count value.

Effects of the Invention According to the present invention, highly accurate correction of a large number of sensor arrays can be realized with a simple configuration. Therefore, it is possible to realize radiation image reception using a pulse counting method with a high S/N ratio, a wide dynamic range, and a rough J-energy discrimination function with a simple configuration. This makes it possible to realize a device with high image quality and high functionality even for radiation workers with low radiation exposure.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a radiation imaging apparatus according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a pulse height discrimination circuit, FIG. 3 is a circuit diagram showing an example of a pulse width constant circuit, and FIG. The figure is a waveform diagram for explaining the operation of these circuits, and FIG. 5 is a block diagram showing an example of a pulse height discrimination circuit that operates at high speed. l...Sensor array, 2...Individual element, 3...
... Pulse amplifier, 4... Wave height discrimination circuit, 5...
・Pulse width constant circuit, 6...counter. Figure 1 Figure 2 Figure 2 Vλ Figure 3 Figure 4 Figure 5 51 Gomparake, s2 feedback circuit

Claims (1)

[Claims] In a radiation imaging apparatus that detects radiation quanta as individual pulse signals with a sensor array, and forms an image by using a count value of the pulse signal and/or a calculated value obtained by calculating the count value as a pixel density. . A radiation imaging apparatus, further comprising a circuit having a function of making constant the pulse width of each sensor output signal pulse corresponding to each sensor of the sensor array.