JP2000131442A - Signal processing device for measuring dose and dose measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processing device for dose measurement and a dose measuring device able of accurately measuring both the dose of high dose rate X-rays of short-time irradiation and the dose of low dose rate X-rays of long-time irradiation without performing complicated work such as switching amplification degree according to detection signals of an X-ray sensor. SOLUTION: An X-ray sensor 10; a signal processing circuit 20 to perform integration processing on a detection signal of high dose rate radiation of short- time irradiation among detection signals outputted form the sensor 10, and to perform amplification processing on a detection signal of low dose rate radiation of long-time irradiation; and an integrated value computing circuit 30 to compute the integrated value of the output signals of the signal processing circuit 20; are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dosimeter for measuring the dose of radiation such as medical X-rays and a signal processor for dosimetry used in the device.

[0002]

2. Description of the Related Art Conventionally, as a dosimeter of this kind,
For example, there is known a method in which a detection signal from a detector for detecting radiation is amplified by an amplifier, and an output signal of the amplifier is integrated to calculate a dose. In the dosimetry by this dosimeter, the dose of high dose rate radiation for short-time irradiation and the dose of low dose rate radiation for long-time irradiation are sometimes measured continuously. For example, in the medical field, X-ray fluoroscopy is performed while irradiating low-dose-rate X-rays for a long time, and X-rays may be taken by irradiating high-dose-rate X-rays for a short time as necessary. In such a case, it is necessary to continuously measure the dose of high dose rate X-rays for short-time irradiation and the dose of low dose rate X-rays for long-time irradiation. FIGS. 6A and 6B
Respectively shows an example of a waveform of a detection signal of a high dose rate X-ray for short-time irradiation and a waveform of a detection signal of a low dose rate X-ray for long time irradiation. The level of the high-dose-rate X-ray detection signal indicated by reference numeral Ia in the figure is the low-dose-rate X-ray indicated by reference numeral Ib.
It is about 1000 times the level of the line detection signal.
Further, the irradiation time of the high dose rate X-ray indicated by the symbol Ta in the drawing is about 5 milliseconds to 1 second, and the low dose rate X
The irradiation time of the line is about several seconds to several minutes.

[0003]

However, using the above conventional dosimeter, the dose of the short-time irradiation high dose rate radiation and the long-time irradiation low dose rate radiation are continuously measured. In such a case, since the magnitude of the output signal from the amplifier must be within a predetermined range, a complicated operation of switching the amplification degree of the amplifier depending on whether the measurement target is high dose rate radiation or low dose rate radiation. Is required. Also, the detection signal corresponding to the high dose rate radiation may reach about 1000 times the detection signal corresponding to the low dose rate radiation, but it is difficult to accurately switch the amplification degree in such a wide dynamic range. There is also a problem that good measurement accuracy may not be obtained.

The present invention has been made in view of the above problems, and has as its object to provide a high dose rate of short-time irradiation without performing a complicated operation of switching the amplification degree according to a detection signal of a detector. It is an object of the present invention to provide a signal processor for dosimetry and a dosimeter capable of accurately measuring both the dose of radiation and the dose of low-dose-rate radiation during long-term irradiation.

[0005]

According to one aspect of the present invention, there is provided a signal processing apparatus for dosimetry for processing a detection signal output from a detector for detecting radiation. Signal processing for performing an integration process on a detection signal of a high dose rate radiation of a short irradiation in a detection signal output from the detector, and performing an amplification process on a detection signal of a low dose rate radiation of a long irradiation. A circuit is provided. In this signal processor for dosimetry, the peak level of the detection signal is suppressed by performing an integration process on the detection signal of the high dose rate radiation of short-time irradiation among the detection signals output from the detector. In this state, an integrated output signal can be output. Since the area of the output signal (integrated waveform) is proportional to the dose of the high dose rate radiation of the short-time irradiation, if the integrated value of the output signal is calculated, the area of the high dose rate radiation of the short time irradiation can be calculated. Dose can be measured. Further, by performing an amplification process on the detection signal of the low dose rate radiation irradiated for a long time, the detection signal is amplified with a predetermined amplification degree, and an output signal having substantially the same waveform shape as the detection signal is output. Can be. Since the area of this output signal is proportional to the dose of the low-dose rate radiation of the long-time irradiation, if the integrated value of the output signal is calculated, the dose of the low-dose-rate radiation of the long-time irradiation can be measured. Can be.

According to a second aspect of the present invention, there is provided a signal processing apparatus for dosimetry for processing a detection signal output from a detector for detecting radiation, wherein the signal processing apparatus is provided in accordance with the type of the detection signal output from the detector. A signal processing circuit capable of functioning as an integrating circuit or an amplifier circuit is provided. The output time width of a detection signal for a short-time irradiation of a high dose rate radiation is Ta, and the output time width of a detection signal for a long-time irradiation of a low dose rate radiation is Tb. , When the high frequency cutoff frequency of the signal processing circuit is fc,
The circuit constant is set so as to satisfy (2 · Ta)｝>fc> {1 / (2 · Tb)}. In this dosimetry signal processing device, the high-frequency cutoff frequency fc of the signal processing circuit is 1 / (2 · T
a) outputting an output signal obtained by integrating the detection signal of the high dose rate radiation of the short-time irradiation out of the detection signals output from the detector by the signal processing circuit while the peak level is suppressed. Can be. Since the area of this output signal (integrated waveform) is proportional to the dose of the high dose rate radiation of the short-time irradiation, if the integrated value of the output signal is calculated, the dose of the high dose rate radiation of the short-time irradiation can be calculated. Can be measured. Further, since the high-frequency cutoff frequency fc of the signal processing circuit is higher than 1 / (2 · Tb), the signal processing circuit amplifies the detection signal of the long-time irradiation low dose rate radiation with a predetermined amplification factor. An output signal having substantially the same waveform shape as the detection signal can be output. Since the area of this output signal is proportional to the dose of the low-dose rate radiation of the long-time irradiation, if the integrated value of the output signal is calculated, the dose of the low-dose-rate radiation of the long-time irradiation can be measured. Can be.

According to a third aspect of the present invention, there is provided a detector for detecting radiation, the signal processing circuit according to the first or second aspect, and an integrated value calculating circuit for calculating an integrated value of an output signal of the signal processing device. It is characterized by the following. In this dosimetry device, the signal processing circuit suppresses and outputs the peak level of the signal for the high dose rate radiation, and amplifies the low dose rate radiation with a predetermined amplification factor. By outputting the signal, the level of the signal input to the integration value calculation circuit can be kept within a certain range without performing the complicated operation of switching the amplification degree according to the detection signal of the detector. Then, by integrating the signal of this fixed level by the integration value calculating circuit, the above-mentioned 2 is obtained.
It is possible to accurately measure the dose of each type of radiation.

According to a fourth aspect of the present invention, in the dosimeter according to the third aspect, the integrated value is calculated within a range where the value of the output signal of the signal processing circuit is larger than a preset minimum reference level. It is characterized by having comprised. In this dosimeter, the calculation of the integral value is not performed on the pulse signal corresponding to the small signal affected by the noise smaller than the reference minimum level, thereby shortening the measurement time and reducing the influence of the noise. Make it smaller.

The above signal processing device can be configured using an inverting amplifier circuit (integrating circuit) in which a parallel circuit of a resistor and a capacitor is connected between an inverting input terminal and an output terminal of an operational amplifier. Further, the integrated value calculation circuit is
A voltage frequency conversion circuit for converting an output signal from the signal processing device into a repetition pulse signal having a cycle proportional to the magnitude of the output signal; and a pulse counting circuit for counting the repetition pulse signal output from the voltage frequency conversion circuit And can be configured using In this case, the peak level of the signal corresponding to the high dose rate radiation can be adjusted by changing the value of the capacitor of the inverting amplifier circuit. Also, by changing the value of the resistance of the inverting amplifier circuit, the level of the signal corresponding to the low dose rate radiation can be adjusted. Further, after once converting the output signal output from the inverting amplifier circuit into a repetitive pulse signal having a cycle proportional to the magnitude of the output signal, integrating the output signal by counting the pulse signal. The calculation of the dose by the method can be performed stably, and the calculated value can be output as a digital signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a medical dose measuring apparatus for measuring the dose of X-rays will be described below with reference to the drawings. FIG. 1 is a block diagram of the dosimeter according to the present embodiment. The dosimeter includes an X-ray sensor 10 as a detector for detecting X-rays,
The apparatus includes a signal processing device 20 for measuring a dose that processes a detection signal output from the X sensor 10, and an integrated value calculating circuit 30 that calculates an integrated value of an output signal of the signal processing device 20.

As shown in FIG. 2A, the X-ray sensor 10 is a parallel plate type ionization chamber fixed with screws so as to sandwich the polyester films 12a and 12b in two layers with a rectangular frame 11 made of aluminum. It has a structure.
The current collecting electrode 13 and the high voltage electrode 14 are adhered inside the polyester films 12a and 12b to form an ionization layer. A transparent electrode material is used for the current collecting electrode 13 and the high voltage electrode 14 so that visible light for confirming the irradiation field can pass through. As shown in FIG. 2B, the X-ray sensor 10 includes polyester films 12a and 1a.
A sensor in which the layers 2b and 12c are fixed in three layers, the protection electrode 15 is provided around the current collecting electrode 13, and the outer surface is covered with the shield electrode 16 may be used. The detection signal (current) i output from the collecting electrode 13 of the X sensor 10 is input to the signal processing device 20, and the bias power supply 17
, A predetermined bias voltage (positive DC high voltage in this embodiment) is applied.

The signal processing device 20 includes an operational amplifier 21
And an inverting amplifier circuit (integrating circuit) in which a parallel circuit of a resistor R and a capacitor C is connected between the inverting input terminal and the output terminal. This inverting amplification circuit (integration circuit)
Is higher than the inequality {1 / (2 · Ta)}>
The value of the capacitor C is set so as to satisfy fc> {1 / (2 · Tb)}. Here, Ta is the output time width of the sensor output signal (detection signal) for X-rays for medical photography as high dose rate radiation of short irradiation, and Tb is the low dose rate radiation of long irradiation. This is the output time width of the sensor output signal (detection signal) for X-rays for medical fluoroscopy. The value of the capacitor C is set so that the maximum value of the sensor output signal when detecting X-rays for medical photography is 10 V within a range satisfying the above inequality. Further, the value of the resistor R is set so that the maximum value of the sensor output signal when detecting X-rays for medical fluoroscopy is 10 V.

The integral value calculating circuit 30 converts a signal output from the signal processing device 20 into a repetitive pulse signal having a cycle proportional to the magnitude of the output signal. And a digital integrator 32 as a pulse counting circuit that counts repetitive pulse signals output from the V / F conversion circuit 31. The output signal of the signal processing device 20 is also input to the comparator 33, and is compared with a voltage Vref corresponding to a preset reference minimum level. By inputting the output signal of the comparator 33 and the repetition pulse signal from the V / F conversion circuit 31 to the NAND circuit element 34, when the value of the output signal of the signal processing circuit 20 is higher than a preset reference minimum level Only in this case, the digital integrator 32 can perform the process of counting the repetitive pulse signal and calculating the integral value. Therefore, it is possible to prevent the calculation of the integral value for a pulse signal corresponding to a small signal affected by noise smaller than the reference minimum level, thereby shortening the measurement time and reducing the influence of noise. it can.

The digital output from the digital integrator 32 is output to a display 40 composed of a liquid crystal panel and can be output to an external computer via an I / O interface 41. The output of the comparator 33 is also connected to the LED 35, which is a light emitting element.
The ED 35 is turned on.

FIG. 3 shows a detection signal (output current i) of the X-ray sensor 10 for an X-ray for medical photography with a high dose rate, an output signal of the operational amplifier 21 (output voltage v1), and a V / F conversion circuit 31. FIG. 4 is an explanatory diagram of a waveform of an output signal (output voltage v2). In this case, integration processing involving charging and discharging of the output signal of the X-ray sensor 10 to and from the capacitor C is performed, and an output signal obtained by integrating the detection signal with the peak level suppressed is output. The area B1 of the output signal (integrated waveform) is proportional to the area A1 of the detection signal of the X-ray sensor 10 corresponding to the dose. V / F conversion circuit 31
From this, a repetitive pulse signal having a period proportional to the amplitude of the output signal (integrated waveform) is output. By counting the repetitive pulse signal by the digital integrator 32, the dose of the X-ray can be measured. .

FIG. 4 shows a detection signal (output current i) of the X-ray sensor 10 for an X-ray for medical photography, which has a slightly smaller dose rate and a slightly longer irradiation time than the case of FIG. 3, and an output signal of the operational amplifier 21. FIG. 5 is an explanatory diagram of (output voltage v1) and a waveform of an output signal (output voltage v2) of the V / F conversion circuit 31. In this case, although the shape of the output signal (integrated waveform) from the operational amplifier 21 is slightly different from that in FIG. 3, the area B2 of the output signal (integrated waveform) is different from that of the X-ray sensor 10 corresponding to the dose. It is proportional to the area A2 of the detection signal. Therefore, the X-ray dose can be measured by counting the repetitive pulse signal output from the V / F conversion circuit 31 by the digital integrator 32.

FIG. 5 shows that the dose rate is about 1/10 of the case of FIG.
A detection signal (output current i) of the X-ray sensor 10 for an X-ray for medical fluoroscopy, which is as small as 00, an output signal of the operational amplifier 21 (output voltage v1), and an output signal of the V / F conversion circuit 31 (output voltage v2) FIG. 4 is an explanatory diagram of a waveform. In this case, an output signal obtained by amplifying the output signal of the X-ray sensor 10 at a predetermined amplification degree is output. This output signal (integrated waveform)
Is proportional to the area A3 of the detection signal of the X-ray sensor 10 corresponding to the dose. The V / F conversion circuit 31 outputs a repetition pulse signal having a period proportional to the amplitude of the output signal (integrated waveform). The repetition pulse signal is counted by the digital integrator 32 to obtain the X signal.
The dose of the radiation can be measured.

As described above, according to the present embodiment, the X-ray sensor 1
The dose of X-rays for medical photography, which is a high dose rate radiation of short time irradiation, and a low dose of long time irradiation, without performing the complicated work of switching the amplification degree with a switch etc. according to the intensity of the detection signal of 0 It is possible to accurately measure both doses of X-rays for medical fluoroscopy, which are rate radiation.

Although the above embodiment has been described with reference to the case of a dosimeter in which the signal processing circuit 20 is combined with the X-ray sensor 10, the integral value calculation circuit 30, and the like, the signal processing circuit 20 is separately provided. A signal processing device for dosimetry may be configured. Further, a signal processing device for dosimetry including the signal processing circuit 20 and the integral value calculating circuit 30 may be configured.

In the above-described embodiment, the case where the integral value calculating circuit 30 is constituted by using the V / F conversion circuit 31 and the digital integrator 32 has been described. However, the integral value calculating circuit 30 includes an operational amplifier. It may be configured by an analog integration circuit used, or may be configured by combining an A / D converter and an externally connected computer.

In the above embodiment, the case of measuring the dose of X-rays has been described. However, the present invention is also applicable to the case of measuring the dose of other radiation such as gamma rays.

[0022]

According to the present invention, the peak level of the high dose rate radiation is suppressed and output, and the low dose rate radiation is amplified with a predetermined amplification. Output, the level of the output signal can be kept within a certain range without switching the amplification degree by operating a switch or the like in accordance with the intensity of the detection signal of the detector. Then, by integrating the constant level signal and calculating the integrated value, it becomes possible to accurately measure the doses of the above two types of radiation. Therefore, it is possible to accurately measure both the dose of high dose rate radiation for short-time irradiation and the dose of low dose rate radiation for long-time irradiation without performing the complicated work of switching the amplification degree according to the intensity of the detection signal of the detector. There is an effect that measurement can be performed well.

In particular, according to the invention of claim 4, there is an effect that the measurement time is shortened and the influence of noise is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a dosimeter according to an embodiment of the present invention.

2 (a) and 2 (b) show X used in the same dosimeter.
FIG. 2 is a cross-sectional view illustrating a schematic configuration of a sensor.

FIG. 3 is an explanatory diagram of waveforms of a sensor output signal, an output signal of an operational amplifier, and an output signal of a V / F conversion circuit for X-rays for medical photography.

FIG. 4 shows a sensor output signal, an output signal of an operational amplifier, and V for an X-ray for medical photography in which irradiation time is relatively short.
FIG. 4 is an explanatory diagram of a waveform of an output signal of the / F conversion circuit.

FIG. 5 is an explanatory diagram of waveforms of a sensor output signal, an output signal of an operational amplifier, and an output signal of a V / F conversion circuit for X-rays for medical fluoroscopy.

FIGS. 6A and 6B are explanatory diagrams showing an example of a waveform of a detection signal of a high dose rate X-ray for short-time irradiation and a waveform of a detection signal of a low dose rate X-ray for long-time irradiation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 X-ray sensor 17 Bias power supply 20 Signal processing circuit 21 Operational amplifier 30 Integration value calculation circuit 31 V / F conversion circuit 32 Digital integrator

Claims (4)

[Claims] 1. A signal processing device for dosimetry for processing a detection signal output from a detector for detecting radiation, wherein a high dose rate radiation of short-time irradiation among the detection signals output from the detector. A signal processing circuit for dosimetry, comprising: a signal processing circuit that performs an integration process on the detection signal of (1) and performs an amplification process on a detection signal of the low dose rate radiation of long-time irradiation. 2. A dose measuring signal processing device for processing a detection signal output from a detector for detecting radiation, comprising: an integration circuit or an amplification circuit according to the type of the detection signal output from the detector. A signal processing circuit capable of functioning as a signal processing circuit, wherein the output time width of a detection signal for a short dose of high dose rate radiation is Ta, the output time width of a detection signal for a long dose of a low dose rate radiation is Tb, {1 / (2 · Ta)}>fc>
A signal processing device for dosimetry, wherein a circuit constant is set so as to satisfy {1 / (2 · Tb)}. 3. A detector for detecting radiation, a signal processing circuit according to claim 1 or 2, and an integrated value calculating circuit for calculating an integrated value of an output signal of the signal processing circuit. Dosimetry device. 4. The dosimeter according to claim 3, wherein the integrated value is calculated within a range in which the value of the output signal of the signal processing circuit is larger than a predetermined reference minimum level. Dosimetry device.