JPH04315985A - Measuring device for radiation - Google Patents

Abstract

PURPOSE:To enable measurement with no error resulting from the temperature fluctuation of fresh air by measuring and holding the dark current of a photoelectric transfer element a fixed time earlier than radiation exposure, and finding from the value the temperature of the photoelectric transfer element at the exposure, and correcting the temperature. CONSTITUTION:An incident X-ray is converted into a current via a fluorescent material 102 and a photoelectric transfer element 101. The current is transmitted to a signal processing unit 201 and a dark current data holding circuit 109. The device 201 converts the current signal into a voltage and then the voltage is A/D converted and subjected to various kinds of processing and stored as data about measurement in a storage device. The circuit 109 stores data about dark current serving as offset data during measurement of offset data immediately before X-ray exposure. The device 201 finds the temperature of the element 101 using a predetermined equation according to the offset data and the temperature characteristic data of dark current stored in a temperature characteristic data memory 110, and further corrects data on measured X-rays according to data on the temperature characteristics of the sensitivity of the combined body of the element 101 and the fluorescent material 102, which is stored in the memory 110.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring device comprising a phosphor and a photoelectric conversion element, and more particularly to a radiation measuring device suitable for an X-ray detector of an X-ray CT device.

0002

[Prior Art] As an X-ray detector for an X-ray CT device,
E-ionization chamber detectors have been the mainstream, but with improved resolution, solid-state detectors with superior X-ray utilization efficiency and sensitivity are being adopted.

The main components of this solid-state detector are a phosphor that converts X-rays into light and a photoelectric conversion element that converts light into electric current.
However, since the dark current of the photoelectric conversion element and the sensitivity of the composite of the photoelectric conversion element and phosphor change depending on the temperature, measures against temperature changes are required.

As a countermeasure against this problem, there is a method of keeping the detector at a constant temperature as shown in FIG. 4 (see Japanese Patent Application No. 1-233260). This will be explained below.

In FIG. 4, incident X-rays are converted into light by a phosphor (generally a scintillator) 102, and then a photoelectric conversion element (generally a silicon photodiode) 10.
1 is converted into current. This current is further applied to the bonding wire 103, the conductive pattern 106 on the substrate 104,
Signal processing device 20 via connector 107 and wiring 108
I am guided by 1.

[0006] Here, the substrate 104 is fixed within a container 105. A heater 2 is provided on the outer surface of the bottom of this container 105.
02 and temperature sensor 203 are fixed. Also container 10
A heat insulating material 205 is installed around the outer periphery of the heat insulating material 5, and a temperature controller 204 is installed outside the heat insulating material 205.

The temperature controller 204 is a temperature sensor 20
The temperature detected in step 3 is compared with the reference temperature, and the heater 202 is turned on and off accordingly to control the temperature. Thereby, the inside of the container 105 is kept at a constant temperature. Furthermore, the thermal resistance is increased by the heat insulating material 205 to reduce the influence of external temperature.

[0008] The signal processing device 201 converts the sent current signal into a voltage, performs A/D conversion, performs various general processing (Log conversion, offset correction, etc.), and then converts the current signal (not shown) into a voltage. It is stored in the storage device as measurement data that has undergone general processing.

[0009]

The conventional technique shown in FIG. 4 has the following problems. (1) Since the temperatures of the phosphor 102 and the photoelectric conversion element 101 are not directly measured, errors are likely to occur due to temperature fluctuations in the outside air. As the temperature sensor 203, for example, it is possible to fix a thermocouple or a temperature sensor to the back surface of the substrate 104, but a multi-channel X-ray detector for an X-ray CT device depends on the characteristics of each detection element (channel). There is a strict requirement for variation reduction, and if the above thermocouples and temperature sensors are directly attached,
It is difficult to install metal near the detection element, which may scatter the radiation and introduce noise. Therefore, the temperature of the photoelectric conversion element 101 is not directly measured as described above, and errors are likely to occur due to temperature fluctuations in the outside air. (2) Since the heater 202 is used, the temperature of the phosphor 102 and the photoelectric conversion element 101 increases, and the temperature of the photoelectric conversion element 10 increases.
As the dark current of 1 increases, their sensitivity decreases,
S/N decreases. (3) Since the heat insulating material 205 is used, the entire device becomes large. (4) There is a risk of fire occurring due to overheating of the heater 202. (5) The number of parts is large and the configuration is complicated. The purpose of the present invention is to obtain measurement data without errors due to temperature fluctuations in the outside air without using a constant temperature device (consisting of a heater, temperature sensor, temperature controller, heat insulating material, etc.), and to achieve a simple and compact configuration. Another object of the present invention is to provide a radiation measuring device that is free from the risk of fire and can obtain highly accurate measurement data with a good S/N ratio.

Another object of the present invention is to perform constant temperature control using a signal based on the dark current of a photoelectric conversion element as a feedback signal for constant temperature control without using a temperature sensor, thereby increasing the accuracy of temperature control. An object of the present invention is to provide a radiation measuring device that can obtain high measurement data.

[0011]

[Means for Solving the Problems] The above object is to provide a phosphor that converts radiation into fluorescence, a photoelectric conversion element that is arranged corresponding to the phosphor and converts the fluorescence into an electric current, and a photoelectric conversion element that converts the fluorescence into an electric current. A radiation measurement device comprising a container for storing a conversion element and a signal processing device for measuring and processing the current, which measures and retains the dark current of the photoelectric conversion element a certain time before radiation exposure. This is achieved by providing a temperature correction processing device that calculates the temperature of the photoelectric conversion element at the time of radiation exposure from the value and performs temperature correction on the measurement data at the time of radiation exposure.

[0012] The other object is to provide a phosphor that converts radiation into fluorescence, a photoelectric conversion element disposed corresponding to the phosphor and converting the fluorescence into electric current, and a housing for the phosphor and the photoelectric conversion element. A radiation measurement device comprising: a container for heating, a constant temperature device for maintaining the inside of the container at a constant temperature, and a signal processing device for measuring and processing the current,
Measure and hold the dark current of the photoelectric conversion element a certain time before radiation exposure, determine the temperature of the photoelectric conversion element at the time of radiation exposure from that value, and use a signal corresponding to the value as a feedback signal for constant temperature control. This is achieved by providing a dark current feedback device to the constant temperature device.

[0013]

[Operation] The dark current of a photoelectric conversion element (silicon photodiode, etc.) changes at a constant rate with respect to temperature changes, as shown in equation (1) below.

[0014]

[Math 1]

##EQU1## where Id(t) is a dark current at a temperature of t.degree. C., Id0 is a dark current at a temperature of t0.degree. C., and α is a temperature coefficient. The value of α is, for example, about 0.07 for a silicon photodiode, and when the temperature increases by 10° C., the dark current approximately doubles.

[0016] By measuring the dark current in this manner, the temperature of the photoelectric conversion element can be determined. If this principle is applied to the temperature characteristic correction means of a radiation measuring device, correction can be made more accurately than before.

[0017] The temperature coefficient α is determined in advance at a specific temperature t°C,
The dark current at t0° C. is actually measured and calculated using equation (1). Then, from the obtained α and the measured dark current, the temperature can be obtained conversely.

The temperature correction processing device measures and holds the dark current of the photoelectric conversion element a certain period of time before radiation exposure, and calculates the dark current of the photoelectric conversion element at the time of radiation exposure from that value using the above equation (1). Calculate the temperature and perform temperature correction on the measurement data during radiation exposure. This makes it possible to obtain measurement data without errors caused by temperature fluctuations in the outside air without using a constant temperature device (heater, temperature sensor, temperature controller, insulation material, etc.), making it possible to simplify the configuration and downsize, and to prevent fires from occurring. There is no danger, and highly accurate measurement data with good S/N ratio can be obtained.

Further, the dark current feedback device measures and holds the dark current of the photoelectric conversion element a certain period of time before radiation exposure, and calculates the value of the dark current of the photoelectric conversion element at the time of radiation exposure from the measured value according to the above equation (1). The temperature of is determined, and a signal corresponding to that value is given to the constant temperature device as a feedback signal for constant temperature control. As a result, it is possible to perform constant temperature control without using a temperature sensor, using a signal based on the dark current of the photoelectric conversion element as a feedback signal for constant temperature control, increasing the precision of temperature control and obtaining highly accurate measurement data. Become.

[0020]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a radiation measuring device according to the present invention. In this Figure 1, 101 to 10
8 are the same as in FIG. Similarly to FIG. 4, 201 also represents a signal processing device, but in the present invention, it also constitutes a part of a temperature correction processing device to be described later. 111 measures and holds the dark current of the photoelectric conversion element 102 a certain time before radiation exposure, calculates the temperature of the photoelectric conversion element 102 at the time of radiation exposure from that value, and performs temperature correction on the measured data at the time of radiation exposure. This is a temperature correction processing device that performs

The temperature correction processing device 111 includes a dark current data holding circuit 109 that measures (measures as offset data) and holds the dark current of the photoelectric conversion element 101 immediately before radiation exposure, and a dark current data holding circuit 109 that measures the dark current of the photoelectric conversion element 101 immediately before radiation exposure. a temperature characteristic data memory 110 in which temperature characteristic data for determining the temperature of the photoelectric conversion element 101 at the time of radiation exposure from the value is recorded;
It is composed of a signal processing device 201. The signal processing device 201 performs general correction processing similar to that in the prior art, and in the present invention, the dark current data holding circuit 10
9 and the data from the temperature characteristic data memory 110, the temperature of the photoelectric conversion element 101 is determined by the above equation (1), and thereby temperature correction is performed on the measurement data at the time of radiation exposure.

Here, the temperature correction processing device 111 also performs temperature correction of the sensitivity of the composite of the photoelectric conversion element 101 and the phosphor 102, and the temperature characteristic data memory 110 stores temperature characteristic data of the photoelectric conversion element 101. In addition, temperature characteristic data of the sensitivity of the composite of the photoelectric conversion element 101 and the phosphor 102 is also recorded.

Next, the operation will be explained. The incident X-rays are converted into light by the phosphor 102, and further converted into electric current by the photoelectric conversion element 101. This current is further applied to the bonding wire 103 and the conductive pattern 10 on the substrate 104.
6, the signal is sent to the signal processing device 201 and the dark current data holding circuit 109 via the connector 107 and the wiring 108. The signal processing device 201 converts the sent current signal into a voltage, performs A/D conversion, performs various general processing (Log conversion, offset correction, etc.), and then converts the current signal into a voltage (not shown). The measured data is stored as processed data.

As shown in FIG. 2, the dark current data holding circuit 109 stores dark current data (dark current value) as offset data when measuring offset data (including dark current data) immediately before X-ray exposure. do.

Further, the signal processing device 201, as a signal processing section of the temperature correction processing device 111, processes offset data (dark current value) measured according to the sequence shown in FIG.
Based on the temperature characteristic data of the dark current stored in the temperature characteristic data memory 110, the temperature of the photoelectric conversion element 101 is determined using the above equation (1), and The measured X-ray data is corrected using the temperature characteristic data of the sensitivity of the composite of the conversion element 101 and the phosphor 102.

According to the above-mentioned invention, it is possible to obtain measurement data free from errors due to temperature fluctuations in the outside air without using a constant temperature device (heater, temperature sensor, temperature controller, heat insulating material, etc.) as in the prior art.

It goes without saying that the configuration of the temperature correction processing device 111 is not limited to the above embodiment. next,
Another embodiment of the invention is shown in FIG. FIG. 3 is a configuration diagram showing an embodiment of a radiation measuring device according to another invention. In this FIG. 3, 101 to 108 and 201 are the same as in FIG. 4, respectively.

301 measures and holds the dark current of the photoelectric conversion element 102 a certain time before radiation exposure, calculates the temperature of the photoelectric conversion element 102 at the time of radiation exposure from that value, and generates a signal according to the value. This is a dark current processing device that provides a constant temperature device (consisting of a heater 202, a temperature controller 204, a heat insulating material 205, etc.) as a feedback signal for constant temperature control.

Next, the operation will be explained. The incident X-rays are converted into light by the phosphor 102, and further converted into electric current by the photoelectric conversion element 101. This current is further applied to the bonding wire 103 and the conductive pattern 10 on the substrate 104.
6, the signal is sent to the signal processing device 201 and the dark current processing device 301 via the connector 107 and wiring 108.

The signal processing device 201 converts the sent current signal into a voltage, performs A/D conversion, performs various general processing (Log conversion, offset correction, etc.), and then
It is stored in a storage device (not shown) as measurement data that has undergone general processing.

[0031] The dark current processing device 301 measures and holds the dark current of the photoelectric conversion element 102 a certain period of time before radiation exposure.
The temperature of the photoelectric conversion element 102 at the time of radiation exposure is determined from the value, and a signal corresponding to the value is given as a feedback signal for constant temperature control to the constant temperature device, specifically, to the temperature controller 204 of the constant temperature device.

The temperature controller 204 compares the temperature feedback signal with a reference temperature signal, and thereby controls the heater 202 by turning it on and off or continuously controlling the power. Thereby, the inside of the container 105 is kept at a constant temperature.

According to the present invention described above, it is possible to accurately measure the temperature of the X-ray detector main body (phosphor 102 and photoelectric conversion element 101 portion), which could not be measured with the conventional technology, and substantial temperature control accuracy can be achieved. can be improved.

It should be noted that all of the above-mentioned embodiments have been explained for one channel of the X-ray detector, but in reality, the above-mentioned operation is performed for all channels.

[0035]

[Effects of the Invention] As explained above, the present invention has the following effects. First, according to the invention shown in FIG.
It has the following effects. (1) A constant temperature device consisting of a heater, a temperature sensor, a temperature controller, a heat insulator, etc. is not required, and the structure is simple and compact. (2) Fire safety is improved by eliminating the heater. (3) The temperature of the photoelectric conversion element is determined based on the dark current of the photoelectric conversion element without using a temperature sensor, and temperature correction is performed for the measurement data during radiation exposure, so high-precision measurement data with good S/N is obtained. is obtained. Moreover, in the case of a multi-channel X-ray detector, the dark current (
Temperature) is measured as normal offset data, so it can be accurately determined as the dark current (temperature) for each X-ray detection element (channel) without adding a special component like in conventional temperature sensors. Therefore, changes in characteristics due to temperature can be corrected individually and with high precision.

Furthermore, the invention shown in FIG. 3 has the following effects. (1) Temperature sensor becomes unnecessary. (2) The temperature of the photoelectric conversion element is determined based on the dark current of the photoelectric conversion element without using a temperature sensor, and constant temperature control is performed using this as a feedback signal for constant temperature control, so high-precision measurement data with good S/N is obtained. is obtained. Moreover, in the case of a multi-channel X-ray detector, the dark current (temperature) of each X-ray detection element (channel) is measured as normal offset data, so it is not added as a special component like the temperature sensor of the conventional technology. At least each X-ray detection element (channel)
It is possible to accurately grasp the dark current (temperature) of the temperature, and to correct characteristic changes due to temperature individually and with high precision.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the device of the present invention.

FIG. 2 is a diagram showing a sequence of data measurement in the apparatus of the present invention.

FIG. 3 is a configuration diagram showing an embodiment of another inventive device.

FIG. 4 is a configuration diagram showing a conventional device.

[Explanation of symbols] 101 Photoelectric conversion element 102 Phosphor 104 Board 105 Container 109 Dark current data retention circuit 110 Temperature characteristic data memory 111 Temperature correction processing device 201 Signal processing device 202 Heater 203 Temperature sensor 204 Temperature controller 205 Insulation material 301 Dark current processing device

Claims (2)

[Claims] 1. A phosphor that converts radiation into fluorescence, a photoelectric conversion element disposed corresponding to the phosphor and converts the fluorescence into an electric current, and a container that stores the phosphor and the photoelectric conversion element. In a radiation measuring device comprising a signal processing device for measuring and processing the current, the dark current of the photoelectric conversion element is measured and held a certain time before radiation exposure, and the dark current of the photoelectric conversion element is determined based on the value at the time of radiation exposure. A radiation measuring device characterized by comprising a temperature correction processing device that calculates the temperature of the photoelectric conversion element and performs temperature correction on measurement data during radiation exposure. 2. A phosphor that converts radiation into fluorescence, a photoelectric conversion element disposed corresponding to the phosphor and converting the fluorescence into electric current, and a container containing the phosphor and the photoelectric conversion element. In a radiation measuring device comprising a constant temperature device that maintains the inside of the container at a constant temperature and a signal processing device that measures and processes the current, the photoelectric conversion element is darkened for a certain period of time before radiation exposure. Measures and holds current,
A radiation measurement device characterized by comprising a dark current feedback device that determines the temperature of the photoelectric conversion element at the time of radiation exposure from the value and provides a signal corresponding to the value to the constant temperature device as a feedback signal for constant temperature control. .