JPH1073668A - X-ray detector constant temperature device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a detector case constant temperature quickly and accurately even in the condition of outer temperature variation in a wide range and avoid ring arch fact from an X-ray detector. SOLUTION: Provided are a first constant temperature heater 12 fixed at a part of a detector case, a first temperature sensor 13 arranged outside and in the vicinity of the detector case, a first temperature control unit 11-b on-off controlling the power source supplying to the first constant temperature heater 12 in accordance with the measured air temperature around the detector with the first temperature sensor and elevating the detector case temperature to the first set temperature TL, a second constant temperature heater 9 fixed at a part of the detector case, a second temperature sensor 10 fixed at a part of the detector case, and a second temperature control unit 11-a on-off controlling the power source supplying to the second constant temperature heater 9 in accordance with the measured air temperature around the detector with the first temperature sensor and maintaining the detector case temperature within the first set temperature TL and the second set temperature TH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermostat for an X-ray detector used for X-ray measurement, and more particularly, to an X-ray of a medical X-ray CT apparatus in which ring artifacts are likely to be generated due to a change in outside air temperature. The present invention relates to an X-ray detector thermostat suitable for improving the characteristics of a detector.

[0002]

2. Description of the Related Art An X-ray detector (hereinafter, also simply referred to as a detector) of a medical X-ray CT apparatus has a large number of detection elements of 500 channels or more, and each channel is constituted by a change in outside temperature of the detector. Due to the thermal expansion of the components, the pitch pitch between the individual channels is slightly changed. Then, there is a problem that the subtle pitch interval shift changes the sensitivity characteristic of each channel and causes ring artifacts.

[0003] Conventionally, a technique for keeping the detector at a constant temperature has been known to solve this problem. FIG. 8 shows a typical example of such a constant temperature technique (an example of application to an ionization chamber type detector). As shown in the figure, a constant temperature heater 9 and a temperature sensor 10
Is incorporated in a part of the detector case 3. The temperature control unit 11 reads the temperature by the temperature sensor 10 and supplies power (ON) to the heater 9 when the temperature is equal to or lower than the set temperature TH as shown in FIG. 9, and supplies power to the heater 9 when the temperature is equal to or higher than the set temperature TH. The temperature of the detector case 3 is kept constant by performing the temperature control for shutting off (OFF).

[0004]

The above prior art has the following problems. FIG. 10 shows a typical temporal change in the temperature of the detector case 3 after the heater 9 is turned on in the conventional apparatus. In FIG. 10, the case where the optimum heater heat capacity is selected is shown by a curve A. In this case, after the heater is turned on, the detector case temperature gradually rises and shows a saturation tendency near the set temperature TH. When the temperature reaches the temperature TH, the heater 9 is turned off, and when the temperature decreases, the heater 9 is turned on again. Therefore, the set temperature T
Nearly constant temperature can be maintained while showing a gradual temperature change near H.

[0005] Curve (b) is an example in the case where the temperature outside the detector is lower. In this case, the heat capacity of the heater becomes insufficient and the detector cannot be maintained at the target set temperature TH. Therefore, there is a case where a plurality of heaters 9 are arranged to control the temperature of the detector to be constant. In this case, temperature non-uniformity occurs between the individual control device setting detector case parts, and a change in sensitivity at the detector occurs. It becomes more noticeable and causes noticeable ring artifacts. It is also conceivable to perform a sensitivity correction measurement (calibration) at a time when the outside air temperature is low. However, this method requires a sensitivity when the outside air temperature rises and the measurement is performed in the original normal detector temperature state. On the contrary, there is a problem that the ring artifact is generated due to the mismatch of the correction.

A curve C shows an example in which the heater capacity is further increased. In this case, even when the outside air temperature is lower, there is a sufficient ability to reach the set temperature TH, but conversely, when the temperature reaches the TH temperature and the heater is turned off, the detector temperature rise does not stop immediately. The time delay in the operation and the temperature fluctuation range of the temperature increase become large, causing a problem that sufficient temperature control cannot be performed.

An object of the present invention is to provide an X-ray detector capable of rapidly and accurately maintaining the temperature of a detector case even in a wider range of outside air temperature change conditions, and obtaining a high-quality X-ray CT image free of ring artifacts. An object of the present invention is to provide an X-ray detector thermostat that can be performed.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide at least one first constant temperature heater attached to a part of a detector case, and at least one first constant temperature heater arranged at a position near the outside of the detector case. ON / OFF control of the first temperature sensor and the power supply to the first constant temperature heater in accordance with the measurement value of the ambient temperature around the detector by the first temperature sensor to set the detector case temperature to the first set temperature A first temperature control unit for raising the temperature, one or more second constant temperature heaters attached to a part of the detector case, and one or more second temperatures attached to a part of the detector case. ON / OFF control of a sensor and a power supply to the second constant temperature heater according to a measured value of a detector case temperature by the second temperature sensor to control the detector case temperature to the first set temperature and the second set temperature. Keep it within the temperature range It is achieved by providing a second temperature control unit.

By setting the first set temperature for measuring the ambient temperature around the detector to be lower than the second set temperature for measuring the temperature of the detector case, when the external temperature is low, both the first and second constant temperature heaters are used. ON operation. That is, it operates with a high heat capacity, so that the temperature of the detector case is quickly raised even in a state of a lower outside air temperature, so that the minimum lower limit temperature at which the second constant temperature heater functions is ensured. After reaching the first set temperature, only the second constant temperature heater, which has the optimal heat capacity for the temperature saturation of the detector, is turned ON, and the ON / OFF control of the second constant temperature heater is performed by the temperature saturation of the detector case. The temperature is set to the second set temperature immediately before reaching the region. For this reason, the detector case temperature gradually reaches the second set temperature by the second constant temperature heater, and the O 2 of the second constant temperature heater thereafter.
Even at the time of the N / OFF operation, the temperature fluctuation of the detector is small and the constant temperature control can be performed with high accuracy.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, but before that, an example of an X-ray CT scanner provided with an X-ray detector to which the present invention is applied will be described. This will be described with reference to FIG.

FIG. 7 is a front view showing an example of the X-ray CT scanner from the bed side. As shown in FIG.
The inside of the scanner 100 is configured as follows. That is, the X-ray detector 10 is located at a position facing the X-ray tube 101.
4 are arranged, and the X-ray emitted from the X-ray tube 101 is
The X-ray beam 103 is narrowed by the collimator unit 102 in the slice direction (the depth direction of the scanner).

The detector 104 converts the X-ray beam 103 transmitted through the subject (not shown) into an electric signal for each channel. These electric signals are transmitted to the detection circuit unit 10
5 and the analog signal is amplified by A /
The signals are sequentially converted into digital signals by a D conversion circuit.

The X-ray tube 101, collimator unit 102, detector 104 and detection circuit unit 105 are arranged and fixed on a rotating base 106.
Reference numeral 6 is fixed to the scanner base 108 by a rotating bearing 107 having a bearing structure.

As described above, the rotation base 106 can freely rotate, and therefore, the X-ray tube 101,
The collimator unit 102, the detector 104, and the detection circuit unit 105 rotate integrally, and can measure from the entire circumference of the subject. These measurement data are sequentially sent to an image processing device (not shown) to perform image reconstruction. Reference numeral 109 denotes a scanner stand.

FIG. 1 is a configuration diagram showing an X-ray detector to which a first embodiment of an X-ray detector thermostat according to the present invention is applied. Here, a representative ionization chamber type detector is taken as an example of the X-ray detector, and a cross section in the X-ray slice direction is shown.

In FIG. 1, an X-ray beam 103 enters from an X-ray entrance of a detector case 3 and reaches a signal electrode plate 6 in the detector case 3. The signal electrode plate 6 and a high-voltage electrode plate (not shown) arranged parallel to both side surfaces of the signal electrode plate 6 are fixed by an insulating plate 5 for supporting the electrode plate. The electrode plate and the insulating plate 5 are fixed to a fixed base 4 as a detector block which is an aggregate of a plurality of detection elements, and the fixed base 4 is fixed to the detector case lid 1 in a form of fastening the signal extraction board 2 together. Have been. Therefore, when the detector case lid 1 and the detector case 3 are completely fixed with screws or the like, the space in the detector case 3 becomes a sealed state,
This space is filled with an inert gas such as xenon.

As a result, the x-ray beam 103 that has reached the signal electrode plate 6 ionizes and decomposes the xenon gas, so that the ionized ions at this time are applied to the signal electrode plate 6 by the voltage applied to the high voltage electrode plate. It reaches and is detected as a current signal. The ionization signal of each of these detection channels is supplied to a signal extraction line 7.
Is led to the conductor pattern on the signal extraction board 2 by
A current signal is extracted to the outside of the detector by the detector connector (signal extraction connector) 8 individually.

Here, the first temperature sensor 13 is disposed in a peripheral space which is not in contact with the detector for use in measuring the outside air temperature, and the first constant temperature heater 12, the second constant temperature heater 9 and the second constant temperature heater 9 are provided.
The temperature sensor 10 is attached to a part of the detector case 3 (a part of the detector case cover 1 or the fixing base 4 can be attached). Further, in order to further improve the constant temperature capability, the heat insulating material 14 may be disposed so as to cover the detector lid 1 and the detector case 3. Each of these constant temperature heaters 12 and 9 and the temperature sensor 10 has an independent first temperature control unit 11-b.
And the second temperature control unit 11-a are connected, and the heater 1
A commercial power supply (100 V AC power supply) or a DC power supply as the power supplies 2 and 9 is supplied. Here, as the constant temperature heaters 9 and 12, for example, a silicon rubber heater made by OM Co., which is excellent in bendability in a sheet state, is a temperature control unit 11-.
As a and 11-b, for example, E5CS-Q manufactured by OMRON Corporation
A 1G or other temperature controller is suitable.

The temperature control units 11-a and 11-b
Detects the temperatures of the temperature sensors 10 and 13 and supplies power (ON) to the heaters 9 and 12 when the temperature is lower than a preset temperature individually set, and supplies power to the heaters 9 and 12 when the temperature is higher than the preset temperature. The operation of stopping (OFF) the power supply is repeated. Here, the heater ON / OFF control set temperature is set individually for both, and the temperature control as shown in FIG. 2 is performed.

That is, the first temperature control unit 11-b
Is set to the first set temperature TL, and the second set temperature TH higher than the first set temperature TL is set to the second temperature control unit 11-a. And the second temperature control unit 1
The set temperature TH in 1-a is set to a value slightly lower than the temperature at which the temperature rise of the detector case 3 reaches the saturation state or to a temperature definitely lower than the saturation temperature by the ON operation of the second constant temperature heater 9, and It is important that the first set temperature TH does not exceed the second set temperature TH even when both the first and second constant temperature heaters 12 and 9 are ON. Therefore, the first and second constant temperature heater capacities and the first and second set temperature values are optimized according to the shape of each detector and the outside air temperature of the detector.

The detailed operation of the constant temperature structure will be described below. First, the temperatures of the detector case lid 1, the detector case 3, and the fixed base 4 before the heater ON operation are substantially the same as the outside air temperature. Therefore, there are the following five states of patterns A to E as operating states in the temperature control.

Pattern A state: when the outside air temperature is constantly below the first set temperature TL, both the first and second constant temperature heaters 12 and 9 are turned on, and the detector case temperature is rapidly increased by the high capacity heater. However, when the detector case temperature approaches the second set temperature TH, the temperature rise becomes gentle, and after reaching the second set temperature TH, only the second constant temperature heater 9 repeats the ON / OFF operation.

Pattern B state: First, when the outside air temperature is equal to or lower than the first set temperature TL, and then becomes equal to or higher than the first set temperature TL and equal to or lower than the second set temperature TH. Both the first and second constant temperature heaters 12 and 9 are turned on. The detector case temperature is quickly increased by the high-capacity heater due to the ON operation. However, when the detector case temperature approaches the second set temperature TH, the temperature rise becomes gentle and reaches the second set temperature TH temperature. After that, only the second constant temperature heater 9 repeats the ON / OFF operation. Thereafter, when the outside air temperature becomes equal to or higher than the first set temperature TL, the first constant temperature heater 12 repeats the OFF operation, and only the second constant temperature heater 9 repeats the ON / OFF operation.

Pattern C state: First, when the outside air temperature fluctuates around the first set temperature TL, both the first and second constant temperature heaters 12 and 9 are turned on / off.
Repeat the operation.

Pattern D state: When the outside air temperature fluctuates from the first set temperature TL to the second set temperature TH from the beginning, the first constant temperature heater 12 is constantly turned off. Only the second constant temperature heater 9 is turned ON to raise the detector case temperature,
When the detector case temperature approaches the second set temperature TH, the temperature rise becomes gentle, and after reaching the second set temperature TH, only the second constant temperature heater 9 repeats the ON / OFF operation.

Pattern E state: when the outside air temperature fluctuates above the second set temperature TH from the beginning Both the first and second constant temperature heaters 12 and 9 are turned off. The detector case temperature fluctuates with the outside air temperature.

Generally, by setting the second set temperature TH in the constant temperature detector to a value larger than the maximum value of the outside air temperature, the operation state of the pattern E can be basically eliminated. With the above operation, the temperature of the detector case can be quickly and accurately adjusted even under a wider range of outside temperature change conditions.

FIG. 3 is a configuration diagram showing an X-ray detector to which the second embodiment of the present invention is applied. 3, the same reference numerals as those in FIG. 2 indicate the same or corresponding parts. In the example of FIG. 1, a commercially available product is used as the first temperature control unit 11-b and the second temperature control unit 11-a, and the temperature is controlled independently. The temperature control unit (heater feed reduction switching type temperature control unit) 11-1 here incorporates various temperature sensor amplifier circuits, a temperature determination circuit, and a control circuit such as a heater power supply relay circuit and the like. It differs from the example of FIG. 1 in that control is enabled. In addition to logic-based hardware control, temperature control by a program using an industrial microcomputer (such as an SH microcomputer manufactured by Hitachi, Ltd.) incorporating a temperature sensor can be supported.

Here, the first and second temperature sensors 13, 1
0, the temperature is detected individually by both of them, that is, ON / OFF control of the first constant temperature heater 12 according to the temperature measurement value of the first temperature sensor 13, and according to the temperature measurement value of the second temperature sensor 10. In addition, a temperature control function for controlling ON / OFF of the second constant temperature heater 9 is provided. That is, in the temperature control unit 11-1, the first set temperature TL and the second set temperature TH are set, and the first and second temperature sensors 13, 1 are set.
When the measured temperature value of 0 is lower than the first set temperature TL and the second set temperature TH, power is supplied to the heaters 12 and 9 (O
N), and when the temperature is higher than the first set temperature TL and the second set temperature TH, the power supply to the heaters 12 and 9 is stopped (OF).
F) Repeat the operation (see FIG. 2). Therefore, in this embodiment, the same temperature control as in the embodiment of FIG. 1 is possible.

In the examples shown in FIGS. 1 and 3, a plurality (two in this case) of constant temperature heaters 12 and 10 are used as constant temperature heaters, but the invention is not limited thereto. For example, as shown in FIG. 4, a plurality of (here, two circuits) heating elements 9-9 are provided in one common heater sheet 9-1.
2, 9-3, and a single heating element switching type heater 91 in which individual heating elements 9-2, 9-3 are provided with independent power supply paths 9-4, 9-4. Good. In this case, a heating element 9-2 is used instead of the first constant temperature heater 12, and a heating element 9-3 is used instead of the second constant temperature heater 9. As a basic operation, the temperature control unit 11-1
Detects the outside air temperature by the first temperature sensor 13 and supplies power to the heating element 9-2 when it is lower than the first set temperature TL (ON), and generates heat when it is higher than the first set temperature TL. The operation of stopping (OFF) the power supply to the body 9-2 is repeated. Similarly, the detector case temperature is detected by the second temperature sensor 10, and when it is lower than the second set temperature TH, power is supplied to the heating element 9-3 (ON), and conversely, the second case is turned on.
When the temperature is higher than the set temperature TH, the operation of stopping (OFF) the power supply to the heating element 9-3 is repeated. Therefore, in this embodiment, the same temperature control as in the embodiment of FIG. 1 is possible.

FIG. 5 is a configuration diagram showing an X-ray detector to which the third embodiment of the present invention is applied. 5, the same reference numerals as those in FIG. 2 indicate the same or corresponding parts. Here, the temperature control unit (heater power supply power switching type temperature control unit) 11-2 detects the detector case temperature by the temperature sensor 10 and supplies power supply power (power supply) to the constant temperature heater 9 under each set temperature condition. Power) to supply power to the constant temperature heater 9. The power supply power may be controlled by a method of controlling the power supply voltage or the power supply current, or both.

That is, as a basic operation, the temperature control unit 11-2 first sets the power supplied to the constant temperature heater 9 to high power WH, and quickly raises the temperature of the detector case due to the high calorific value of the heater 9. After the detector case temperature reaches the first set temperature TL, the power supply is reduced to WL and changed to a gradual rise in temperature. The detector case temperature is equal to the second set temperature T
H, the power supply of the heater 9 is completely set to 0, and then the ON / OFF operation (HL) near the second set temperature TH is performed.
Power supply) is repeated.

FIG. 11 is a graph showing an example of a temporal change of the detector case temperature after the constant temperature heater is turned on in the apparatus of the present invention.

In the above example, an ionization chamber type detector is taken as an example of an X-ray detector to which the present invention is applied. However, the present invention can be applied to a solid state detector as well.
In addition, the temperature setting and the supply power control (switching) method are binary threshold control for simplicity. However, the threshold value control may be set to a plurality of values, or a curve temperature may be used instead of stepwise control. According to this, more precise temperature control for various temperatures becomes possible.

[0035]

As described above, according to the present invention, the temperature of the detector case can be quickly and accurately adjusted even under a wider range of outside air temperature change, and a high-quality X-ray CT image free from ring artifacts can be obtained. There is an effect that the X-ray detector can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an X-ray detector to which a first embodiment of the device of the present invention is applied.

FIG. 2 is an operation explanatory view of the apparatus of the present invention shown in FIG. 1;

FIG. 3 is a configuration diagram illustrating an X-ray detector to which a second embodiment of the device of the present invention is applied.

FIG. 4 is a plan view showing another example of the constant temperature heater in the examples of FIGS. 1 and 3.

FIG. 5 is a configuration diagram showing an X-ray detector to which a third embodiment of the device of the present invention is applied.

6 is an operation explanatory view of the device of the present invention shown in FIG. 5;

FIG. 7 shows an X-ray having an X-ray detector to which the apparatus of the present invention is applied.
It is a front view showing an example of a line CT scanner.

FIG. 8 is a configuration diagram showing an X-ray detector including a conventional device.

FIG. 9 is an operation explanatory diagram of the conventional device shown in FIG. 8;

FIG. 10 is a graph showing a temporal change of a detector case temperature after a constant temperature heater is turned on in a conventional apparatus.

FIG. 11 is a graph showing a temporal change of a detector case temperature after the constant temperature heater is turned on in the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detector case cover 2 Signal extraction board 3 Detector case 4 Fixing stand 5 Insulating plate 6 Signal electrode plate 7 Signal extraction line 8 Detector connector (signal extraction connector) 9 Second constant temperature heater 91 Heating element switching type heater 9- DESCRIPTION OF SYMBOLS 1 Heater sheet 9-2, 9-3 Heating element 10 2nd temperature sensor 11 Temperature control unit 11-a 2nd temperature control unit 11-b 1st temperature control unit 11-1 Heater feed reduction switching type temperature control unit 11- 2 Heater power supply switching type temperature control unit 12 First constant temperature heater 13 First temperature sensor 14 Insulation material 100 X-ray CT scanner 101 X-ray tube 102 Collimator unit 103 X-ray beam 104 X-ray detector 105 Detection circuit unit 106 Rotation base 107 Rotation bearing 108 Scanner base 109 Scanner stand

Claims (3)

[Claims] 1. A device mounted on a part of a detector case.
One or more first temperature-maintaining heaters, one or more first temperature sensors arranged at positions near the outside of the detector case, and a detector ambient temperature measured by the first temperature sensor. Turn ON / OF the power supplied to the first constant temperature heater
A first temperature control unit for performing F control to raise the detector case temperature to a first set temperature; one or more second constant temperature heaters attached to a part of the detector case; One or more second temperature sensors attached to a part thereof and a detector case temperature detected by the second temperature sensor detected by ON / OFF control of a power supply to the second constant temperature heater in accordance with a measured value. Vessel case temperature to the first
An X-ray detector thermostat, comprising: a set temperature and a second temperature control unit for maintaining the set temperature within a range between the set temperature and the second set temperature. 2. A plurality of constant temperature heaters attached to a part of a detector case, one or more first temperature sensors arranged at a position near the outside of the detector case, and the detector case. ON / OFF control of power supply to one or more second temperature sensors attached to a part of the heater and power supply to the plurality of constant temperature heaters in accordance with a measurement value of the ambient temperature around the detector by the first temperature sensor. The detector case temperature is raised to a first set temperature, and after reaching the first set temperature, the power supply path to a predetermined constant temperature heater among the plurality of constant temperature heaters is cut off to reduce the number of operating heaters. During this time, the power supply to the constant temperature heater is controlled to be ON / OFF in accordance with the measured value of the detector case temperature by the second temperature sensor to control the detector case temperature between the first set temperature and the second set temperature. To keep it within the range An X-ray detector thermostat comprising: a power supply reduction switching type temperature control unit. 3. A constant temperature heater includes a plurality of heating elements arranged on a single heater sheet, a power supply path formed independently for each heating element, and power supply switching control for each power supply path. The X-ray detector thermostat according to claim 1 or 2, wherein the heater is a heating element switching type heater capable of combining a plurality of types of heating capacities.