JP2023169908A - radiation detector - Google Patents

Abstract

To suppress noise inflow from peripheral parts to an X-ray sensor while taking into account the thickness constraints of a cassette device.SOLUTION: A radiation detector 1 includes an X-ray sensor 26 that detects X-ray irradiation, a shield 28 that reduces electro-magnetic noise to the X-ray sensor 26, and a base 31 on which the X-ray sensor 26 is assembled. The X-ray sensor 26, the shield 28, and the base 31 are respectively arranged so that a distance (H1) between the X-ray sensor 26 and the shield 28 in the thickness direction of the radiation detector 1 is larger than a distance (H2) between the shield 28 and the base 31.SELECTED DRAWING: Figure 5

Description

The present invention relates to radiation detectors.

Conventionally, a lightweight and thin radiation detector called a flat panel detector (FPD) has been used to take radiation (hereinafter also referred to as X-ray) images. Regarding this radiation detector, for example, Patent Document 1 discloses a technique in which a housing that covers the internal components constitutes a shield that protects the internal components from external electrical noise.

Patent No. 5580971

However, in the technology disclosed in Patent Document 1, when considering the thickness of the cassette device (15 mm (+1/-2 mm; in case of cassette size 14 inch x 17 inch)) standardized by ISO4090 and JIS Z 4905, Space for storing internal parts within the housing is limited. As a result, for example, the X-ray sensor, which is an internal component, is likely to be capacitively coupled with peripheral components (surrounding internal components), and if the distance between the X-ray sensor and the peripheral components changes due to vibration, the capacitive component will increase. This causes noise to flow into the X-ray sensor, resulting in false detection of X-ray irradiation.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to suppress the inflow of noise from peripheral components to the X-ray sensor while taking into account the limitations of the thickness of the cassette device.

In order to solve the above problems, the radiation detector according to the present invention includes:
an X-ray sensor that detects X-ray irradiation;
a shield that reduces electromagnetic noise to the X-ray sensor;
a base on which the X-ray sensor is assembled;
A radiation detector comprising:
Each of the X-ray sensor, the shield, and the base is arranged such that the distance between the X-ray sensor and the shield in the thickness direction of the radiation detector is larger than the distance between the shield and the base. It is arranged.

According to the present invention, it is possible to suppress noise from flowing into the X-ray sensor from peripheral components while taking into account the limitations of the thickness of the cassette device.

FIG. 1 is a perspective view showing the appearance of a radiation detector according to the present embodiment. 2 is a sectional view taken along line XX in FIG. 1. FIG. FIG. 2 is a plan view showing the configuration of a substrate. FIG. 2 is a block diagram showing an equivalent circuit of a radiation detector. FIG. 3 is an enlarged partial schematic sectional view of a portion of the X-ray sensor unit in FIG. 2; FIG. 6 is a diagram illustrating an example of an X-ray sensor unit in which a capacitive component occurs between a base and a shield. FIG. 6 is a diagram illustrating an example of equal potential processing in which the potentials of the base and the shield are made the same potential. FIG. 6 is a diagram illustrating an example of equal potential processing in which the potentials of the base and the shield are made the same potential. FIG. 6 is a diagram showing an example of an X-ray sensor unit in which an opening provided in the ceiling of a shield is closed with a conductor having a higher X-ray transmittance than the shield. It is a figure showing an example of a radiation detector when a plurality of X-ray sensor units are provided.

Embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to the following embodiments and illustrated examples.

[Configuration of radiation detector]
First, a radiation detector according to this embodiment will be explained. FIG. 1 is a perspective view showing the appearance of a radiation detector according to this embodiment, and FIG. 2 is a cross-sectional view taken along line XX in FIG. In addition, below, the vertical direction in the radiation detector 1 will be explained based on the case where the radiation detector 1 is arranged in the state shown in FIG.

As shown in FIG. 1, a power switch 37, a changeover switch 38, a connector 39, an indicator 40, etc. are arranged on one side of the housing 2 of the radiation detector 1. Further, although not shown, an antenna 41 (see FIG. 4 described later) for wirelessly communicating with the outside is provided on the opposite side surface of the casing 2.

As shown in FIG. 2, a base 31 is disposed inside the casing 2, and a board 4 is disposed on the upper surface side of the base 31 via a thin lead plate (not shown) or the like. . An X-ray detection element 7 and the like are provided on the upper surface of the substrate 4, and this point will be explained later. The scintillator 3 and the scintillator substrate 34 are arranged above the substrate 4 in such a manner that the scintillator 3 formed on the scintillator substrate 34 and the X-ray detection element 7 of the substrate 4 are opposed to each other.

A PCB board 33 on which electronic components 32 and the like are arranged, a built-in power supply 24, and the like are attached to the lower surface side of the base 31. Further, an X-ray sensor unit 25 is attached to the lower surface side of the base 31. The configuration of the X-ray sensor unit 25 will be explained later. In this embodiment, the sensor panel SP is formed in this manner. Further, in this embodiment, a cushioning material 35 is provided between the sensor panel SP and the side surface of the housing 2 to prevent them from colliding with each other.

As shown in FIG. 3, on the upper surface 4a of the substrate 4 (that is, the surface facing the scintillator 3), a plurality of scanning lines 5 and a plurality of signal lines 6 are arranged so as to intersect with each other. Further, each region r defined by the plurality of scanning lines 5 and the plurality of signal lines 6 is provided with an X-ray detection element 7, respectively. In this embodiment, the X-ray detection elements 7 are thus arranged in a two-dimensional form (matrix form).

Further, in this embodiment, a plurality of bias lines 9 are arranged in parallel to each signal line 6, and each bias line 9 is connected to a connection 10. A plurality of input/output terminals 11 are provided on the periphery of the substrate 4, and each input/output terminal 11 is connected to each scanning line 5, each signal line 6, and connection line 10, respectively. Although not shown, each input/output terminal 11 is connected to a flexible circuit board in which a chip such as a readout IC 16 (described later) is incorporated on a film, and the flexible circuit board is routed around the back side of the board 4. It is designed to be connected to the aforementioned PCB board 33 and the like.

Here, the circuit configuration of the radiation detector 1 will be explained. FIG. 4 is a block diagram showing an equivalent circuit of the radiation detector 1 according to this embodiment. In each X-ray detection element 7, a charge is generated in each X-ray detection element 7 according to the dose of X-rays irradiated through an object (not shown) (or the amount of electromagnetic waves converted by the scintillator 3). It has become. In addition, although the case where the X-ray detection element 7 is comprised by a photodiode is demonstrated below, it is also possible to use the phototransistor, CCD (Charge Coupled Device), etc. for the X-ray detection element 7, for example.

A bias line 9 is connected to one electrode 7a of each X-ray detection element 7, and a reverse bias voltage is applied to each X-ray detection element 7 from a bias power supply 14 via the bias line 9 and connection 10. It is now possible to do so. Further, a TFT 8 is connected to the other electrode 7b of each X-ray detection element 7 as a switch element, and the TFT 8 is connected to the signal line 6.

Further, the TFT 8 is turned on when an on-voltage is applied via the scanning line 5 from a scanning driving means 15, which will be described later, and causes the charge accumulated in the X-ray detection element 7 to be released to the signal line 6. Further, when an off-voltage is applied through the scanning line 5, it becomes an off state, and the discharge of charge from the X-ray detection element 7 to the signal line 6 is stopped, so that the charge is accumulated in the X-ray detection element 7. It has become.

Each scanning line 5 is connected to a gate driver 15b of the scanning driving means 15, respectively. In the scan driving means 15, on voltage and off voltage are supplied from the power supply circuit 15a to the gate driver 15b via the wiring 15c, and the gate driver 15b applies them to each line L1 to Lx of the scanning line 5. The voltage is switched between on voltage and off voltage.

Further, each signal line 6 is connected to each readout circuit 17 built in the readout IC 16, respectively. In this embodiment, the readout circuit 17 includes an integrating circuit 18, a correlated double sampling circuit 19, and the like. In the readout IC 16, an analog multiplexer 21 and an A/D converter 20 are further provided. In addition, in FIG. 4, the correlated double sampling circuit 19 is expressed as CDS.

During imaging, when the radiation detector 1 is irradiated with X-rays from an X-ray irradiation device (not shown) with each TFT 8, which is a switch element, in an off state, the radiation inside each X-ray detection element 7 is caused by the irradiation of X-rays. The generated charges are accumulated in the X-ray detection element 7. Then, when reading the image data d from each X-ray detection element 7, an on-voltage is sequentially applied from the gate driver 15b of the scanning drive means 15 to each line L1 to Lx of the scanning line 5, and each Charges are released from within the line detection element 7 to the signal line 6, respectively.

Then, the charge flows into the integrating circuit 18 of each readout circuit 17 and is accumulated, and a voltage value corresponding to the amount of accumulated charge is output. The correlated double sampling circuit 19 outputs the difference between the output values output from the integrating circuit 18 before and after charges flow from each X-ray detection element 7, respectively, as image data d of an analog value.

The output image data d is then sequentially transmitted to the A/D converter 20 via the analog multiplexer 21, where it is sequentially converted into digital value image data d, and stored in the storage means 23. It is output and saved sequentially. In this way, the image data d is read out.

The control means 22 is a computer, an FPGA (Field Programmable Gate Array), etc. in which a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), input/output interface, etc. (not shown) are connected to a bus. It is configured. It may be configured with a dedicated control circuit.

The control means 22 includes a storage means 23 composed of an SRAM (Static RAM), an SDRAM (Synchronous DRAM), a NAND flash memory, etc., a built-in power supply 24 composed of a lithium ion capacitor, etc., and the aforementioned X-ray sensor unit. 25 X-ray sensors 26, etc. are connected. Further, a communication section 42 is connected to the control means 22 for communicating with the outside via the antenna 41 and the connector 39 in a wireless or wired manner.

Note that, for example, in order to shield the wiring so that the wiring connecting the X-ray sensor 26 and the control means 22 does not pick up noise, or to make it easier for X-rays to reach the X-ray sensor 26, the base 31 (see FIG. 5) corresponding to the X-ray sensor 26 is appropriately processed such as not providing a thin lead plate.

On the other hand, the control means 22 detects the start of X-ray irradiation based on the output of the X-ray sensor 26. When the start of X-ray irradiation is detected, an off voltage is applied from the gate driver 15b of the scan drive means 15 to each line L1 to Lx of the scanning line 5 to turn off each TFT 8, and the X-ray irradiation starts. A transition is made to a charge accumulation state in which charges generated within the X-ray detection elements 7 are accumulated in each X-ray detection element 7.

Then, when a predetermined period of time has passed since the transition to the charge accumulation state, the control means 22 causes the gate driver 15b to sequentially apply an on-voltage to each line L1 to Lx of the scanning line 5, and causes each readout circuit 17 to perform a readout operation. Then, the image data d from each X-ray detection element 7 is read out as described above.

[Configuration of X-ray sensor unit]
Next, the X-ray sensor unit 25 will be explained. FIG. 5 is an enlarged partial schematic sectional view of the X-ray sensor unit 25 in FIG. 2. As shown in FIG.

As shown in FIG. 5, the X-ray sensor unit 25 includes an X-ray sensor 26 and a shield 28. In addition, in the X-ray sensor unit 25, an X-ray sensor board 27, which will be described later, is fixed to a rib (not shown) vertically provided on the lower surface side of the base 31.

The X-ray sensor 26 is a sensor for detecting X-rays irradiated onto the radiation detector 1 from an X-ray irradiation device (not shown). The X-ray sensor 26 includes a sensor element (for example, a photodiode) that converts X-ray energy into electric charge. The X-ray sensor 26 is built into an X-ray sensor board 27.

The shield 28 is a shield for reducing electromagnetic noise to the X-ray sensor 26, and is formed in a box shape to cover the top and side surfaces of the X-ray sensor 26. More specifically, the shield 28 covers the top surface and side surfaces of the X-ray sensor 26 while leaving a gap between the shield 28 and the top surface and side surfaces of the X-ray sensor 26, respectively. The shield 28 is formed using copper, aluminum, or the like, which has high electrical conductivity.

[Positional relationship between the X-ray sensor unit and the base]
Next, the positional relationship between the X-ray sensor unit 25 and the base 31 in the thickness direction of the radiation detector 1 will be explained.
As shown in FIG. 5, the height from the ceiling 28a of the shield 28 to the X-ray sensor 26 (the top surface of the X-ray sensor board 27) is H1, and the height from the bottom surface of the base 31 to the ceiling 28a of the shield 28 is H1. When is H2, the X-ray sensor unit 25 is arranged on the lower surface side of the base 31 so that H1>H2. Here, the capacitance component C1 generated between the X-ray sensor 26 and the shield 28 becomes smaller in inverse proportion to the above-mentioned H1. Therefore, by disposing the X-ray sensor unit 25 on the lower surface side of the base 31 so that H1>H2, the above-mentioned H1 can be increased, so there is a gap between the X-ray sensor 26 and the shield 28. The generated capacitance component C1 can be reduced. As a result, electromagnetic noise generated due to the capacitance component C1 described above can be reduced, so that erroneous detection of X-ray irradiation by the X-ray sensor 26 can be suppressed.

Note that when the base 31 is made of a dielectric material (for example, a hard foam material), the base 31 is easily charged. As shown in FIG. 6, when the base 31 is in a charged state, a capacitive component C2 is generated between the base 31 and the shield 28. Therefore, when the base 31 is in a charged state, the capacitive component Cshunt (=C1//C2) is coupled to the X-ray sensor 26 (capacitive coupling). Here, when the value of H1+H2 is constant, the value of the capacitance component Cshunt does not change. However, when the value of H1+H2 changes due to vibration, the value of the capacitive component Cshunt also changes. This may generate electromagnetic noise, which may cause the X-ray sensor 26 to erroneously detect X-ray irradiation. Therefore, as described above, it is preferable to arrange the X-ray sensor unit 25 on the lower surface side of the base 31 so that H1>H2, and to prevent the above-mentioned capacitive component C2 from occurring. In other words, it is preferable to perform equal potential processing in which the potentials of the base 31 and the shield 28 are set to the same potential. Here, as a method for making the respective potentials of the base 31 and the shield 28 the same, for example, the base 31 may be added with a conductive material (for example, carbon, etc.) to prevent it from being charged. There is a method in which the potential with the shield 28 is set to be the same potential. As a result, it is possible to prevent the above-mentioned capacitive component C2 from occurring, and only the capacitive component C1 is coupled to the X-ray sensor 26 (capacitive coupling), but as described above, H1>H2 is satisfied. Since the X-ray sensor unit 25 is disposed on the lower surface side of the base 31, the capacitance component C1 can be reduced. As a result, electromagnetic noise generated due to the capacitance component C1 described above can be reduced, so that erroneous detection of X-ray irradiation by the X-ray sensor 26 can be suppressed.

(Modified example)
Next, another example of the same potential processing in which the potentials of the base 31 and the shield 28 are made to be the same potential will be described. FIG. 7 is a diagram showing an example of potential equalization processing in which the potentials of the base 31 and the shield 28 are set to the same potential. Similar to FIG. 5, FIG. 7 is an enlarged partial schematic cross-sectional view of the X-ray sensor unit 25.

As shown in FIG. 7, by covering at least the area facing the X-ray sensor 26 on the lower surface side of the base 31 with a conductor 29 such as a copper plate or aluminum plate, and connecting this conductor 29 and the shield 28, The potentials of the base 31 and the shield 28 are set to be the same potential. Note that the method for fixing the conductor 29 is not limited to the above method, and as shown in FIG. The conductor 29 may be fixed to the X-ray sensor board 27 by inserting and attaching the end of the conductor 29.

[effect]
As described above, the radiation detector 1 according to the present embodiment includes the X-ray sensor 26 that detects X-ray irradiation, the shield 28 that reduces electromagnetic noise to the X-ray sensor 26, and the X-ray sensor 26. The radiation detector 1 is equipped with a base 31 to be assembled, and the distance (H1) between the X-ray sensor 26 and the shield 28 in the thickness direction of the radiation detector 1 is equal to the distance (H2) between the shield 28 and the base 31. ), the X-ray sensor 26, the shield 28, and the base 31 are each arranged so as to be larger than the X-ray sensor 26, the shield 28, and the base 31.
Therefore, according to the radiation detector 1, H1 can be increased by arranging the X-ray sensor 26 on the lower surface side of the base 31 so that H1>H2. The capacitance component C1 generated between the shield 28 and the shield 28 can be reduced. As a result, it is possible to suppress noise from flowing into the X-ray sensor 26 from peripheral components while taking into account the constraints on the thickness of the cassette device.

Further, in the radiation detector 1 according to the present embodiment, when the base 31 is subjected to the same potential treatment to make the potential with the shield 28 the same, there is a gap between the base 31 and the shield 28. Since the capacitance component C2 (see FIG. 6) can be prevented from occurring, the capacitance component that is coupled to the X-ray sensor 26 (capacitive coupling) is reduced to the capacitance component C1 that occurs between the X-ray sensor 26 and the shield 28. It can be done.
As a result, the same potential processing is performed to make the potentials of the base 31 and the shield 28 the same, and the X-ray sensor unit 25 is arranged on the lower surface side of the base 31 so that H1>H2 as described above. By providing this, it is possible to further suppress noise from entering the X-ray sensor 26 from peripheral components.

[others]
It goes without saying that the present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present invention.

For example, in the above embodiments, the radiation detector is a so-called indirect radiation detector that includes a scintillator or the like and converts emitted X-rays into electromagnetic waves of other wavelengths such as visible light to obtain an electrical signal. Although the present invention has been described using an example, the present invention can also be applied to a so-called direct type radiation detector in which X-rays are directly detected by a detection element without using a scintillator or the like.

Further, in the above embodiments, in order to make it easier for X-rays to reach the X-ray sensor 26, as shown in FIG. , and the opening may be closed with a conductor 30 having a higher X-ray transmittance than the shield 28.

Further, in the above embodiments, the case where only one X-ray sensor unit 25 is provided in the radiation detector 1 is shown, but for example, as shown in FIG. 10, it is also possible to provide a plurality of X-ray sensor units 25. It is. That is, it is possible to arrange the X-ray sensor unit 25 not only at the center position on the lower surface side of the base 31 but also at a position other than the center position. Although FIG. 10 shows a case where two X-ray sensor units 25 are provided, three or more may be provided. With this configuration, even if the radiation detector 1 is irradiated with X-rays with a narrowed irradiation field, the X-rays can be detected by any one of the plurality of X-ray sensor units 25. becomes.

1 Radiation detector 25 X-ray sensor unit 26 X-ray sensor 27 X-ray sensor board 28 Shield 29 Conductor 30 Conductor 31 Base

Claims (10)

an X-ray sensor that detects X-ray irradiation;
a shield that reduces electromagnetic noise to the X-ray sensor;
a base on which the X-ray sensor is assembled;
A radiation detector comprising:
Each of the X-ray sensor, the shield, and the base is arranged such that the distance between the X-ray sensor and the shield in the thickness direction of the radiation detector is larger than the distance between the shield and the base. is arranged,
A radiation detector characterized by: The base is subjected to potential equalization treatment to make the potential the same as that of the shield,
The radiation detector according to claim 1, characterized in that: The base is added with a conductive material,
The radiation detector according to claim 2, characterized in that: The surface of the base is covered with a conductor.
The radiation detector according to claim 2, characterized in that: the base is a dielectric;
The radiation detector according to claim 4, characterized in that: The base is made of foam material.
The radiation detector according to claim 5, characterized in that: comprising a plurality of the X-ray sensors;
The radiation detector according to any one of claims 1 to 6, characterized in that: the X-ray sensor is a photodiode;
The radiation detector according to claim 7, characterized in that: The shield is provided with an opening at a position facing the X-ray sensor in the thickness direction,
the opening is closed with a conductor having a higher radiation transmittance than the shield;
The radiation detector according to any one of claims 1 to 6, characterized in that: comprising a plurality of the X-ray sensors;
The radiation detector according to claim 9, characterized in that:

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