JP7768035B2 - radiation detector - Google Patents

Description

The present invention relates to a radiation detector.

Conventionally, lightweight, thin radiation detectors known as flat panel detectors (FPDs) have been used to capture radiation (hereinafter also referred to as X-ray) images. Regarding this type of radiation detector, for example, Patent Document 1 discloses technology that uses a housing that covers the internal components to form a shield that protects the internal components from external electrical noise.

Patent No. 5580971

However, with the technology disclosed in Patent Document 1, when taking into account the cassette device thickness (15 mm (+1/-2 mm; for a cassette size of 14 inches x 17 inches)) standardized by ISO 4090 and JIS Z 4905, the space available for storing internal components within the housing is limited. As a result, for example, the X-ray sensor, which is an internal component, is prone to capacitive coupling with surrounding components (surrounding internal components), and if the distance between the X-ray sensor and surrounding components fluctuates due to vibration, the capacitive component fluctuates, causing noise to flow into the X-ray sensor and resulting in false detection of X-ray irradiation.

The present invention was made in consideration of the above-mentioned problems, and aims to suppress the inflow of noise from peripheral components into the X-ray sensor while taking into account the constraints on the thickness of the cassette device.

In order to solve the above problems, the radiation detector according to the present invention comprises:
an X-ray sensor for detecting X-ray irradiation;
a shield for reducing electromagnetic noise to the X-ray sensor;
a base on which the X-ray sensor is mounted;
A radiation detector comprising:
The X-ray sensor, the shield, and the base are arranged so that the distance between the X-ray sensor and the shield in the thickness direction of the radiation detector is greater than the distance between the shield and the base.

This invention makes it possible to suppress noise from entering the X-ray sensor from peripheral components while taking into account the constraints of the cassette device thickness.

1 is a perspective view showing the appearance of a radiation detector according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line XX in 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. 3 is a partial schematic cross-sectional view showing an enlarged portion of the X-ray sensor unit in FIG. 2. FIG. 10A and 10B are diagrams illustrating an example of an X-ray sensor unit in which a capacitance component occurs between the base and the shield. 10A and 10B are diagrams illustrating an example of equal potential processing in which the base and the shield are set to the same potential. 10A and 10B are diagrams illustrating an example of equal potential processing in which the base and the shield are set to the same potential. 10 is a diagram showing an example of an X-ray sensor unit in which an opening provided in a ceiling portion of a shield is blocked with a conductor having a higher X-ray transmittance than the shield. FIG. FIG. 10 is a diagram showing an example of a radiation detector in which 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, the radiation detector according to this embodiment will be described. Fig. 1 is a perspective view showing the appearance of the radiation detector according to this embodiment, and Fig. 2 is a cross-sectional view taken along line X-X in Fig. 1. Note that the following description of the up-down direction of the radiation detector 1 will be based on the case where the radiation detector 1 is positioned as shown in Fig. 2.

As shown in Figure 1, a power switch 37, a selector switch 38, a connector 39, an indicator 40, etc. are arranged on one side of the housing 2 of the radiation detector 1. In addition, although not shown, an antenna 41 (see Figure 4, described below) for wireless communication with the outside is provided on the opposite side of the housing 2.

As shown in FIG. 2, a base 31 is disposed inside the housing 2, and a substrate 4 is disposed on the upper surface of the base 31 via a thin lead plate or the like (not shown). X-ray detection elements 7 and the like are provided on the upper surface of the substrate 4, which will be explained later. Then, above the substrate 4, the scintillator 3 and the scintillator substrate 34 are disposed so that the scintillator 3 formed on the scintillator substrate 34 faces the X-ray detection elements 7 and the like of the substrate 4.

A PCB board 33 on which electronic components 32 and the like are mounted, an internal power supply 24, and the like are attached to the underside of the base 31. An X-ray sensor unit 25 is also attached to the underside of the base 31. The configuration of the X-ray sensor unit 25 will be described later. In this embodiment, the sensor panel SP is formed in this manner. In addition, in this embodiment, a buffer material 35 is provided between the sensor panel SP and the side of the housing 2 to prevent them from colliding with each other.

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

In addition, in this embodiment, multiple bias lines 9 are arranged 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 each connection 10. Although not shown, each input/output terminal 11 is connected to a flexible circuit board on which chips such as a readout IC 16 (described below) are embedded on a film, and the flexible circuit board is routed to the back side of the substrate 4 and connected to the aforementioned PCB board 33, etc.

The circuit configuration of the radiation detector 1 will now be described. Figure 4 is a block diagram showing an equivalent circuit of the radiation detector 1 according to this embodiment. Each X-ray detection element 7 generates an electric charge according to the dose of X-rays irradiated through a subject (not shown) (or the amount of electromagnetic waves converted by the scintillator 3). The following describes a case where the X-ray detection element 7 is configured as a photodiode, but it is also possible to use a phototransistor or a CCD (Charge Coupled Device) as 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. A TFT 8 is connected as a switching element to the other electrode 7b of each X-ray detection element 7, and the TFT 8 is connected to a signal line 6.

When an on voltage is applied to the TFT 8 from the scan driver 15 (described later) via the scan line 5, the TFT 8 turns on, causing the charge accumulated in the X-ray detection element 7 to be released to the signal line 6. When an off voltage is applied to the TFT 8 via the scan line 5, the TFT 8 turns off, stopping the release of charge from the X-ray detection element 7 to the signal line 6 and allowing the charge to be accumulated in the X-ray detection element 7.

Each scanning line 5 is connected to a gate driver 15b of the scanning drive means 15. In the scanning drive means 15, an on voltage and an off voltage are supplied from the power supply circuit 15a to the gate driver 15b via wiring 15c, and the gate driver 15b switches the voltage applied to each line L1 to Lx of the scanning lines 5 between the on voltage and the off voltage.

Furthermore, each signal line 6 is connected to a respective readout circuit 17 built into the readout IC 16. In this embodiment, the readout circuit 17 is composed of an integration circuit 18, a correlated double sampling circuit 19, etc. The readout IC 16 also includes an analog multiplexer 21 and an A/D converter 20. In Figure 4, the correlated double sampling circuit 19 is abbreviated as CDS.

When X-rays are irradiated onto the radiation detector 1 from an X-ray irradiation device (not shown) while each TFT 8, which acts as a switching element, is in the OFF state during imaging, electric charge generated in each X-ray detection element 7 by the X-ray irradiation is accumulated in the X-ray detection element 7. Then, when image data d is read from each X-ray detection element 7, an ON voltage is sequentially applied from the gate driver 15b of the scan drive means 15 to each line L1 to Lx of the scanning line 5, causing electric charge to be released from each X-ray detection element 7 to the signal line 6.

The charge then flows into and accumulates in the integration circuit 18 of each readout circuit 17, 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 integration circuit 18 before and after the charge flows in from each X-ray detection element 7 as analog image data d.

Then, each output image data d is sequentially sent to the A/D converter 20 via the analog multiplexer 21, where it is sequentially converted into digital image data d, output to the storage means 23, and stored sequentially. In this way, the image data d is read out.

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

Connected to the control means 22 are a storage means 23 composed of SRAM (Static RAM), SDRAM (Synchronous DRAM), NAND flash memory, etc., an internal power supply 24 composed of a lithium ion capacitor, etc., and the X-ray sensor 26 of the X-ray sensor unit 25 mentioned above. Also connected to the control means 22 is a communication unit 42 for communicating with the outside world wirelessly or via a wired system via the antenna 41 and connector 39 mentioned above.

In addition, appropriate measures may be taken, such as shielding the wiring connecting the X-ray sensor 26 and the control means 22 to prevent noise from being picked up, or removing the lead sheet from the portion of the base 31 (see Figure 5) corresponding to the X-ray sensor 26 to allow X-rays to reach the X-ray sensor 26 more easily.

Meanwhile, 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, the gate driver 15b of the scan drive means 15 applies an off voltage to each line L1 to Lx of the scanning line 5, turning off each TFT 8 and transitioning to a charge accumulation state in which charge generated in the X-ray detection elements 7 due to X-ray irradiation is accumulated in each X-ray detection element 7.

Then, when a predetermined time has elapsed 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, causing each readout circuit 17 to perform a readout operation, thereby reading out image data d from each X-ray detection element 7 as described above.

[Configuration of X-ray sensor unit]
Next, a description will be given of the X-ray sensor unit 25. Fig. 5 is a partial schematic cross-sectional view showing an enlarged portion of the X-ray sensor unit 25 in Fig. 2.

As shown in FIG. 5, the X-ray sensor unit 25 includes an X-ray sensor 26 and a shield 28. The X-ray sensor unit 25 is configured so that an X-ray sensor board 27 (described below) is fixed to a rib (not shown) extending downward from the underside 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 is composed of a sensor element (e.g., a photodiode) that converts X-ray energy into an electric charge. The X-ray sensor 26 is configured in a state where it is incorporated into the 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 that covers the top and side surfaces of the X-ray sensor 26. More specifically, the shield 28 covers the top and side surfaces of the X-ray sensor 26 while leaving a gap between the shield 28 and the top and side surfaces of the X-ray sensor 26. The shield 28 is made of copper, aluminum, or other materials with 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 described.
As shown in FIG. 5 , if the height from the ceiling 28a of the shield 28 to the X-ray sensor 26 (the upper surface of the X-ray sensor substrate 27) is H1 and the height from the lower surface of the base 31 to the ceiling 28a of the shield 28 is H2, the X-ray sensor unit 25 is disposed on the lower surface of the base 31 so that H1 > H2. Here, the capacitance component C1 generated between the X-ray sensor 26 and the shield 28 decreases in inverse proportion to H1. Therefore, by disposing the X-ray sensor unit 25 on the lower surface of the base 31 so that H1 > H2, the above-mentioned H1 can be increased, and the capacitance component C1 generated between the X-ray sensor 26 and the shield 28 can be reduced. As a result, electromagnetic noise generated due to the capacitance component C1 can be reduced, thereby suppressing erroneous detection of X-ray irradiation by the X-ray sensor 26.

If the base 31 is made of a dielectric material (e.g., a hard foam material), it is prone to charging. As shown in Figure 6, when the base 31 is charged, a capacitance component C2 is generated between the base 31 and the shield 28. Therefore, when the base 31 is charged, the capacitance component Cshunt (= C1//C2) is coupled (capacitively coupled) to the X-ray sensor 26. Here, if the value of H1 + H2 is constant, the value of the capacitance component Cshunt does not change. However, if the value of H1 + H2 changes due to vibration, the value of the capacitance component Cshunt also changes. This may generate electromagnetic noise, which may lead to erroneous detection of X-ray irradiation by the X-ray sensor 26. Therefore, as described above, it is preferable to arrange the X-ray sensor unit 25 on the underside of the base 31 so that H1 > H2, and to prevent the generation of the capacitance component C2. In other words, it is preferable to perform an equal potential treatment to equalize the potentials of the base 31 and the shield 28. One method for ensuring that the base 31 and shield 28 are at the same potential is to add a conductive material (e.g., carbon) to the base 31 to prevent it from becoming charged, thereby ensuring the same potential as the shield 28. This prevents the generation of the capacitance component C2, and only capacitance component C1 couples (capacitively couples) to the X-ray sensor 26. However, since the X-ray sensor unit 25 is disposed on the underside of the base 31 so that H1 > H2, as described above, this capacitance component C1 can be reduced. As a result, electromagnetic noise caused by the capacitance component C1 can be reduced, thereby preventing erroneous detection of X-ray irradiation by the X-ray sensor 26.

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

As shown in FIG. 7, at least the area of the underside of the base 31 facing the X-ray sensor 26 is covered with a conductor 29, such as a copper or aluminum plate, and this conductor 29 is connected to the shield 28, thereby making the base 31 and the shield 28 at the same potential. Note that the method for fixing the conductor 29 is not limited to the above method. As shown in FIG. 8, the conductor 29 may be fixed to the X-ray sensor board 27 by inserting the end of the conductor 29, which has a substantially L-shaped cross section, into a clip CL used to fix the shield 28 to the X-ray sensor board 27.

[effect]
As has been described above, the radiation detector 1 according to this embodiment is a radiation detector 1 including an X-ray sensor 26 that detects X-ray irradiation, a shield 28 that reduces electromagnetic noise to the X-ray sensor 26, and a base 31 on which the X-ray sensor 26 is mounted, and the X-ray sensor 26, the shield 28, and the base 31 are each disposed so that the distance (H1) between the X-ray sensor 26 and the shield 28 in the thickness direction of the radiation detector 1 is greater than the distance (H2) between the shield 28 and the base 31.
Therefore, according to the radiation detector 1, by arranging the X-ray sensor 26 on the underside of the base 31 so that H1 > H2, H1 can be increased, thereby reducing the capacitance component C1 generated between the X-ray sensor 26 and the shield 28. As a result, it is possible to suppress the inflow of noise from peripheral components into the X-ray sensor 26 while taking into consideration the constraints on the thickness of the cassette device.

Furthermore, in the radiation detector 1 according to this embodiment, when an equal potential treatment is performed on the base 31 to make it have the same potential as the shield 28, it is possible to prevent the generation of a capacitance component C2 (see FIG. 6) between the base 31 and the shield 28, so that the capacitance component coupled (capacitively coupled) to the X-ray sensor 26 can be limited to the capacitance component C1 generated between the X-ray sensor 26 and the shield 28.
As a result, by performing an equal potential treatment to make the base 31 and the shield 28 have the same potential, and by arranging the X-ray sensor unit 25 on the underside of the base 31 so that H1 > H2 as described above, it is possible to further suppress the inflow of noise from peripheral components into the X-ray sensor 26.

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

For example, in the above embodiments, a so-called indirect type radiation detector has been described as an example of a 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. However, the present invention can also be applied to so-called direct type radiation detectors that detect X-rays directly with a detection element without passing through a scintillator or the like.

Furthermore, in the above-described embodiments, in order to allow X-rays to easily reach the X-ray sensor 26, as shown in FIG. 9, an opening may be provided in the area of the ceiling portion 28a of the shield 28 facing the X-ray sensor 26, and the opening may be blocked with a conductor 30 having a higher X-ray transmittance than the shield 28.

In addition, while the above embodiments and the like have shown cases where only one X-ray sensor unit 25 is provided in the radiation detector 1, it is also possible to provide multiple X-ray sensor units 25, for example, as shown in FIG. 10. That is, it is possible to configure the X-ray sensor unit 25 to be placed not only in the central position on the underside of the base 31, but also in positions other than the central position. Note that while FIG. 10 shows a case where two X-ray sensor units 25 are provided, three or more may be provided. With this configuration, even when X-rays are irradiated onto the radiation detector 1 with a narrowed irradiation field, any of the multiple X-ray sensor units 25 can detect the X-rays.

REFERENCE SIGNS LIST 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 for detecting X-ray irradiation;
a shield for reducing electromagnetic noise to the X-ray sensor;
a base on which the X-ray sensor is mounted;
A radiation detector comprising:
the X-ray sensor, the shield, and the base are arranged so that the distance between the X-ray sensor and the shield in the thickness direction of the radiation detector is greater than the distance between the shield and the base.
A radiation detector characterized by: The base is subjected to an equipotential treatment to make the base and the shield have the same potential.
2. The radiation detector according to claim 1. The base is doped with a conductive material.
3. The radiation detector according to claim 2. The surface of the base is covered with a conductor.
3. The radiation detector according to claim 2. The base is a dielectric material.
5. The radiation detector according to claim 4. The base is made of a foam material.
6. The radiation detector according to claim 5. A plurality of the X-ray sensors are provided.
7. The radiation detector according to claim 1, wherein the radiation detector is a radiation detector having a wavelength of 100 nm or less. the X-ray sensor is a photodiode;
8. The radiation detector according to claim 7. the shield has an opening at a position facing the X-ray sensor in the thickness direction;
The opening is filled with a conductor having a higher radiation transmittance than the shield.
7. The radiation detector according to claim 1, wherein the radiation detector is a radiation detector having a wavelength of 100 nm or less. A plurality of the X-ray sensors are provided.
10. The radiation detector according to claim 9.