JP2002000590A - X-ray equipment - Google Patents

Abstract

[PROBLEMS] To provide an X-ray imaging apparatus capable of performing automatic exposure imaging without separately providing a detector for automatic X-ray exposure as a light receiving unit in front of a flat panel imaging sensor. SOLUTION: A detection area setting unit 29 sets a pixel area corresponding to an interest detection area of a subject 11, and a density setting circuit 1 is provided.
In step 6a, the photographing density is set. The X-ray transmitted through the subject 11 is incident on the flat panel image sensor 12, and a charge signal proportional to the X-ray is accumulated in each pixel. A gate signal is sent from the gate driver circuit 2 to the pixel, and the charge signal is read by the amplifier circuit 3. The pixel selection circuit 25 selectively takes in the signal of the set pixel area from the image signal from the amplifier circuit 3, sends the signal to the addition circuit 15a, and compares it with the imaging density set by the comparator 17a. The high voltage of the X-ray high-voltage device 19 is cut off by the line cut-off signal generation circuit 18a, and the imaging ends.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an X-ray imaging apparatus having a flat panel imaging sensor, and more particularly to an X-ray imaging apparatus having an X-ray automatic exposure control mechanism for automatically setting X-ray conditions.

[0002]

2. Description of the Related Art An automatic exposure control device in X-ray photography is used for most indirect photography, and is also widely used for direct photography of the chest, abdomen and the like. This automatic exposure control device operates so as to keep the film density constant by automatically controlling the photographing time. The automatic exposure control device converts the amount of X-ray transmitted through the subject into an electric signal, and this electric amount reaches a certain value. Then, X-rays are cut off to obtain a desired film density. FIG. 2 shows an X-ray imaging apparatus using the X-ray automatic exposure control device 14 and a flat panel image sensor. After the X-ray high-voltage device 19 sets the tube voltage and tube current as the imaging conditions, X-rays are emitted from the X-ray tube 20,
The aperture 21 narrows down to an effective field of view, transmits through the subject 11,
The light enters the X-ray automatic exposure detector 10 and passes through the X-ray automatic exposure detector 10 to enter the flat panel image sensor 12. The X-ray automatic exposure detector 10 converts the X-ray dose into a signal current 13 and inputs the signal current 13 to the X-ray automatic exposure control device 14. Since the signal current 13 is proportional to the X-ray intensity incident on the X-ray automatic exposure detector 10, the exposure amount is equal to the signal current 1
3 is proportional to the integrated value. Signal current 13 is integrated circuit 1
5 and the integrated value is compared with the set value of the concentration setting circuit 16 by the comparator 17. If they match, an X-ray cutoff signal is generated by the X-ray cutoff signal generator 18, and the X-ray high voltage device 19 X-ray exposure is stopped. In the automatic exposure control (photo timer control) for general photographing, the flat panel image sensor 12
The X-ray automatic exposure detector 10 is placed in front of the device.

Conventionally, a detector 10 for automatic exposure of X-rays as a mechanism for detecting X-rays transmitted through a subject is of a fluorescent lighting type, an ionization chamber type, a semiconductor type, or the like. The ionization chamber detection method uses X-ray ionization to detect X-rays, and the surrounding frame and the X-ray input and output sides are
Inside the chamber using the plate, an insulating plate is provided inside the Al plate on the X-ray input side, an insulating plate is provided inside the Al plate on the X-ray output side, electrodes are provided on the surfaces thereof, and both electrodes are parallel. In this structure, a spacer is attached near the electrodes, and the distance between the electrodes is accurately adjusted. Then, a DC voltage is applied between both electrodes. When X-rays enter the chamber of the ionization space, gas atoms that have sufficiently absorbed X-ray energy are in a state where the outermost electrons have jumped out of the attractive sphere of the nuclei, and the atoms are positively charged. Then, the electrons and the positively charged atoms are respectively captured by the electrodes and taken out to the outside as a signal current 13.

In recent years, a flat panel image sensor using a semiconductor X-ray surface sensor has been developed instead of an X-ray film or an imaging plate used in a simple X-ray imaging apparatus. This X-ray surface sensor is usually composed of an X-ray conversion film for converting X-rays into light, a photodiode array arranged directly below the X-ray conversion film, and a TFT switch connected to each photodiode array. X
After irradiating the line, by sequentially turning on each TFT switch, a signal charge stored in each pixel is read out to form an X-ray image, and a charge signal corresponding to an incident dose is output directly in response to radiation. It has a radiation sensor array consisting of a conversion layer, TF
There are two types, a T switch is connected, and a signal charge stored in each pixel is read out to form an X-ray image by sequentially turning on each TFT switch at the time of irradiation. Here, the latter type will be described.

FIG. 3 shows the structure of a flat panel image sensor having an X-ray conversion layer 30 of the latter type. In this flat panel image sensor, a bias voltage is supplied to the X-ray conversion layer 30 from the upper electrode 22, and the pixel electrodes 7 arranged in a matrix on the active matrix substrate 4 immediately below the X-ray conversion layer 30 are provided with a TFT 8. The switch elements are connected, and the switch elements of each TFT 8 are sequentially turned on by the gate driver circuit 2 via the FPC 24a at the time of irradiation, so that the signal charges accumulated in the storage capacitor 9 of each pixel are transmitted to the amplifier circuit 3 by the FPC. (Flexible Prin
ted Circuit: a printed circuit board using a flexible insulating substrate) 24. And
From the amplifier circuit 3 via the A / D converter 26 in FIG.
The signal is input to the circuit 27. The signal processing is performed by the TV circuit 27 and an X-ray image is displayed on the monitor 28. FIG. 4 is a circuit diagram for explaining the operation of the flat panel image sensor. Each pixel 1 is regularly and vertically arranged on the active matrix substrate 4, and a gate driver circuit 2 is driven by a signal from a control circuit 23, and is applied to a pixel electrode 7 of each pixel 1 from a row direction via a gate line 5. Connected T
The pulse signal is applied to the gate electrode of FT8 by G1, G2, G3,
, And the amplifier circuit 3 is driven by a signal from the control circuit 23, and the video charge signal of each pixel 1 is transmitted from the drain electrode of the TFT 8 to R 1, R 2 through the read signal line 6 in the column direction. , R3,... FIG.
2 shows a cross-sectional configuration of the pixel 1. The pixel 1 is formed on an active matrix substrate 4 on which an XY matrix electrode wiring (gate line 5 and readout signal line 6), a thin film transistor TFT 8, a storage capacitor 9, and the like are formed on a glass substrate, and is formed almost entirely over the active matrix substrate. X-ray conversion layer 30, lower pixel electrode 7, and upper upper electrode 22.

The X-ray conversion layer 30 has good photoconductive characteristics according to the intensity of X-ray irradiation and generates a charge signal. For example, it is easy to form a large area film by vapor deposition, and the thickness is 300 to 60.
Amorphous (amorphous) selenium (a-Se) formed to a thickness of 0 μm is used. The upper electrode 22 of the X-ray conversion layer 30 is formed on the surface on the X-ray incident side, and the pixel electrode 7 is formed on the side opposite to the X-ray incident side at a position corresponding to each pixel 1. The storage capacitor 9 is connected between the pixel electrode 7 and the ground. Then, a bias voltage is applied to the X-ray conversion layer 30 from the bias application unit, and the charges generated in the X-ray conversion layer 30 according to the X-ray irradiation intensity are stored in the capacitor of the storage capacitor 9. Transistor switches, for example, TFTs 8 having a signal readout switch function are two-dimensionally arranged for each pixel 1, and the switch signal from the gate line terminal 5a causes the charge signal of the storage capacitor 9 to be transferred via the readout signal line terminal 6a. The data is read out to the amplifier circuit 3.

[0007]

The conventional X-ray imaging apparatus is configured as described above. However, in order to perform automatic exposure imaging with an X-ray imaging apparatus having a flat panel imaging sensor, as shown in FIG. In addition, the X-ray automatic exposure detector 10 is required separately from the flat panel imaging sensor 12, and the X-ray automatic exposure detector 10 must be placed on the front surface of the flat panel imaging sensor 12 as a light receiving unit. for that reason,
The subject 11 and the flat panel imaging sensor 12 are deteriorated due to the deterioration of the image quality and the increase of invalid exposure due to the X-ray absorption of the X-ray automatic exposure detector 10 and the thickness of the X-ray automatic exposure detector 10.
In this case, there is a problem in that the distance between them becomes large, and it is necessary to consider the deterioration of the image quality due to the increase in the expansion blur.

The present invention has been made in view of the above circumstances, and an automatic exposure system without an X-ray automatic exposure detector 10 as a light receiving unit is provided in front of a flat panel image sensor 12. It is an object of the present invention to provide an X-ray imaging apparatus capable of imaging.

[0009]

In order to achieve the above object, an X-ray imaging apparatus according to the present invention comprises an X-ray conversion layer which is sensitive to X-rays and outputs a charge signal corresponding to the intensity of incident X-rays; The switching elements arranged and connected in a matrix just below them, a gate driver circuit that sequentially turns on each switching element via a gate line at the time of signal reading, and a charge signal accumulated in each pixel via a read signal line. An X-ray imaging apparatus including a flat panel imaging device including an amplification circuit for reading and a control circuit for controlling the gate driver circuit and the amplification circuit, wherein the flat panel imaging device corresponding to an interest detection part of a subject is provided. A detection region setting device for setting a pixel region, a pixel selection circuit for selecting a signal of the set pixel region from an image signal, and an addition for adding a signal of the selected pixel region Path, a density setting circuit for setting a reference photographing density level, a comparison circuit for comparing signals of the addition circuit and the density setting circuit, and X when a signal of the addition circuit reaches a reference value of the density setting circuit. An X-ray cut-off signal generator for outputting a signal for cutting off a line, an X-ray high-voltage device for cutting off a high voltage applied to the X-ray tube by a signal from the X-ray cut-off signal generator, and an X-ray tube. X-ray automatic exposure control mechanism composed of

[0010] The X-ray imaging apparatus of the present invention is configured as described above, and includes a detection region setting device for setting a pixel region of a flat panel imaging sensor corresponding to a region of interest detection of a subject; From the amplifier circuit to A
A pixel selection circuit for selecting from image signals output to the / D converter is provided in the X-ray automatic exposure control circuit, and the signals of the extracted pixel areas are added and compared with the reference photographing density level;
When the reference value is reached, a signal for shutting off X-rays is output to the X-ray high-voltage device, and X-ray imaging can be performed with the high voltage shut off. Therefore, automatic exposure shooting can be performed without separately providing a detector for X-ray automatic exposure as a light receiving unit on the front surface of the flat panel image sensor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the X-ray imaging apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a block circuit diagram of an automatic X-ray imaging mechanism of the X-ray imaging apparatus according to the present invention. The present X-ray imaging apparatus is a flat panel imaging sensor having an X-ray conversion layer that is sensitive to X-rays and outputs a charge signal corresponding to the intensity of incident X-rays, and switching elements arranged in a matrix and connected directly below the X-ray conversion layer. 12, a gate driver circuit 2 for sequentially turning on each switching element via a gate line when reading a signal, an amplifier circuit 3 for reading out a charge signal accumulated in each pixel via a readout signal line, and a gate driver circuit 2 And a control circuit (not shown) for controlling the amplifier circuit 3
A detection region setting unit 29 for setting a pixel region of the flat panel imaging sensor 12 corresponding to a region of interest of the subject 11; a pixel selection circuit 25 for selecting a signal of the set pixel region from an image signal; An addition circuit 15a for adding the signals of the pixel regions, a density setting circuit 16a for setting a reference photographing density level, and a comparison circuit 17a for comparing the signals of the addition circuit 15a and the density setting circuit 16a.
And an X-ray cutoff signal generator 1 for outputting a signal for cutting off X-rays when the signal of the adding circuit reaches the reference value of the density setting circuit.
8a and the X-ray tube 2 by a signal from the X-ray cutoff signal generator.
X-ray high voltage device 19 for cutting off high voltage applied to zero
And an X-ray tube 20.

The present X-ray imaging apparatus includes a flat panel imaging sensor 12, a gate driver circuit 2, an amplification circuit 3, an A / D
The X-ray imaging system of the converter 26, the TV circuit 27, and the monitor 28 is the same as the conventional X-ray imaging system shown in FIG. 2, but the X-ray automatic exposure control device 14 is As shown in FIG. 1, a detection region setting unit 29 for setting a pixel region of the flat panel image sensor 12 corresponding to a detection region of interest of the subject 11, and a pixel selection circuit for selecting a signal of the set pixel region from an image signal 25 in that an adder 15a for adding the signal of the selected pixel area is provided.

X-ray automatic exposure control circuit 1 of the present X-ray imaging apparatus
4a comprises a detection site setting unit 29, a pixel selection circuit 25, an addition circuit 15a, a density setting circuit 16a, a comparator 17a, and an X-ray cutoff signal generator 18a. The detection site setting unit 29 sets a pixel area of the flat panel image sensor 12 corresponding to the interest detection site of the subject 11. A pixel area at the center position of the image sensor 12 is set. In the case of imaging of the chest, a pixel region corresponding to the image above the center of the flat panel image sensor 12 is set. A method for setting a pixel area will be described with reference to an image signal readout circuit of the flat panel image sensor 4 shown in FIG. The gate signal from the gate driver circuit 2 is applied to the gate electrode of the TFT 8 connected to each pixel 1 via the gate line 5.
, G2, G3,..., The electric charge accumulated in the storage capacitor 9 of each pixel 1 is taken out from the source electrode of the TFT 8 to the drain electrode, and R1, R2, R3,. Is read out. Here, the address of each pixel 1 is determined as follows, for example. From the top row, pixel (11), pixel (12), pixel (13)..., The second column is pixel (21), pixel (22), pixel (23). ), Pixel (32), pixel (33)... The pixel area of the flat panel image sensor 12 corresponding to the interest detection part of the subject 11 from the pixel 1 is set as, for example, a pixel (12), a pixel (22), and a pixel (32) in a vertical center portion. Here, for convenience of explanation, one vertical column is defined as a pixel region, but it is desirable to select a region having a large area as the pixel region. The pixel selection circuit 25 is connected to the gate driver circuit 2, a gate signal is sent to the pixel selection circuit 25, and at the same time, connected to the amplification circuit 3, a readout signal is sent to the pixel selection circuit 25, and the detection site setting is performed in real time. The signal of the pixel area set by the detector 29 is selected from the image signal. By this area setting value,
When the pixel selection circuit 25 operates and the pixel region is set as described above from the image signals sent from the amplification circuit 3 to the A / D converter 26, the gate signal from the gate driver circuit 2 becomes G1. When the readout signal from the amplifier circuit 3 is R2, and when the gate signal is G2, when the readout signal is R2, and when the gate signal is G3 and the readout signal is R2, the pixel selection circuit 25 selects only the image signal. take in. Then, the signals sent from the pixel selection circuit 25 are added by the addition circuit 15a. The sum is used as a density setting circuit 16a.
The X-ray cutoff signal generator 18a generates an X-ray cutoff signal, and the X-ray cutoff signal is sent to the X-ray high-voltage device 19 to stop the X-ray irradiation.

The operation of the present X-ray imaging apparatus will be described.
The surgeon determines the imaging detection site of the subject 11 and, for example, in the case of imaging the abdomen, sets the detection site setting unit 29 to the abdomen pixel region. Then, the X-ray conditions are set by the controller, and the imaging density is set by the density setting unit 16a. Next, subject 1
1 is positioned in front of the flat panel image sensor 12. By operating the imaging switch, the X-ray tube 20 stops the aperture 21
X-rays are emitted through. Electric charges proportional to the incident X-ray intensity are accumulated in each pixel 1 of the flat panel image sensor. The charge signal of each pixel 1 is read by the amplifying circuit 3 by the gate signal from the gate driver circuit 2, the image signal is sent to the A / D converter 26, the signal is processed by the TV circuit 27, and the X-ray image is displayed on the monitor 28. Is displayed. On the other hand, at the same time, the pixel selection circuit 25 outputs only the signal of each pixel 1 in the abdominal pixel area set by the detection site setting unit 29 to the amplification circuit 3.
From the image signal sent to the A / D converter 26 and sent to the addition circuit 15a where they are added. The added value is compared with the set value of the density setting circuit 16a by the comparator 17a.
An X-ray cutoff signal is generated at a, and sent to the X-ray high voltage device 19 to stop the X-ray exposure.

In the above embodiment, the method of setting each pixel 1 as the method of setting the pixel area of the flat panel image sensor 12 corresponding to the interest detection part of the subject 11 in the detection part setting device 29 has been described. It is also possible to adopt a method in which a region (area) of the pixel 1 of a representative imaging region is set in advance in normal imaging, and the region is selected. In addition, the addition circuit 15a incorporates a circuit for calculating an average value in order to average the time series of the pixel region,
The average value and the set value of the density setting circuit 16a are compared with a comparator 17a.
May be used for comparison.

[0016]

The X-ray imaging apparatus of the present invention is configured as described above, and includes a detection region setting device for setting a pixel region corresponding to a region of interest detection of a subject, and a signal of the set pixel region. And a pixel selection circuit for selecting from image signals output from the amplification circuit, and performs X-ray automatic exposure control using a signal of a set pixel area in the flat panel imaging sensor. Automatic exposure photography can be performed without separately providing a detector for automatic exposure of X-rays as a light receiving unit in front of the flat panel image sensor. Therefore, X
Deterioration of image quality due to X-ray absorption of the X-ray automatic detector and increase of invalid exposure, and the distance between the subject and the flat panel imaging sensor due to the thickness of the X-ray automatic exposure detector, The image quality is not degraded due to the increase in the magnification blur.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an X-ray imaging apparatus of the present invention.

FIG. 2 is a diagram showing a conventional X-ray imaging apparatus.

FIG. 3 is a diagram illustrating a structure of a flat panel image sensor.

FIG. 4 is a diagram showing an image signal reading circuit of the flat panel image sensor.

FIG. 5 is a diagram illustrating a pixel structure of a flat panel image sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pixel 2 ... Gate driver circuit 3 ... Amplifier circuit 4 ... Active matrix substrate 5 ... Gate line 5a ... Gate line terminal 6 ... Readout signal line 6a ... Readout signal line terminal 7 ... Pixel electrode 8 ... TFT 9 ... Storage capacitance 10 ... X-ray automatic exposure detector 11 ... Subject 12 ... Flat panel image sensor 13 ... Signal current 14 ... X-ray automatic exposure control device 14a ... X-ray automatic exposure control circuit 15 ... Integration circuit 15a ... Addition circuit 16 ... Density setting circuit 16a ... Concentration setting circuit 17 ... Comparator 17a ... Comparator 18 ... X-ray cutoff signal generator 18a ... X-ray cutoff signal generator 19 ... X-ray high voltage device 20 ... X-ray tube 21 ... Aperture 22 ... Top electrode 23 ... Control Circuit 24 FPC 24a FPC 25 Pixel selection circuit 26 A / D converter 27 TV circuit 28 Monitor 29 Detection part setting device 30 X-ray conversion layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05G 1/44 H05G 1/44 A

Claims (1)

[Claims] 1. An X-ray conversion layer which responds to X-rays and outputs a charge signal corresponding to the intensity of incident X-rays, a switching element arranged and connected immediately below the X-ray conversion layer, and a gate line at the time of signal reading. A gate driver circuit for sequentially turning on each switching element through the amplifier, an amplifier circuit for reading out a charge signal accumulated in each pixel via a readout signal line, and a control circuit for controlling the gate driver circuit and the amplifier circuit. A detection region setting device for setting a pixel region of the flat panel imaging device corresponding to a detection region of interest of a subject, and a signal of the set pixel region as an image signal. A pixel selection circuit for selecting from among the above, an addition circuit for adding a signal of the selected pixel area, a density setting circuit for setting a reference photographing density level, A comparison circuit for comparing a signal between the path and the density setting circuit, an X-ray cutoff signal generator for outputting a signal for cutting off X-rays when a signal of the adding circuit reaches a reference value of the density setting circuit, and an X-ray cutoff An X-ray automatic exposure control mechanism comprising an X-ray high-voltage device configured to cut off a high voltage applied to the X-ray tube by a signal from a signal generator, and an X-ray automatic exposure control mechanism. Shooting equipment.