JP2002055164A - Device and method for photographing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for photographing image capable of photographing an image reduced in cross-talk among picture elements. SOLUTION: This image photographing device has a sensor means 8 and a driving means 145 for driving the sensor means. The driving means starts reading-out of a data from the sensor means after a prescribed time has lapsed after finish of radiation exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image photographing technique, for example, an image photographing technique in which a subject is directly detected by a sensor to photograph an object.

[0002]

2. Description of the Related Art Radiation (X-ray, α-ray,
(β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, It is known that the phosphor emits photostimulated light, and the phosphor exhibiting such properties is called a stimulable phosphor (stimulable phosphor).

Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet is scanned by excitation light such as laser light. The photostimulated light is generated, and the obtained photostimulated light is photoelectrically read to obtain an image signal. Based on the image signal, a radiation image of a subject is displayed on a recording material such as a photographic photosensitive material or a display device such as a CRT. A radiation image information recording / reproducing system for outputting a visible image has been proposed (Japanese Patent Laid-Open No. Sho 55-55).
12429 and 56-11395).

[0004] In recent years, an apparatus for similarly capturing an X-ray image using a semiconductor sensor has been developed. These systems have the practical advantage of being able to record images over a very wide radiation exposure area compared to conventional radiographic systems using silver halide photography. That is, an X-ray having a very wide dynamic range is read by a photoelectric conversion unit and converted into an electric signal, and the electric signal is used as a visible image on a recording material such as a photographic photosensitive material or a display device such as a CRT using the electric signal. By outputting, a radiation image which is not affected by the fluctuation of the radiation exposure amount can be obtained.

[0005]

In a flat panel sensor using a semiconductor sensor, a TFT (thin film transistor) is used as a switching element for reading out each pixel.
Is mainly used. In rare cases, a diode may be used.

In the X-ray apparatus, the light input time corresponds to the X-ray exposure period. As a requirement of the system, it is possible to provide an X-ray image to a user in a short time after the irradiation by reading data immediately after the X-ray irradiation.

[0007] Even if the increase in the offset corresponding to the pixel is taken into account, it is logically appropriate to read out immediately after irradiation. However, when charges are read from the sensor immediately after light input corresponding to the X-ray irradiation period, there is a problem that crosstalk between pixels occurs.

An object of the present invention is to provide an image photographing apparatus and an image photographing method capable of photographing an image with reduced crosstalk between pixels.

[0009]

According to one aspect of the present invention, there are provided sensor means and driving means for driving the sensor means, wherein the driving means is provided with a predetermined time after the end of radiation exposure. An image photographing apparatus is provided which starts reading data from the sensor means. According to another aspect of the present invention, there is provided an image capturing method for reading data from a sensor unit and capturing an image, comprising: (a) waiting for a predetermined time from the end of radiation exposure; Starting the reading of data from the sensor means.

According to the present invention, an image with reduced crosstalk between pixels can be obtained by starting reading data from the sensor means after waiting for a predetermined time after the end of radiation exposure.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below along with examples with reference to the drawings. In the image capturing apparatus, it was found that one of the causes of crosstalk between pixels was leakage of the TFT switch immediately after light incidence.
Therefore, after detecting the signal of the end of the X-ray exposure, the apparatus waits for a time during which the leakage characteristics of the TFT switch disappears, and then turns on the TFT switch to start reading of each pixel. The determination of the read standby time may depend on variations in the sensor manufacturing process. Therefore, individual X-rays must be incident before the product is shipped, and the crosstalk for each read standby time must be measured. Is possible.

Regarding the detection of the signal of the end of the X-ray exposure, a sensor for automatic exposure control (AEC or photo timer) arranged in front of the flat panel sensor,
Alternatively, it can be realized by monitoring the amount of incident X-rays in real time with a semiconductor sensor arranged on the back of the flat panel sensor. On the other hand, by utilizing the fact that the X-ray generator is connected on-line, a signal for monitoring the tube current during the application period of the high voltage of the X-ray generator or the tube current is input to the sensor driver. It is also possible to read out the irradiation end signal a fixed time after the end of X-ray irradiation.

An entire X-ray imaging system (image photographing apparatus) of the present embodiment will be described with reference to FIG. 101 denotes an X-ray room, 102 denotes an X-ray control room, and 103 denotes a diagnostic room. The overall operation of the X-ray imaging system is controlled by the system control unit 110. The functions of the system control unit 110 are mainly described below.

First, an instruction is received from the operator via the operator interface 111. The operator interface 111 is configured to include a photographing start input unit.

The operator interface 111 includes a touch panel on a display, a mouse, a keyboard, a joystick, a foot switch, and the like. From the operator interface 111, setting of imaging conditions (still image, moving image, X-ray tube voltage, tube current, X-ray irradiation time, etc.) and imaging timing, image processing conditions, subject ID, processing method of captured images, and the like are performed. Although it can be done, most information is transferred from the radiation information system and does not need to be entered separately. An important task of the operator is a task of confirming a captured image. That is, it is determined whether the angle is correct, whether the patient is moving, whether image processing is appropriate, and the like.

Then, the system control unit 110 instructs the imaging control unit 214, which is responsible for the X-ray imaging sequence, imaging conditions based on the instruction of the imaging person 105, and fetches data.
Based on the instruction, the imaging control unit 214 controls the X-ray generator 120, the imaging bed 130, and the X-ray detector 1 which are radiation sources.
The image processing unit 10 drives the image processing unit 10 to capture the image data.
After that, the image processing is performed by the operator and displayed on the display 160, and at the same time, the basic image processing data is stored in the external storage device 161.

Further, the system controller 110 controls the photographer 1
Based on the instruction in step 05, re-image processing and reproduction display, transfer and storage of image data to a device on the network, display display, printing on film, and the like are performed.

Next, a description will be given sequentially following the flow of signals. The X-ray generator 120 includes an X-ray tube 121 and an X-ray diaphragm 123. The X-ray tube 121 is the imaging control unit 21
4 driven by the high voltage generation power supply 124 controlled to
An X-ray beam 125 is emitted. The X-ray stop 123 is driven by the imaging control unit 214, and shapes the X-ray beam 125 so that unnecessary X-ray irradiation is not performed when the imaging area is changed. The X-ray beam 125 is an X-ray transparent imaging bed 1
It is pointed at the subject 126 lying on 30. The imaging bed 130 is driven based on an instruction from the imaging control unit 214. The X-ray beam 125 irradiates the X-ray detector 140 after passing through the subject 126 and the imaging bed 130.

The X-ray detector 140 comprises a grid 141, a scintillator 142, a photodetector array 8, an X-ray exposure monitor (AEC) 144, and a drive circuit 145. The drive circuit 145 detects an X-ray exposure end signal of the X-ray exposure monitor (AEC) 144 or a high-voltage application power supply or a signal of an X-ray tube current from the high-voltage generation power supply 124 as shown in FIG. TFT after waiting for a certain period
The switch is driven to read the charge. As the read wait time, a constant may be used as long as the TFT characteristics of the sensor to be manufactured are stable. However, if there is a variation among manufacturing lots, the read wait time is set beforehand by a read circuit to be described later. Data may be read while changing the time, the amount of crosstalk in the data may be calculated, and a wait time that does not affect the image noise may be determined for each sensor. Further, the wait time may be set to be different for each shooting, or may be set to be always constant regardless of each shooting.

In FIG. 4, a drive circuit 145 includes a read wait circuit 501 and a read time setting circuit 502.
And controls the photodetection array 8 by inputting from the AEC 144 and the high voltage generation power supply 124.

FIG. 5 shows the timing of the delay. When an X-ray high voltage application signal or an X-ray tube current signal is used, there is a possibility that more X-rays are emitted after the signal has fallen. (AEC) is set longer than in the case of using (AEC). The details of the drive circuit 145 will be described later, but the read wait time set here is
This is a wait time for the start of reading, and the wait time in this embodiment is about 100 msec. After the wait time, reading is performed in the reading section.

The grid 141 reduces the influence of X-ray scattering caused by transmission through the subject 126. The grid 141 includes an X-ray low absorption member and a high absorption member,
For example, it has a stripe structure of Al and Pb. Then, at the time of X-ray irradiation, the grid 141 is vibrated based on an instruction from the imaging control unit 214 so that moire does not occur due to the relationship between the grid ratio of the photodetector array 8 and the grid 141.

In the scintillator 142, the base substance of the phosphor is excited by high-energy X-rays, and fluorescence in the visible region is obtained by recombination energy at the time of recombination. The fluorescence may be due to the host itself such as CaWO ₄ or CdWO _4, or may be due to the emission center substance activated in the host such as CsI: Tl or ZnS: Ag.

The photodetector array 8 is arranged adjacent to the scintillator 142. This photodetector array 8 converts photons into electrical signals. The X-ray exposure monitor 144 monitors the amount of X-ray transmission. X-ray exposure monitor 1
Numeral 44 may directly detect X-rays using a light receiving bare hand of crystalline silicon or the like, an ion chamber type may be disposed on the front surface of the photodetector array 8, or the scintillator 1
The light from 42 may be detected. In this example, the visible light (proportional to the X-ray dose) transmitted through the photodetector array 8 is detected by an amorphous silicon light receiving element formed on the back surface of the photodetector array 8 substrate, and the information is transmitted to the imaging control unit 214. Send
The imaging control unit 214 determines the high-voltage generation power supply 1 based on the information.
24 is driven to block or adjust X-rays. The drive circuit 145 drives the photodetector array (flat panel sensor) 8 under the control of the imaging control unit 214, and reads a signal from each pixel. Photodetector array 8, peripheral drive circuit 145
Will be described in detail later.

The image signal from the X-ray detector 140 is transferred from the X-ray room 101 to the image processing unit 10 in the X-ray control room 102. At the time of this transfer, since the noise inside the X-ray room 101 due to the generation of X-rays is large, the image data may not be accurately transferred due to the noise, and therefore, it is necessary to increase the noise resistance of the transfer path. It is desirable to use a transmission system having an error correction function or to use, for example, a shielded twisted pair cable using a differential driver or a transfer path using an optical fiber. The image processing unit 10 switches display data based on an instruction from the imaging control unit 214 (described in detail later). In addition, image data correction, spatial filtering, recursive processing, and the like can be performed in real time, and gradation processing, scattered radiation correction, DR compression processing, and the like can be performed.

The processed image is displayed on the display adapter 1
The information is displayed on the display 160 via the display 51. At the same time as the real-time image processing, the basic image in which only the data is corrected is stored in the high-speed storage device 161. As the high-speed storage device 161, a data storage device that satisfies a large capacity, high speed, and high reliability is preferable. For example, a hard disk array such as a RAID is preferable. Further, based on an instruction from the operator, the image data stored in the high-speed storage device 161 is stored in an external storage device. At this time, the image data is reconfigured to satisfy a predetermined standard (for example, IS & C), and then stored in an external storage device. The external storage device is, for example, a magneto-optical disk 162 or a hard disk in the file server 170 on the LAN.

This X-ray imaging system uses a LAN board 16
It is also possible to connect to LAN via HIS3.
It has a structure that has data compatibility with. The LAN is connected to a plurality of X-ray imaging systems, as well as a monitor 174 for displaying moving images and still images, a file server 170 for filing image data, an image printer 172 for outputting images to film, An image processing terminal 173 for performing complicated image processing and diagnosis support is connected. The X-ray imaging system outputs image data according to a predetermined protocol (for example, DICOM). In addition, a doctor can perform real-time remote diagnosis at the time of X-ray imaging using a monitor connected to a LAN.

FIG. 2 shows an equivalent circuit of an example of the light detection array 8. In the following example, a two-dimensional amorphous silicon sensor will be described. However, the detection element does not need to be particularly limited. Even A
The function and configuration of the / D converter are the same.

Returning to FIG. 2, description will be added. The structure of one element is composed of a photodetector 21 and a switching TFT 22 for controlling the accumulation and reading of electric charge, and is generally formed of amorphous silicon (α-) disposed on a glass substrate.
Si). In this example, 21C in the light detecting unit 21 may be a photodiode having simply a parasitic capacitance, or a photodetector including an additional capacitor 21C in parallel with the photodiode 21D so as to improve the dynamic range of the detector. You may catch it. The anode A of the diode 21D is connected to a bias line Lb, which is a common electrode, and the cathode K is connected to a controllable switching TFT 22 for reading out the charge stored in the capacitor 21C. In this example, the switching TFT 22 is a thin film transistor connected between the cathode K of the diode 21D and the charge readout amplifier 26.

The signal charge operates the switching TFT 22 and the reset switching element 25 to operate the capacitor 21.
After resetting C, by radiating the radiation 1, charges are generated in the photodiode 21D according to the radiation dose and accumulated in the capacitor 21C. After that, the signal charge is transferred to the capacitor by operating the switching TFT 22 and the reset switching element 25 again. Then, the pre-amplifier 26 reads out the amount accumulated by the photodiode 21D as a potential signal, and performs A / D conversion to detect the amount of incident radiation.

FIG. 3 is an equivalent circuit diagram showing a two-dimensionally arranged photoelectric conversion device. FIG. 3 shows a photoelectric conversion operation when the photoelectric conversion element shown in FIG. State.

The pixels of the light detection array 8 are 2000 × 20
It is composed of about 00 to 4000 × 4000 pixels, and the array area is 200 mm × 200 mm to 500 mm × 50.
It is about 0 mm. In FIG. 3, the light detection array 8 has 4
It consists of 096 × 4096 pixels, and the array area is 4
It is 30 mm × 430 mm. Therefore, the size of one pixel is about 105 μm × 105 μm. 4 in 1 block
Each of the pixels is two-dimensionally arranged by arranging 096 pixels in the horizontal direction and arranging 4096 lines sequentially in the vertical direction.

In the above example, an example is shown in which the photodetector array 8 of 4096 × 4096 pixels is constituted by one substrate.
The photodetector array 8 of 4096 × 4096 pixels is 2048
It can also be composed of four photodetectors having × 2048 pixels. 2048 × 2048 detectors are 1 in 4
When two photodetector arrays 8 are formed, there is an advantage that the yield is improved by dividing and manufacturing them.

As described above, one pixel includes the photoelectric conversion element 21 and the switching TFT 22. 21 (1,
1) to 21 (4096, 4096) correspond to the photoelectric conversion element 21 described above, and the cathode side of the photodetection diode is represented by K, and the anode side is represented by A. 22
(1, 1) to 22 (4096, 4096) correspond to the switching TFT 22.

The K electrodes of the photoelectric conversion elements 21 (m, n) in each row of the two-dimensional photodetector array 8 have a corresponding switching T
A common column signal line (Lc1 to Lc4096) for the column by the source and drain conductive paths of FT22 (m, n)
It is connected to the. For example, the photoelectric conversion element 21 in row 1
(1,1) to 21 (1,4096) are connected to the first column signal line Lc1. A of the photoelectric conversion element 21 of each row
The electrodes are commonly connected to a bias power supply 31 for operating the above-described mode through a bias wiring Lb. T for each row
The gate electrode of FT22 is connected to a row selection line (Lr1 to Lr40).
96). For example, the TFT 22 in row 1
(1,1) to 22 (4096,1) are the row selection lines Lr1
Connected to. The row selection line Lr is connected to the line selector 32.
Is connected to the imaging control unit 33 through the. The line selector section 32 includes, for example, an address decoder 34 and 4096 switch elements 35. With this configuration, an arbitrary line Lrn can be read. If the simplest configuration is used, the line selector section 32 can be configured simply by a shift register used for a liquid crystal display or the like.

The column signal line Lc is connected to a signal readout unit 36 controlled by the imaging control unit 33. 25 is a switch for resetting the column signal line Lr to the reference potential of the reset reference power supply 24, 26 is a preamplifier for amplifying the signal potential, 38 is a sample and hold circuit, 39
Denotes an analog multiplexer, and 40 denotes an A / D converter. The signal on each column signal line Lrn is amplified by the preamplifier 26 and held by the sample and hold circuit 38. The output is sequentially output to an A / D converter 40 by an analog multiplexer 39, converted into a digital value, and transferred to the image processing unit 10.

The photoelectric conversion device of this embodiment is 4096 × 40
The 96 pixels are divided into 4096 lines Lcn, and the output of 4096 pixels per column is simultaneously transferred, and 4096 preamplifiers 26 and 409 are transmitted through this column signal line Lc.
The signals are sequentially output to the A / D converter 40 by the analog multiplexer 39 through the six sample-and-hold units 38.

FIG. 3 shows the A / D converter 40 as if it were composed of one unit.
A / D conversion is performed simultaneously in 32 systems. This is because it is required to shorten the image signal reading time without unnecessarily increasing the analog signal band and the A / D conversion rate. Details of the A / D converter will be described later.

The accumulation time and the A / D conversion time are closely related. If the A / D conversion is performed at a high speed, the bandwidth of the analog circuit is widened and it is difficult to achieve a desired S / N.
Therefore, without unnecessarily increasing the A / D conversion speed,
It is required to shorten the reading time of the image signal.
For this purpose, the A / D converter is used by using many A / D converters 40.
Conversion may be performed, but in that case, the cost increases. Therefore, it is necessary to select an appropriate value in consideration of the above points.

The irradiation time of the radiation 1 is about 10 to 500.
msec, it is appropriate to set the capture time or charge storage time for the entire screen to the order of 100 msec or slightly shorter.

For example, all the pixels are sequentially driven for 100 ms.
In order to capture an image with ec, the analog signal band is set to 50.
When the A / D conversion is performed at a sampling rate of about 10 MHz, for example, at a sampling rate of 10 MHz, at least four A / D converters 40 are required. In this imaging apparatus, A / D conversion is performed simultaneously in 16 systems. The outputs of the 16 A / D converters 40 are input to the corresponding 16 memories (not shown) such as FIFO (not shown). By selecting and switching the memory, the image data is transferred to the subsequent image processing unit 10 or the memory as image data corresponding to one continuous scanning line. Thereafter, images and graphs are displayed on a display device such as a display.

As described above, by giving the wait time in consideration of the leakage of the TFT switch immediately after light is input to the sensor, it is possible to obtain an image in which crosstalk between pixels is reduced or eliminated. become.

The present invention also includes a software program code for realizing the functions of the above-described embodiments, which is implemented by operating according to a program stored in a computer (CPU or MPU) of the system. included.

In this case, the program code itself of the software realizes the functions of the above-described embodiment, and the program code itself and means for supplying the program code to the computer, for example, storing the program code The recorded recording medium constitutes the present invention. As a recording medium for storing such a program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-RO
M, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

It should be noted that each of the above-described embodiments is merely an example of the embodiment for carrying out the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. It is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features.

[0046]

As described above, according to the present invention, the reading of data from the sensor means is started after the radiation exposure is completed and after waiting for a predetermined time, whereby an image with reduced crosstalk between pixels can be obtained. Obtainable.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a detailed configuration of an X-ray imaging apparatus.

FIG. 2 is a diagram showing a sensor equivalent circuit.

FIG. 3 is a circuit diagram of a flat sensor panel.

FIG. 4 is a diagram illustrating a configuration of a drive circuit.

FIG. 5 is a diagram showing read timing.

[Explanation of symbols]

 Reference Signs List 8 photodetector array 10 image processing unit 21 photodetection unit 22 TFT 101 X-ray room 102 X-ray control room 103 diagnostic room 105 photographer 110 system control unit 111 operator interface 120 X-ray generator 121 X-ray tube 123 X Line diaphragm 124 High-voltage generating power supply 125 X-ray beam 126 Subject 130 Imaging bed 140 X-ray detector 141 Grid 142 Scintillator 144 X-ray exposure monitor 145 Drive circuit 151 Display adapter 160 Display 161 External storage device 163 LAN board 170 File server 172 image printer 173 image processing terminal 174 monitor 214 imaging control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/32 H04N 5/32 F term (Reference) 2G088 EE02 EE27 FF02 FF14 GG21 JJ05 KK24 KK27 KK32 LL12 LL13 4C093 CA01 EB13 EB30 5B047 AA17 BA02 BB06 CB17 CB30 EB03 5C024 AX12 AX16 AX17 CX11 GX03 GY31 GZ00 HX03 HX15 HX23

Claims (10)

[Claims] 1. A sensor device comprising: a sensor unit; and a driving unit that drives the sensor unit, wherein the driving unit starts reading data from the sensor unit a predetermined time after the end of radiation exposure. Image capturing device. 2. A radiation detecting means disposed on the front or back of the sensor means for detecting radiation, and in accordance with the radiation detected by the radiation detecting means,
2. The image photographing apparatus according to claim 1, further comprising: a radiation irradiation end detecting unit that detects the end of the radiation irradiation. 3. The apparatus according to claim 1, further comprising: a radiation generating unit configured to generate radiation, wherein the radiation irradiation end detecting unit receives the irradiation completion signal from the radiation generating unit and detects the end of radiation irradiation. The image photographing apparatus according to claim 2, wherein: 4. A time until the reading is started is as follows:
2. The time interval for reducing or eliminating crosstalk between pixels of the sensor means is determined.
4. The image photographing device according to any one of claims 1 to 3. 5. The apparatus according to claim 1, further comprising a determination unit that measures a crosstalk between pixels of the sensor unit and determines a time until the reading is started.
The image photographing apparatus according to any one of claims 1 to 4. 6. The apparatus according to claim 1, wherein the predetermined time is a time that is always determined from the end of the radiation exposure.
An image capturing device according to any one of the above. 7. The apparatus according to claim 1, wherein the predetermined time is a fixed time for each imaging from the end of the radiation exposure.
An image capturing device according to any one of the above. 8. An image photographing apparatus according to claim 1, wherein said sensor means is formed by a semiconductor sensor. 9. The method according to claim 1, wherein the driving unit includes a thin film transistor for reading data.
9. The image photographing apparatus according to any one of 8. 10. An image capturing method for reading data from a sensor means and capturing an image, comprising: (a) waiting for a predetermined time from the end of radiation exposure; and (b) receiving from the sensor means after the standby. Starting data reading.