Radiation image detection method and apparatus

A radiation image detection method including the steps of: detecting from a radiation image detector including multitudes of pixels disposed two-dimensionally, each having a TFT switch, an analog image signal of each pixel flowing out through each data line by sequentially switching ON the TFT switches connected to each scanning line on a scanning line-by-scanning line basis; detecting an analog leak level flowing out through each data line with the TFT switches connected to each of the scanning lines being switched OFF each time before switching ON the TFT switches on a scanning line-by-scanning line basis when converting the detected analog image signal to a digital image signal and outputting; and correcting the analog image signal before being converted to the digital image signal based on the leak level.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation image detection method and apparatus for detecting a radiation image from a radiation image detector which includes multitudes of pixels, each having a TFT switch, disposed two-dimensionally.

2. Description of the Related Art

Radiation image detection systems having a TFT (Thin Film Transistor) active matrix array on which a radiation sensitive layer is disposed are known. Such systems are capable of tentatively storing latent image charges generated according to radiation transmitted through a subject and reading out the stored latent image charges as electrical signals, and have an advantage over conventional imaging plates using a storage phosphor in that they allow instantaneous image verification and motion image monitoring, so that they are spreading rapidly.

First, the structure of a conventional radiation image detection system will be described with reference toFIG. 8.FIG. 8is a schematic equivalent circuit of 3×3 pixels. InFIG. 8, the reference numerals111,112,113, and114respectively denote a capacitor, a TFT switch, a scanning line, and a data line.

Radiation, such as X-rays or the like, enters from a direction normal to the surface ofFIG. 8, which is converted to electrical signals by the photoelectric conversion elements and the charges thereof are stored in the capacitor111of each pixel. Thereafter, the TFT switches112are sequentially activated by the scanning lines113to transfer the stored charges to the data lines114connected to either one of the source/drain electrodes of the TFT switches112, and the signals flowing out through the data lines are detected by the signal detectors115, which are then converted to digital signals by the A/D converter116and outputted.

In such type of radiation image detection system, there may be cases in which various types of noise are added to the essential image signals to be detected due to various reasons. For example, one type of noise is caused by leak current of the TFT switch. It is preferable that no leak current flows through the TFT switch that selects a pixel to be detected while it is in OFF state. But, irradiation of a larger amount of X-rays causes a larger amount of charges to be generated in the charge generation layer, which causes the drain voltage to become high, resulting in a large amount of leak current to flow and added to the image signals. In order to solve this problem, for example, Japanese Unexamined Patent Publication No. 2003-319264 proposes a method in which the leak current is read out while the TFT switches are in OFF state, and digital image signals are corrected using the leak current value.

The method described in the aforementioned patent publication, however, reduces, in effect, a usable dynamic range. More specifically, the image signal correction is performed using a process for subtracting the leak current component from the obtained digital image signal, so that the possible value range of the corrected image signal is reduced by the amount corresponding to the amount of the leak current from the dynamic range at the output of the A/D converter. This causes a problem, in particular, where a large amount of X-rays is irradiated, since the leak current becomes great in such a case.

In view of the circumstances described above, it is an object of the present invention to provide a radiation image detection method and apparatus capable of appropriately correcting the image signal by the amount corresponding to the amount of the error caused by leak currents, and preventing the reduction in the dynamic range of the image signal after correction.

SUMMARY OF THE INVENTION

The radiation image detection method of the present invention is a method for detecting from a radiation image detector including a charge generation layer that generates charges by receiving radiation and a detection layer stacked on top of another, the detection layer including: multitudes of pixels, each having a collection electrode for collecting the charges generated in the charge generation layer, a capacitor for storing the charges collected by the charge collection electrode, and a TFT switch for reading out the charges stored in the capacitor; multitudes of scanning lines for switching ON/OFF the TFT switches; and multitudes of data lines for transferring the charges stored in the capacitors, an analog image signal of each of the pixels flowing out through each of the data lines by sequentially switching ON the TFT switches connected to each of the scanning lines on a scanning line-by-scanning line basis, and converting the detected analog image signal to a digital image signal and outputting, wherein the method further includes the steps of:

detecting an analog leak level flowing out through each of the data lines with the TFT switches connected to each of the scanning lines being switched OFF each time before switching ON the TFT switches on a scanning line-by-scanning line basis; and

correcting the analog image signal based on the leak level prior to the conversion.

The radiation image detection apparatus of the present invention is an apparatus including:

a radiation image detector including a charge generation layer that generates charges by receiving radiation and a detection layer stacked on top of another, the detection layer including: multitudes of pixels, each having a collection electrode for collecting the charges generated in the charge generation layer, a capacitor for storing the charges collected by the charge collection electrode, and a TFT switch for reading out the charges stored in the capacitor; multitudes of scanning lines for switching ON/OFF the TFT switches; and multitudes of data lines for transferring the charges stored in the capacitors;

an image signal detection means that detects an analog image signal of each of the pixels flowing out through each of the data lines from the radiation image detector by sequentially switching ON the TFT switches connected to each of the scanning lines on a scanning line-by-scanning line basis;

an analog/digital conversion means that converts the detected analog image signal to a digital image signal;

a leak level detection means that detects an analog leak level flowing out through each of the data lines with the TFT switches connected to each of the scanning lines being switched OFF each time before the TFT switches are switched ON on a scanning line-by-scanning line basis; and

a correction means that corrects the analog image signal based on the leak level prior to the conversion.

In the radiation image detection apparatus of the present invention, the correction means may be a means that subtracts the leak level detected from each of the data lines with the TFT switch of each of the pixels connected thereto being switched OFF before the TFT switch is switched ON from the analog image signal of each of the pixels.

Further, the image signal detection means may be a means that detects the analog image signal of each of the pixels by comparing a signal flowing out through each of the data lines when the TFT switches connected to each of the scanning lines are sequentially switched ON on a scanning line-by-scanning line basis with a predetermined reference voltage; and the correction means is a means that control the reference voltage based on the analog leak level detected from each of the data lines to which each of the pixels are connected with the TFT switch thereof being switched OFF before the TFT switch is switched ON.

According to the radiation image detection method and apparatus, which is a method and apparatus for detecting from a radiation image detector including a charge generation layer that generates charges by receiving radiation and a detection layer stacked on top of another, the detection layer including: multitudes of pixels, each having a collection electrode for collecting the charges generated in the charge generation layer, a capacitor for storing the charges collected by the charge collection electrode, and a TFT switch for reading out the charges stored in the capacitor; multitudes of scanning lines for switching ON/OFF the TFT switches; and multitudes of data lines for transferring the charges stored in the capacitors, an analog image signal of each of the pixels flowing out through each of the data lines by sequentially switching ON the TFT switches connected to each of the scanning lines on a scanning line-by-scanning line basis, and converting the detected analog image signal to a digital image signal and outputting, an analog leak level flowing out through each of the data lines is detected with the TFT switches connected to each of the scanning lines being switched OFF each time before the TFT switches are switched ON on a scanning line-by-scanning line basis and the analog image signal is corrected based on the leak level prior to the conversion. This allows the amount of error in the image signal caused by the leak currents may be corrected properly, and at the same time the reduction in the dynamic range of the corrected image signal may be prevented.

Further, if the correction means is a means that subtracts the leak level detected from each of the data lines with the TFT switch of each of the pixels connected thereto being switched OFF before the TFT switch is switched ON from the analog image signal of each of the pixels, the amount of error in the image signal of each of the pixels may be corrected properly.

Still further, if the image signal detection means is a means that detects the analog image signal of each of the pixels by comparing a signal flowing out through each of the data lines when the TFT switches connected to each of the scanning lines are sequentially switched ON on a scanning line-by-scanning line basis with a predetermined reference voltage, and the correction means is a means that control the reference voltage based on the analog leak level detected from each of the data lines to which each of the pixels are connected with the TFT switch thereof being switched OFF before the TFT switch is switched ON, an error corrected image signal may be obtained by estimating the amount of error in the image signal caused by the leak currents in advance, and controlling the reference voltage used for the image signal detection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the radiation image detection apparatus of the present invention will be described with reference to the accompanying drawings.

A schematic configuration of the radiation image detection apparatus according to an embodiment of the present invention is illustrated inFIG. 1. The illustrated radiation image detection apparatus100includes: a radiation image detector110; a signal detection section120that detects analog image signals outputted from the radiation image detector110and analog leak levels; a scan signal control unit103that outputs scan signals to scanning lines (gate electrodes)2of the radiation image detector110; and a signal processing unit130that obtains the signals detected by the signal detection section120and outputs the signals to a display200as video signals, and outputs control signals to the scan signal control unit103and signal detection section120.

The radiation image detector110includes multitudes of pixels disposed two-dimensionally, each including: an image sensor section105having a bias electrode, a semiconductor film of charge generation layer, and a charge collection electrode, to be described later; a capacitor5for storing charge signals detected by the image sensor section105; and a TFT switch4for reading out the charges stored in the capacitor5. In addition, multitudes of scanning lines (gate electrodes)2for switching ON/OFF the TFT switches4and multitudes of data lines (source electrodes)3for transferring the charges stored in the capacitors5are provided.

The signal processing section130includes: a leak error correction means140that performs correction on analog image signals detected by the signal detection section120based on leak levels also detected by the signal detection section120; and an A/D converter150for converting analog image signals corrected by the leak error correction means140to digital image signals.

Now, the radiation image detector110will be described in more detail.FIG. 2is a cross-sectional view of the radiation image detector110, illustrating the structure of a single pixel, andFIG. 3is a plan view thereof.

As illustrated inFIG. 2, the radiation image detector110includes an active matrix substrate10on which a semiconductor film6having electromagnetic conductivity, and a bias electrode (common electrode)7connected to a not shown high voltage power source are stacked in this order. The semiconductor film6generates charges (electron-hole pairs) when irradiated with an electromagnetic wave, such as X-rays or the like. That is, the semiconductor film6has electromagnetic conductivity, and provided for converting image information represented by X-rays to charge information. The semiconductor film6is, for example, made of selenium-based amorphous a-Se (amorphous selenium). The referent of “selenium-based” as used herein means that selenium is included 50% or more.

Hereinafter, the active matrix substrate10will be described in more detail.

The active matrix substrate10includes a glass substrate1, a scanning line (gate electrode)2, a capacitor electrode (Cs electrode)14, a gate insulation film15, a connection electrode13, a channel layer8, a contact layer9, a data line (source electrode)3, an insulation protection film17, and an interlayer insulation film12.

The thin film transistor (TFT)4is formed by the gate insulation film15, connection electrode13, channel layer8, contact layer9, and the like, and the capacitor (Cs)5is formed by the Cs electrode14, gate insulation film15, connection electrode13, and the like.

The glass substrate1is the supporting substrate and, for example, non-alkali glass may be used for this purpose. The scanning lines2and data lines3are electrode wires disposed in a grid pattern, and the thin film transistor (TFT switch)4is formed at each intersection thereof. The TFT switch4is a switching element, and the source and drain thereof are connected to the data line3and connection electrode13respectively. The data line3is the source electrode and the connection electrode13is the drain electrode of the TFT switch4. That is, the data line includes a linear portion serving as the signal line and an extended portion for forming the TFT switch4. The connection electrode13is provided to connect the TFT switch4with the capacitor5.

The gate insulation film15is made of SiNx, SiOx, or the like. The gate insulation film15is disposed to cover the scanning line2and Cs electrode14, and the portion located over the scanning line2acts as the gate insulation film of the TFT switch4, and the portion located over the Cs electrode14acts as the dielectric layer of the capacitor5. That is, the capacitor5corresponds to the region where the Cs electrode14, which is formed on the same layer as the scanning line2, and the connection electrode13are stacked on top of another. It is noted that an anodized oxide film obtained by anodizing the scanning line2and Cs electrode14may also be used in combination with SiNx or SiOx for the gate insulation film15.

The channel layer (i layer)8corresponds to the channel section of the TFT switch4, which is a current channel for connecting between the data line3and connection electrode13. The contact layer (n+layer)9provides a contact between the data line3and connection electrode13.

The insulation protection film17extends substantially the entire surface (area) over the data line3and connection electrode13, i.e., over the glass substrate1. The insulation protection film17provides electrical insulation between the data line3and connection electrode13, as well as protecting them. The insulation protection film17has a contact hole16at a predetermined position, i.e., the position over the portion of the connection electrode13facing the Cs electrode14across the capacitor5.

The charge collection electrode11is made of a transparent conductive amorphous oxide film. The charge collection electrode11is formed to fill the contact hole16and stacked over the data line3and connection electrode13. The charge collection electrode11is electrically communicating with the semiconductor film6so as to be able to collect charges generated in the semiconductor film6.

The interlayer insulation film12is made of an acrylic resin having photosensitivity and provides electrical insulation for the TFT switch4. The contact hole16runs through the interlayer insulation film12, and the charge collection electrode11is connected to the connection electrode13.

The scanning line2and Cs electrode14are provided on the glass substrate1. The channel layer (i layer)8and contact layer (n+layer)9are stacked in this order over the scanning line2via the gate insulation film15. The data line3and connection electrode13are formed on the contact layer9. The connection electrode13is stacked over the layer forming the capacitor5. The insulation protection layer17is disposed on the connection electrode13and data line3.

The interlayer insulation film12of the TFT switch4is provided on the insulation protection layer17. The charge collection electrode11is provided in the upper layer of the interlayer insulation film12, i.e., the uppermost layer of the active matrix substrate10. The charge collection electrode11is connected to the TFT switch4through the connection electrode13.

The gate insulation film15is provided on the Cs electrode14, and the connection electrode13is disposed on the gate insulation film15. The charge collection electrode11is connected to the connection electrode13through the contact hole16running through the interlayer insulation film12.

A not shown high voltage power source is connected between the bias electrode7and Cs electrode14. A voltage is applied between the bias electrode7and Cs electrode14by the high voltage power source, which causes an electric field to be generated between the bias electrode7and Cs electrode14across the capacitor5. Here, the semiconductor film6and capacitor5are electrically connected in series, so that when a bias voltage is applied to the bias electrode7, charges (electron-hole pairs) are generated in the semiconductor film6. The electrons generated in the semiconductor film6are moved to the positive electrode side and holes are moved to the negative electrode side, causing charges to be stored in the capacitor5.

The entire radiation image detector101includes a plurality of charge collection electrodes11disposed two-dimensionally, a plurality of capacitors5, each connected to each charge collection electrode11, and a plurality of TFT switches4, each connected to each capacitor5. This allows two-dimensional electromagnetic information to be tentatively stored in the capacitors5, and the two-dimensional charge information may be read out easily by sequentially scanning the TFT switches4.

An example manufacturing process of the radiation image detector will now be described.

First, a metal film of Ta, Al, or the like is formed on the glass substrate1by sputter deposition with a thickness of approximately 300 nm, and the scanning lines2and Cs electrodes14are formed by patterning the film in a desired shape.

Next, the gate insulation film15made of SiNx, SiOx, or the like is formed substantially over the entire surface of the glass substrate1with a thickness of approximately 350 nm by CVD (Chemical Vapor Deposition) so as to cover the scanning lines2and Cs electrodes14. It is noted that an anodized oxide film obtained by anodizing the scanning lines2and Cs electrodes14may also be used in combination with SiNx or SiOx for the gate insulation film15.

Then, amorphous silicon (a-Si) film is formed by CVD with a thickness of approximately 100 nm such that the channel layers8are disposed over the scanning lines2via the gate insulation film15, and the channel layers8are formed by patterning the film in a desired shape.

Next, a-Si film is formed by CVD with a thickness of approximately 40 nm such that the contact layers9are disposed in the upper layer of the channel layers8, and the contact layers9are formed by patterning the film in a desired shape.

Further, a metal film of Ta, Al, or the like is formed on the contact layers9with a thickness of approximately 300 nm, and data lines3and connection electrodes13are formed by patterning the film in a desired shape.

Then, in order to form the insulation protection film17, a SiNx film substantially covering the entire region of the glass substrate1, having the TFT switches4, capacitors5, and the like formed thereon, is formed by CVD with a thickness of approximately 300 nm. Thereafter, the SiNx film formed on a predetermined portion of the connection electrode13is removed to create a portion of the contact hole16.

Next, in order to form the interlayer film12, an acrylic resin film or the like having photosensitivity is formed with a thickness of approximately 3 μm to cover substantially the entire surface of the insulation protection film17. Then, patterning is performed by photolithography technique to form a portion of the contact hole16by aligning with the portion of the contact hole16of the insulation protection film17.

Then, a transparent conductive amorphous oxide film, such as ITO (Indium-Tin-Oxide) film, is formed on the interlayer insulation layer12by sputter deposition with a thickness of approximately 200 nm, and the charge collection electrodes11are formed by patterning the film in a desired shape. Here, each charge collection electrode11is electrically communicated (short-circuited) with each connection electrode13through each contact hole16running through the insulation protection layer17and interlayer insulation film12.

In the present embodiment, the active matrix substrate10adopts a so-called roof structure (mushroom electrode structure) in which the charge collection electrode11overlaps with the TFT switch4on the upper side thereof as described above. But, a non-roof structure may also be adopted. Further, as the switching element, the TFT4using a-Si is employed, but p-Si (poly silicon) may also be used. Still further, although an inversely staggered structure in which the data lines3and connection electrodes13are positioned above the scanning lines2via the gate insulation film15is adopted, a staggered structure may also be employed.

Next, the semiconductor film6of a-Se (amorphous selenium) having conductivity for electromagnetic wave is formed to cover the entire pixel array region of the active matrix substrate10by vacuum deposition with a thickness of approximately 0.5 to 1.5 mm.

Finally, the bias electrode7of Au, Al, or the like is formed on substantially the entire surface of the semiconductor film6by vacuum deposition with a thickness of approximately 200 nm.

It is noted that a charge injection blocking layer for blocking electrons or holes from entering into the semiconductor film6, or a buffer layer for improving contact between the semiconductor layer6and charge collection electrode11may be provided at the interface between the semiconductor layer6and charge collection electrode11. Likewise, a charge injection blocking layer or a buffer layer may be provided at the interface between the semiconductor film6and bias electrode7. As for the material of the charge injection blocking layer or buffer layer, a-Se including a-As2Se3, alkali element ion, or halogen element ion added thereto, or the like may be used.

Next, the operational principle of the radiation image detector110structured in the aforementioned manner will be described. When X-rays are irradiated on the semiconductor film6while a voltage is applied between the bias electrode7and Cs electrodes14, charges (electron-hole pairs) are generated in the semiconductor film6. The electrons generated in the semiconductor film6are moved to the positive electrode side and holes are moved to the negative electrode side, causing charges to be stored in the capacitors5, since the semiconductor film6and each of the capacitors5are electrically connected in series.

Charges stored in each of the capacitors5may be read out to outside through the data line3by inputting a signal to the scanning line2and switching ON the TFT switch.

The scanning lines2, data lines3, TFT switches4, and capacitors5are all provided in XY matrices, so that the image information represented by the X-rays may be obtained two-dimensionally by sequentially scanning the signal to be inputted to the scanning lines2and detecting charge signals from the data lines3by the signal detection section120with respect to each data lines.

It is preferable that the charges stored in the capacitor5do not flow into the data line3at all when the TFT switch4is in OFF state. When irradiating high-dose radiation, however, the charges are intentionally flowed out to the data line3. This is because of the adoption of the roof structure (mushroom electrode structure) in which the charge collection electrode11overlaps with the TFT switch4on the upper side thereof as described above in order to prevent the TFT4from breakage arising from a large potential difference between the gate and source when high-dose radiation is irradiated. In the structure, when an excessive potential difference (about 60 to 100V) is developed, the charge collection electrode11overlapping with the TFT switch4functions as a pseudo top gate, thereby the TFT4is switched and the charges are caused to overflow into the data line3. Thereby, the TFT is protected from breakage. In the present embodiment, the description has been made of a case in which the roof structure is adopted, but an alternative structure may also be adopted, in which a protective diode structure is employed in each pixel to cause the charges to overflow into the data line3when an excessive potential difference is developed. When such structures as described above are adopted, if a high-dose of X-rays is irradiated onto each pixel, a certain amount of leak current (overflow current) flows out into the data line3, and a leak level, which is the sum of the leak currents of all of the TFT switches4connected to a single data line3, is detected. Further, the leak level is superimposed on the image signal detected through the data line3by selectively switching ON the TFT switches4.

The signal detection section120detects analog leak levels L outputted from the radiation image detector110with the TFT switches4being switched OFF and analog image signals R outputted from the radiation image detector110with the TFT switches4being selectively switched ON by making comparison with a reference voltage Vref, and includes a plurality of differential amplifiers121, each connected to each data line3. Each differential amplifier121is a charge amplifier and includes a reset switch122and an integration capacitor123.

The scan signal control unit103selectively and sequentially outputs a control signal to each scanning line2of the radiation image detector110to ON/OFF control the TFT switch4of each pixel, and the scan signal outputted to each scanning line2is controlled by a control signal inputted from the signal processing unit130to be described later.

The signal processing unit130includes the leak error correction means140, A/D converter150, and the like. The leak error correction means140performs correction on the analog image signals R detected by the signal detection section120based on the leak levels R. The leak error correction means140includes pairs of a first sample-and-hold circuit131and a second sample-and-hold circuit132, each pair connected to each data line3, in which a signal detected by each differential amplifier121when the TFT switches4of all of the scanning lines2are in OFF state, i.e., the analog leak level L is sampled and held by each of the first sample-and-hold circuits131, and a signal detected by each differential amplifier121when the TFT switches are selectively switched ON on a scanning line-by-scanning line basis, i.e., the analog image signal R is sampled and held by each of the second sample-and-hold circuits132.

Further, the leak error correction means140includes: a first multiplexer133connected to each of the first sample-and-hold circuits131and outputs a plurality of analog leak levels L held by the first sample-and-hold circuits131by selectively switching them to a subtraction circuit; a second multiplexer134connected to each of the second sample-and-hold circuits132and outputs a plurality of analog image signals R held by the second sample-and-hold circuits132by selectively switching them to the subtraction circuit; and a subtraction means135, e.g., a subtraction circuit, that subtracts the analog leak level L inputted from the first multiplexer133from the analog image signal R inputted from the second multiplexer134.

The A/D converter150converts the corrected analog image signal outputted from the leak error correction means140to digital image signal.

Recording and reading out operations of the present radiation image detection apparatus will be described with reference toFIGS. 1 and 4.FIG. 4is a timing chart illustrating an operation of the present radiation image detection apparatus.

When X-rays are irradiated on the radiation image detector110while a voltage is applied between the bias electrode7and Cs electrodes14, X-ray image data are recorded on the detector110. Charges generated in the semiconductor film6according to the amount of irradiated X-rays are collected by the charge collection electrodes11and stored in the capacitors electrically connected to the charge collection electrodes11.

Then, as illustrated inFIG. 4, a control signal for leak level detection is outputted from the signal processing unit130to the signal detection section120and scan signal control unit103, and a signal flowing out through each data line3when the TFT switches of each scanning line2is in OFF state is detected by each differential amplifier121connected to each data line3. The detected signal detected by each differential amplifier121is outputted to the first sample-and-hold circuit131of the signal processing unit130connected to each differential amplifier121and held thereby as an analog leak level L. The leak level L obtained from each data line3and held by each of the first sample-and-hold circuit131is sequentially outputted to the subtraction means135in the order of the data lines by the first multiplexer133.

Next, a control signal for image signal detection is outputted from the signal processing unit130to the scan signal control unit103. In response to the control signal, a scan signal for switching ON the TFT switches4is outputted from the scan signal control unit103to the scanning line G1, and each of the TFT switches on the scanning line G1is switched ON and a signal flows out to each data line3from each capacitor5on the scanning line G1. Further, the control signal for image signal detection is also outputted to the signal detection section120from the signal processing unit130, and in response to the control signal, a signal flowing out through each data line3is detected by each differential amplifier121connected to each data line3. The detected signal detected by each differential amplifier121is outputted to the second sample-and-hold circuit132of the signal processing unit130connected to each differential amplifier121and held thereby as an analog image signal R. The analog image signal R obtained from each data line3and held by each of the second sample-and-hold circuit132is sequentially outputted to the subtraction means135in the order of the data lines by the second multiplexer134. Thereafter, the output of the control signal for image signal detection by the signal processing unit130is terminated and TFT switches on all of the scanning lines2are switched OFF.

Then, the analog leak level L detected by each data line3is subtracted from the analog image signal R detected by each corresponding data line3in the subtraction means135. Thereby, a corrected analog image signal of each of the pixels connected to the scanning line G1is obtained. The corrected analog image signal is outputted to the A/D converter150.

When image signal reading for the scanning line G1is completed, then image signal reading for the scanning line G2is performed. First, as in the scanning line G1, the control signal for leak level detection is outputted from the signal processing unit130to the signal detection section120and scan signal control unit103, and a signal flowing out through each data line3when the TFT switches of each scanning line2is in OFF state is detected by each differential amplifier121connected to each data line3. The detected signal detected by each differential amplifier121is outputted to the first sample-and-hold circuit131of the signal processing unit130connected to each differential amplifier121and held thereby as an analog leak level L. The leak level L obtained from each data line3and held by each of the first sample-and-hold circuit131is sequentially outputted to the subtraction means135in the order of the data lines by the first multiplexer133.

Next, a control signal for image signal detection is outputted from the signal processing unit130to the scan signal control unit103. In response to the control signal, the scan signal for switching ON the TFT switches4is outputted from the scan signal control unit103to the scanning line G2, and each of the TFT switches on the scanning line G2is switched ON and a signal flows out to each data line3from each capacitor5on the scanning line G2. Further, the control signal for image signal detection is also outputted to the signal detection section120from the signal processing unit130, and in response to the control signal, a signal flowing out through each data line3is detected by each differential amplifier121connected to each data line3. The detected signal detected by each differential amplifier121is outputted to the second sample-and-hold circuit132of the signal processing unit130connected to each differential amplifier121and held thereby as an analog image signal R. The analog image signal R obtained from each data line3and held by each of the second sample-and-hold circuit132is sequentially outputted to the subtraction means135in the order of the data lines by the second multiplexer134. Thereafter, the output of the control signal for image signal detection by the signal processing unit130is terminated and TFT switches on all of the scanning lines2are switched OFF.

Then, the analog leak level L detected by each data line3is subtracted from the analog image signal R detected by each corresponding data line3in the subtraction means135. Thereby, a corrected analog image signal of each of the pixels connected to the scanning line G2is obtained. The corrected analog image signal is outputted to the A/D converter150.

Thereafter, with respect to each of the scanning lines G3, - - - , Gk, the control signal for leak level detection and control signal for image signal detection are outputted alternately from the signal processing unit130, and an analog leak level L and an analog image signal R of each pixel connected to each of the scanning lines G3, - - - , Gk are detected alternately by the signal detection section120in the same manner as described above. Then, the detected analog image signal R of each pixel and analog leak level L are held by the second sample-and-hold circuit132and first sample-and-hold circuit131of the leak error correction means140respectively, and in the subtraction means135, the analog leak level L of each pixel detected through the data line3connected to the pixel when the TFT switch is in OFF state prior to switched ON and inputted from the first sample-and-hold circuit131through the first multiplexer133is subtracted from the analog image signal R of each corresponding pixel inputted from the second sample-and-hold circuit132through the second multiplexer134. Then the corrected analog image signal of each pixel obtained by the subtraction is outputted to the A/D converter150.

Then, the corrected analog image signal obtained by the leak error correction means140is converted to a digital image signal by the A/D converter150, and outputted to an external device, such as the display200, a printer, a video processing unit, or the like.

According to the embodiment described above, from the radiation image detector110including a charge generation layer that generates charges by receiving radiation and a detection layer stacked on top of another, the detection layer including: multitudes of pixels, each having a collection electrode for collecting the charges generated in the charge generation layer, a capacitor for storing the charges collected by the charge collection electrode, and a TFT switch for reading out the charges stored in the capacitor; multitudes of scanning lines for switching ON/OFF the TFT switches; and multitudes of data lines into which the charges stored in the capacitors flow in, an analog image signal R of each pixel flowing out through each data line3is detected by sequentially switching ON the TFT switches connected to each of the scanning lines on a scanning line-by-scanning line basis, and the detected analog image signal R is converted to a digital image signal and outputted. Here, in the radiation image detection method described above, an analog leak level L flowing out through each of the data lines3is detected with the TFT switches connected to each of the scanning lines2being switched OFF each time before the TFT switches are switched ON on a scanning line-by-scanning line basis, and the analog image signal R is corrected based on the leak level L before being converted to a digital image signal. In this way, the amount of error in the image signal caused by the leak currents may be corrected properly, and the reduction in the dynamic range of the corrected image signal may be prevented.

More specifically, in the conventional radiation image detection apparatus shown inFIG. 8, an analog image signal with a leak level superimposed thereon is detected by the signal detection section, as illustrated in the graph ofFIG. 9A, and converted to a digital signal by the A/D converter. At that time, an image signal larger than the upper limit DR2of the output dynamic range 0 to DR2of the A/D converter is set to the upper limit value (saturated value) as illustrated inFIG. 9B. Then, as illustrated inFIG. 9C, the corrected image signal obtained by subtracting the leak level from the image signal outputted from the A/D converter takes a value within a second dynamic range from 0 to DR3which is smaller that the original dynamic range of the A/D converter. Here, the upper limit value DR3of the second dynamic range corresponds to a value obtained by subtracting the leak level L from the upper limit value DR2of the original dynamic range of the A/D converter, so that a possible value range of the digital image signal, i.e., the second dynamic range is, in effect, further reduced as the leak level L becomes greater.

In contrast, in the radiation image detection apparatus of the present invention, an analog image signal with a leak level superimposed thereon is detected by the signal detection section, as illustrated inFIG. 5A. Then, leak error correction is performed by subtracting the leak level from the detected analog image signal before being converted to a digital image signal by the A/D converter, as illustrated inFIG. 5B. Thereafter, the corrected analog image signal is converted to a digital image signal by the A/D converter, as illustrated inFIG. 5C. This allows the corrected image signal to be represented using the entire output range of the A/D converter from zero to DR2regardless of the magnitude of the leak level, thereby the reduction in the dynamic range of the corrected image signal may be avoided.

Next, a second embodiment of the radiation image detection apparatus of the present invention will be described with reference toFIGS. 6 and 7.FIG. 6is a schematic configuration diagram of the radiation image detection apparatus300according to a second embodiment of the present invention, andFIG. 7is a timing chart illustrating an operation of the radiation image detection apparatus300. In the radiation image detection apparatus300shown inFIG. 6, components identical to those of the radiation image detection apparatus100shown inFIG. 1are given the same reference symbols and will not be elaborated upon further here. In the radiation image detection apparatus300, a leak error correction means240controls the reference voltage Vref of each data line, which is referenced when obtaining an analog image signal R of each pixel on each data line3, based on an analog leak level L detected from each data line3with the TFT switch4of each pixel being switched OFF, thereby offsetting an error component arising from the leak current before obtaining analog image signals R by switching ON the TFT switch4of each pixel.

More specifically, a control signal for leak level detection is outputted from a signal processing unit230to the signal detection section120and scan signal control unit103, as illustrated inFIG. 6. In response to the control signal, the reference voltage Vref of each differential amplifier121of the signal processing unit230is set to an initial reference voltage, for example, ground voltage, and with the TFT switches4on each scanning line2being switched OFF, a signal flowing out through each data line3is detected by each differential amplifier121connected to each data line3. The signal detected by each differential amplifier121is outputted to a first sample-and-hold circuit231of the signal processing unit230connected to each differential amplifier121and held as an analog leak level L. Then each held leak level L is buffered with plus one magnification and determined as the reference voltage Vref of each differential amplifier121.

Next, a control signal for image signal detection is outputted from the signal processing unit230to the scan signal control unit103, and in response to the control signal, a scan signal for sequentially switching ON the TFT switches4is outputted from the scan signal control unit103to the scanning line G1. The control signal for image signal detection is outputted from the signal processing unit230also to the signal detection section120, and in response to the control signal, a signal flowing out through each data line3is detected by each differential amplifier121connected to each data line3. Here, the signal detected by each differential amplifier121is a signal obtained by subtracting a leak level set as the reference voltage Vref from an analog image signal of each pixel connected to the scanning line G1with the leak level of the data line being superimposed thereon. The signal detected by each differential amplifier121is outputted to a second sample-and-hold circuit232of the signal processing unit230connected to each differential amplifier121and held as an analog image signal R. The analog image signals R obtained from the respective data lines3and held by the respective second sample-and-hold circuits232are sequentially outputted to the A/D converter150by a multiplexer236in the order of the data line. Then, the output of the control signal for image signal detection from the signal processing unit230is terminated and TFT switches4on each scanning line2is switched OFF.

When image signal reading for the scanning line G1is completed, then image signal reading for the scanning line G2is performed. First, as in the scanning line G1, the control signal for leak level detection is outputted from the signal processing unit230to the signal detection section120and scan signal control unit103. In response to the control signal, the reference voltage Vref of each differential amplifier121of the signal processing unit230is set to an initial reference voltage, and with the TFT switches4on each scanning line2being switched OFF, a signal flowing out through each data line3is detected by each differential amplifier121connected to each data line3. The signal detected by each differential amplifier121is outputted to the first sample-and-hold circuit231of the signal processing unit230connected to each differential amplifier121and held as an analog leak level L. Then each held leak level L is buffered with plus one magnification and determined as the reference voltage Vref of each differential amplifier121.

Next, the control signal for image signal detection is outputted from the signal processing unit230to the scan signal control unit103, and in response to the control signal, the scan signal for sequentially switching ON the TFT switches4is outputted from the scan signal control unit103to the scanning line G2. The control signal for image signal detection is outputted from the signal processing unit230also to the signal detection section120, and in response to the control signal, a signal flowing out through each data line3is detected by each differential amplifier121connected to each data line3. The signal detected by each differential amplifier121is outputted to the second sample-and-hold circuit232of the signal processing unit230connected to each differential amplifier121and held as an analog image signal R. The analog image signals R obtained from the respective data lines3and held by the respective second sample-and-hold circuits232are sequentially outputted to the A/D converter150by the multiplexer236in the order of the data line. Then, the output of the control signal for image signal detection from the signal processing unit230is terminated and TFT switches4on each scanning line2is switched OFF.

Thereafter, with respect to each of the scanning lines G3, - - - , Gk, the control signal for leak level detection and control signal for image signal detection are outputted alternately from the signal processing unit230in the same manner as described above. Then, the reference voltage Vref of each differential amplifier121is controlled for the subsequent image signal detection based on an analog leak level flowing out and detected with the TFT switches4on each scanning line2being switched OFF and the reference voltage Vref of each differential amplifier121being set to the initial voltage, and with respect to each of the scanning lines G3, - - - , Gk, analog image signals of the respective pixels on the scanning line are sequentially read out by the signal detection section120and held by the respective second sample-and-hold circuits. The analog image signals R obtained from the respective data lines3and held by the respective second sample-and-hold circuits are sequentially outputted to the A/D converter150by the multiplexer236and converted to digital image signals.

In the radiation image detection apparatus300according to the second embodiment, a leak level removal operation for removing a leak level from an analog image signal of each pixel with an analog leak level superimposed thereon flowing out through each data line3of the radiation image detector is performed first, and then the analog image signal removed of the leak level is converted to a digital image signal, as in the radiation image detection apparatus100according to the first embodiment. In this way, the amount of error in the image signal caused by the leak current may be corrected properly, and the reduction in the dynamic range of the corrected image signal may be prevented. Further, an error corrected image signal may be obtained by estimating the amount of error in the image signal caused by the leak currents in advance and controlling the reference voltage used for the image signal detection.

Further, according to the radiation image detection apparatus300of the second embodiment, reduction in the dynamic range of the corrected analog image signal may also be avoided. For example, an assumption is made here for comparison where the dynamic range of the image signal detectable by the signal detection section120is from zero to DR1, and an analog image signal not including a leak level is smaller than the upper limit value DR1of the dynamic range but greater than that when the leak level is superimposed thereon. In the radiation image detection apparatus100of the first embodiment, an analog image signal R with a leak level superimposed thereon and a leak level L are detected respectively by the signal detection section120first, then the leak level L is subtracted from the analog image signal R to obtain a corrected analog image signal. Consequently, if the analog image signal R is greater than the upper limit value (saturated value) DR1, the detected analog image signal is set to the upper limit value DR1, and the leak level L is subtracted from the detected analog image signal to obtain a corrected analog image signal. Accordingly, the dynamic range of the detected analog signal becomes smaller than the dynamic range of zero to DR1with increase in the leak level L. In contrast, in the radiation image detection apparatus300, the analog image signal detected by the signal detection section120is a corrected analog image signal not including a leak level, so that the dynamic range thereof is identical to the dynamic range of zero to DR1of the signal detection section120.

In each of the embodiments, the description has been made of a case in which the A/D converter is integrated in the radiation image detection apparatus, but it may be provided as a separate unit outside of the apparatus.

Further, in each of the embodiments described above, a correlated double sampling circuit for removing noise may be provided between the differential amplifier of the signal detection section and the sample-and-hold circuit of the signal processing unit.