JP2010212741A - Radio ray image detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation ray image detection device which can reduce the correction time, without deteriorating the offset correction accuracy. <P>SOLUTION: The radiation ray image detection device includes a photodiode 152, which generates and accumulates electric charges; a signal read-out circuit 17, which reads out an accumulated electric charge as an imaging signal after accumulating the electric charge generated, when radiation ray ares applied for an accumulation period T0 in the photodiode 152; the signal read-out circuit 17, which reads out the accumulated electric charges as an offset signal after accumulating the electric charge generated, when radiation rays are not applied for an accumulation time T1 in the photodiode 152; and an image data correction unit 28, which performs an offset correction, based on a correction signal obtained by multiplying the offset signal by T0/T1 for the imaging signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiological image detection apparatus.

  Conventionally, in the field of radiography for the purpose of medical diagnosis, there have been widely used radiographic imaging systems that obtain a radiographic image of a subject by irradiating the subject with radiation and detecting the intensity distribution of the radiation transmitted through the subject. Are known. Further, in recent radiographic imaging systems, a so-called “Flat Panel Detector” (hereinafter referred to as “FPD”) having a thin flat plate shape in which a large number of photoelectric conversion elements are arranged in a matrix form. Is being developed and used. The FPD can easily and quickly obtain a radiation image of a subject by detecting radiation transmitted through the subject, photoelectrically converting the radiation into an electrical signal, and performing image processing on the electrical signal after the photoelectric conversion.

  The radiological image detection apparatus is roughly classified into a stationary type that is installed at a predetermined position as a part of the system and a portable type that is portable (cassette type). Therefore, the use of a cassette-type radiation image detection apparatus has been widely studied.

  In such a cassette-type radiographic image detection apparatus, it is necessary to provide a power source for driving the radiographic image detection apparatus, and those having a built-in battery, a removable battery, and the like are known.

  In the radiation image detection apparatus, when radiation is irradiated according to imaging conditions or the like, the charge is accumulated for a predetermined time, and then the image pickup signal is acquired by reading the charge. Also known is a technique for shifting the imaging means from a charge accumulation state to a signal readout state for reading out a signal based on charges in accordance with the determination of the end of radiation irradiation based on the output of the detection means (see, for example, Patent Document 1). .

However, in such a radiation image detection apparatus, even when radiation is not irradiated, electric charges are generated for each pixel due to heat or the like over time. This is called noise (offset component) due to dark current (factors other than irradiation of radiation), and if the so-called offset correction is not performed to remove noise (offset component) due to this dark current from the radiographic image, a high-quality image will be obtained. Can't get. Specifically, the offset correction is performed by a method in which an image signal (offset signal) is acquired in an unexposed state where no radiation is irradiated, and is subtracted from an imaging signal obtained by radiographic imaging.
However, this noise due to dark current appears differently when the time and conditions differ, so in order to perform offset correction with high accuracy, it is necessary to acquire an offset signal at a stage where there is as little time difference as radiographic imaging. .

  Therefore, conventionally, mainly in a stationary radiographic image detection apparatus, an offset signal (dark current image) is periodically acquired and stored in a storage unit or the like even during non-imaging, and when radiographic imaging is performed, A technique for performing offset correction using an offset signal acquired most recently is known. For example, Patent Document 2 discloses that initialization of a radiation image detection apparatus and acquisition of a dark current image are repeatedly performed during non-imaging. Patent Document 3 proposes a technique for determining the number of dark current images to be acquired according to a radiographic image capturing menu. Furthermore, Patent Document 4 discloses a technique for acquiring a dark current image used for offset correction for a preview image by limiting the shooting time to several types before shooting.

Since various noises are included in the offset signal, it is necessary to average the noise and remove the influence of the noise. For this reason, in the techniques described in Patent Document 2 to Patent Document 4, a plurality of offset signals (dark current images) obtained by accumulating dark current for the same accumulation time as the charge accumulation time at the time of radiographic imaging. When the offset correction is performed once and the offset correction is performed, a method is employed in which the correction is performed after taking the average value of these values.
Japanese Patent No. 3413084 JP 2002-369084 A JP 2003-194949 A JP 2004-343525 A

  However, in order to endure long-time use of a cassette-type radiation image detection device driven by a battery or the like, it is necessary to save power as much as possible. When not in use for imaging, the power is turned off. It is preferable to keep it. However, if the offset signal is acquired at any time even during non-photographing, there is a problem that the power cannot be turned off during non-photographing.

  Thus, it is conceivable to obtain an offset image immediately after imaging. However, there is a request to confirm a radiographic image as soon as possible immediately after imaging, and it is not preferable to repeat charge accumulation and charge readout multiple times.

  Further, in the techniques described in Patent Document 2 to Patent Document 4, an offset signal is acquired by accumulating dark current for the same accumulation time as the charge accumulation time during radiographic imaging. When the end of radiation irradiation is determined based on the detection result of the detection unit, and the charge read timing, that is, the charge accumulation time is determined according to the determination as in the technique described in Document 1. Therefore, it is impossible to know in advance the same accumulation time as the charge accumulation time at the time of radiographic imaging. For this reason, there is a problem that the charge accumulation time for obtaining the offset signal cannot be properly determined, and the offset correction with high accuracy cannot be performed.

  Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide a radiological image detection apparatus that can shorten the correction time without degrading the accuracy of offset correction. .

In order to solve the above-described problem, a radiological image detection apparatus according to claim 1 comprises:
An image sensor that generates and stores charge;
In the imaging element, after the charge generated when radiation is irradiated is accumulated for the accumulation time T0, an imaging signal reading unit that reads the accumulated charge as an imaging signal;
In the imaging device, after the charge generated when radiation is not irradiated is accumulated for the accumulation time T1, an offset signal reading unit that reads the accumulated charge as an offset signal;
A correction unit that performs offset correction based on a correction signal obtained by multiplying the offset signal by T0 / T1 with respect to the imaging signal;
It is characterized by having.

The invention according to claim 2 is the radiological image detection apparatus according to claim 1,
It is characterized by T0 <T1.

The invention according to claim 3 is the radiological image detection apparatus according to claim 1 or 2,
Detecting means for detecting radiation irradiation;
Control means for determining the accumulation time T0 according to the determination of radiation irradiation start or radiation irradiation end based on the output of the detection means, and controlling the readout timing of the imaging signal by the imaging signal readout unit;
It is characterized by having.

  According to the first aspect of the present invention, when the accumulation time T0 for obtaining the imaging signal and the accumulation time T1 for obtaining the offset signal are used, the imaging signal is corrected based on the correction signal obtained by multiplying the offset signal by T0 / T1. Perform offset correction. For this reason, the offset signal readout time can be shortened, and the time required for offset correction can be minimized without degrading the accuracy of offset correction compared to the case of acquiring the offset signal in multiple steps. There is an effect that it can be suppressed.

  According to the second aspect of the present invention, since T0 <T1, even when noise is included in the offset signal, it can be averaged to obtain an appropriate correction signal.

  According to the third aspect of the present invention, the charge accumulation time T0 is not predetermined, and the accumulation time T0 is determined according to the determination of the start of radiation irradiation or the end of radiation irradiation. In this way, even when the charge accumulation time can vary arbitrarily, the offset correction is performed on the imaging signal based on the correction signal obtained by multiplying the offset signal by T0 / T1, so even if the accumulation time T0 cannot be specified in advance, Since the correction signal can be generated, compared to the case where the offset signal obtained by accumulating the dark current for the same accumulation time as the accumulation time of the charge at the time of radiographic imaging is acquired and corrected, Offset correction can be performed with high accuracy.

  The following explanation shows the form recognized by the inventor as the best for carrying out the invention, and the terms used in the scope of the invention and claims are defined, defined or defined at a glance. Although there are also expressions, these are only expressions for specifying the form that the inventor recognizes as the best, and do not specify or limit the terms used in the scope of the invention or the claims. Absent.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram showing a schematic configuration of an embodiment of a radiographic imaging system to which a radiographic image detection apparatus according to the present invention is applied.

  The radiographic image capturing system 1 according to the present embodiment is a system that is applied in, for example, radiographic image capturing performed in a hospital. As shown in FIG. The radiography operation apparatus 3 that performs operations related to radiographic image capture, the base station 4 for performing communication by a wireless communication method such as a wireless local area network (LAN), and the radiographic image detection apparatus 5 and radiographic image detection A console 6 that performs image processing and the like of the radiation image detected by the apparatus 5 is connected through a network 7.

  A radiographic image capturing apparatus 10 is connected to the imaging operation apparatus 3 via a cable 8 to irradiate a patient as the subject 9 with radiation and capture a radiographic image. The radiographic image capturing device 10 and the radiographic image detection device 5 are installed one by one in, for example, one radiographing room 11. The radiographic image capturing device 10 is operated by the radiographing operation device 3, and the radiographic image detection device 5 performs radiographic image detection. Radiation image information can be obtained by detecting. A single radiographing room 11 may be provided with a plurality of radiation image detection devices 5.

  The network 7 may be a dedicated communication line for the system, but is preferably an existing line such as Ethernet (registered trademark) because the degree of freedom of the system configuration becomes low. . In addition to what is illustrated here, a plurality of imaging operation devices 3, radiographic image detection devices 5, and consoles 6 for operating the radiographic imaging devices 10 in other imaging rooms 11 may be connected to the network 7.

  The imaging operation device 3 is composed of an operation panel or the like, and operates the radiographic imaging device 10, for example, an input operation unit for inputting signals such as imaging conditions, a display unit for displaying information such as imaging conditions and various instructions, And the power supply part etc. (all are not shown) which supplies electric power with respect to the radiographic imaging apparatus 10 are comprised.

  The radiographic imaging device 10 is disposed inside a radiographing room 11 and has a radiation source 12, and radiation is generated when a tube voltage is applied to the radiation source 12. As the radiation source 12, for example, a radiation tube is used, and the radiation tube generates radiation by accelerating electrons generated by thermal excitation with a high voltage to collide with the cathode.

  In the present embodiment, the radiation image detection device 5 detects radiation transmitted from the radiation source 12 and transmitted through the subject 9 to acquire a radiation image, and is irradiated from the radiation source 12 when performing imaging. It is arranged in the radiation range. For example, as shown in FIG. 1, the radiological image detection device 5 is arranged between the subject 9 and a bed 13 on which the subject 9 is placed, but the position where the radiographic image detection device 5 is arranged is limited to this. Instead, for example, a detection device mounting port (not shown) for mounting the radiographic image detection device 5 may be provided below the bed 13 so that the radiographic image detection device 5 is mounted in the detection device mounting port.

  In the present embodiment, the radiation image detection device 5 is a flat panel type radiation image detection device 5. Hereinafter, the structure of the radiation image detection apparatus 5 will be described with reference to FIGS. 2 and 3.

  As shown in FIG. 2, the radiological image detection apparatus 5 includes a housing 14 that protects the inside, and is configured to be portable as a cassette.

  An imaging panel 15 that converts irradiated radiation into an electrical signal is formed in layers inside the housing 14. A light emitting layer (not shown) that emits light according to the intensity of incident radiation is provided on the radiation irradiation side of the imaging panel 15.

  The light emitting layer is generally called a scintillator layer. For example, a phosphor is a main component, and based on incident radiation, an electromagnetic wave having a wavelength of 300 nm to 800 nm, that is, visible light to ultraviolet light to infrared light. It is designed to output electromagnetic waves (light).

The phosphor used in the light emitting layer is, for example, a material having CaWO ₄ or the like as a base material, or a luminescent center substance activated in a base material such as CsI: Tl, Cd ₂ O ₂ S: Tb, or ZnS: Ag. Things can be used. Further, when the rare earth element is M, a phosphor represented by a general formula of (Gd, M, Eu) ₂ O ₃ can be used. In particular, CsI: Tl and Cd ₂ O ₂ S: Tb are preferable because of high radiation absorption and light emission efficiency. By using these, high-quality images with low noise can be obtained.

  The electromagnetic wave (light) output from the light emitting layer is converted into electric energy and accumulated on the surface opposite to the surface on which the radiation of the light emitting layer is irradiated, and an image signal based on the accumulated electric energy is stored. A signal detection unit 151 that performs output is formed.

  Here, the circuit configuration of the imaging panel 15 will be described. FIG. 3 is an equivalent circuit diagram of the photoelectric conversion unit for one pixel constituting the signal detection unit 151.

  As shown in FIG. 3, the configuration of the photoelectric conversion unit for one pixel is a photodiode 152 and a thin film transistor (hereinafter referred to as “TFT”) 153 that extracts electrical energy accumulated in the photodiode 152 as an electrical signal by switching. It consists of and. The photodiode 152 is an image sensor that generates and accumulates charges. The electrical signal taken out from the photodiode 152 is amplified by an amplifier 154 to a level that can be detected by the signal readout circuit 17.

  The amplifier 154 is connected to a reset circuit (not shown) constituted by a TFT 153 and a capacitor, and a reset operation for resetting the accumulated electric signal is performed by switching on the TFT 153. The photodiode 152 may simply be a photodiode having a regulation capacitance, or may include an additional capacitor in parallel so as to improve the dynamic range of the photodiode 152 and the photoelectric conversion unit.

  FIG. 4 is an equivalent circuit diagram in which such photoelectric conversion units are two-dimensionally arranged. Between the pixels, the scanning lines Ll and the signal lines Lr are arranged so as to be orthogonal to each other. A TFT 153 is connected to the photodiode 152 described above, and one end of the photodiode 152 on the side to which the TFT 153 is connected is connected to the signal line Lr via the TFT 153. On the other hand, the other end of the photodiode 152 is connected to one end of an adjacent photodiode 152 arranged in each row, and is connected to a bias power source 155 through a common bias line Lb.

  One end of the bias power source 155 is connected to the main body control unit 27 so that a voltage is applied to the photodiode 152 through the bias line Lb according to an instruction from the main body control unit 27. The TFTs 153 arranged in each row are connected to a common scanning line Ll, and the scanning line Ll is connected to the main body control unit 27 via the scanning drive circuit 16. Similarly, the photodiodes 152 arranged in each column are connected to a signal readout circuit 17 connected to a common signal line Lr and controlled by the main body control unit 27.

  The signal readout circuit 17 is provided with the amplifier 154 for each signal line Lr described above, and a sample hold circuit 156 is connected to each amplifier 154. Each sample and hold circuit 156 is connected to an analog multiplexer 157 provided in the signal readout circuit 17, and the signal read out by the signal readout circuit 17 is described above from the analog multiplexer 157 via the A / D converter 158. It is output to the main body control unit 27.

  Note that the TFT 153 may be either an inorganic semiconductor type used in a liquid crystal display or the like, or an organic semiconductor type.

  Further, in the present embodiment, the case where the photodiode 152 as a photoelectric conversion element is used as the imaging element is illustrated, but a solid-state imaging element other than the photodiode may be used as the photoelectric conversion element.

  As shown in FIG. 2, the side of the signal detection unit 151 sends a pulse to each photoelectric conversion element to scan and drive each photoelectric conversion element, and the photoelectric conversion element is stored in each photoelectric conversion element. A signal readout circuit 17 for reading out electrical energy is arranged.

  The radiological image detection apparatus 5 includes an image storage unit 18 including a rewritable read-only memory such as a RAM (Random Access Memory) and a flash memory. The image storage unit 18 is output from the imaging panel 15. The stored image signal is stored. The image storage unit 18 may be a built-in memory or a removable memory such as a memory card.

  The radiological image detection device 5 includes a plurality of drive units (for example, a scanning drive circuit 16, a signal readout circuit 17, a communication unit 24 (described later), an image storage unit 18, and a charge amount detection that constitute the radiographic image detection device 5. A rechargeable battery 21 is provided as a power supply source for supplying power to a unit (not shown), an indicator 25 (described later), an input operation unit 26 (described later), the imaging panel 15 and the like.

  As the rechargeable battery 21, a rechargeable battery such as a nickel cadmium battery, a nickel metal hydride battery, a lithium ion battery, a small sealed lead battery, or a lead storage battery can be used. Further, instead of the rechargeable battery 21, a fuel cell or the like may be applied.

  A terminal 22 for charging is formed at one end of the housing 14. For example, as shown in FIG. 1, the radiation image detecting device 5 is mounted on a charging device 23 such as a cradle connected to an external power source. Thus, a terminal (not shown) on the charging device 23 side and a terminal 22 on the housing 14 side are connected to charge the rechargeable battery 21. Note that the shape of the rechargeable battery 21 as the power supply source is not limited to that illustrated in FIG. 2. For example, a plate-shaped battery may be provided in parallel with the imaging panel 15. By forming the battery in such a shape, the area of the imaging panel 15 can be increased, and the imageable area can be widened.

  The radiological image detection device 5 is provided with a communication unit 24 (see FIG. 5) that transmits and receives various signals to and from an external device such as the console 6. For example, the communication unit 24 is configured to transfer an image signal output from the imaging panel 15 to the console 6 or receive a shooting start signal transmitted from the console 6 or the like.

  In addition, a phototimer 29 (see FIG. 5) that detects radiation irradiated to the radiation image detection device 5 is provided on the surface of the housing 14. In the present embodiment, the phototimer 29 functions as a detection unit that detects radiation irradiation, and outputs a detection result to the main body control unit 27. The detection means is not limited to the photo timer 29. Further, the detection means is not an essential component, and the photo timer 29 may not be provided.

  In addition, an indicator 25 that displays the charging status of the rechargeable battery 21 and various operation statuses is provided at one end of the front surface of the housing 14 so that the operator can charge the rechargeable battery 21 of the radiation image detection device 5. Can be visually confirmed.

An input operation unit 26 is provided outside the housing 14 for an operator such as a radiologist to input and set various instructions. The contents input from the input operation unit 26 include, for example, imaging conditions, patient identification information, and selection settings for the operation state of the radiation image detection device 5. The contents that can be input from the input operation unit 26 Are not limited to those illustrated here.
In the present embodiment, as the operation state of the radiation image detection device 5, for example, among the members constituting the radiation image detection device 5, power is supplied to all the drive units used for a series of imaging operations. "Shooting ready state" that is operating, "Shooting standby state" that consumes less power than the shooting ready state, and complete power saving state in which all power supply to each drive unit of the radiation image detection device 5 is stopped The “photographing pause state” can be selected.
In the present embodiment, the radiological image detection apparatus 5 supplies power to each drive unit by the rechargeable battery 21. Therefore, in order to realize a rapid and efficient imaging operation while suppressing power consumption, it is preferable to select and set “imaging standby state” as a default operation state of the radiation image detection apparatus 5. On the other hand, when there is no scheduled shooting for a while, the shooting pause state may be selected as the basic state.

A functional configuration of the radiation image detection apparatus 5 will be described with reference to FIG.
The radiation image detection apparatus 5 includes a control device 30 having a main body control unit 27 and an image data correction unit 28. The main body control unit 27 and the image data correction unit 28 are composed of, for example, a general-purpose CPU, ROM, RAM, and the like (all not shown), and read a predetermined program stored in the ROM to work the RAM. The CPU executes various processes according to the program.

  Information input from the input operation unit 26, information received from the communication unit 24, and the like are transmitted to the main body control unit 27 as electrical signals. The main body control unit 27 is based on the transmitted signal. Each part is controlled.

  The radiographic image detection device 5 includes a charge amount detection unit (not shown), and the main body control unit 27 receives a signal indicating the charge status of the rechargeable battery 21 detected by the charge amount detection unit (for example, the voltage value of the rechargeable battery 21). The main body control unit 27 displays the charge amount of the rechargeable battery 21 on the indicator 25 based on the transmitted signal.

  Further, the operating state of the radiation image detection apparatus 5 is transmitted to the console 6 by the main body control unit 27 via the communication unit 24 as needed.

  In addition, when the operation state of the radiation image detection apparatus 5 is selected and set by an input operation of the input operation unit 26 by the operator, the main body control unit 27 recognizes the operation state selected and set by the operator, and recognizes the recognition. Thus, the power supply from the rechargeable battery 21 to each drive unit is controlled so that the operation state of each drive unit is controlled so that the operation state is achieved.

Further, the main body control unit 27 drives the scanning drive circuit 16 to send a pulse to each photoelectric conversion element to scan and drive each photoelectric conversion element. The image signal read out by the signal reading circuit 17 that reads out the electrical energy accumulated in each photoelectric conversion element is sent to the main body control unit 27.
In the present embodiment, the signal readout circuit 17 functions as an imaging signal readout unit that reads out, as an imaging signal, the charges generated and accumulated during the accumulation time T0 when radiation is irradiated in the photodiode 152 that is an imaging element. To do. Further, the signal readout circuit 17 functions as an offset signal readout unit that reads out the generated / accumulated charge as an offset signal during the accumulation time T1 in the photodiode 152 that is an imaging element when no radiation is irradiated.
Further, the main body control unit 27 sends the image pickup signal and the offset signal sent from the signal reading circuit 17 to the image data correction unit 28 described later. The imaging signal is corrected by the image data correction unit 28, sent to the image storage unit 18, and stored as radiation image information of the subject 9. Further, the image signal stored in the image storage unit 18 is appropriately sent to the console 6 via the communication unit 24.

Further, the main body control unit 27 determines the start of radiation irradiation or the end of radiation irradiation based on the output from the phototimer 29 serving as a detection means, and according to this, the charge in the photodiode 152 is generated when radiation is irradiated. Is determined as an accumulation time T0 (charge accumulation time when the imaging signal is acquired), and functions as a control means for controlling the readout timing of the imaging signal by the signal readout circuit 17 serving as the imaging signal readout unit.
The main body control unit 27 also generates an accumulation time T1 (offset) for generating and accumulating charges in the photodiode 152 when no radiation is irradiated based on the imaging conditions input from the input operation unit 26 and the like and the accumulation time T0. The charge accumulation time at the time of signal acquisition is determined, and the offset signal readout timing by the signal readout circuit 17 which is an offset signal readout unit is controlled.

Note that the relationship between the charge accumulation time T0 when the imaging signal is acquired and the charge accumulation time T1 when the offset signal is acquired is T0 <T1, and T1 is N times T0. N is not limited to an integer. For example, N may be set to 3.5 or the like.
For example, when the dark current that affects the photodiode 152 of the radiological image detection device 5 is likely to fluctuate, the main body control unit 27 takes a longer accumulation time T1, that is, increases the value of N. Yes.
In addition, when the radiation dose is large, the charge remains in the photodiode 152, and in the offset signal immediately after the radiographic image is captured, the charge remaining in the photodiode 152 not only by the dark current but also by the previous radiation irradiation. May come out. For this reason, when it is determined that the radiation dose is large from the imaging conditions or the like, the main body control unit 27 may take a longer accumulation time T1, that is, increase the value of N. As described above, by extending the accumulation time T1, it is possible to reduce the influence of dark current fluctuation, the charge remaining in the photodiode 152, and the like, and to obtain an offset signal suitable for performing offset correction.

  In addition, the element which the main body control part 27 determines accumulation | storage time T1 is not limited to what was illustrated here. In addition, the accumulation time T1 may be set to a predetermined value as a default in advance for each radiographic image detection device 5, or in accordance with imaging conditions, the length of the accumulation time T0, or the like. May be input and set by the operator. As will be described later, as the accumulation time T1 is longer, an offset signal suitable for performing offset correction can be acquired. On the other hand, if the accumulation time T1 is increased, offset correction takes time, and imaging is immediately performed. The merit of the radiation image detection apparatus 5 that the confirmed image can be confirmed is impaired. Therefore, it is desirable that N is about 7-8, preferably about 10.

Here, the control of the readout timing of the imaging signal and the readout timing of the offset signal by the main body control unit 27 will be described with reference to FIG.
FIG. 6 is an explanatory diagram for explaining an operation state according to ON / OFF of a switch by extracting any four photodiodes 152 in FIG. 4 for convenience of explanation.

The radiological image detection apparatus 5 reads out electric charges from the photodiode 152 sequentially for each row and each column shown in FIGS. 4 and 6.
This will be specifically described with reference to FIG. 6. First, SWr1 and SWr2 are switches for each row, and SWc1 and SWc2 are switches for each column. Each switch can be switched ON / OFF according to control by the main body control unit 27.
SWr1 is a switch for the photodiodes 152a and 152b in the first row in FIG. 6. When SWr1 is turned on in accordance with an instruction signal from the main body control unit 27, the TFTs 153a and 153b in the first row are turned on, and the photodiodes 152a and 152b are turned on. The accumulated charges flow toward the amplifier 154 at the same time. Similarly, SWr2 is a switch for the photodiodes 152c and 152d in the second row in FIG. 6. When SWr2 is turned on, the TFTs 153c and 153d in the second row are turned on, and the charges accumulated in the photodiodes 152c and 152d are changed. At the same time, it flows toward the amplifier 154.
Next, SWc1 corresponds to the switches of the photodiodes 152a and 152c in the first column in FIG. 6, and when SWc1 is turned on according to the instruction signal from the main body control unit 27, the charge stored in the photodiodes 152a or 152c is read out. The data is read by the circuit 17. SWc2 corresponds to the switch of the photodiodes 152b and 152d in the second column in FIG. 6. When SWc2 is turned on, the charge accumulated in the photodiode 152b or 152d is read out to the signal readout circuit 17. .

The image data correction unit 28 is a correction unit that performs offset correction on the imaging signal acquired by the signal readout circuit 17 based on a correction signal obtained by multiplying the offset signal by T0 / T1. For example, when T1 is T0 × 7 (N = 7), an offset component (noise due to dark current) on the imaging signal is subtracted by subtracting one-seventh of the offset signal from the imaging signal. It is supposed to be removed.
The corrected imaging signal is sent from the image data correction unit 28 to the image storage unit 18 and stored as radiation image information of the subject 9.

A functional configuration of the console 6 will be described with reference to FIG.
The console 6 includes a control device 41 having a control unit 40 composed of, for example, a general-purpose CPU, ROM, RAM, etc. (all not shown). The control unit 40 is a predetermined unit stored in the ROM. The program is read out and expanded in the work area of the RAM, and the CPU executes various processes according to the program.

  In addition, the console 6 is a communication that transmits and receives signals to and from an external device such as an input operation unit 42 for inputting various instructions, a display unit 43 for displaying images and various messages, and the radiation image detection device 5. Part 44 and the like.

  The input operation unit 42 includes, for example, an operation panel, a keyboard, a mouse, and the like, and outputs, to the control unit 40, a key press signal or a mouse operation signal pressed by the operation panel or keyboard as an input signal. It is supposed to be.

  The display unit 43 includes, for example, a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display), and the like, and in accordance with instructions of a display signal output from the control unit 40, a radiographic image such as a thumbnail image or an input Various information such as various information input from the operation unit 42 is displayed.

  In the present embodiment, in addition to the radiation image information sent from the radiation image detection device 5, the display unit 43 has a charge amount of the rechargeable battery 21 of the radiation image detection device 5 and whether or not charging of the rechargeable battery 21 has been completed. In addition, various kinds of information sent via the communication unit 44 of the radiation image detection device 5 such as the operation state of the radiation image detection device 5 are displayed. The contents displayed on the display unit 43 are not limited to those exemplified here, and more information may be displayed. Also, not all of the examples illustrated here may be displayed, and at least one of these may be displayed.

  The communication unit 44 communicates various types of information with the radiation image detection apparatus 5 via the base station 4 by a wireless communication method such as a wireless LAN.

  A signal input from the input operation unit 42, a signal received from the outside via the communication unit 44, or the like is sent to the control unit 40. Further, for example, the control unit 40 performs predetermined image processing based on the radiographic image information detected by the radiographic image detection device 5, thereby obtaining a thumbnail image or a radiographic image desired by a doctor or the like.

  Next, the operation of the radiographic imaging system 1 including the radiographic image detection apparatus 5 according to the present embodiment will be described with reference to FIGS. 6 and 8 to 10.

FIG. 8 is a timing chart for explaining reading of signals from the four photodiodes 152 shown in FIG.
When an instruction to start radiographic imaging is input from the input operation unit 42 or the like of the console 6, as shown in FIG. 8, the console 6 inquires of the radiographic image detection apparatus 5 whether imaging radiography is ready. When a radiation irradiation request signal is transmitted (t1) and a signal indicating that radiography is ready from the radiographic image detection apparatus 5 to the console 6, a radiation source of the radiographic imaging apparatus 10 is transmitted from the console 6 side. A radiation irradiation permission signal is transmitted to 12 (t2), and radiation is irradiated from the radiation source 12 (t3). The irradiated radiation is detected by the phototimer 29, and the detection result is sent to the main body control unit 27 as a signal.

  The main body control unit 27 determines the radiation irradiation start (t3) and the radiation irradiation end (t4) based on the signal from the phototimer 29, determines the readout timing of the imaging signal, and charges the charge only for the charge accumulation time T0. After the accumulation, SWr1 is turned on (t5). As a result, the TFTs 153a and 153b in the first row are turned on, and the charges accumulated in the photodiodes 152a and 152b are simultaneously sent to the amplifier 154 to amplify the signal. Next, the main body control unit 27 turns on SWc1 (t6), and the charge accumulated in the photodiode 152a in the first column in FIG. 6 and amplified by the amplifier 154 is read out to the signal readout circuit 17. Thereafter, when SWc1 is turned off and SWc2 is turned on (t7), the charge accumulated in the photodiode 152b in the second column in FIG. 6 and amplified by the amplifier 154 is read out to the signal readout circuit 17.

  Subsequently, the main body control unit 27 turns on SWr2 (t8) and turns on the TFTs 153c and 153d in the second row. As a result, the charges accumulated in the photodiodes 152c and 152d are simultaneously sent to the amplifier 154 to amplify the signal. Next, the main body control unit 27 turns on SWc1 (t9), and the charge accumulated in the photodiode 152c in the first column in FIG. 6 and amplified by the amplifier 154 is read out to the signal readout circuit 17. Thereafter, when SWc1 is turned off and SWc2 is turned on (t10), the charge accumulated in the photodiode 152d in the second column in FIG. 6 and amplified by the amplifier 154 is read out to the signal readout circuit 17.

When charges are read from all the photodiodes 152, the main body control unit 27 turns off SWc2 (t11), and charges are accumulated in the photodiodes 152 for a predetermined charge accumulation time T1 in a state where no radiation is irradiated. When a predetermined charge accumulation time T1 elapses, the main body control unit 27 first turns on SWr1 and reads the charges accumulated in the photodiodes 152a and 152b in the first row by the amplifier 154, as in the case of reading the imaging signal. Amplify (t12). Thereafter, SWc1 is turned on, the charge accumulated in the photodiode 152c in the first column in FIG. 6 is read (t13), and further, SWc1 is turned off and SWc2 is turned on to turn on the photodiode in the second column in FIG. The charge accumulated in 152d is read (t14). When the readout of the charges for the photodiodes 152a and 152b in the first row is completed (t15), the readout of the charges is similarly performed for the photodiodes 152c and 152d in the second row (t15 to t16).
As a result, the imaging signal obtained by the charge accumulation at the charge accumulation time T0 and the offset signal obtained by the charge accumulation at the charge accumulation time T1 are acquired, and the main body control unit 27 converts these signals into the image data correction unit. 28 to send.

Next, the image data correction unit 28 performs offset correction on the imaging signal based on a correction signal obtained by multiplying the offset signal by T0 / T1.
The corrected imaging signal is sent from the image data correction unit 28 to the image storage unit 18 and stored as radiation image information of the subject 9.

Here, a conventional method of acquiring an offset signal will be described with reference to FIG. Conventionally, an offset signal is generally acquired before radiographic imaging, but here, for convenience of comparison with the present embodiment, an example in which an offset signal is acquired after radiographic imaging will be described.
As shown in FIG. 9, when the acquisition of the imaging signal is completed (t20), the photodiode is charged in a state where the radiation is not irradiated for the same charge accumulation time T1 (T0 = T1) as the charge accumulation time T0 in the case of radiographic imaging. Is accumulated (t21). Thereafter, as in the present embodiment, SWr1, SWr2, SWc1, and SWc2 are sequentially turned on to read out the charge, and first obtain the first offset signal (t22). Further, charges are accumulated in the photodiode in a state where the radiation is not irradiated for the same charge accumulation time T1 (T0 = T1) as the charge accumulation time T0 in the case of radiographic imaging (t23), and the second offset image is performed in the same procedure. Is acquired (t24).

Note that since the offset signal includes noise due to dark current, when the offset signal is acquired and corrected once for the same charge accumulation time T0 as in the case of radiographic imaging, the noise is averaged. Cannot be corrected properly. For this reason, conventionally, an offset signal is acquired about 7 to 8 times, and preferably about 10 times, and the offset signal is averaged to remove noise and perform offset correction.
As described above, the charge accumulation time T1 is N times the charge accumulation time T0, and satisfies the relationship T0 <T1. FIG. 8 shows an example in which the charge accumulation time T1 is T0 × 2, that is, N = 2, but the charge accumulation time T1 is not limited to this.

  Here, since the dark current is shot noise noise, its distribution follows a Poisson distribution in which the average value and the variance are both N. For this reason, when N is the number of times the offset signal is acquired, the noise becomes 1 / √N when the number is increased N times. Therefore, it is better to acquire the offset signal more times and take the average value thereof. Noise is averaged and the influence of noise can be removed. This applies not only when the number of times the offset signal is acquired but also when the charge accumulation time T1 when acquiring the offset signal is increased. Therefore, in the present embodiment, instead of acquiring an offset signal having a short charge accumulation time T1, the charge accumulation time T1 is set to N times the charge accumulation time T0, and one offset signal is obtained by one reading. It has become.

Note that when the offset signal is obtained by one reading with the charge accumulation time T1 extended as in the present embodiment, the addition of electrical noise due to switching that occurs every time the charge is read can be minimized. .
That is, as shown in FIG. 10, charge accumulation is started from an initial value state in which the charge accumulated in the photodiode 152 is zero, and the charge is read after a predetermined time has elapsed (first offset signal acquisition). As a result, the charge accumulated in the photodiode 152 is read out and the amount of charge decreases (A in FIG. 10). However, since the charge cannot be completely read out, a phenomenon occurs in which it does not return to the initial value even when the reading is finished, and fluctuates in the vicinity of V ₁ (B in FIG. 10). This is referred to as electrical noise caused by a switching, as shown in FIG. 10, when trying to get a plurality of times offset signal, electricity to first offset signal reading at the end of the second offset signal reading at the end summed electrical noise V ₁ is the as referred noise V ₂ is added, the electrical noise is added every time the readout, the charge readout after the end of the photodiode 152 moves away from the initial value. In this regard, when obtaining the offset signal by one read as in the present embodiment, the electrical noise V ₁ even only once, the influence of electrical noise can be minimized.

In addition, the main body control unit 27 appropriately transmits the image signal stored in the image storage unit 18 to the console 6.
The control unit 40 of the console 6 determines whether or not an image signal has been received from the main body control unit 27 of the radiological image detection apparatus 5, and when determining that the image signal has been received, the control unit 40 Predetermined image processing is executed on the signal, a thumbnail image, a radiographic image desired by a doctor or the like is acquired, and the radiographic image is displayed on the display unit 43.

  As described above, according to the present embodiment, when the accumulation time T0 for obtaining the imaging signal and the accumulation time T1 for obtaining the offset signal are used, the imaging signal is based on the correction signal obtained by multiplying the offset signal by T0 / T1. Perform offset correction for. For this reason, only the accumulation time T1 for obtaining the offset signal can be lengthened and the offset signal can be read once. Compared with the case where the offset signal is obtained in a plurality of times, the offset correction is performed. The time required for offset correction can be minimized without reducing accuracy.

  Also, by reading the offset signal once, the addition of electrical noise due to switching that occurs every time the charge is read can be minimized.

  Since T0 <T1, even when noise is included in the offset signal, it can be averaged to obtain an appropriate correction signal.

  T1 is T0 × N, but N is not limited to an integer, so it is possible to set T1 to 7.5 times T0, etc., and obtain the offset signal multiple times and average it Compared with the case where it does, flexible operation according to an operator and imaging conditions is attained.

  In addition, the charge accumulation time T0 is not predetermined, and is determined according to the determination of radiation irradiation start or radiation irradiation end. In this way, even when the charge accumulation time can vary arbitrarily, the offset correction is performed on the imaging signal based on the correction signal obtained by multiplying the offset signal by T0 / T1, so even if the accumulation time T0 cannot be specified in advance, Since the correction signal can be generated, compared to the case where the offset signal obtained by accumulating the dark current for the same accumulation time as the accumulation time of the charge at the time of radiographic imaging is acquired and corrected, Offset correction can be performed with high accuracy.

  In the present embodiment, the offset signal is acquired after radiographic imaging is performed and the imaging signal is acquired. However, the timing at which the offset signal is acquired is not limited to that illustrated here. An offset signal may be acquired before radiographic imaging is performed.

Further, in the present embodiment, the configuration is such that the start or end of radiation irradiation is detected by the phototimer 29 serving as detection means, and the charge accumulation time T0 is determined based on this, but the charge accumulation time T0 is determined. The determination method is not limited to this.
For example, when an operator or the like inputs from the input operation unit 26 of the radiation image detection device 5 or the input operation unit 42 of the console 6, the charge accumulation time T0 in the radiation imaging may be determined. The charge accumulation time T0 may be set in advance according to the photographing conditions and the like, and the charge accumulation time T0 corresponding thereto may be determined by inputting the photographing conditions and the like.
In addition, the charge accumulation time T0 is not limited to the case where it is determined by the main body control unit 27. For example, the main body control unit 27 has a timer function for measuring the electrification accumulation time T0, and T0 is measured and measured. The offset signal may be multiplied by T0 / T1 based on T0.

  In addition, it is needless to say that the present invention is not limited to the above embodiment and can be modified as appropriate.

It is a figure which shows schematic structure which illustrates one Embodiment of a radiographic imaging system. It is a perspective view which shows the principal part structure of a radiographic image detection apparatus. It is an equivalent circuit block diagram for 1 pixel of the photoelectric conversion part which comprises a photoelectric converting layer. FIG. 4 is an equivalent circuit configuration diagram in which the photoelectric conversion units illustrated in FIG. 3 are two-dimensionally arranged. It is a block diagram which shows the principal part structure of a radiographic image detection apparatus. FIG. 5 is an equivalent circuit configuration diagram illustrating a part of the photoelectric conversion unit illustrated in FIG. 4. It is a block diagram which shows the principal part structure of a console. It is a timing chart which showed the timing which acquires an image pick-up signal and an offset signal in this embodiment. It is a timing chart which showed the timing which acquires an image pick-up signal and an offset signal in a comparative example. It is a graph explaining the electrical noise by switching.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiographic imaging system 5 Radiographic image detection apparatus 6 Console 16 Scan drive circuit 17 Signal read-out circuit 27 Main body control part 28 Image data correction part 29 Photo timer 30 Control apparatus

Claims (3)

An image sensor that generates and stores charge;
In the imaging element, after the charge generated when radiation is irradiated is accumulated for the accumulation time T0, an imaging signal reading unit that reads the accumulated charge as an imaging signal;
In the imaging device, after the charge generated when radiation is not irradiated is accumulated for the accumulation time T1, an offset signal reading unit that reads the accumulated charge as an offset signal;
A correction unit that performs offset correction based on a correction signal obtained by multiplying the offset signal by T0 / T1 with respect to the imaging signal;
A radiological image detection apparatus comprising:   The radiological image detection apparatus according to claim 1, wherein T0 <T1. Detecting means for detecting radiation irradiation;
Control means for determining the accumulation time T0 according to the determination of radiation irradiation start or radiation irradiation end based on the output of the detection means, and controlling the readout timing of the imaging signal by the imaging signal readout unit;
The radiological image detection apparatus according to claim 1, further comprising:

Images