JP2005177113A - Image reading apparatus and x-ray photography apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable image without hindering the super-sensitivity even when a continuous noise from outside exists. <P>SOLUTION: An image reading apparatus is equipped with a detectors array consisting of a two-dimensional disposition of the detectors, reading means (62, 901, 92, 100 and 108) which read out signals form the above detectors making a line in the above detectors array as a unit and store the same in a storing section, a detection means of an electromagnetic field noise from outside, a phase detecting means for the above detected noise, and a controlling means which adjusts from the detected phase a timing of sample holding of the reading line data making the line as the unit, so that the stable image is provided even when the noise from the outside exists. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to drive control of an imaging apparatus that performs imaging of a subject using radiation.

  In recent years, so-called flat panel sensors have emerged as X-ray digital imaging devices. These sensors have the potential to replace conventional imaging systems that use film, and are expected to expand over a wide range in the future because they directly output X-digitized data.

  Many of such flat panel sensors mainly use amorphous silicon, and at the same time, a large photographing area and high definition are demanded, and at the same time, high sensitivity and high SN are demanded.

  However, recent medical devices, information devices, mobile phones, and the like generate various exogenous noises in the hospital and leak electromagnetic field noise around them, and problems that are affected by such devices are occurring.

  Among them, some of the inverter type X-ray generators arranged in the imaging room or in the vicinity thereof leak a strong high-frequency leakage magnetic field. When a flat panel sensor must be placed in close proximity to these devices due to the size of the shooting room or layout restrictions, the external noise affects the flat panel sensor and noise is superimposed on the captured image. There is a problem that the image quality deteriorates.

  When the X-ray generator and the flat panel sensor in the adjacent room are installed over the wall, the image may leak through the wall and seriously affect the image. The inverter type X-ray generator drives an inverter circuit at a frequency of about several tens of KHz during X-ray explosion, and at this time, an alternating magnetic field is generated around the inverter circuit and leakage to the outside occurs. For this reason, when the distance is relatively short due to the arrangement over the wall, the leakage magnetic field from the generator is likely to be superimposed on the imaging unit sensor, and intense line noise is generated on the image.

  Exogenous noise that affects the flat panel sensor includes radioactive noise from equipment and conductive noise. Although it is possible to take measures against conductive noise relatively easily by strengthening the filter of the power supply system, etc., radiated noise is electromagnetic noise radiated into the space and directly enters the flat panel from various angles. Therefore, the countermeasure is not easy. In particular, it is generally difficult to shield against magnetic field noise.

  The entire flat panel is covered with a metal casing or a molded casing with an electromagnetic shield, and basically has a structure with an electromagnetic shield. With such a structure, even a thin metal foil has a sufficient effect on electric field noise that can provide a shielding effect, and clears the EMC test. However, the shielding effect against a strong alternating magnetic field is low. This is because the magnetic field shield can be effectively enhanced by sealing the flat panel sensor and the peripheral circuit with a casing having a high magnetic shielding effect, but the shield for extraneous noise protection on the X-ray incident surface. It is difficult to dispose a material (such as aluminum through which X-rays pass) because the X-ray transmittance is lowered and high sensitivity is prevented. For this reason, there is a limit in preventing noise entering from the X-ray incident surface.

  As a countermeasure on the device side where the AC magnetic field is leaking, it is possible to cover as much as possible with a shielding material, but although such a countermeasure can be reduced to some extent, the signal level to be handled is very low. In this case, even a reduced leakage magnetic field causes electromagnetic induction in the signal detection system circuit including the sensor panel and the amplifier IC, thereby affecting noise on the image. In particular, when the photographing unit comes close to the noise generation source, the influence is further increased because the spatial distance between them is shortened.

  When such AC magnetic field noise is superimposed, line noise appears periodically on the image. This is because when the signal line is sampled and held, the induced noise due to the external AC magnetic field is superimposed on the signal, and the phase relationship with this noise is shifted sequentially for each line, so that the image is a beat of a predetermined frequency. This is because it appears as the upper line noise.

  Since line noise is superimposed on the photographed image, the image quality is remarkably deteriorated, and in the case of a medical image, it causes a misdiagnosis and the like, which is a serious problem.

  In order to prevent such a problem, the magnetic field shield is practically difficult as described above, and therefore, the distance from the source is increased. However, as a practical matter, where multiple shooting rooms are laid out next to each other, it may be next to such equipment across the wall of the adjacent room, so the layout cannot be changed due to ease of use or installation restrictions. There is a case. The same applies when the layout is not so flexible, such as an examination car.

  Therefore, in general X-ray imaging, there has been proposed a method of detecting the single noise generated when X-rays are bombarded in a short time and shifting the readout timing from the sensor (for example, patents). Reference 1).

  That is, it is a method in which the presence or absence of external noise is confirmed immediately before reading out the sensor, and if there is noise, the reading is not performed and the reading is performed after the noise disappears.

  Note that the external noise affects the image quality at the time of reading an image in which the charge charged in the sensor pixel is transferred to the amplifier. The X-ray generator in the room leaks an AC magnetic field of several tens of KHz during the blasting time (approximately 0.3S as a rough guide) when generating X-rays, but the blasting is already over at the read timing. Because there is no problem. The extraneous noise does not affect the charge accumulated in the sensor pixel, and when the charge is transferred to the amplifier, if the X-ray generator in the adjacent room is generating X-rays, This is due to superimposition of extraneous noise.

However, although the above-mentioned method can cope with single noise, a strong periodic magnetic field from CT or Margen X-ray inverter, CRT, USP, etc. leaks constantly or for a long time, that is, continuous. It was not effective against general noise and was a problem. In addition to the above-mentioned power system devices, a liquid crystal display or the like may cause the same problem even when placed in close proximity for mobile use or the like.
Japanese Patent Application No. 2003-172867

  An object of the present invention is to provide an X-ray imaging apparatus capable of providing a stable image even when there is continuous exogenous noise without hindering high sensitivity in view of the above problems. It is a thing.

  In order to achieve the above object, an image reading apparatus according to the present invention comprises the following arrangement. That is, a detector array in which detectors are two-dimensionally arranged, a reading means (62,901,92,100,108) for reading a signal from the detector and holding it in a holding unit in units of rows in the detector array, and an external property Electromagnetic field noise detection means, phase detection means for the detection noise, and control means for adjusting the timing for sample-holding read line data in units of rows from the detected phase.

  According to the present invention, an X-ray imaging apparatus including an X-ray generation apparatus and the image reading apparatus is provided.

  According to the present invention as described above, an inverter type X-ray generator such as an X-ray CT or a margen, and a CRT, a liquid crystal display or the like that continuously leaks extraneous noise such as a medical examination vehicle or a mobile device are close to each other. Even when installed in a mobile environment, it is possible to reduce the influence of external noise on the image and provide a stable image quality. Etc.

  Furthermore, the same effect can be obtained even when the oscillation of the noise source is unstable.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Configuration of X-ray Imaging System FIG. 1 is a block diagram showing a configuration of an X-ray imaging system according to the present embodiment. In FIG. 1, 10 is an X-ray room, 12 is an X-ray control room, and 14 is a diagnostic room.

  In the X-ray room 10, an X-ray generator 40 for generating X-rays and an X-ray detector 52 as an imaging unit are placed. The X-ray generator 40 narrows the X-ray beam generated by the X-ray tube 42 that generates X-rays, the high-voltage power source 44 that drives the X-ray tube 42, and the X-ray tube 42 to a desired imaging region. A line stop 46 is provided.

  The X-ray detector 52 detects an X-ray beam generated from the X-ray generator 40 and transmitted through the subject 50, and includes a grid 54, a scintillator 56, a photodetector array 58, and an X-ray exposure monitor 60. A driver 62 and a DC / DC power source 902. The grid 54 includes an X-ray low-absorption member and an X-ray high-absorption member (for example, has a stripe structure of Al and Pb), and reduces the influence of scattered X-rays generated by passing through the subject 50. Note that X-ray irradiation may be performed while moving the grid 54 so that moire does not occur due to the relationship of the lattice ratio between the photodetector array 58 and the grid 54.

The scintillator 56 converts the X-rays into visible light by exciting (absorbing) the host substance of the phosphor with high-energy X-rays and generating fluorescence in the visible region by the recombination energy. The fluorescence of the scintillator 56, due to maternal itself such as CaWO ₄ or CdWO ₄ or, CsI: T1 or ZnS: is by luminescence center substance added to the inside base such as Ag. The photodetector array 58 is a two-dimensional arrangement of photodetectors, and converts visible light output from the scintillator 56 into an electrical signal. A so-called flat panel sensor is formed by the scintillator 56 and the photodetector array 58. The X-ray exposure monitor 60 is arranged for the purpose of monitoring the X-ray transmission amount. The X-ray exposure monitor 60 may detect X-rays directly using a crystalline silicon light receiving element or the like, or may detect fluorescence by the scintillator 56. In this embodiment, the X-ray exposure monitor 60 is composed of an amorphous silicon light receiving element formed on the back surface of the substrate of the photodetector array 58.

  The driver 62 drives the photodetector array 58 under the control of the imaging controller 24 and reads a signal from each photodetector. Details of operations of the photodetector array 58 and the driver 62 will be described later. The DC / DC power source 902 converts the DC voltage from the AC / DC power source 903 into one or a plurality of types of voltages, and supplies a predetermined voltage to each circuit in the X-ray detector 52. The AC / DC power source 903 is a power source that converts a predetermined DC voltage from a commercial AC power source line.

  A system controller 20 is disposed in the X-ray control room 12. The central processing unit 22 executes various controls in the system. For example, the central processing unit 22 includes display control of the monitor 30, analysis of operation input via the operation panel 32, imaging controller 24, image processor 26, and external storage device 28. to manage.

  The imaging controller 24 controls the high-voltage power supply 44 based on information from the X-ray light amount monitor 60, controls the X-ray diaphragm 16 to form an X-ray beam corresponding to the imaging region, and detects X-rays. A drive instruction is given to the driver 62 in the device 52. The image processor 26 applies, for example, image data correction, spatial filtering, recursive processing, gradation processing, scattered ray correction, and dynamic range (DR) compression processing to the X-ray image data obtained from the driver 62. And other image processing.

  The external storage device 28 is a large-capacity high-speed storage device that stores basic image data processed by the image processor 26. The external storage device 28 stores image information reconfigured so as to satisfy a predetermined standard (for example, Image Save & Carry (IS & C)). The central processing unit 22 is connected to an external device such as the terminal 70, the image printer 74, and the file server 76 in the diagnosis room 14 via a LAN, and is in accordance with a predetermined protocol (for example, Digital Imaging and Communications in Medicine (DICOM)). Transmit image data.

  The terminal 70 performs image processing or the like for diagnosis support on an image (moving image / still image) transmitted through the LAN, or displays the image on a display. The image printer 74 prints out an image (still image) transmitted via the LAN, for example, on a film. The file server 76 stores images (moving images / still images) transmitted via the LAN and provides a search function for X-ray captured images. Needless to say, captured images may be exchanged between hospitals by WAN connection. Of course, a plurality of X-ray imaging systems can be connected to the LAN.

[2] Configuration of Photodetector Array 58 Next, the configuration and operation of the photodetector array 58 will be described in detail. FIG. 2 is a diagram showing an equivalent circuit of the photodetector array 58 having a two-dimensional array of photoelectric conversion elements.

One photodetection element is provided corresponding to one pixel, and each photodetection element is a photodetection unit (photoelectric conversion element PD _{(m, n)} ) and a switching thin film transistor (TFT) for controlling charge accumulation and reading. Switch SW _{(m, n)} ). These photodetectors are generally formed on a glass substrate from amorphous silicon (a-Si). In the present embodiment (FIG. 2), the photodetector array 58 is configured by two-dimensionally arranging 4096 × 4096 photodetectors, and the array area is 430 mm × 430 mm. Accordingly, the size of one pixel is about 105 μm × 105 μm.

The photoelectric conversion element PD _{(m, n)} gate electrode (G electrode) of, TFT switches SW _{(m, n)} are connected to a common column signal line Lc _n to the column through a. For example, the photoelectric conversion elements PD _{(1,1) to} PD _(4096,1) in the first column are connected to the column signal line Lc ₁ in the first column. In addition, the D electrode of each photoelectric conversion element PD _{(m, n)} is connected to the bias power supply 85 via the bias wiring Lb. The control terminals of the same row TFT switches SW _{(m, n)} are connected to a common row selection line Lr _m. For example, the control terminals of the TFT switches SW _{(1,1) to} SW _{( 1,4096)} in the first row are connected to the row selection line Lr ₁ in the first row.

Row selection lines Lr _{1 to} Lr ₄₀₉₆ are connected to line selector 92. The line selector 92 determines which line's photoelectric conversion element signal charge should be read based on the control signal from the driver 62, and outputs to the control terminal of each TFT switch SW according to the output of the address decoder 94. 4096 switching elements (96 _{1 to} 96 ₄₀₉₆ ) for switching the supply voltage (Vgl or Vgh) are provided. Note that the line selector 92 may be configured by a shift register simply used for a liquid crystal display or the like as the simplest configuration.

With the above configuration, by switching only the switch element 96 _x connected to an arbitrary x-th row selection line Lr _x to the Vgh side, the TFT switches SW _{(x, 1) to} SW _{(x, 4096)} in the x-th row The ON state is established, and the accumulated charge signals from the photoelectric conversion elements PD _{(x, 1) to} PD _{(x, 4096) in the} row are extracted onto the column signal lines Lc _{1 to} Lc ₄₀₉₆ .

The column signal lines Lc _{1 to} Lc ₄₀₉₆ are connected to the signal readout circuit 100. In the signal readout circuit 100, reference numerals 102 _{1 to} 102 ₄₀₉₆ denote reset switches that turn on / off the connection between the column signal lines Lc _{1 to} Lc ₄₀₉₆ and the power source 101 that supplies the reset reference potential (Vbt). Preamplifier 106 _{1-106 4096,} respectively amplifies a signal potential from the column signal line Lc ₁ Lc _4096. Sample hold (S / H) circuit 108 ₁ to 108 ₄₀₉₆ samples and holds the output of the preamplifier 106 _{1-106 4096} respectively. An analog multiplexer 110 multiplexes the outputs of the S / H circuits 108 _{1 to} 108 ₄₀₉₆ on the time axis. Reference numeral 112 denotes an A / D converter that digitizes analog outputs sequentially supplied from the multiplexer 110. The output of the A / D converter 112 is supplied to the image processor 26.

  The signal charge accumulation time and the A / D conversion time are closely related. When A / D conversion is performed at high speed, the band of the analog circuit becomes wide and it becomes difficult to achieve a desired S / N. Therefore, it is required to shorten the reading time of the image signal without unnecessarily increasing the analog signal band and the A / D conversion rate. One technique for realizing this is to divide the photodetector array of 4096 × 4096 pixels shown in FIG. 2 into, for example, two vertically or four horizontally, and the multiplexer 110 and the A / A for each divided region. It is possible to provide a set of D converters 112 and drive them simultaneously. However, as the number of A / D converters and multiplexers increases, the cost increases accordingly. Therefore, it is preferable not to use many A / D converters indiscriminately but to apply an appropriate number of A / D converters (number of divisions) in consideration of balance with cost.

  FIG. 3 shows an example of an equivalent circuit of one photodetecting element shown in FIG. The light detection unit PD includes a parallel circuit of a photodiode 80a and a capacitor 80b, and a capacitor 80c connected in series with the capacitor 80b. A charge due to the photoelectric effect is described as a constant current source 81. Capacitor 80b may be a parasitic capacitance of photodiode 80a or an additional capacitor that improves the dynamic range of photodiode 80a. A common bias electrode (hereinafter referred to as “D electrode”) of the light detection unit PD is connected to a bias power source 85 via a bias wiring Lb. An electrode (hereinafter referred to as G electrode) on the TFT switch SW side of the photodetection part PD is connected to the capacitor 86 and the charge readout preamplifier 106 via the TFT switch SW. The input of the preamplifier 106 is also connected to the ground via the reset switch 102 and the signal line bias power supply 101.

[3] Operation of Photodetector Array 58 Next, the operation of the X-ray detector 52 of the present embodiment including the photodetector array 58 will be described. First, the driving form of the photodetector array 58 of this embodiment will be described. The driving mode of the photodetector array 58 includes a refresh mode and a photoelectric conversion mode classified according to the voltage application method of the D electrode and the G electrode of the photoelectric conversion element. In the photoelectric conversion mode, empty reading, main reading, and correction reading are performed. Executed.

<Photoelectric conversion mode>
In the photoelectric conversion mode, three types of reading operations, blank reading, main reading, and correction reading are performed. First, prior to these “reading” operations, the driver 62 sets the voltage of the power supply 85 to the bias value Vs (> Vbt), all switch elements 102 _{1 to} 102 ₄₀₉₆ are turned off (all column signal wirings Lc _{1 to} Lc ₄₀₉₆ are released from the power supply 101), and all switch elements 96 _{1 to} 96 ₄₀₉₆ are connected to the Vgl side (all TFTs). Set the switches SW _{(1,1) to} SW _{( 4096,4096)} to OFF). Hereinafter, this state is referred to as a basic state of the photoelectric conversion mode.

[About blank reading]
The idle reading was accumulated in the holes accumulated in the capacitors 86 and 89, and thus in the capacitors 80b and 80c by applying Vs to the D electrode and Vbt to the G electrode of the photoelectric conversion element PD in FIG. It is a drive for emitting holes.

In the idle reading of the present embodiment, from the basic state of the photoelectric conversion mode (Vs is applied to the D electrodes of all the photoelectric conversion elements PD in this state),
(1) All the switch elements 102 _{1 to} 102 ₄₀₉₆ are turned on to supply the reset reference potential Vbt to all the column signal wirings Lc _{1 to} Lc ₄₀₉₆ ,
(2) Applying Vbt to the G electrodes of the photoelectric conversion elements PD _{(x, 1) to} PD _{(x, 4096)} corresponding to the row with only the switch element 96 _x on the Vgh side,
(3) The above (2) is sequentially executed from x = 1 to 4096.

  It is possible to set all the row selection lines Lr to Vgh at the same time by the above-described idle reading operation. In this case, however, the signal wiring potential greatly deviates from the reset voltage Vbt when the read preparation is completed, resulting in high S / N. It is difficult to get a signal. In the above procedure, the row selection line Lr is sequentially selected from 1 to 4096 and reset. However, the reset can be performed in any order by the control of the driver 62 based on the setting of the imaging controller 24. .

[About main reading and correction reading]
The main reading is a drive for reading the signal charge of the photoelectric conversion element PC after the X-ray exposure. The correction reading is a drive for acquiring a correction dark image after the main reading. In the main reading and the correction reading, the operation itself in the photodetector array 58 is the same. That is, by applying Vs to the electrode D and turning on the TFT switch SW with the switch element 102 turned off, a potential corresponding to the amount of received light is supplied from the photoelectric conversion element PD onto the column signal wiring Lc.

A general procedure of the main reading and the correction reading according to the present embodiment is as follows. That is, from the basic state of the photoelectric conversion mode,
(1) The charge accumulated in the capacitors 86 and 89 is released by turning ON / OFF the switch elements 102 _{1 to} 102 ₄₀₉₆ (reset of the amplifier input unit),
(2) The photoelectric conversion element PD of only the to Vgh side switching element 96 _x on the row select line Lr _{x (x, 1)} ~PD column signal lines accumulated charge signals from _{(x, 4096) Lc 1 ~Lc} 4096 Take it out and
(3) The accumulated charge signal is amplified by the preamplifiers 106 ₁ to 106 ₄₀₆₉ and held in the S / H circuits 108 _{1 to} 108 ₄₀₉₆ .
(4) The signals held by the S / H circuits 108 _{1 to} 108 ₄₀₉₆ are serialized by the multiplexer 110, converted into digital data by the A / D converter 112, and output.
(5) The above operation is sequentially repeated from x = 1 to 4096 to acquire all pixel data.
During the execution of (4) above, (1) to (2) are executed for the next row selection line Lr _{x + 1} ,
After completion of (4), execute (3) for the selected row (x + 1).

<Refresh mode>
The refresh mode is for eliminating the saturation state of the holes generated in the photoelectric conversion element PD, and is performed especially for releasing holes accumulated in the capacitors 80b, 80c and the like that cannot be completely eliminated by the idle reading. . In the refresh mode, the bias power supply 85 is set to Vr, the switch element 102 and the TFT switch SW are turned on, and the D electrode potential <G electrode potential (Vr <Vbt) is established, so that holes accumulated in the capacitors 80b, 80c, etc. Let it go.

In the refresh mode, the driver 62 operates the photodetector array 58 of FIG. 2 according to the following procedure. That is
(1) Vr is applied to the D electrodes of all photoelectric conversion elements PD by setting the power supply 85 to the bias voltage Vr,
(2) The switch elements 102 _{1 to} 102 ₄₀₉₆ are turned on to apply the reset reference potential Vbt to all the column signal wirings Lc _{1 to} Lc ₄₀₉₆ ,
(3) The reset reference potential Vbt is applied to the G electrodes of all the photoelectric conversion elements PD by switching all the switch elements 96 _{1 to} 96 ₄₀₉₆ to the Vgh side.

<Drive control of photodetector array in imaging system>
Next, with reference to the timing chart of FIG. 4, the execution timing of each of the drive modes will be described in detail. In FIG. 4, 400 is an imaging request signal generated by a user operation on the operation panel 32, 401 is an X-ray generator ready signal, 402 is an actual X-ray exposure state, and 403 is imaging control based on an instruction from the operator 21. An imaging request signal from the detector 24 to the driver 62, 404 is an imaging ready signal of the X-ray detector 52, and 405 is a driving state of the X-ray detector 52 (especially, a charge reading operation from the photodetector array 58). ing. Reference numeral 406 conceptually represents a transfer state of image data and a state of image processing or display.

  When an imaging preparation request is instructed from the operation panel 32 (400, 1st SW), the imaging controller 24 instructs the X-ray generator 40 and the X-ray detector 52 to shift to an imaging preparation state (imaging preparation request instruction). put out. Receiving the imaging preparation request instruction, the driver 62 starts idling driving that repeats one refresh mode operation (R) and n idle readings (F1 to Fn) as one set (405). Note that when a sensor that does not require the refresh mode operation is used, the refresh mode operation is not necessary. The X-ray generator 40 that has received the imaging preparation request instruction starts, for example, a tube rotor up, and outputs an X-ray generator ready signal 401 to the imaging controller 24 when imaging preparation is completed.

  Note that the above-described shooting preparation request instruction may not be intentionally issued by the operator 21. That is, when patient information, radiographing information, or the like is input to the operation panel 32, the imaging controller 24 interprets it as a request for preparation for radiography preparation, and detects the X-ray generator 40 and the X-ray detector 52. You may make it transfer to a vessel ready state.

  Next, when an imaging request instruction (400: 2ndSW) is input by operating the operation panel 32, the imaging controller 24 controls the imaging operation while synchronizing the X-ray generator 40 and the X-ray detector 52. . First, an X-ray imaging request signal 403 is asserted to the X-ray detector 52 in accordance with an imaging request instruction (400: 2ndSW). In response to the X-ray imaging request signal, the driver 62 immediately switches the operation from idling driving to imaging driving (405).

  In the imaging driving, as shown in the imaging device driving state 405, X-ray image acquisition driving and correction dark image acquisition driving are performed. The X-ray image acquisition drive further includes a detection preparation drive (T3), an exposure period (T4), and a main reading (Frx). In the detection preparation drive, refresh operation (R) and idle reading (Fp: Fp1, Fp2, Fpf in FIG. 4) are executed in a predetermined sequence. When these operations are finished, the driver 62 returns an X-ray detector ready signal 404 to the imaging controller 24 on the assumption that the X-ray detector 52 is ready for imaging. The imaging controller 24 detects the transition of the X-ray detector ready signal 404 and asserts the X-ray generation request signal 402 to the X-ray generator 40.

  The X-ray generator 40 generates X-rays while the X-ray generation request signal 402 is given. When a predetermined X-ray dose is generated (that is, when a predetermined time has elapsed), the imaging controller 24 negates the X-ray imaging request signal 403 and the X-ray generation request signal 402 and ends the X-ray exposure. The X-ray imaging request signal 403 is negated to notify the X-ray detector 52 of the image acquisition timing. Based on this timing, after a predetermined wait time for stabilization of the signal readout circuit 100, the driver 62 negates the X-ray detector ready signal 404 and reads out the image data from the photodetector array 58 (main reading). (Frx)). The read image data (raw image) is supplied to the image processor 26. When this process is completed, the driver 62 shifts the readout circuit 100 to the standby state again. Note that a period from the end of the detection preparation drive to the start of reading of image data is defined as an X-ray exposure period (T4).

  When the main reading is finished as described above, the X-ray image acquisition drive is finished. In the main reading described above, the charge accumulation time of each sensor is from when the reset operation is completed, that is, from when the TFT switch SW is turned off in the idle reading (Fpf) immediately before the main reading until the TFT is turned on in the main reading. Become. Therefore, the charge accumulation time and time differ for each selected row. Therefore, the correction dark image obtained by performing the correction reading is used to correct the image obtained by the main reading to absorb the difference in the above conditions.

  For this reason, the X-ray detector 52 starts the correction dark image acquisition drive following the X-ray image acquisition drive, acquires the correction dark image, and transfers it to the image processor 26. The dark image acquisition drive for correction includes detection preparation drive (T3), a delay period (T5) without X-ray exposure, and correction reading (Frn), but the operation of the X-ray detector 52 itself is X-ray image acquisition drive. This is exactly the same as the detection preparation drive (T3), X-ray exposure period (T4), and main reading (Frx). In other words, the X-ray image acquisition drive sequence and the correction dark image acquisition drive sequence are the same except that X-ray exposure is not executed.

  Note that the X-ray image acquisition drive may have slightly different X-ray exposure times each time an image is taken, but the correction dark image acquisition drive reproduces the same sequence including that and acquires a dark image. . By correcting the X-ray image using the dark image thus obtained, a high-quality X-ray image can be obtained. However, when the grid is moved during the X-ray exposure period, the grid may not be moved during dark image acquisition.

  Further, the number of idle readings (Fp) and the time interval T2 in the X-ray image acquisition driving are set in advance prior to the imaging request from the imaging controller 24. However, the number of idle readings (Fp) and the time interval T2 are automatically selected to be optimal values based on whether the operability is important or the image quality is important, or on the imaging part or the like according to the request of the operator 21. In addition, since it is required for practical use that the period (T3) from the exposure request to the completion of imaging preparation is required in practice, it is preferable to shorten the time interval T2 of idle reading (Fp) as much as possible. Furthermore, when an exposure request is generated, the imaging sequence driving is immediately started in any idling driving state. By doing so, the period (T3) from the exposure request to the completion of the preparation for photographing can be shortened, and the operability is improved.

  Furthermore, in this embodiment, the operation mode is changed between idle reading (Fi) during idling driving and idle reading (Fp) during detection preparation driving during X-ray image acquisition driving. In the idling driving period, the idle reading (Fi) execution interval T1 is set to be longer than that in the detection preparation driving (T2) in order to minimize the reading operation that puts a load on the photodetector array 58 (particularly the TFT switch SW). The on time of the TFT switch SW is also set shorter than that at the time of actual reading. Further, in this embodiment, even in the detection preparation drive, idle reading with a short TFT on-time is executed a predetermined number of times, and idle reading (Fpf) having the same TFT on-time as the actual reading is executed immediately before the actual reading is started.

[4] Operation of Image Processor 26 FIG. 5 is a diagram showing the flow of image data of the image processor 26. 501 is a multiplexer for selecting a data path, 502 and 503 are X-ray image and dark image frame memories, 504 is an offset correction circuit, 505 is a gain correction data frame memory, 506 is a gain correction circuit, and 507 is a defect. Each of the correction circuits is represented. Reference numeral 508 represents another image processing circuit.

  The X-ray image acquired in the main reading (Frx) of the X-ray image acquisition drive in FIG. 4 is stored in the X-ray image frame memory 502 via the multiplexer 501. Subsequently, the correction dark image acquired by the correction reading (Frn) of the dark image acquisition drive is stored in the dark image frame memory 503 via the multiplexer 501.

  The offset correction circuit 504 performs offset correction by subtracting the image in the frame memory 503 from the image in the frame memory 502, for example. The gain correction circuit 506 performs gain correction by, for example, dividing the offset-corrected image by gain correction data acquired in advance and stored in the gain correction frame memory. The gain-corrected data is subsequently transferred to the defect correction circuit 507, and the image is continuously interpolated so as not to cause a sense of incongruity in the insensitive pixel portion or the joint portion of the X-ray detector 52 composed of a plurality of panels. The sensor-dependent correction process derived from the line detector 52 is completed. Further, after other general image processing such as gradation processing, frequency processing, and enhancement processing is performed by other image processing circuit 508, the image is stored in the external storage device 28 or the captured image is displayed on the monitor 30. Is displayed.

[5] Measures against image noise caused by extraneous electromagnetic field noise The operation of the X-ray imaging system of this embodiment, particularly the image reading operation from the photodetector array 58 has been described above.

  The above description has described the operation in the normal state.

  In the present embodiment, even when extraneous noise is superimposed, in order to further improve the image quality, information from the external electromagnetic field detection means built in the X-ray detector 52 performs the above-described main reading and correction reading operations. By controlling the sensor readout scanning frequency, an image with less noise can be provided.

  Furthermore, the same effect can be obtained even when the external noise has some frequency fluctuation.

  Hereinafter, this point will be described in detail.

FIG. 7 is a block diagram showing a detailed configuration relating to signal reading from the photodetector array 58. The photodetector array 58, the driver 62, the line selector 92, the multiplexer 110, the A / D converter 112, and the DC / DC power source 902 are as described with reference to FIGS. In addition, the switch element 102, the preamplifier 106, and the S / H circuit 108 collectively represent the switch elements 102 _{1 to} 102 ₄₀₉₆ , the preamplifiers 106 _{1 to} 106 ₄₀₉₆ , and the S / H circuits 108 _{1 to} 108 ₄₀₉₆ in FIG. .

  Reference numeral 902 denotes an external noise detector.

  External noise detectors are classified into electric field and magnetic field detectors. However, as described above, AC magnetic field noise is used because it is AC magnetic field noise that easily affects the sensor.

  As the AC magnetic field detector, a loop coil, a Hall element, and the like can be considered, and a dummy sensor arranged around the effective area in the panel can also be used. The dummy sensor is a sensor that is arranged around the effective area as the horizontal and vertical pixel areas where light is not incident among the panel signal outputs, and is mainly used for the black reference of the signal, that is, the dark current due to thermal excitation or the output stage amplifier. This is used for detecting components such as noise.

  The external noise detector detects with high sensitivity that the influence from the external noise varies depending on the relationship between the incident direction of the external magnetic field noise and the signal line of the sensor, etc. This is preferable because it is possible. The external noise detector is provided in the vicinity of the photographing unit or its periphery.

  The AC output from the external noise detector is amplified and then output after being limited to a predetermined frequency region with an LPF or the like in order to reduce unnecessary high frequency noise.

  Reference numeral 903 denotes a noise phase measuring device which receives an AC output from the external noise detector 902 and measures a phase with a CPV described later.

  As a specific configuration example and operation, noise detection is confirmed in a time division manner by an MPU or the like incorporating an ADC. That is, the MPU always samples noise in the ADC, and if the sampled data exceeds a predetermined allowable level that is known to affect the image, the timing from the CPV to the point described later and the period of the noise Also measure. These pieces of information are sent to a line SH (hereinafter referred to as sample hold SH) signal timing adjuster 904.

  If the noise period exceeds the allowable correction range, a warning indicating that the noise cannot be corrected is generated and transmitted to the driver 62.

  As another configuration, digitized data may be directly input to the MPU port of the noise phase measuring device 903 by adding a comparator for comparing with an allowable level to the external detector 902.

  Reference numeral 904 denotes a line SH (hereinafter referred to as SH) signal timing adjuster, which adjusts the line SH timing to reduce the influence of external noise based on the noise phase from the external noise frequency measuring device 903, and generates a timing signal. Output to the unit 901.

  These operations may be processed in the MPU, or a calculator dedicated to the processing may be configured with a PLD or the like. If the SH movable range is exceeded, a warning indicating that the noise cannot be corrected is generated and transmitted to the driver 62.

  A timing signal generator 901 outputs SH, RC, OE, and CS signals based on instructions from the driver 62. SH is set based on information from the line SH signal timing adjuster 904, and switching, setting, and the like with the default SH timing are all based on an instruction from the driver 62. Detailed description of each signal will be described later.

  Note that the timing signal generator 901 generates the various timing signals described above by dividing the high-frequency master clock.

  Here, noise on an image caused by external noise will be described.

  FIG. 9 is an image diagram of image noise generated when an alternating magnetic field, which is external noise, is superimposed on the light detection unit to cause electromagnetic induction, that is, line noise generated for each gate line (row selection line Lr). A gate line is laid out in the horizontal direction, and a signal line (column signal line Lc) is laid out in the vertical direction. As an example, a case where strong line noise is generated every five gate lines is shown. In this way, line noise is superimposed on the captured image, so that the image quality is remarkably deteriorated. In the case of a medical image, it causes a misdiagnosis in particular, which is a problem.

  This line noise is a line noise on the image as a beat of a predetermined frequency because the position (timing) at which the signal on the signal line is sampled and held and the phase relationship in which the external noise is superimposed on the signal are sequentially shifted for each line. It occurs when it appears.

  Here, assuming that the scanning frequency of one line is Fl (sampling frequency) and the external noise frequency is Fn, the line noise frequency Fln of the image is a beat of noise and sampling assuming that noise is superimposed during sampling. Therefore, it can be shown as follows.

Fln = ABS (Fn-i * Fl) ≤Fl (where i is a positive integer greater than or equal to zero)
Fln / Fl = ABS (Fn / Fl-i) ≦ 1
Here, assuming that Fn / Fl = i + d (where d is a decimal part), this is substituted into the above equation,
Fln / Fl = d ≦ 1. Therefore, the line noise frequency Fln is
Fln = d × Fl.

  For example, when d = 0.2, line noise occurs every 5 lines. Therefore, it can be understood that the influence of line noise can be reduced by setting d to 0, that is, if the relationship between the external noise frequency Fn and the sampling frequency Fl is an integer multiple. However, uniform reduction is difficult when the frequency of the noise source slightly varies.

  Therefore, in this case, the noise phase is measured and the line SH is adjusted for each line at the point where the noise becomes a predetermined phase. Therefore, the noise phase on the image becomes a constant phase on all lines, and the noise on the image Can be reduced.

  Hereinafter, details of the operation at the time of the main reading (Frx) and the correction reading (Frn) will be described with reference to the block diagram of FIG. 6 and the timing chart of FIG. Note that external noise affects only main reading and correction reading, and does not cause a problem in other empty readings.

  When the image information is read from the photodetector array 58, the timing signal generator 901 generates a line drive signal CPV. Since the sample hold signal SH is synchronized with the line drive signal CPV, it has the same frequency as the line drive signal CPV.

  In the main reading (Frx) and the correction reading (Frn), pixel signals are read in units of rows. FIG. 8 shows the reading operation in the Nth row. The timing signal generator 901 first generates a reset signal RC in synchronization with the master clock signal CLK. The switch element 102 is turned on and off by the reset signal RC to reset the column signal line Lc. In response to the line drive signal CPV, the line selector 92 turns on the TFT switch SW of the selected row selection line and turns on the OE signal to enable the output of the multiplexer 110. The charges accumulated in each photoelectric conversion element PD on the selected row selection line Lr are transferred to the readout circuit 100 via the column signal line Lc and integrated by the preamplifier 106. The timing signal generator 901 sends a sample hold signal SH to cause the S / H circuit 108 to hold the output voltage value of the preamplifier 106.

  Thereafter, the timing signal generator 901 similarly sends a line drive signal and sends a signal line reset signal RC in order to read the next line. The voltage value held in the previous line is sent to the AD converter 112 and converted into a digital signal until the next sample and hold signal is sent.

  In terms of mounting, the switch element 102, the preamplifier 103, and the sample hold circuit 108 have a switch element, preamplifier, and S / H circuit corresponding to one signal line as one system, for example, 256 systems are integrated into one IC. To be implemented. In the case of the photodetector array 58 having 4096 rows as in this embodiment, 16 ICs are required. As described above, since there are a plurality of ICs, the ICs are sequentially selected one by one according to the selection signal. FIG. 11 described later shows a state in which five ICs are sequentially selected by CS signals 0 to 4. The output of the selected IC is sent to the AD converter 112 via the multiplexer 110, and 256 outputs from the IC are sequentially converted into digital signals by the AD converter 112.

  The above operation is repeated to read all lines.

  In each signal transmitted from the timing signal generator 901, the timing (phase) within one line is not changed and is made constant. For example, the reset signal RC and the line drive signal CPV have a cycle that is an integral multiple of the clock signal CLK, and the sample hold signal SH is turned on after a predetermined time has elapsed since turning on the RC or CPV. Here, for example, the sample hold signal SH may be turned on by counting a predetermined number of master clocks after turning on RC or CPV.

  For this reason, if the timing of sample-holding is always performed at a predetermined phase timing for each line with respect to the noise phase, all lines are maintained at the same noise phase. Therefore, even if the sample-and-hold timing is a point where the external noise is large, all lines are read out at the same point, that is, because the noise of the same phase is superimposed, the noise on the line on the image is difficult to see. Become.

  FIG. 9 is an enlarged view of a part of the timing chart of FIG. The above description will be supplemented using FIG.

  The SH movable range is a range from the point at which the OE signal for turning on the TFT turns from ON to OFF until the CPV signal of the next line comes. The sample hold signal SH is a noise phase signal, and is switched from sample to hold after a predetermined time Ts from the falling in the drawing. As a result, the phase relationship of all signals SIG output from the preamplifier 106 is fixed in one line.

  The output signal SIG of the preamplifier 106 is superposed with a noise signal (simply a triangular wave) synchronized with the external noise due to the electromagnetic coupling of the noise to the signal detection system due to the external noise. According to the present embodiment, when the point of SIG held from the sample state by the S / H circuit 108 is A, the point held also for the next line remains A. Thus, even when noise is superimposed on the SIG signal, line noise in the case of imaging can be reduced by sampling each line with the same phase. On the other hand, in the normal case, each phase relationship is sequentially shifted for each line, so that the held points are sequentially changed as A, B, and C, and line noise as shown in FIG. 9 is generated. .

  As a matter of course, it is more effective to adjust the sample hold point to a timing with less noise.

  Here, a series of operations for reducing external noise in the drive control of the imaging system described above will be described.

  In the timing chart of FIG. 4, when an imaging preparation request is instructed from the operation panel 32 (400, 1st SW), the imaging controller 24 instructs the X-ray detector 52 to shift to an imaging preparation state (imaging preparation request instruction). Put out. Upon receiving the imaging preparation request instruction, the driver 62 operates the external noise detector 902, the noise phase measuring device 903, and the line SH signal timing adjuster 904 in addition to the above-described operations, and a series of settings to the timing signal generation unit 901. The above operation is repeated until just before the main reading operation. Note that noise measurement may be further performed and updated before correction reading.

  When no external noise is generated, the driver 62 instructs the timing generation unit 901 to perform a read operation as usual with the default line SH timing, but when it occurs, the line SH signal timing is generated. An instruction is given to switch to the SH timing calculated by the adjuster 904. Further, in the case of noise that cannot be corrected or a frequency that exceeds the corresponding range, the device notifies the imaging controller 24 that the correction cannot be made and warns the operator. Alternatively, it may be instructed to stop the explosion or to change the installation environment.

  When the series of operations is completed and the next shooting is resumed, the scanning cycle is returned to the default value to prepare for the next shooting.

  As described above, according to the present embodiment, an inverter type X-ray generator such as an X-ray CT or a margen, and a device that continuously leaks external noise such as a CRT or a liquid crystal display in an examination car or a mobile device. Even when installed in close proximity, it is possible to reduce the influence on the image due to external noise and provide a stable image quality, so that the installation environment is flexible and downsizing progresses. Compatible with mobile environments.

  Furthermore, the same effect can be obtained even when the oscillation of the noise source is unstable.

It is a schematic diagram which shows the outline | summary of the X-ray imaging system by embodiment. It is a schematic diagram which shows the structural example of the photodetector array by embodiment. It is a schematic diagram explaining the photon detection element in the photodetector array shown in FIG. It is a timing chart of the X-ray imaging system of an embodiment. It is a flow block diagram which shows the process of the acquired image by embodiment. It is the figure which showed the main circuit structures of the X-ray imaging system of embodiment. It is a figure which shows the example of a line noise generation | occurrence | production image. It is a timing chart of the X-ray imaging system of an embodiment. It is a partial enlarged view of the timing chart of the X-ray imaging system of the embodiment.

Claims (7)

  A detector array in which detectors are arranged two-dimensionally, reading means (62,901,92,100,108) for reading out signals from the detector and holding them in a holding unit in units of rows in the detector array, and external electromagnetic fields An image reading apparatus comprising: a noise detecting unit; a phase detecting unit for the detected noise; and a control unit for adjusting a timing for sample-holding read line data in units of rows based on the detected phase.   The control means always generates the sample hold signal at a predetermined phase of noise within a predetermined time (TFToff⇒next line CLK) with respect to the detected external noise phase signal for each selected line. The image reading apparatus according to claim 1, wherein:   The external electromagnetic field noise detection means mainly detects an AC magnetic field and uses a loop coil, a Hall element, or a dummy sensor outside the effective area of the detector array as a detector, and its output is amplified by an amplifier. 2. The image reading apparatus according to claim 1, wherein after that, the image reading apparatus passes through an LPF limited within a predetermined band.   2. The image reading apparatus according to claim 1, wherein the extraneous electromagnetic field noise detection means is disposed in proximity to the detector array.   The image reading apparatus according to claim 1, wherein the control unit issues a warning when extraneous noise that cannot be adjusted beyond the phase adjustment range is superimposed. An image reading method for reading an image signal from a detector array in which detectors are arranged in two dimensions,
Reading a signal from the detector array in units of rows in the detector array and holding the read signal in a holding unit; the external electromagnetic noise detection step; and the detection noise phase detection step; And a control step of adjusting sample hold timing for each readout line in units of rows from the detected phase.   An image reading apparatus according to claim 1 and an X-ray generator, wherein the detector array holds a signal based on the X-rays emitted from the X-ray generator. X-ray imaging apparatus.

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