JP2005204983A - Radiographic system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic system capable of surely deciding whether or not the calibration of this time is correct. <P>SOLUTION: A data comparison part 14 compares both of calibration data in the calibration of this time and calibration data in the calibration of the previous time or before that were read from a calibration memory part 22, and an abnormality detection part 15 detects whether or not the calibration data in the calibration of this time are abnormal on the basis of the compared result of the calibration data. Thus, whether or not the calibration data of this time are abnormal compared to the calibration data in the calibration made in the past is recognized, and whether or not the calibration of this time is correct is surely decided by a compared result and abnormality detection. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiation imaging apparatus used in the medical field, industrial fields such as non-destructive inspection, RI (Radio isotope) inspection, and optical inspection, and nuclear power field, and more particularly to a technique for calibrating pixels.

  Conventionally, as a typical shielding object for shielding radiation, an X-ray grid that removes scattered X-rays, a compensation filter that performs filtering on pixels of a captured image, and a top plate (bed) on which a subject is placed There is. The X-ray grid is configured by alternately arranging lead (Pb) and aluminum (Al), and scattered X-rays are blocked by lead. The X-ray grid is disposed adjacent to the X-ray irradiation side (detection side) of radiation detection means represented by, for example, a flat panel radiation detector (FPD).

By the way, the above-mentioned FPD is configured by laminating a sensitive film on a substrate, detects the radiation incident on the sensitive film, converts the detected radiation into electric charges, and arranges it in a two-dimensional array. Charge is stored in the capacitor. The accumulated charge is read by turning on the switching element and sent to the image processing means as an electrical signal. Therefore, there is a variation in the amount of charge accumulated for each detection element constituting the capacitor or the switching element, and accordingly, there is also a variation for pixels based on the electrical signal for each detection element. In order to eliminate such variations, for example, calibration is performed to adjust the gains of the amplifiers (amplifiers) for each detection element so that the output sides are aligned (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2001-245877 (page 3, FIG. 2)

  However, each X-ray grid used for imaging differs depending on the imaging region of the subject and the subject to be imaged. At the time of calibration, calibration data (calibration information, that is, correction coefficient) differs depending on each X-ray grid. Therefore, the calibration is performed by switching to the X-ray grid corresponding to the imaging region of the subject or the subject to be imaged. Perform

  There are situations in which the user forgets to perform the calibration even when the X-ray grid is switched, or the calibration is performed although the X-ray grid is not switched. In addition to the X-ray grid, it is necessary to determine whether or not the current calibration is correct in consideration of a shielding object such as a top plate or a compensation filter.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radiation imaging apparatus that can reliably determine whether or not the current calibration is correct.

  In order to achieve such an object, the present invention has the following configuration.

  That is, the invention according to claim 1 is a pixel detection unit that calibrates each detection element constituting the radiation detection unit with respect to a radiation detection unit that detects radiation transmitted through the subject and a pixel based on the detected radiation. And a radiographic imaging device that images a subject by calibrating the pixel by the pixel calibration unit and performing the image processing by the image processing unit, and image processing unit that performs image processing based on the detected radiation The calibration information storage means for storing the calibration information for pixel calibration obtained in the past, and the previous calibration read from the calibration information / calibration information storage means in the current calibration or a past calibration from the previous time. Calibration information comparing means for comparing the calibration information in the camera and an abnormality detecting means for detecting whether or not the calibration information in the current imaging is abnormal based on the comparison result of the calibration information. It is characterized by that.

  [Operation / Effect] According to the invention described in claim 1, the calibration information comparison unit reads the calibration information in the previous calibration or the previous calibration read from the calibration information / calibration information storage unit in the current calibration. Comparing the two, the abnormality detection means detects whether or not the calibration information in the current calibration is abnormal based on the comparison result of the calibration information. Therefore, it can be determined whether or not the current calibration information is not abnormal compared with the calibration information in the calibration performed in the past, and whether or not the current calibration is correct can be reliably determined by the comparison result and the abnormality detection. .

  In the above-described invention, the calibration information is information obtained by performing calibration in a state in which a shielding object (for example, an X-ray grid, a top plate, etc.) that shields radiation from the detection side of the radiation detection means is inserted, The calibration information storage means may compare both calibration information obtained by inserting the shielding object, or is information obtained by performing calibration in a state where the shielding object is removed. You may compare the both calibration information obtained except the thing (invention of Claim 2).

  When the shielding is removed as in the latter case, both the calibration information in the previous calibration and the calibration information in the previous calibration and the calibration information in the current calibration should both be obtained under the same conditions except for the shielding. . Therefore, even if it is forgotten to remove the shielding object in the current calibration, it is immediately understood that the current calibration information obtained by forgetting to remove the shielding object is abnormal by the comparison result and the abnormality detection. Therefore, the latter is preferable. In addition, it is possible to prevent a situation where calibration is forgotten to remove the shielding object. In addition, the maximum value of the radiation-based data is obtained by removing the shielding object, and the resolution is improved compared to the case where the shielding object is inserted by obtaining the maximum value data (that is, the dynamic range is widened). ) By performing pixel calibration, more accurate imaging can be performed.

  Further, by providing a notifying means for notifying when an abnormality is detected from the abnormality detecting means (the invention according to claim 3), if the calibration information in the current calibration is abnormal, the abnormality is immediately reported by the notification from the notifying means. Understand.

  According to the radiation imaging apparatus according to the present invention, the calibration information comparison unit compares both the calibration information in the previous calibration read from the calibration information / calibration information storage unit in the current calibration or the previous calibration from the previous calibration, The abnormality detection means detects whether or not the calibration information in the current calibration is abnormal based on the comparison result of the calibration information, so whether or not the current calibration information is abnormal compared to the calibration information in the calibration performed in the past. Whether or not the current calibration is correct can be surely determined based on the comparison result and the abnormality detection.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of an X-ray diagnostic apparatus according to an embodiment, FIG. 2 is an equivalent circuit of a flat panel X-ray detector used in the X-ray diagnostic apparatus as viewed from the side, and FIG. It is the equivalent circuit of the seen flat panel type X-ray detector. In this embodiment, a flat panel X-ray detector (hereinafter referred to as “FPD” as appropriate) is taken as an example of radiation detection means, and an X-ray diagnostic apparatus is taken as an example of a radiation imaging apparatus.

  As shown in FIG. 1, the X-ray diagnostic apparatus according to the present embodiment includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that irradiates the subject M with X-rays, and a subject. An FPD 3 that detects X-rays transmitted through M, an X-ray grid 4 that removes scattered X-rays, a grid drive mechanism 5 that moves the X-ray grid 4, and the like are provided. The X-ray grid 4 is disposed adjacent to the detection side (X-ray irradiation side) of the FPD 3. The grid drive mechanism 5 is a mechanism that moves the X-ray grid 4 between the imaging position and the retracted position. The FPD 3 corresponds to the radiation detection means in the present invention, and the top plate 1 and the X-ray grid 4 correspond to the shield in the present invention.

  In addition, the X-ray diagnostic apparatus includes a top plate control unit 7 that controls the elevation and horizontal movement of the top plate 1, a unit control unit 8 that controls scanning of the detection unit 6, and the tube voltage and tube of the X-ray tube 2. An X-ray tube control unit 10 having a high voltage generation unit 9 that generates a current, a calibration unit 11 that calibrates an X-ray detection signal that is a charge signal from the FPD 3, and a digital signal that has been calibrated. The A / D converter 12 that is extracted and converted, the image processing unit 13 that performs various processes based on the X-ray detection signal output from the A / D converter 12, and the calibration data for calibration are compared. Based on the comparison result in the data comparison unit 14 or the data comparison unit 14, it is possible to detect whether or not the calibration data in the current calibration is abnormal. The detection unit 15, the controller 16 that controls each of these components, the memory unit 17 that stores processed images, calibration data, abnormality setting values that serve as a standard for abnormality detection, and the operator perform input settings. When an abnormality is detected by the input unit 18 or the abnormality detection unit 15, a lamp 19 / buzzer 20 for notifying the operator and a monitor 21 for displaying a processed image are provided. The calibration unit corresponds to the pixel calibration unit in the present invention, the A / D converter 12 and the image processing unit 13 correspond to the image processing unit in the present invention, and the data comparison unit 14 corresponds to the calibration information comparison unit in the present invention. The abnormality detection unit 15 corresponds to the abnormality detection means in the present invention, and the lamp 19 and the buzzer 20 correspond to the notification means in the present invention.

  The top board control unit 7 moves the top board 1 horizontally to accommodate the subject M up to the imaging position, moves up and down and horizontally moves the subject M to a desired position, or performs imaging while horizontally moving the subject M. Or performing horizontal control after the completion of imaging and retreating from the imaging position. The unit control unit 8 performs control related to scanning by moving the FPD 3 horizontally or rotating around the body axis of the subject M. The high voltage generator 9 generates a tube voltage and a tube current for irradiating X-rays and applies them to the X-ray tube 2. The X-ray tube controller 10 moves the X-ray tube 2 horizontally, Control relating to scanning by rotating around the axis of the body axis of M, control of the setting of the irradiation field of the collimator (not shown) on the X-ray tube 3 side, and the like are performed. When scanning the X-ray tube 2 or the FPD 3, the X-ray tube 2 and the FPD 3 move while facing each other so that the FPD 3 can detect the X-rays emitted from the X-ray tube 2.

  The calibration unit 11 calibrates the charge signal output from the FPD 3, that is, the pixel. In this embodiment, the gain of an amplifier (amplifier) 38 (see FIG. 3) for each switching element 32 described later is set. Adjust to align the output side. The A / D converter 12 converts the calibrated charge signal from analog to digital, and outputs a digitized X-ray detection signal. The controller 16 is configured by a central processing unit (CPU) and the like, and the memory unit 17 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Yes. The input unit 18 includes a pointing device represented by a mouse, keyboard, joystick, trackball, touch panel, and the like. In the X-ray diagnostic apparatus, the FPD 3 detects X-rays transmitted through the subject M, performs calibration by the calibration unit 11 based on the detected X-rays, and performs image processing by the image processing unit 13. The sample M is imaged. Note that the gain in the above-described past calibration is stored in advance in a calibration memory unit 22 to be described later as calibration data for performing calibration.

  In the present embodiment, the memory unit 15 further includes a calibration data memory unit 22 that stores calibration data obtained in the past, and an abnormal setting value memory unit 23 that stores the above-described abnormal setting value. Therefore, the calibration data corresponds to the calibration information in the present invention, and the calibration data memory unit 22 corresponds to the calibration information storage means in the present invention.

  The data comparison unit 14 and the abnormality detection unit 15 are configured by a comparator or the like. In the case of the data comparison unit 14, the calibration data in the current calibration is compared with the calibration data in the previous calibration read from the calibration data memory unit 15 or in the previous calibration. The abnormality detection unit 15 compares the comparison result in the data comparison unit 14 with the abnormality setting value read from the abnormality setting value memory unit 23, and further compares the comparison result with the calibration data in the current calibration. Whether or not is abnormal is detected. For example, when the gain value of the amplifier 38 for the current calibration is a and the gain value of the amplifier 38 in the previous calibration or the previous calibration is b, the comparison result is obtained by the data comparison unit 14. "(Ab)" is obtained. As the abnormal setting value, a gain difference equal to or larger than a predetermined value that has been regarded as abnormal in the past is stored in the calibration data memory unit 15. If the gain difference is c, if the absolute value of (ab) is less than the gain difference c which is also the abnormal setting difference, the abnormality detection unit 15 determines that there is no abnormality, and the absolute value of (ab) is If the gain difference is greater than or equal to c, the abnormality detection unit 15 determines that there is an abnormality.

  As shown in FIG. 2, the FPD 3 includes a glass substrate 31 and a thin film transistor TFT formed on the glass substrate 31. As shown in FIGS. 2 and 3, the thin film transistor TFT has a large number of switching elements 32 (for example, 1024 × 1024) formed in a vertical / horizontal two-dimensional matrix arrangement. The switching elements 32 are formed separately from each other. That is, the FPD 3 is also a two-dimensional array radiation detector.

  As shown in FIG. 2, an X-ray sensitive semiconductor 34 is stacked on the carrier collection electrode 33, and the carrier collection electrode 33 is connected to the source S of the switching element 32 as shown in FIGS. 2 and 3. Has been. A plurality of gate bus lines 36 are connected from the gate driver 35, and each gate bus line 36 is connected to the gate G of the switching element 32. On the other hand, as shown in FIG. 3, a plurality of data bus lines 39 are connected to a multiplexer 37 that collects charge signals and outputs them to one through an amplifier 38, as shown in FIGS. Thus, each data bus line 39 is connected to the drain D of the switching element 32.

  With the bias voltage applied to the common electrode (not shown), the gate of the switching element 32 is turned on by applying the voltage of the gate bus line 36 (or 0 V), and the carrier collection electrode 33 is on the detection surface side. The charge signal (carrier) converted from the incident X-ray through the X-ray sensitive semiconductor 34 is read out to the data bus line 39 via the source S and drain D of the switching element 32. Until the switching element is turned on, the charge signal is temporarily accumulated and stored in a capacitor (not shown). The charge signals read to the respective data bus lines 39 are amplified by the amplifiers 38 and are collectively output as one charge signal by the multiplexer 37. The output charge signal is digitized by the A / D converter 12 and output as an X-ray detection signal.

  Next, a series of calibration control sequences in the apparatus of this embodiment will be described with reference to the flowchart of FIG. In this sequence, the description will be made on the assumption that the obstruction such as the top plate 1 and the X-ray grid 4 has already moved to the retreat position except forgetting to remove it.

(Step S1) Obtaining Calibration Data The calibration unit 11 obtains the gain of each amplifier 38 so that the pixels for each switching element 32 on the output side are the same. The obtained gain is sent as calibration data to the data comparison unit 14 via the calibration unit 11. At this time, calibration for actually adjusting the gain according to the value of the charge signal is not performed.

(Step S2) Data comparison The calibration data in the current calibration sent to the data comparison unit 14 and the calibration data in the previous calibration read from the calibration data memory unit 15 or the previous calibration read out from the calibration data memory unit 15 The data comparison unit 14 performs comparison. The comparison result is sent to the abnormality detection unit 15.

(Step S3) Abnormality detection?
The comparison result in the data comparison unit 14 sent to the abnormality detection unit 15 is compared with the abnormality setting value read from the abnormality setting value memory unit 23, and the comparison result is further used for calibration in the current calibration. The abnormality detection unit 15 detects whether or not the action data is abnormal. In the case of abnormality detection, the process proceeds to step S4 to notify the operator that the calibration in this calibration is incorrect. If it is not an abnormality detection, it is determined that the calibration data in the current calibration is correct, and the process jumps to step S6 to actually perform the calibration.

(Step S4) Notification with lamp / buzzer In order to notify the operator, the lamp 19 is turned on and the buzzer 20 is sounded.

(Step S5) Shield evacuation The operator moves the shield to the evacuation position on the assumption that the calibration in the current calibration is wrong due to forgetting to remove the shield such as the top board 1 and the X-ray grid 4 Remove it. Then, the process returns to step S1.

(Step S6) Calibration Execution Assuming that the calibration data in this calibration is correct, calibration is executed using the calibration data.

(Step S7) Calibration Data Storage When calibration is executed, calibration data in the current calibration is written and stored in the calibration data memory unit 22 in preparation for the next calibration.

  According to the apparatus of the present embodiment configured as described above, the data comparison unit 14 performs the previous calibration read from the calibration data / calibration memory unit 22 in the current calibration or the previous calibration from the previous calibration. Both of the calibration data are compared, and the abnormality detection unit 15 detects whether or not the calibration data in the current calibration is abnormal based on the comparison result of the calibration data. Therefore, it can be determined whether or not the current calibration data is normal compared to the calibration data in the calibration that was performed in the past, and the comparison result and abnormality detection are used to reliably determine whether or not the current calibration is correct. can do.

  In this embodiment, the calibration data is a gain obtained by performing calibration in a state in which the shielding object such as the top plate 1 or the X-ray grid 4 is excluded, and the data comparison unit 14 excludes the shielding object. Both calibration data obtained are compared. When the shield is removed in this way, the calibration data in the previous calibration or the calibration before the previous time and the calibration data in the current calibration should both be originally obtained under the same conditions except for the shield. is there. Therefore, even if it is forgotten to remove the shielding object in the current calibration, the current calibration data obtained by forgetting to remove the shielding object is based on the comparison result in step S2 and the abnormality detection in step S3. You can see immediately that it is abnormal. In addition, it is possible to prevent a situation where calibration is performed without forgetting to remove the shielding object. In addition, the maximum pixel value based on radiation is obtained by removing the shielding object, and the resolution is improved compared to the case where the shielding object is inserted by obtaining the maximum value data (that is, the dynamic range is widened). ), More accurate imaging can be performed by executing calibration.

  In the present embodiment, the lamp 19 / buzzer 20 that notifies when an abnormality is detected from the abnormality detection unit 15 is provided. If the calibration data in the current calibration is abnormal, the abnormality is detected by the notification from the lamp 19 / buzzer 20. Is immediately known.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiment, the X-ray diagnostic apparatus as shown in FIG. 1 has been described as an example. However, the present invention is also applied to an X-ray diagnostic apparatus disposed on a C-type arm, for example. Also good. The present invention may also be applied to an X-ray CT apparatus.

  (2) In the above-described embodiment, the flat panel X-ray detector (FPD) 3 has been described as an example. However, the present invention is applicable to any X-ray detector configured from each detection element. be able to.

  (3) In the above-described embodiments, the X-ray detector for detecting X-rays has been described as an example. However, in the present invention, a radioisotope (RI) is administered like an ECT (Emission Computed Tomography) apparatus. The radiation detector is not particularly limited as long as it is a radiation detector that detects radiation, as exemplified by a γ-ray detector that detects γ-rays emitted from a subject. Similarly, the present invention is not particularly limited as long as it is an apparatus that performs imaging by detecting radiation, as exemplified by the ECT apparatus described above.

  (4) In the above-described embodiment, the FPD 3 includes a radiation (in the embodiment, X-ray) sensitive semiconductor and directly converts the incident radiation into a charge signal by the radiation sensitive semiconductor. However, instead of the radiation-sensitive type, it is equipped with a light-sensitive semiconductor and a scintillator, and the incident radiation is converted into light by the scintillator, and the converted light is converted into a charge signal by the light-sensitive semiconductor. It may be an indirect conversion type detector.

  (5) The shield is not limited to the top plate 1 and the X-ray grid 4 described above. The present invention can be applied to any shielding object that shields radiation before the detection side of the radiation detection means (FPD in the embodiment), as exemplified by a compensation filter that performs a filter related to pixels of the captured image. it can.

  (6) In the above-described embodiment, the lamp 19 and the buzzer 20 are used as the notification means in the present invention. However, the notification means is not particularly limited as long as the notification is made by appealing to the five senses such as the operator's vision and hearing.

  (7) In the above-described embodiment, the notification means represented by the lamp 19 and the buzzer 20 is provided, but the notification means is not necessarily required. For example, if an abnormality is detected in step S3 of the embodiment, the controller 16 controls the grid driving mechanism 5, the top panel control unit 7 and the like without notifying the operator, and shields such as the X-ray grid 4 and the top board 1 are provided. The controller 16 may control the calibration unit 11 so as to execute calibration after automatically retracting. Moreover, you may combine both such control and alerting | reporting.

  (8) In the above-described embodiment, the gain of the amplifier is compared as calibration data. However, the pixel for each switching element 32 on the output side may be compared as calibration data.

  (9) In the above-described embodiment, the calibration data is compared in a state where the shielding object is removed. However, the abnormality may be detected by comparing the calibration data in a state where the shielding object is inserted. In this case, the calibration data is compared in consideration of the shielding object. However, since the calibration data is compared in consideration of the shielding object, the embodiment is preferable in view of the fact that it can be immediately recognized that it is abnormal.

1 is a block diagram of a flat panel X-ray detector and an X-ray diagnostic apparatus according to an embodiment. It is the equivalent circuit of the flat panel type X-ray detector used for the X-ray diagnostic apparatus viewed from the side. 2 is an equivalent circuit of a flat panel X-ray detector in plan view. It is a flowchart which shows a control sequence of a series of calibrations.

Explanation of symbols

1 ... Top plate 3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 4 ... X-ray grid 11 ... Calibration part 12 ... A / D converter 13 ... Image processing part 14 ... Data comparison part 15 ... Abnormality detection part 19 ... Lamp 20 ... Buzzer 22 ... Calibration data memory part M ... Subject

Claims (3)

  Radiation detection means for detecting radiation transmitted through the subject, pixel calibration means for calibrating each detection element constituting the radiation detection means for pixels based on the detected radiation, and an image based on the detected radiation An image processing unit that performs processing, calibrates the pixel by the pixel calibration unit, and performs image processing by the image processing unit, thereby imaging the subject, and includes a pixel image obtained in the past Calibration information comparison that compares both calibration information storage means for storing calibration information for calibration and calibration information in the previous calibration read from the calibration information / calibration information storage means in the current calibration or a previous calibration from the previous calibration. A radiation imaging apparatus comprising: means for detecting whether the calibration information in the current imaging is abnormal based on a comparison result of the calibration information. .   2. The radiation imaging apparatus according to claim 1, wherein the calibration information is information obtained by performing calibration in a state in which a shielding object that shields radiation is removed from the detection side of the radiation detection unit. The information storage means compares both pieces of calibration information obtained by removing the shielding object, and the radiation imaging apparatus. The radiation imaging apparatus according to claim 1, further comprising a notification unit that notifies when an abnormality is detected from the abnormality detection unit.

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