JP2006075359A - X-ray diagnostic system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high image quality of an image data by offset correction using the newest offset compensation data in X-ray photography. <P>SOLUTION: In the non-photographing period of intermittent X-ray photography on a subject, an offset correction data production part 42 of an offset compensation part 4 performs production and update of the offset correction data using the dark-time image data sequentially supplied from an X-ray detection part 3, and stores the newest offset correction data in an offset correction data storage part 43. On the other hand, an image arithmetic unit 44 reads out the offset correction data stored in the offset correction data storage part 43 in the photographing period of X-ray photography, and performs offset correction for the image data by subtracting the offset correction data from the image data supplied from the X-ray detection part 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray diagnostic apparatus, and more particularly to an X-ray diagnostic apparatus including a flat panel detector.

  Medical image diagnostic technology using an X-ray diagnostic apparatus, an MRI apparatus, an X-ray CT apparatus or the like has made rapid progress with the development of computer technology in the 1970s and has become indispensable in today's medical care.

  Conventionally, as a detector used in an X-ray diagnostic apparatus, an X-ray film or I.D. I. (Image Intensifier) has been used. This I.I. I. In the imaging method using X-rays, X-ray image information obtained by irradiating a subject with X-rays generated from an X-ray tube and passing through the subject is I.D. I. Is converted into an optical image. Further, this optical image is taken by an X-ray TV camera, converted into an electric signal, and displayed on the TV monitor after A / D conversion. For this reason, I.I. I. The image capturing method using can enable real-time image capturing that was not possible with the film system and can collect image data with digital signals, thereby enabling various image processing.

  By the way, the X-ray TV camera used in the conventional X-ray imaging always generates a dark signal that does not depend on the X-ray irradiation. Therefore, the electric signal output from the X-ray TV camera is an X-ray. The image signal resulting from irradiation and the dark signal were mixed. The dark signal is one factor that deteriorates the X-ray image data.

  In order to solve such problems of the X-ray TV camera, the dark signal before the optical image is input is continuously collected, and then the latest dark signal is obtained from the electric signal obtained by inputting the optical image. A method for subtraction of a time signal has been proposed (see, for example, Patent Document 1).

On the other hand, the above-mentioned I.D. I. In recent years, two-dimensional array flat detectors have attracted attention and have already been put into practical use. This flat detector includes a method of directly converting X-rays into electric charges and a method of converting X-rays into light and then converting them into electric charges. For example, the flat detector in the former method uses incident X-ray energy. It is composed of a photoelectric film that converts it into a charge amount, a charge storage capacitor that stores this charge, and a TFT (thin film transistor) that reads out the stored charge at a predetermined timing, and is generated in proportion to the amount of X-ray irradiation in the photoelectric film. The charge once stored in the charge storage capacitor is sequentially read out to the signal output line through the TFT having a switching function. Then, the electric charge output to the signal output line is converted into a digital signal by an A / D converter via a charge / voltage converter, and image storage circuit as X-ray image data (hereinafter referred to as image data). And stored on the display unit (for example, see Patent Document 2).
JP-A-2-164184 JP 2001-340324 A

  In the image data output from the above-mentioned charge / voltage converter, an offset component described later is mixed as an artifact component with respect to the original signal component proportional to the irradiated X-ray dose. This offset component includes charges generated in the photoelectric film when X-rays are not irradiated, leakage charges from other pixels due to TFT switching characteristics, accumulated in stray capacitance between TFT terminals, and injected when the TFT is turned on / off. In addition, there is a direct current component of the charge / voltage converter, and these offset components are usually included in the signal component differently for each pixel.

  Conventionally, in order to remove an offset component from image data and extract only a signal component, image data obtained in a non-imaging period before starting X-ray imaging on the subject (hereinafter referred to as dark image data) So that the offset correction data is generated in advance and the offset correction data is subtracted from the image data obtained during the X-ray imaging period. Has been done.

  However, the offset component included in the image data constantly changes with time depending on the temperature of the flat panel detector, the application time of the bias voltage to the photoelectric film, and the driving state of the TFT. Accordingly, it is impossible to sufficiently reduce the offset component by the offset correction using the offset correction data generated before the X-ray imaging.

  The present invention has been made in order to solve the problems in photographing using such a conventional flat detector, and its purpose is to perform offset using dark image data sequentially generated in a non-shooting period. Provided is an X-ray diagnostic apparatus capable of improving image quality of image data by generating and updating correction data and performing offset correction using the latest offset correction data on image data generated during an imaging period. There is.

  In order to solve the above-described problem, an X-ray diagnostic apparatus according to a first aspect of the present invention includes an imaging period in which X-ray irradiation is performed on a subject to generate image data and a non-imaging period in which X-ray irradiation is stopped. An X-ray diagnostic apparatus that performs X-ray imaging in combination detects a first charge accumulated based on a transmitted X-ray dose of the subject during the imaging period and a second charge accumulated during the non-imaging period. A planar detector having a plurality of detection elements; image data generating means for generating image data based on the first charge; and dark image data based on the second charge; and the dark image data Offset correction data generation means for generating offset correction data based on the offset correction data, and the latest offset correction data among the plurality of offset correction data generated by the offset correction data generation unit is used. It is characterized by comprising an image operation means for performing inter-image calculation for offset correction of the image data Te.

  According to the present invention, the offset correction data is generated and updated using the dark image data sequentially generated in the non-imaging period of the X-ray imaging, and the latest image data updated in the imaging period is updated. By performing offset correction using the offset correction data, it is possible to generate high-quality image data.

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

  The feature of the first embodiment of the present invention described below is that the dark image data obtained in the non-imaging period of the X-ray imaging performed intermittently is continuously collected and generated based on the dark image data. The offset correction is performed on the image data during the shooting period using the latest offset correction data.

(Device configuration)
The configuration of the X-ray diagnostic apparatus according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the overall configuration of the X-ray diagnostic apparatus, and FIG. 2 is a diagram showing the configuration of a flat detector used in the X-ray diagnostic apparatus.

  The X-ray diagnostic apparatus 100 includes an X-ray generation unit 1 that irradiates a subject 150 with X-rays, a high voltage generation unit 2 that generates a high voltage necessary for X-ray irradiation and supplies the X-ray generation unit 1 The X-ray detection unit 3 that two-dimensionally detects X-rays transmitted through the subject 150 to generate image data and generates dark-time image data during non-imaging, and the X-ray detection unit 3 An offset correction unit 4 that performs offset correction on image data obtained at the time of shooting using dark image data is provided.

  The X-ray diagnostic apparatus 100 also displays a gain correction unit 5 that performs gain correction on image data after offset correction, an image data storage unit 6 that stores gain-corrected image data, and the image data. A display unit 7; a holding unit 8 that holds the X-ray generation unit 1 and the X-ray detection unit 3; a top plate 9 on which the subject 150 is placed; and the rotation of the holding unit 8 and the top plate 9 A mechanism unit 10 that performs movement and control thereof, an input unit 11 in which various inputs and settings necessary for X-ray imaging are performed by an operator, and a system that controls the above units of the X-ray diagnostic apparatus 100 in an integrated manner. A control unit 12 is provided.

  The X-ray generation unit 1 includes an X-ray tube 101 that irradiates the subject 150 with X-rays, and an X-ray diaphragm that forms an X-ray weight (cone beam) with respect to the X-rays irradiated from the X-ray tube 101. A container 102 is provided. The X-ray tube 101 is a vacuum tube that generates X-rays, and accelerates electrons emitted from a cathode (filament) by a high voltage to collide with a tungsten anode to generate X-rays. On the other hand, the X-ray diaphragm 102 is located between the X-ray tube 101 and the subject 150 and has a function of narrowing the X-ray beam irradiated from the X-ray tube 101 to a predetermined irradiation field size.

  The high voltage generator 2 includes a high voltage generator 21 that generates a high voltage applied between the anode and the cathode in order to accelerate thermoelectrons generated from the cathode of the X-ray tube 101, and a system controller 12. An X-ray control circuit 22 is provided for setting X-ray irradiation conditions such as tube current, tube voltage, and irradiation time in the high voltage generator 21 in accordance with the instruction signal.

  On the other hand, the detection method of the X-ray detection unit 3 includes a method of directly converting X-rays into electric charges, and a method of converting the X-rays into light and then converting them into electric charges. In this embodiment, the former will be described as an example. The latter may be used. That is, the X-ray detector 3 includes a flat detector 31 that accumulates charges generated based on X-rays transmitted through the subject 150 during the imaging period and charges generated during the non-imaging period, and the flat detector 31. A gate driver 32 for reading out the accumulated charge, and an image data generation unit 33 for generating image data in the shooting period and dark image data in the non-shooting period from the read charge.

  As shown in FIG. 2, the flat detector 31 is composed of minute detection elements 51 that are two-dimensionally arranged in the column direction and the line direction. Each detection element 51 senses X-rays and emits X-rays. The photoelectric film 52 that generates charges in response to the charge, the charge storage capacitor 53 that stores the charge generated in the photoelectric film 52, and the TFT (thin film transistor) 54 that reads the charge stored in the charge storage capacitor 53 at a predetermined timing. ing. In the following, for the sake of simplicity, the configuration of the flat detector 31 in the case where two detection elements 51 are arranged in the column direction (vertical direction in FIG. 2) and in the line direction (horizontal direction in FIG. 2). Will be described.

  First terminals of the photoelectric films 52-11, 52-12, 52-21, and 52-22 in FIG. 2 and first terminals of the charge storage capacitors 53-11, 53-12, 53-21, and 53-22. Are connected to the source terminals of the TFTs 54-11, 54-12, 54-21, and 54-22. On the other hand, the second terminals of the photoelectric films 52-11, 52-12, 52-21, 52-22 are connected to a bias power supply (not shown), and charge storage capacitors 53-11, 53-12, 53-21, 53 are connected. The second terminal of -22 is grounded. Further, the gate terminals of the TFTs 54-11 and 54-21 in the line direction are commonly connected to the output terminal 55-1 of the gate driver 32, and the gate terminals of the TFT 54-12 and the TFT 54-22 are output terminals of the gate driver 32. 55-2 is commonly connected.

  On the other hand, the drain terminals of the TFTs 54-11 and 54-12 in the column direction are commonly connected to the signal output line 59-1, and the drain terminals of the TFTs 54-21 and 54-22 are commonly connected to the signal output line 59-2. Is done. The signal output lines 59-1 and 59-2 are connected to the image data generation unit 33.

  Next, the gate driver 32 supplies a driving pulse to the gate terminal of the TFT 54 in order to read out the electric charge generated in the photoelectric film 52 of the detection element 51 and stored in the charge storage capacitor 53 during shooting or non-shooting. To do.

  Returning to FIG. 1, the image data generation unit 33 of the X-ray detection unit 3 includes a charge / voltage converter 331 that converts the electric charge read from the flat detector 31 into a voltage, and a line unit from the flat detector 31. A multiplexer 332 that converts charge data read in parallel into a time-series signal and an A / D converter 333 are provided.

  Next, a method for generating image data will be described with reference to FIG. 3 showing a more detailed configuration of the X-ray detection unit 3 and FIG. 4 showing a charge read time chart in the flat detector 31.

  In FIG. 3, the flat detector 31 is composed of two detection elements 51 arranged two-dimensionally, with M in the line direction and N in the column direction. In the flat detector 31, the drive terminals of the M detection elements 51 arranged in the line direction (that is, the gate terminal of the TFT 54 shown in FIG. 2) are connected in common and connected to the output terminal of the gate driver 32. . For example, the output terminal 55-1 of the gate driver 32 is connected to each drive terminal of the detection elements 51-11, 51-21, 51-31,... 51-M1, and the output terminal 55-N of the gate driver 32 is connected. Are connected to the respective drive terminals of the detection elements 51-1N, 51-2N, 51-3N,... 51-MN.

  On the other hand, the output terminals of the N detection elements 51 arranged in the column direction (that is, the drain terminals of the TFTs 54 shown in FIG. 2) are commonly connected to a signal output line 59. The signal output line 59 is connected to the image data. The generator 33 is connected to the input terminal of the charge / voltage converter 331. For example, the output terminals of the detection elements 51-11, 51-12, 51-13,..., 51-1N are commonly connected to a signal output line 59-1, and the signal output line 59-1 is a charge / voltage converter. 331-1. Similarly, the output terminals of the detection elements 51-M1, 51-M2, 51-M3,... 51-MN are commonly connected to the signal output line 59-M, and the signal output line 59-M is charge / voltage conversion. Connected to the device 331-M.

  FIG. 4 shows the X-ray irradiation timing, the output signal of the gate driver 32 and the output signal of the detection element 51 during the imaging period. Based on the X-ray irradiation request from the input unit 11, the X-ray generation unit 1 irradiates the subject 150 with X-rays in the period from time t0a to t0b in FIG. On the other hand, the detection element 51 receives X-rays transmitted through the subject 150 and accumulates charges in the charge storage capacitor 53 in proportion to the X-ray irradiation amount.

  When this X-ray irradiation is completed, the system control unit 12 supplies a control signal to the gate driver 32 in order to read out the charge accumulated in the charge storage capacitor 53 of the detection element 51, and the gate driver 32 Driving pulses as shown in FIGS. 4B to 4D are sequentially output from 55-1 to 55-N. When a reading drive pulse (ON voltage) is supplied to the gate terminal of the TFT 54, the TFT 54 is turned on (ON), and the charge stored in the charge storage capacitor 53 is output to the signal output line 59.

  After X-ray irradiation is performed in the period from time t0a to t0b in FIG. 4A, the output terminal 55-1 of the gate driver 32 becomes the ON voltage in the period from time t1a to t1b (FIG. 4B). , 51-M1 are driven. Then, the electric charge accumulated in the charge accumulation capacitors 53 of the detection elements 51-11,... 51-M1 in the first line is output to the signal output lines 59-1 to 59-M by this drive signal.

  The charges output to the signal output lines 59-1 to 59-M are converted from charges to voltages by the charge / voltage converters 331-1 to 331-M of the image data generation unit 33, and parallel-serial by the multiplexer 332. Converted. The output of the multiplexer 332 is converted into a digital signal by the A / D converter 333 to generate image data in the first line, and is supplied to the offset correction unit 4 in FIG.

  Next, in the period from time t2a to t2b, the gate driver 32 sets only the output terminal 55-2 to the ON voltage (FIG. 4C), and the detection elements 51-12, 51-22, 51- of the second line. 32,..., 51-M2 are read out to the signal output lines 59-1 to 59-M. The read charges are converted into image data of the second line by the charge / voltage converters 331-1 to 331-M, the multiplexer 332, and further the A / D converter 333, and supplied to the offset correction unit 4. Is done.

  Similarly, when the output terminals 55-3 to 55-N of the gate driver 32 are sequentially turned on, the charges accumulated in the charge accumulation capacitors 53 of the detection elements 51 arranged in the third to Nth lines. Are sequentially output to the signal output lines 59-1 to 59-M. The charges are converted into image data of the third line to the Nth line by the charge / voltage converters 331-1 to 331-M, the multiplexer 332, and the A / D converter 333 and supplied to the offset correction unit 4.

  In the above description, the method for generating the image data in the imaging period has been described. However, the X-ray detection unit 3 generates the dark image data by performing the same operation as in the imaging period even in the non-imaging period. .

  Next, the configuration and operation of the offset correction unit 4, which is the most important unit in the present embodiment, will be described with reference to the block diagram of FIG. 5 and the time charts shown in FIGS.

  FIG. 5 shows the offset correction unit 4 and the X-ray detection unit 3 already described. The offset correction unit 4 performs an averaging process on a plurality of dark image data obtained in the non-imaging period to perform an offset. An offset correction data generation unit 42 that generates correction data, an offset correction data storage unit 43 that stores the latest offset correction data among the offset correction data sequentially generated by the offset correction data generation unit 42, and an imaging period An image calculation unit 44 that performs offset correction by subtraction processing between each obtained image data and the latest offset correction data stored in the offset correction data storage unit 43 is provided.

  Further, the offset correction unit 4 includes a changeover switch 41 for selecting a supply destination of image data generated during the imaging period and dark image data generated during the non-imaging period in the X-ray detection unit 3, and the offset correction unit 4 An offset correction control unit 45 that controls each unit described above is provided.

  FIG. 6 is a time chart showing the generation order of the image data and dark image data generated by the X-ray detection unit 3, and here, in order to make the figure easy to understand, three images are respectively taken in the imaging periods T1 and T3. Although a case where image data is generated and four dark image data are generated in the non-shooting period T2 is shown, more image data and dark images are usually used in the above-described shooting period and non-shooting period. Data is generated.

  In the following description, a case will be described in which offset correction is performed on image data in the shooting period T3 using offset correction data generated based on dark image data in the non-shooting period T2.

  FIG. 6A shows irradiation periods T11 to T13 and irradiation periods T31 to T33 in which X-rays are irradiated to the flat detector 31 of the X-ray detector 3 through the subject 150 in the imaging periods T1 and T3. FIG. 6B shows charge accumulation periods C3 to C12 and charge readout periods R3 to R12 of the flat panel detector 31 in the imaging periods T1 and T3 and the non-imaging period T2.

  FIGS. 6C to 6E are enlarged views of the imaging period T1, FIG. 6C shows the irradiation periods T11 to T13, and FIG. 6D shows the X-ray detector 3. The output timing of image data output from the first to Nth lines is shown. As shown in FIG. 6E, the charge accumulation periods C3 to C5 in the flat panel detector 31 correspond to the irradiation periods T11 to T13, and the charge readout periods R3 to R5 are periods in which image data is generated. It corresponds. Then, in each of the charge reading periods R3 to R5, the charges on the first line to the Nth line of the flat detector 31 are read to generate one piece of image data.

  On the other hand, in the non-imaging period T2, the flat detector 31 repeats the same operation as in the imaging periods T1 and T3, and charges are accumulated in the charge accumulation periods C6 to C9, and charges are read in the charge reading periods R6 to R9. At. Then, in each of the charge reading periods R6 to R9, the charges accumulated in the first line to the Nth line of the flat detector 31 are read, and one piece of dark image data is generated.

  In the plane detector 31 in the X-ray detection unit 3 described above, the plane detection is performed via the subject 150 emitted from the X-ray generation unit 1 during the charge accumulation periods C3 to C5 and C10 to C12 in the imaging periods T1 and T3. Charges that are approximately proportional to the amount of X-rays irradiated to the device 31 are accumulated, and in the charge accumulation periods R6 to R9 of the non-imaging period T2, as described above, the photoelectric film 52 is charged regardless of the X-ray irradiation. Accumulated charges, leakage charges from other pixels due to the switching characteristics of the TFT 54, and the like are accumulated.

  Next, FIG. 7 is a time chart showing the order of offset correction performed in the offset correction unit 4, FIG. 7A is a charge accumulation / readout period, and FIG. 7B is an X-ray detection unit 4. FIG. 7C shows the offset correction data generation period, and FIG. 7D shows the image data generation period after offset correction. However, in FIG. 7, the offset correction data generated based on the four dark image data obtained in the non-shooting period T2 is used as in FIG. 6, and the offset correction is performed on the image data in the shooting period T3. Is described.

  In this case, the dark image data obtained immediately before the shooting period T3, that is, in the charge readout period R9 in the non-shooting period T2 may be used as it is as offset correction data, but the device noise superimposed on the dark image data, etc. In order to reduce the influence of the above, a method of generating offset correction data by performing an averaging process on a plurality of dark image data is desirable. Hereinafter, a case will be described in which offset correction data is generated by adding and averaging two dark image data.

  That is, in the non-imaging period T2 in FIG. 7, the dark image data A21 and the dark image data A22 generated in the charge readout periods R6 and R7 of the X-ray detector 3 are stored in the offset correction unit 4 shown in FIG. This is supplied to the offset correction data generation unit 42 via the changeover switch 41. The offset correction data generation unit 42 adds and averages the supplied dark image data A21 and dark image data A22 to generate offset correction data D22, and stores the offset correction data D22 in the offset correction data storage unit 43.

  Next, the dark image data A23 generated in the charge readout period R8 of the non-photographing period T2 is supplied to the offset correction data generation unit 42. The offset correction data generation unit 42 and the newly supplied dark image data A23 The offset correction data D23 is generated by performing an averaging process on the already supplied dark image data A22. Then, the offset correction data D23 is supplied to the offset correction data storage unit 43 to update the already stored offset correction data D22.

  Further, the offset correction data D24 obtained by the addition averaging process of the dark image data A24 generated during the charge readout period R9 and the dark image data A23 is supplied to the offset correction data storage unit 43, thereby providing the offset correction data. D23 is updated.

  Note that the addition processing of dark image data is not limited to the moving addition method as described above. For example, the dark image data A23 and the dark image data A23 are added to the dark image data A21 and A22. A method such as the averaging process of A24 may be used.

  If an X-ray imaging start command is supplied from the input unit 11 to the offset correction control unit 45 via the system control unit 12 immediately after the dark image data A24 and offset correction data D24 are generated, the offset correction is performed. The control unit 45 controls the changeover switch 41 to supply image data B31, R32,... Generated in the charge readout periods R10, R11,.

  On the other hand, the image calculation unit 44 reads the latest offset correction data D24 stored in the offset correction data storage unit 43, and further, the image data B31 and B32 supplied from the X-ray detection unit 3 via the changeover switch 41. The offset correction is performed by subtracting the offset correction data D24 from.

  The changeover switch 41 performs a switching operation in accordance with a control signal supplied from the offset correction control unit 45, supplies image data supplied from the X-ray detection unit 3 during the imaging period to the image calculation unit 44, and performs a non-imaging period. Has a function of supplying dark image data supplied to the offset correction data generation unit 42.

  Next, returning to FIG. 1, the gain correction unit 5 of the X-ray diagnostic apparatus 100 corrects the sensitivity variation existing for each pixel with respect to the pixel value of the image data offset-corrected by the image calculation unit 44. Make corrections.

  The image data storage unit 6 includes a storage circuit and an image processing circuit (not shown), and the gain-corrected image data is temporarily stored in the storage circuit. The image processing circuit performs desired image processing on the image data after gain correction stored in the storage circuit. In addition, the image processing circuit can perform image calculation for generating DSA image data, long image data, three-dimensional image data, etc. by subtraction between image data before and after contrast agent injection, as necessary. is there.

  On the other hand, the display unit 7 is for displaying image data that has been subjected to offset correction and gain correction and stored in the storage circuit of the image data storage unit 6, and includes a display data generation circuit and a conversion circuit (not shown). Has a monitor. Then, the display data generation circuit reads out the image data stored in the image data storage unit 6 and combines it with the accompanying information to generate display data. Next, the conversion circuit performs D / A conversion and TV format conversion on the generated display data to generate a video signal and display it on a liquid crystal or CRT monitor.

  Next, the mechanism unit 10 includes a mechanism control circuit (not shown), a top plate moving mechanism, and a holding unit moving mechanism. The top plate moving mechanism has a function of moving the top plate 9 in the body axis direction in order to relatively move the X-ray generation unit 1 and the X-ray detection unit 3 in the body axis direction of the subject 150, and moves the holding unit. The mechanism has a function of rotating / moving the holding unit 8 holding the X-ray generation unit 1 and the X-ray detection unit 3 around the subject 150. Then, the mechanism control circuit controls the above-described top plate moving mechanism and holding unit moving mechanism according to the instruction signal supplied from the input unit 11 or the system control unit 12, so that the X-ray generation unit 1 and the X-ray detection unit 3 are covered. A desired position is set with respect to the specimen 150.

  The input unit 11 includes an input device such as a keyboard, a trackball, a joystick, and a mouse, a display panel, or various switches. The input unit 11 inputs subject information, selects an imaging target organ or imaging target region, and selects an imaging method. In addition, an imaging start command is input, and further, setting and updating of an optimal X-ray irradiation condition for an imaging method or an organ to be imaged, and settings relating to rotation / movement of the mechanism unit 10 are performed. The X-ray irradiation conditions include tube voltage applied to the X-ray tube 101, tube current, X-ray irradiation period, etc., and subject information includes age, sex, physique, examination site, examination method, past diagnosis history, etc. There is.

  Next, the system control unit 12 includes a CPU and a storage circuit (not shown). The system control unit 12 temporarily stores the above-described setting conditions, selection information, and the like supplied from the input unit 11 in the storage circuit. Control is performed for data generation, offset correction, display of image data, rotation / movement of the X-ray generator 1 and X-ray detector 3 and the like. The storage circuit previously stores various imaging methods in X-ray imaging and standard setting values such as imaging conditions and X-ray irradiation conditions in these imaging methods.

(Offset correction procedure for image data)
Next, an offset correction procedure for image data according to the present embodiment will be described with reference to FIGS. 8 and 9 are a flowchart and a time chart showing the procedure for generating image data and correcting the offset for the image data in this embodiment. However, in the following description, in the same manner as described above, three image data are generated in the shooting period, and three or four dark image data are generated in the non-shooting period. The case where offset correction is performed on the image data during the shooting period using the offset correction data generated by adding and averaging the latest two dark image data from the image data will be described. The number of dark image data in the period, and further, the number of dark image data used for the averaging process is not limited to the above values.

  Prior to the X-ray imaging, the operator uses the input unit 11 of the X-ray diagnostic apparatus 100 to input subject information and an imaging target region, select an imaging method, and the like. At this time, the system control unit 12 that has received the information about the selected imaging method reads out the standard setting values of the imaging conditions and X-ray irradiation conditions for the imaging method stored in advance in its own storage circuit, and the input unit 11 On the display panel. Then, the operator performs the final setting after updating the displayed standard setting value as necessary (step S1 in FIG. 8).

  Further, the operator rotates / moves the X-ray generation unit 1, the X-ray detection unit 3, and the top plate 9 using the input device of the input unit 11, and sets it to a desired position with respect to the subject 150. To do.

  On the other hand, the system control unit 12 supplies a control signal to the gate driver 32 of the X-ray detection unit 3 based on the imaging method set by the input unit 11, and the gate driver 32 detects the plane based on the control signal. A drive pulse is supplied to the device 31 to start reading the charges accumulated therein. At this time, the control signal is also supplied to the X-ray detection unit 3 and the offset correction unit 4, and an operation for generating dark image data is started at time t0.

  That is, the X-ray detection unit 3 shown in FIG. 5 sequentially generates dark image data A01 and A02 in the non-imaging period T0 without performing the X-ray irradiation by the X-ray generation unit 1 (step of FIG. 8). S2 to S3), and supplied to the offset correction data generation unit 42 via the changeover switch 41 of the offset correction unit 4 shown in FIG. On the other hand, the offset correction data generation unit 42 generates offset correction data D02 from the addition averaging process of the supplied dark image data A01 and A02, and stores it in the offset correction data storage unit 43 (step S4 in FIG. 8).

  Next, the offset correction data D03 is generated from the addition averaging process of the dark image data A03 generated by the X-ray detection unit 3 and the dark image data A02, and the offset correction data stored in the offset correction data storage unit 43 is generated. Update D02. Similarly, the offset correction data D04 is generated from the addition averaging process of the dark image data A04 generated by the X-ray detection unit 3 and the dark image data A03, and is supplied to the offset correction data storage unit 43 to be offset corrected. Data D03 is updated (steps S3 to S4 in FIG. 8).

  By repeating such a procedure, the offset correction data storage unit 43 stores the offset correction data D04 generated by the latest two consecutive dark image data in the non-shooting period T0.

  Next, at time t1 immediately after the saving of the offset correction data D04 is completed, an input of a shooting start command by the operator is performed at the input unit 11, and this shooting start command is supplied to the system control unit 12 to X-ray imaging for the subject 150 is started (step S5 in FIG. 8).

  At the start of X-ray imaging, the X-ray control circuit 22 of the high voltage generation unit 2 receives an imaging start command from the system control unit 12 at time t1 in the imaging period T1, and is based on already set X-ray irradiation conditions. The high voltage generator 21 is controlled to apply a high voltage to the X-ray tube 101 of the X-ray generator 1. Next, the X-ray tube 101 to which a high voltage is applied irradiates the subject 150 with X-rays via the X-ray diaphragm 102. Then, the X-ray transmitted through the subject 150 is detected by the flat detector 31 of the X-ray detector 3 provided behind the subject 150.

  Next, the electric charges accumulated in the flat detector 31 by the X-ray irradiation are sequentially read out by the drive pulse of the gate driver 32, and the image data generation unit 33 generates the image data B11 shown in FIG. Step S6 in FIG.

  At this time, the offset correction control unit 45 of the offset correction unit 4 controls the changeover switch 41 based on the imaging start command signal supplied from the input unit 11 via the system control unit 12, and is supplied from the X-ray detection unit 3. The image data B11 to be processed is supplied to the image calculation unit 44.

  On the other hand, the image calculation unit 44 reads the latest offset correction data D04 stored in the offset correction data storage unit 43, and further from the image data B11 supplied from the X-ray detection unit 3 via the changeover switch 41. Image data E11 after offset correction is generated by subtracting the offset correction data D04 (step S7 in FIG. 8).

  FIG. 10 schematically shows image data before and after offset correction. 10A shows image data B11 before offset correction generated by the X-ray detection unit 3, and FIG. 10B shows offset correction data D04 generated from dark image data by the offset correction data generation unit. FIG. 10C shows image data E11 after offset correction by the image calculation unit 44, and in each case, the pixel value (vertical axis) for each pixel (horizontal axis) is shown. Then, the offset correction composed only of the signal component is obtained by subtracting the offset correction data D04 (FIG. 10B) from the uncorrected image data B11 (FIG. 10A) in which the offset component is superimposed on the signal component. The subsequent image data E11 (FIG. 10C) is generated.

  The image data E11 after the offset correction is subjected to gain adjustment in the gain correction unit 5, and then supplied to the display unit 7 through the image data storage unit 6 and displayed on the monitor of the display unit 7 (FIG. 8). Step S8).

  Similarly, image data B12 and B13 are sequentially generated in the imaging period T1, and the image calculation unit 44 uses the offset correction data D4 from the image data B12 and B13 supplied from the image data generation unit 33 of the X-ray detection unit 3. To generate image data E12 and E13 after offset correction. These obtained image data are displayed on the display unit 7 via the gain correction unit 5 and the image data storage unit 6 (steps S6 to S8 in FIG. 8).

  Next, if an imaging end instruction signal is output from the system control unit 12 or the input unit 11 at time t2, the X-ray control circuit 22 of the high voltage generation unit 2 controls the high voltage generator 21 to perform X-rays. Is stopped (step S9 in FIG. 8). The offset correction control unit 45 of the offset correction unit 4 controls the changeover switch 41 based on the instruction signal, and the output terminal of the A / D converter 333 in the X-ray detection unit 3 is connected to the offset correction data generation unit 42. Connecting. The imaging end instruction signal may be input by the operator through the input unit 11 or may be output by the system control unit 12 based on a preset X-ray imaging plan.

  In the following, the X-ray detection unit 3 generates dark image data A21 to A24 by the same procedure as in the non-imaging period T0, and the offset correction data generation unit 42 performs offset correction data D22 to D24 based on the above-described image data. Is generated. Then, the latest offset correction data D24 is stored in the offset correction data storage unit 43 (steps S2 to S4 in FIG. 8).

  Next, if a command signal for starting X-ray imaging is again input from the input unit 11 at time t3 (step S5 in FIG. 8), image data B31 to B33 are sequentially generated in the imaging period T3 by the same apparatus operation, The image calculation unit 44 subtracts the offset correction data D24 from these image data to generate corrected image data E31 to E33. These corrected image data are displayed on the display unit 7 via the gain correction unit 5 and the image data storage unit 6 (steps S6 to S8 in FIG. 8). Thereafter, generation of offset correction data using dark image data during the non-shooting period and offset correction of the image data during the shooting period are repeated by the same procedure, and the offset-corrected image data is displayed on the display unit 7 (FIG. 8). Steps S2 to S9).

  Note that the above-described X-ray imaging start command is normally input from the input unit 11 at an arbitrary timing by the operator, and therefore the length of the non-imaging period is not determined. For example, when a shooting start command is input at time t5 when three dark image data A41 to A43 are generated in the non-shooting period T4 in FIG. 9, the offset correction data storage unit 43 stores the time The offset correction data D43 generated by the averaging process of the dark image data A42 and A43 closest to t5 is stored, and the image calculation unit 44 calculates the offset correction from the image data B51 to B53 obtained in the shooting period T5. The corrected image data E51 to E53 can be obtained by subtracting the data D43.

  According to the first embodiment of the present invention described above, offset correction data is generated in advance using dark image data obtained in a non-shooting period, and obtained in a shooting period subsequent to the non-shooting period. Since the offset component in the image data is eliminated by subtracting the offset correction data from the image data, it is possible to obtain high-quality image data with reduced artifacts.

  Further, the offset correction data is sequentially updated by dark image data obtained continuously in a non-shooting period, and offset correction using the latest offset correction data is always performed. Even when it fluctuates with time, the optimum correction is possible.

  Furthermore, even when an imaging start command is input by an operator at an arbitrary time, offset correction using the latest offset correction data updated in the non-imaging period is always possible, so the operator's X-ray imaging Optimal offset correction can be performed without limiting the requirements.

  In addition, since each of the offset correction data is generated by the addition averaging process of a plurality of dark image data, it is not easily affected by apparatus noise and the like. Therefore, for the image data having no sufficient S / N. However, effective offset correction can be performed.

  Next, a second embodiment of the present invention will be described. In the second embodiment, a method of generating offset correction data using dark image data in which the afterimage component in the flat detector is sufficiently reduced will be described.

  Conventionally, when X-rays are irradiated, several tens of images following the image data generated at the end of the imaging period due to the afterimage characteristics of the photoelectric film based on the dose history of the X-rays and the unreadness of the TFT with respect to the accumulated charges. The dark image data of the sheet includes an afterimage component of the image data.

  When the offset correction data is generated using the dark image data including such an afterimage component, the temporal change (decrease) in the afterimage component is significant as compared with the change in the offset component described above. Good offset correction becomes impossible.

  The present embodiment aims to generate offset correction data from which afterimage components are eliminated, and its feature is that the offset correction data is based on dark image data obtained during a non-imaging period of X-ray imaging performed intermittently. When the afterimage amount of the image data generated in the shooting period is measured from the dark image data in the subsequent non-shooting period and the afterimage amount becomes equal to or less than a preset allowable afterimage amount Then, updating of the offset correction data by the dark image data is started.

(Device configuration)
The configuration of the X-ray diagnostic apparatus according to the second embodiment of the present invention will be described with reference to FIGS. However, since the X-ray diagnostic apparatus in the present embodiment is the same except for the offset correction section 4 of the X-ray diagnostic apparatus 100 shown in FIG. 1, hereinafter, the configuration and operation of the offset correction section in the present embodiment. Only explained.

  That is, as shown in the block diagram of FIG. 11, the offset correction unit 14 of the X-ray diagnostic apparatus 200 in the present embodiment performs an averaging process on a plurality of dark image data obtained in the non-imaging period to perform offset correction. An offset correction data generation unit 142 that generates data, an offset correction data storage unit 143 that stores the latest offset correction data among the offset correction data sequentially generated by the offset correction data generation unit 142, and an image obtained during the shooting period. Offset correction is performed by a subtraction process between the obtained image data and the latest offset correction data stored in the offset correction data storage unit 143, and further, from dark image data generated in a non-shooting period immediately after the shooting period. Offset correction already stored in the offset correction data storage unit 143 The image calculation unit 144 that generates the dark image data after correction by subtracting the data (hereinafter referred to as afterimage data), the image data generated in the imaging period by the X-ray detection unit 3, and the non-imaging period A changeover switch 141 is provided for selecting a supply destination of the generated dark image data.

  Further, the offset correction unit 14 includes an afterimage amount measurement unit 146 that measures an afterimage amount for the afterimage data generated by the image calculation unit 144, an elapsed time measurement unit 147 that measures an elapsed time of the afterimage amount measurement, and an afterimage Based on the instruction signal supplied from the quantity measuring unit 146 or the instruction signal supplied from the elapsed time measuring unit 147, the offset correction data generation start timing is controlled and the switching operation of the changeover switch 141 is controlled. It has.

  The afterimage amount measurement unit 146 includes a calculation circuit and a storage circuit (not shown), and implicit image data generated immediately after a predetermined shooting period performed by the image calculation unit 144 and offset correction generated or updated before the predetermined shooting period. The afterimage amount is measured for the afterimage data obtained by the subtraction process with the data.

  FIG. 12 shows the attenuation characteristic of the afterimage component when the charge accumulated in the X-ray detector 31 is read out by X-ray irradiation. The accumulated charge is 1 immediately after the X-ray irradiation stops. Most of them are read out in the second reading, and the remaining charge (afterimage component) is read out in 1 second to 2 seconds.

  The afterimage amount measuring unit 146 measures the change in the afterimage amount in the afterimage data supplied from the image calculation unit 144. For example, as shown in FIG. 13, the arithmetic circuit of the afterimage amount measuring unit 146 divides the afterimage data into a plurality of regions, and averages the afterimage amount in each region (hereinafter referred to as an average afterimage amount). calculate. Next, the arithmetic circuit compares the calculated average afterimage amount with an allowable afterimage amount stored in the storage circuit in advance, and if the average afterimage amount in all the regions becomes smaller than the allowable afterimage amount, an offset is set. An instruction signal for permitting generation or updating of correction data is supplied to the offset correction control unit 145. Although FIG. 13 shows the case where the afterimage data is divided into 16, the present invention is not limited to this, and the afterimage data may be divided into more regions.

  By the way, the afterimage amount of afterimage data is distributed depending on the X-ray absorption distribution of the subject 150, and the local afterimage amount in the pixel corresponding to the tissue having the least X-ray absorption is less than the allowable afterimage amount. Need to be. For this reason, as described above, a method of dividing afterimage data into a plurality of regions and calculating an average afterimage amount in each region is effective.

  Next, the elapsed time measuring unit 147 includes a timer and a storage circuit (not shown), and the storage circuit stores in advance a maximum waiting time until the average afterimage amount in the afterimage data is attenuated to an allowable afterimage amount or less. . This maximum waiting time is set empirically, for example, based on the afterimage component attenuation characteristics in the flat panel detector 31 shown in FIG.

  The timer continuously measures the elapsed time in generating the dark image data based on the shooting / non-shooting period information supplied from the system control unit 12, and the elapsed time exceeds the maximum waiting time. At this point, an instruction signal for permitting generation or updating of the offset correction data is supplied to the offset correction control unit 145.

  On the other hand, the offset correction control unit 145 generates a control signal for generating or updating offset correction data based on the instruction signal supplied from the afterimage amount measuring unit 146 or the elapsed time measuring unit 147. 142.

(Offset correction procedure for image data)
Next, an image data offset correction procedure in the present embodiment will be described with reference to FIGS. 14 and 15 are a flow chart and a time chart showing the offset correction procedure. For easy understanding, three image data in the shooting period and eight dark images in the non-shooting period are shown. A case where data is generated and offset correction is performed using offset correction data generated by adding and averaging the latest two dark image data from the eight dark image data will be described. However, the number of image data in the shooting period, the number of dark image data in the non-shooting period, and the number of dark image data used for the averaging process are not limited to the above values.

  15, FIG. 15A shows the output period of the image data / dark image data output from the X-ray detector 3, FIG. 15B shows the afterimage amount in the flat detector 31, and FIG. FIG. 15C shows an offset correction data generation period, and FIG. 15D shows a generation period of image data and afterimage data after offset correction.

  Prior to the X-ray imaging, the operator inputs subject information, selects an imaging method, sets imaging conditions, and the like using the input unit 11 of the X-ray diagnostic apparatus 100 (step S11 in FIG. 15), and then. Using the input device of the input unit 11, the X-ray generation unit 1, the X-ray detection unit 3, and the top plate 9 are rotated / moved and set to desired positions.

  On the other hand, the system control unit 12 supplies a rate pulse of a predetermined cycle to the gate driver 32 of the X-ray detection unit 3 based on the imaging method set by the input unit 11, and the gate driver 32 synchronizes with this rate pulse. Then, a driving pulse is supplied to the flat panel detector 31 to start reading out the charges accumulated therein. At this time, the control signal is also supplied to the X-ray detection unit 3 and the offset correction unit 14, and an operation for generating dark image data is started at time t0.

  That is, the X-ray detection unit 3 in FIG. 11 sequentially generates the dark image data A01 and A02 in the non-imaging period T0 without performing the X-ray irradiation by the X-ray generation unit 1, and switches the offset correction unit 14. The data is supplied to the offset correction data generation unit 142 via the switch 141 (step S12 in FIG. 14). On the other hand, the offset correction data generation unit 142 generates offset correction data D02 from the addition averaging process of the supplied dark image data A01 and A02, and stores it in the offset correction data storage unit 143 (step S13 in FIG. 14).

  Next, the offset correction data D03 is generated from the addition averaging process of the dark image data A03 generated by the X-ray detection unit 3 and the dark image data A02, and the offset correction data stored in the offset correction data storage unit 143 is generated. Update D02. Similarly, the offset correction data D04 is generated from the averaging process of the dark image data A04 generated by the X-ray detection unit 3 and the dark image data A03, and the offset stored in the offset correction data storage unit 143 is generated. The correction data D03 is updated (steps S12 to S13 in FIG. 14). By repeating such a procedure, the latest offset correction data D04 is stored in the offset correction data storage unit 142.

  Next, at time t 1 immediately after the offset correction data D 04 has been saved, an imaging start command is input at the input unit 11, and this imaging start command is supplied to the system control unit 12, whereby X for the subject 150 is recorded. Line imaging is started (step S14 in FIG. 14).

  At the start of X-ray imaging, the X-ray control circuit 22 of the high voltage generation unit 2 receives an imaging start command from the system control unit 12 at time t1 in the imaging period T1, and is based on already set X-ray irradiation conditions. The high voltage generator 21 is controlled to apply a high voltage to the X-ray tube 101 of the X-ray generator 1. Next, the X-ray tube 101 to which a high voltage is applied irradiates the subject 150 with X-rays via the X-ray diaphragm 102. And the X-ray which permeate | transmitted the test object 150 is detected by the plane detector 31 of the X-ray detection part 3 provided in the back.

  Next, the charges accumulated in the flat detector 31 by the X-ray irradiation are sequentially read out by the drive pulse of the gate driver 32, and the image data generation unit 33 generates the image data B11 shown in FIG. 14 step S15).

  At this time, the offset correction control unit 145 of the offset correction unit 14 controls the changeover switch 141 based on the imaging start command signal supplied from the input unit 11 via the system control unit 12, and is supplied from the X-ray detection unit 3. The image data B11 to be processed is supplied to the image calculation unit 144.

  On the other hand, the image calculation unit 144 reads the offset correction data D04 stored in the offset correction data storage unit 143, and further, offset correction data from the image data B11 supplied from the X-ray detection unit 3 via the changeover switch 141. D04 is subtracted to perform offset correction, and image data E11 after offset correction is generated (step S16 in FIG. 14).

  The image data E11 after the offset correction is subjected to gain adjustment in the gain correction unit 5, and then supplied to the display unit 7 through the image data storage unit 6 and displayed on the monitor of the display unit 7 (step in FIG. 14). S17).

  Similarly, image data B12 and B13 in the imaging period T1 are sequentially generated, and the image calculation unit 144 subtracts the offset correction data D04 from the image data B12 and B13 supplied from the X-ray detection unit 3 to perform offset. The corrected image data E12 and E13 are generated. These obtained image data are displayed on the display unit 7 via the gain correction unit 5 and the image data storage unit 6 (steps S15 to S17 in FIG. 14).

  Next, when an X-ray imaging end instruction signal is output from the system control unit 12 or the input unit 11 at time t2, the X-ray control circuit 22 of the high voltage generation unit 2 controls the high voltage generator 21. X-ray irradiation is stopped (step S18 in FIG. 14), and the elapsed time measuring unit 147 measures an elapsed time in afterimage amount measurement described later, which starts from time t2 (step S19 in FIG. 14).

  On the other hand, the X-ray detection unit 3 reads out the electric charge accumulated in the flat detector 31 in a state where X-ray irradiation is not performed, generates dark image data, and supplies the dark image data to the image calculation unit 144 via the changeover switch 141. (Step S20 in FIG. 14). Then, the image calculation unit 144 reads the offset correction data D04 stored in the offset correction data storage circuit 143, and subtracts the offset correction data D04 from the dark image data supplied from the X-ray detection unit 3. Afterimage data E21 is generated and supplied to the afterimage amount measuring unit 146 (step S21 in FIG. 14).

  Next, the calculation circuit of the afterimage amount measurement unit 146 divides the afterimage data supplied from the image calculation unit 144 into predetermined regions and measures the average afterimage amount in each region (step S22 in FIG. 14). The average afterimage amount in at least one region of afterimage data is larger than the allowable afterimage amount preset in the storage circuit, and the elapsed time during measurement in the elapsed time measurement unit 147 has a preset maximum waiting time. If not, the image calculation unit 144 continues to generate afterimage data E22 for the dark image data A22 generated by the X-ray detection unit 3. Next, the afterimage amount measurement unit 146 measures an afterimage amount for the afterimage data E22 supplied from the image calculation unit 144 (steps S20 to S22 in FIG. 14).

  When the average afterimage amount in the afterimage data E22 is less than or equal to the allowable afterimage amount, or when the elapsed time measured by the elapsed time measurement unit 147 exceeds the maximum waiting time, the afterimage amount measurement unit 146 or the elapsed time The measurement unit 147 supplies an instruction signal for updating the offset correction data to the offset correction control unit 145, and the offset correction control unit 145 controls the control signal based on the supplied update instruction signal of the offset correction data. Is supplied to the offset correction data generation unit 142 (steps S23 and S24 in FIG. 14).

  In the following, the X-ray detection unit 3 generates dark image data A23 to A28 by the same procedure as in the non-imaging period T0, and the offset correction data generation unit 142 generates offset correction data based on the dark image data described above. D23 to D28 are generated. Then, the latest offset correction data D28 is stored in the offset correction data storage unit 143 (steps S12 and S13 in FIG. 14).

  Next, if a command signal for starting X-ray imaging is input again from the input unit 11 at time t3 (step S14 in FIG. 14), image data B31 to B33 are sequentially generated in the imaging period T3 by the same apparatus operation. The image calculation unit 144 subtracts the offset correction data D28 from these image data to generate corrected image data E31 to E33. Then, these corrected image data are displayed on the display unit 7 via the gain correction unit 5 and the image data storage unit 6 (steps S15 to S17 in FIG. 14). Thereafter, generation of offset correction data using dark image data during the non-shooting period and image data offset correction during the shooting period are repeated in the same procedure, and the offset-corrected image data is displayed on the display unit 7 (FIG. 14). Steps S12 to S24).

  According to the second embodiment of the present invention described above, the same effect as that of the first embodiment described above can be obtained. Further, the temporal change of the afterimage amount in the dark image data is measured, Since the offset correction data is generated using the dark image data obtained in a period when the afterimage amount is sufficiently small, it is possible to perform highly accurate offset correction excluding the influence of the afterimage.

  Further, since the elapsed time of the afterimage amount measurement is simultaneously measured in parallel with the measurement of the afterimage amount with respect to the dark image data, for example, an offset component with little temporal change remains in the afterimage data. Even in this case, the update of the offset correction data can be started after a desired elapsed time, and therefore, a series of X-ray imaging can be reliably performed without being interrupted. For this reason, the diagnostic efficiency is greatly improved.

  As mentioned above, although the Example of this invention has been described, this invention is not limited to said Example, It can change and implement. For example, in the above-described first and second embodiments, the case of a single shooting method has been described, but a plurality of shooting methods may be used. In particular, in X-ray imaging performed in combination with catheter treatment, the imaging mode and fluoroscopy mode are frequently repeated, and the X-ray irradiation conditions and the image data collection rate are changed each time. The offset component of the X-ray detection unit 3 and dark image data also change in accordance with changes in irradiation conditions, imaging conditions, and the like.

  In such a case, the same effect as in the above-described embodiment can be obtained by generating and updating offset correction data for a plurality of shooting modes. FIG. 16 shows a time chart of X-ray imaging including the fluoroscopy mode and the radiographing mode. The dark mode image data Aa01 of the fluoroscopy mode generated in the non-imaging period T0 after the radiographing conditions and the like are initially set. And offset correction data Da02 is generated based on Aa02, and offset correction data Db02 is generated based on the dark image data Ab01 and Ab02 in the shooting mode generated subsequently.

  Then, the fluoroscopic image data Ba11 to Ba13 generated in the photographing period T1 set by the fluoroscopic mode start command are offset-corrected by the offset correction data Da02 to obtain corrected fluoroscopic image data Ea11 to Ea13. Next, the offset correction data Da02 is updated to Da24 using the fluoroscopic mode dark image data Aa21 to Aa24 generated in the non-shooting period T2 subsequent to the shooting period T1.

  Next, the corrected perspective image data Eb11 to Eb13 are generated by performing offset correction using the offset correction data Db02 on the captured image data Bb11 to Bb13 generated in the imaging period T3 set by the imaging mode start command. Next, the offset correction data Db02 is updated to Db24 with the dark image data Ab21 to Ab24 in the shooting mode generated in the non-shooting period T4.

  Similarly, each image data is generated in response to the input shooting mode or fluoroscopic mode start command, and offset correction is performed on the image data using the latest offset correction data. However, in FIG. 16, offset correction in X-ray imaging in which two types of imaging methods are combined has been described taking the fluoroscopic mode and the imaging mode as an example, but other imaging methods may be used, and three or more types may be used. X-ray imaging combining these imaging methods may be used. For example, the above-described offset correction method is also effective when a plurality of imaging is performed in each of the fluoroscopic mode and the imaging mode. However, if offset correction is performed in order for all of these shootings, the correction frequency may decrease and a sufficient effect may not be obtained. In such a case, the identification in each of the fluoroscopic mode and the shooting mode may occur. It is desirable to maintain the correction frequency by performing the offset correction only in the shooting. Further, as described in the second embodiment, the above-described procedure can also be applied to the offset correction method in which the influence of the afterimage is eliminated.

  In the above-described first and second embodiments and the modification thereof, the case where a plurality of dark image data is added and averaged to generate offset correction data has been described. Alternatively, a calculation method may be used. Further, the measurement of the afterimage amount in a predetermined area of the afterimage data is not limited to the average afterimage amount based on the average value of each pixel value, and may be, for example, an accumulated value of each pixel value.

1 is a block diagram showing the overall configuration of an X-ray diagnostic apparatus according to a first embodiment of the present invention. The block diagram of the plane detector used for the X-ray diagnostic apparatus of the Example. The block diagram which shows the structure of the X-ray detection part in the Example. 3 is a time chart of charge readout in the flat panel detector of the same embodiment. The block diagram which shows the structure of the offset correction part in the Example. The time chart which shows the production | generation of the image data and dark image data in the Example. The time chart which shows the order of the offset correction in the Example. The flowchart which shows the procedure of the offset correction in the Example. The time chart which shows the offset correction in the Example. The figure for demonstrating typically the image data before and behind offset correction in the Example. The block diagram which shows the structure of the offset correction part in 2nd Example of this invention. The figure which shows the attenuation characteristic of the afterimage component in the X-ray detector of a present Example. The figure which shows the division | segmentation method of the afterimage data in the Example. The flowchart which shows the procedure of the offset correction in the Example. The time chart which shows the offset correction in the Example. The time chart which shows the offset correction in the modification of the 1st Example of this invention, and a 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray generation part 2 ... High voltage generation part 3 ... X-ray detection part 4, 14 ... Offset correction part 5 ... Gain correction part 6 ... Image data storage part 7 ... Display part 8 ... Holding part 9 ... Top plate 10 ... Mechanism unit 11 ... Input unit 12 ... System control unit 21 ... High voltage generator 22 ... X-ray control circuit 31 ... Plane detector 32 ... Gate driver 33 ... Image data generation unit 41, 141 ... Changeover switch 42, 142 ... Offset correction Data generation units 43, 143 ... Offset correction data storage units 44, 144 ... Image calculation units 45, 145 ... Offset correction control unit 51 ... Detection element 52 ... Photoelectric film 53 ... Charge storage capacitor 54 ... TFT (Thin Film Transistor)
DESCRIPTION OF SYMBOLS 100, 200 ... X-ray diagnostic apparatus 101 ... X-ray tube 102 ... X-ray aperture 146 ... Afterimage amount measurement part 147 ... Elapsed time measurement part 331 ... Charge-voltage converter 332 ... Multiplexer 333 ... A / D converter

Claims (10)

In an X-ray diagnostic apparatus that performs X-ray imaging by combining an imaging period in which X-ray irradiation is performed on a subject to generate image data and a non-imaging period in which X-ray irradiation is stopped,
A flat panel detector having a plurality of detection elements for detecting the first charge accumulated based on the transmitted X-ray dose of the subject in the imaging period and the second charge accumulated in the non-imaging period;
Image data generating means for generating image data based on the first charge and dark image data based on the second charge;
Offset correction data generating means for generating offset correction data based on the dark image data;
An image calculation means for performing an inter-image calculation for offset correction of the image data using the latest offset correction data among the plurality of offset correction data generated by the offset correction data generation unit is provided. X-ray diagnostic equipment.   The offset correction data generation means sequentially generates offset correction data using dark image data sequentially generated during the non-shooting period, and updates the already generated offset correction data to newly generated offset correction data. The X-ray diagnostic apparatus according to claim 1, wherein:   Input means for inputting an imaging start command for X-ray imaging is provided, and the offset data generation means interrupts generation of the offset correction data when the imaging start command is input from the input means. The X-ray diagnostic apparatus according to claim 1.   3. The X-ray diagnosis apparatus according to claim 2, wherein the offset correction data generation unit generates one piece of offset correction data using a plurality of dark image data.   The X-ray diagnostic apparatus according to claim 4, wherein the offset correction data generation unit generates the offset correction data by performing an averaging process on a plurality of dark image data.   An afterimage amount measuring unit that measures an afterimage amount included in the dark image data and an offset correction control unit that controls generation start timing of offset correction data are provided, and the offset correction control unit is measured by the afterimage amount measuring unit. When the afterimage amount of dark image data in a predetermined non-photographing period decreases below a preset allowable afterimage amount, the offset correction data generation unit is controlled to start updating the offset correction data. The X-ray diagnostic apparatus according to claim 2.   The afterimage amount measuring unit is generated based on dark image data generated in a non-shooting period subsequent to a predetermined shooting period and latest offset correction data generated or updated in a non-shooting period preceding the shooting period. 7. The X-ray diagnostic apparatus according to claim 6, wherein the afterimage amount is measured in the afterimage data.   When the elapsed time measurement means for measuring the elapsed time in the measurement of the afterimage amount is further provided, and the offset correction control means is when the elapsed time of the afterimage amount measurement by the elapsed time measurement means exceeds a preset maximum waiting time 8. The X-ray diagnosis apparatus according to claim 6, wherein control for starting updating of the offset correction data is performed on the offset correction data generation means.   The X-ray diagnostic apparatus according to claim 7, wherein the afterimage amount measuring unit compares the afterimage amount in each region of the afterimage data divided into a plurality of regions with the allowable afterimage amount.   A storage unit that stores a plurality of shooting methods having different shooting conditions; and a selection unit that selects the shooting method. The offset correction data generation unit updates the offset correction data based on the shooting method selected by the selection unit. The X-ray diagnostic apparatus according to claim 1, wherein:

Images