JP2015112459A - X-ray diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray diagnostic device which suppresses uneven brightness generated in an image by suppressing influence of variation in bias voltage.SOLUTION: In an X-ray diagnostic device 1, an X-ray tube control part 6 and an FPD control circuit 29 allow X-ray irradiation and image reading-out to be performed on the basis of synchronization signals in an equal cycle. The image reading-out is performed after the elapse of a preset period from the X-ray irradiation with an equal interval for every two or more synchronization signals. If the image reading-out is performed immediately after the X-ray irradiation, a charge amount to be accumulated other than an electric charge generated in a conversion layer is changed between the image reading-out and image reading-out immediately before the X-ray irradiation in especially successive photographing at a low rate and one-shot photographing due to influence of variation in bias voltage Vh with the X-ray irradiation, and the changed charge amount affects an X-ray irradiation image to be acquired. However, the image reading-out is performed after elapse of the preset period from the X-ray irradiation, therefore uneven brightness can be suppressed by suppressing influence of variation in the bias voltage Vh.

Description

  The present invention relates to an X-ray diagnostic apparatus that irradiates a subject with X-rays, detects X-rays transmitted through the subject, and images the subject.

  The X-ray diagnostic apparatus includes an X-ray tube that irradiates a subject with X-rays and an X-ray detector that detects X-rays transmitted through the subject. In the field of digital X-ray diagnosis, various X-ray detectors have been invented recently.

  The X-ray detector includes a conversion layer that generates charges in response to incident X-rays, a common electrode that is provided on one surface of the conversion layer, to which a bias voltage is applied, and a conversion layer that faces the common electrode. And a plurality of collecting electrodes arranged in a two-dimensional matrix. The X-ray detector also includes a readout circuit having a capacitor for accumulating charges generated in the conversion layer and a switching element for reading out the charges accumulated in the capacitor. The electric charge accumulated in the capacitor is read out by driving the switching element.

  In such an X-ray diagnostic apparatus, a sequence for acquiring an image of one frame (sheet) is generally a readout period for reading out charges and a period other than the readout period, and X-ray irradiation is possible. It is comprised by the accumulation | storage period which is a period (for example, refer patent documents 1-6). This sequence is used not only for single image shooting but also for continuous shooting of moving images and the like by repeating the same sequence.

International Publication No. 2008/073310 JP 2010-034661 A JP 2010-220651 A JP 2007-144064 A JP 2007-111253 A JP 2000-284058 A (FIG. 1 etc.)

  However, the conventional apparatus has the following problems. That is, when a large dose of X-rays is incident on the conversion layer of the X-ray detector, there is a problem that the bias voltage applied to the common electrode fluctuates and luminance unevenness occurs in the image. This problem will be described with reference to FIG. FIG. 8 is a diagram showing the relationship among X-ray irradiation, readout, and bias voltage with respect to time. Usually, it is designed to read out an image immediately after X-ray irradiation so as not to delay the response of the entire image acquisition system. When the X-rays are irradiated, the bias voltage temporarily varies as shown in FIG. When the bias voltage varies, the charge accumulated in the capacitor is affected. Therefore, if image reading is performed while the bias voltage is fluctuating, the difference between the charges other than the charges generated from the X-rays is compared with the image reading that is not affected by fluctuations in the bias voltage. Brightness unevenness occurs.

  This will be described more specifically. First, it is assumed that image reading that is not affected by fluctuations in the bias voltage is image reading without X-ray irradiation indicated by an arrow A in FIG. In FIG. 8, for example, an arrow A indicates the timing of the start point of image reading without X-ray irradiation. An arrow B indicates the timing of the start point of image reading when the bias voltage is changed by performing X-ray irradiation. In the code A, it is assumed that 100 pixel values can be obtained without being affected by fluctuations in the bias voltage. On the other hand, with reference B, it is assumed that 20 pixel values excluding the charges generated from the X-rays are affected by the fluctuation of the bias voltage. In this case, the difference value is 100−20 = 80. Further, as shown in FIG. 8, the bias voltage recovers after the arrow B.

  That is, normally, in the acquired image of FIG. 9A, uniform 100 pixel values are obtained from the start point to the end point of image reading. However, as described above, when an image is read out immediately after X-ray irradiation, it is affected by fluctuations in the bias voltage due to X-ray irradiation, and charges generated from X-rays as shown in FIG. 9B are excluded. Images are obtained. For this reason, uneven brightness due to the difference as shown in FIG. 9C occurs in the normal state of FIG.

  The problem of uneven brightness appears remarkably in low-rate continuous shooting or single-image shooting. That is, in the case of continuous imaging at a low rate or single imaging, the X-ray irradiation dose for one time may increase. The bias voltage fluctuates according to the X-ray irradiation dose, and appears in the acquired image as a local luminance change as shown in FIG.

  There are also the following problems. In other words, it is conceivable to control the bias voltage fluctuation directly by monitoring the fluctuation of the bias voltage due to X-ray irradiation and reading after the fluctuation disappears. However, since the bias voltage is a high voltage, it is difficult to accurately monitor the fluctuation. In addition, since control is performed with a synchronization signal having a period of several tens of ms, it is difficult to ensure responsiveness to the fluctuation.

  In Patent Document 2, there are problems of the influence of power supply fluctuation due to X-ray irradiation and the reduction of the dynamic range due to the large leak current of TFT pixels when X-ray irradiation is not performed. Therefore, only when X-ray irradiation is performed, the time until the charge is read from the frame synchronization signal is adjusted. However, when offset correction is performed, offset data corresponding to a change in accumulation time must be prepared.

  Further, in Patent Document 3, there is a problem that a false image appears in an image due to the influence of fluctuations in the bias voltage. Therefore, the reflection of the false image is suppressed by delaying the start of reading. However, in Patent Document 3, the synchronization signal and the start point of the X-ray irradiation period are matched to delay the start of reading, but it is desirable to secure a period until the fluctuation of the bias voltage becomes more stable.

  Further, in Patent Document 6, when an image is read out over two frames or more, means such as providing a plurality of frame memories to perform addition processing is required, and there is a problem that the apparatus becomes complicated and expensive. Therefore, the sequence is set so that one frame is equal to or more than a value obtained by adding a predetermined X-ray irradiation time and a time required to read out charges for one frame. The sequence is set so that X-ray irradiation is started immediately after the charge reading is completed. However, it is sufficient that the image is not read over two frames or more, and generally, since the immediate drawing property is emphasized, the charge is read out immediately after the X-ray irradiation.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an X-ray diagnosis apparatus that suppresses the influence of bias voltage fluctuations and suppresses unevenness in luminance that occurs in an image.

In order to achieve such an object, the present invention has the following configuration.
That is, an X-ray diagnostic apparatus according to the present invention is an X-ray source that irradiates an X-ray toward a subject and an X-ray detector that detects X-rays that have passed through the subject. The X-ray detector having a conversion layer that generates a charge in response, and a common electrode provided on one surface of the conversion layer to which a bias voltage is applied, and stores the charge generated in the conversion layer Then, based on a readout circuit that reads out the accumulated charge and a synchronization signal given at an equal cycle, the X-ray irradiation is performed by the X-ray source, and the image readout that reads out one frame image by the readout circuit is performed. A period of the synchronization signal is equal to or longer than a period obtained by adding an X-ray irradiation period for performing the X-ray irradiation and an image reading period for performing the image reading, and the control unit includes the image reading period. And overlap The X-ray irradiation is performed, and the control unit causes the image reading to be performed at equal intervals for each of two or more synchronization signals, and the image reading is performed after a preset period has elapsed after the X-ray irradiation. It is characterized in that it is performed.

  According to the X-ray diagnostic apparatus of the present invention, the control unit performs X-ray irradiation and image reading based on the synchronization signal having the same period. Image reading is performed at equal intervals for every two or more synchronization signals after elapse of a preset period after X-ray irradiation. If an image is read out immediately after X-ray irradiation, it is affected by fluctuations in the bias applied to the common electrode due to X-ray irradiation. In particular, X-ray irradiation is used for low-rate continuous imaging or single imaging. The amount of charge such as leakage current accumulated in addition to the charge generated from the incident X-ray changes between the previous image readout, and the changed amount of charge affects the acquired X-ray irradiation image. It was. However, since the image reading is performed after the elapse of a preset period after the X-ray irradiation, it is possible to suppress the influence of the fluctuation of the bias voltage and suppress the luminance unevenness generated in the image.

  Further, one cycle of the synchronization signal is equal to or longer than a period obtained by adding the X-ray irradiation period and the image readout period, and one frame image can be acquired in one cycle of the synchronization signal. However, image reading is performed at equal intervals for every two or more synchronization signals. For this reason, image reading is performed at a low rate. By performing image readout at a low rate, it is easy to ensure a period from X-ray irradiation to image readout. Further, since the image reading is performed at an equal cycle, it is not necessary to prepare offset data corresponding to a change in accumulation time as in Patent Document 2. Therefore, offset correction can be performed using existing offset data, so that image reading can be easily performed.

  Further, in the X-ray diagnostic apparatus according to the present invention, the control unit causes the X-ray irradiation to be performed at equal intervals for each synchronization signal of 4 or more and a multiple of 2 so as not to overlap with the image readout period. The control unit causes the image reading to be performed at equal intervals for each synchronization signal that is a multiple of 2 that is less than the number of synchronization signals that engrave the cycle of the X-ray irradiation and is divisible by the number of synchronization signals. It is preferable that the image reading is performed after a preset period has elapsed.

  That is, X-ray irradiation is performed at equal intervals for each synchronization signal of 4 or more and a multiple of 2 so as not to overlap with the image readout period. On the other hand, image readout is less than the number of synchronization signals that divide the cycle of X-ray irradiation, and is equal to the number of synchronization signals that is a multiple of 2 that can divide the number of synchronization signals, and a period set in advance after X-ray irradiation. Performed after elapse. If an image is read out immediately after X-ray irradiation, it is affected by fluctuations in the bias applied to the common electrode due to X-ray irradiation. In particular, in “low-rate continuous imaging”, an image immediately before X-ray irradiation is used. The amount of charge such as leakage current accumulated in addition to the charge generated from the incident X-rays changed between the readout and the changed amount of charge had an effect on the acquired X-ray irradiation image. However, since the image reading is performed after the elapse of a preset period after the X-ray irradiation, it is possible to suppress the influence of the fluctuation of the bias voltage and suppress the luminance unevenness generated in the image.

  Moreover, in the X-ray diagnostic apparatus according to the present invention, it is preferable that the control unit performs the X-ray irradiation by matching an end point of the X-ray irradiation period with a synchronization signal. Accordingly, it is possible to secure a period until image reading, that is, a period until the bias voltage is stabilized, as compared with the case where the start point of the X-ray irradiation time coincides with the synchronization signal.

  In the X-ray diagnostic apparatus according to the present invention, it is preferable that the control unit performs the image reading by matching an end point of the image reading period with a synchronization signal. For example, it is assumed that the X-ray irradiation is performed so that the end point of the X-ray irradiation period coincides with the synchronization signal, and the image reading is performed at the period of the synchronization signal next to the X-ray irradiation. At this time, the period from the X-ray irradiation to the image readout can be secured at a minimum.

  In the X-ray diagnostic apparatus according to the present invention, the control unit performs the X-ray irradiation by matching an end point of the X-ray irradiation period with a synchronization signal, and the control unit performs the next synchronization after the X-ray irradiation. It is preferable that the image reading is performed with a signal cycle and an end point of the image reading period coincided with the synchronization signal. Thereby, the period from the X-ray irradiation to the image reading can be secured at a minimum. In addition, it is possible to read an image at a period of a synchronization signal next to X-ray irradiation, and an image can be acquired relatively early after X-ray irradiation.

  In the X-ray diagnostic apparatus according to the present invention, it is preferable that the control unit causes the image reading to be performed after a period of one cycle or more of the synchronization signal has elapsed after the X-ray irradiation. A sufficient period from the X-ray irradiation to the image reading can be secured.

  According to the X-ray diagnostic apparatus of the present invention, since image reading is performed after a predetermined period has elapsed since X-ray irradiation, it is possible to suppress the influence of fluctuations in bias voltage and to suppress luminance unevenness that occurs in an image. it can.

1 is a schematic configuration diagram of an X-ray diagnostic apparatus according to Embodiment 1. FIG. It is sectional drawing which shows the structure of 1 pixel of a flat panel type X-ray detector (FPD). It is a top view which shows the structure of a flat panel type X-ray detector (FPD). It is a figure which shows sequences, such as X-ray irradiation and image reading which concern on Example 1. FIG. FIG. 7 is a diagram illustrating a sequence of X-ray irradiation and image reading according to a modification of Example 1. (A) And (b) is a figure which shows sequences, such as X-ray irradiation and image reading which concern on the modification of Example 1. FIG. (A) And (b) is a figure which shows sequences, such as X-ray irradiation and image reading which concern on the modification of Example 2. FIG. It is a figure which shows sequences, such as X-ray irradiation and image reading for demonstrating a subject. (A) And (b) is a figure which shows the acquired image for demonstrating a subject, (c) is an image which shows the difference of the image of (a), and the image of (b).

  Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of the X-ray diagnostic apparatus according to the first embodiment.

  Please refer to FIG. The X-ray diagnostic apparatus 1 includes a top plate 2 on which the subject M is placed, an X-ray tube 3 that irradiates the subject M with X-rays, and a flat panel type that detects X-rays transmitted through the subject M. An X-ray detector 4 (hereinafter referred to as “FPD” as appropriate) is provided. The X-ray tube 3 corresponds to the X-ray source of the present invention, and the FPD 4 corresponds to the X-ray detector of the present invention.

  Further, the X-ray diagnostic apparatus 1 has a high voltage generator 5 that generates a tube voltage and a tube current of the X-ray tube 3 and is output from an FPD 4 and an X-ray tube controller 6 that controls X-ray irradiation. An A / D converter 7 for digitizing an image (X-ray detection signal), and an image processing unit 8 for performing various processes on the digital image (X-ray detection signal) converted by the A / D converter 7 I have.

  In addition, the X-ray diagnostic apparatus 1 includes a main control unit 9 that controls and controls each component, an image processed by the image processing unit 8, a storage unit 10 that stores a sequence of FIG. 4 to be described later, and an operator Includes an input unit 11 that performs input setting and a display unit 12 that displays an image processed by the image processing unit 8.

  The main control unit 9 is composed of a central processing unit (CPU) and the like. The storage unit 10 is configured by a storage medium including a removable medium such as a ROM (Read-only Memory), a RAM (Random-Access Memory), or a hard disk. The input unit 11 includes a joystick, a mouse, a touch panel, and the like. The display unit 12 includes a liquid crystal monitor or the like.

  FIG. 2 is a cross-sectional view showing a configuration of one pixel of the FPD 4. As shown in FIG. 2, the FPD 4 includes a semiconductor layer 16 that directly generates charges in response to incident X-rays, a common electrode 17 that is provided on one surface of the semiconductor layer 16 and to which a bias voltage Vh is applied, The pixel electrode 18 is provided on the other surface of the semiconductor layer 17, which is a surface facing the common electrode 17, and is divided into a plurality of pixels in a two-dimensional matrix.

  The semiconductor layer 16 is made of, for example, a-Se (amorphous selenium), CdTe (cadmium telluride), CdZnTe (zinc cadmium telluride), or the like. The pixel electrode 18, the semiconductor layer 16, and the common electrode 17 are formed on the active matrix substrate 19 by vapor deposition or the like so as to be in the order. The semiconductor layer 16 corresponds to the conversion layer of the present invention, and the active matrix substrate 19 corresponds to the readout circuit of the present invention.

  The active matrix substrate 19 includes a capacitor 21 that accumulates charges generated in the semiconductor layer 16, a TFT (thin film transistor) 22 that functions as a switching element that reads the charges accumulated in the capacitor 21, and an insulating substrate 23 made of glass or the like. And. A capacitor 21 and a TFT 22 are formed on the insulating substrate 23, and a gate line 24 and a data line 25, which will be described later, are formed.

  As shown by a broken line in FIG. 2, the X-ray detection element DU corresponding to one pixel includes a semiconductor layer 16, a common electrode 17, a pixel electrode 18, a capacitor 21, a TFT 22, and the like. FIG. 3 is a plan view showing the configuration of the FPD 4. As shown in FIG. 3, a plurality of X-ray detection elements DU are configured in a two-dimensional matrix. Therefore, the capacitor 21 and the TFT 22 are provided for each pixel in the two-dimensional matrix. Further, in FIG. 3, the X-ray detection element DU is 3 × 3 pixels for convenience of illustration, but is composed of, for example, 1024 × 1024 pixels.

  The active matrix substrate 19 includes a gate line 24 connected to the gates of a plurality of TFTs 22 arranged in one column in the row direction (X direction) in FIG. 3, and one column in the column direction (Y direction) in FIG. A data line 25 connected to the sources of the plurality of TFTs 22 arranged side by side is provided. A capacitor 21 and the like are connected to the drain of the TFT 22.

  A gate driver circuit 26 is connected to one end side of the gate line 24. The gate driver circuit 26 drives the TFTs 22 in order for each gate line 24 (each line). For example, the gate driver circuit 26 turns on the TFT 22 connected to the gate line 24 by giving a drive signal to the gate line 24 sequentially from the upper side in FIG. Thereby, the electric charge accumulated in the capacitor 21 is sent to the data line 25 through the TFT 22 in the ON state, and is read out to the array amplifier circuit 27 side through the data line 25.

  On the output side of the data line 25, an array amplifier circuit 27 and a multiplexer 28 are connected in order. The array amplifier circuit 27 amplifies the charge and converts it into a voltage signal. The multiplexer 28 selects and outputs one voltage signal from a plurality of voltage signals.

  The gate driver circuit 26, the array amplifier circuit 27, and the multiplexer 28 are controlled by the FPD control circuit 29. The FPD control circuit 29 is controlled by the main control unit 9. The A / D converter 7 may be provided in the FPD 4, and in that case, is controlled by the FPD control circuit 29.

  The X-ray tube control unit 6 and the FPD control circuit 29 correspond to the control unit of the present invention. The main control unit 9 that controls the X-ray tube control unit 6 and the FPD control circuit 29 may be the control unit of the present invention.

  Next, with reference to FIG. 4, the sequence of X-ray irradiation and image readout of the X-ray diagnostic apparatus 1 which is a characteristic part of the present invention will be described. In FIG. 4, operations related to X-ray irradiation are shown shaded.

  The X-ray tube control unit 6 and the FPD control circuit 29 cause the X-ray tube 3 to perform X-ray irradiation based on the synchronization signal given at an equal period and the sequence shown in FIG. Image reading is performed to read an image. And the FPD control circuit 29 suppresses the influence by the fluctuation | variation of a bias voltage by performing the said image reading after progress of the preset period after X-ray irradiation.

  In the sequence of FIG. 4, an image of one frame is a period obtained by adding an image reading period RD for reading an image and an accumulation period (X-ray irradiation permission period) AC for accumulating charges other than the image reading period RD. Obtained by TA. The image reading period RD is a period for reading the entire effective pixel region in which the pixels function effectively, but may be partial reading for driving a specific gate line 24.

  In the accumulation period AC, X-ray irradiation is performed. That is, the X-ray tube controller 6 performs X-ray irradiation so as not to overlap with the image readout period RD. An image obtained by X-ray irradiation is an X-ray irradiation image. On the other hand, depending on the accumulation period AC, X-ray irradiation may not be performed (see symbol NX in FIG. 4), and an image obtained without X-ray irradiation is a non-irradiated image. That is, in FIG. 4, X-ray irradiation is performed with the synchronization signal S10, and an image is read with the synchronization signal S12 to acquire an X-ray irradiation image. On the other hand, the X-ray irradiation is not performed with the synchronization signal S12, and the non-irradiation image is acquired by performing the image reading with the synchronization signal S20. Thus, in the sequence of FIG. 4, an X-ray irradiation image and an X-ray non-irradiation image are obtained.

  The synchronization signal is generated at regular intervals by a synchronization signal generator (not shown). The synchronization signal having the same period is given to the X-ray tube control unit 6 and the FPD control circuit 29. The synchronization signal is given, for example, 30 times per second. In this embodiment, it is represented by 30 fps (frames per second), but it is also represented by 30 Hz.

  In FIG. 4, X-ray irradiation is performed at equal intervals (equal period) at a rate of once every four synchronization signals. That is, X-ray irradiation is performed at a rate (speed) of 7.5 (= 30/4) fps, and X-ray irradiation is performed at a rate lower than 30 fps. Note that image reading is performed as X-ray irradiation is performed at 7.5 fps, and fluoroscopic imaging (also referred to as fluoroscopy or imaging) is performed at 7.5 fps. X-ray irradiation performed at 7.5 fps is expressed as “7.5 fps fluoroscopy”. X-ray irradiation is performed based on an X-ray irradiation command synchronized with a synchronization signal. Further, the X-ray irradiation is performed in synchronization with the synchronization signal so that the end point of the X-ray irradiation period TX substantially coincides with the synchronization signal.

  Also, in FIG. 4, image reading is performed at equal intervals at a rate of once every two synchronization signals. That is, image reading is performed at a rate of 15 (= 30/2) fps. Image readout performed at 15 fps is expressed as “15 fps accumulation”. Further, image reading is performed based on the synchronization signal, with the start point of the image reading period RD being substantially coincident with the synchronization signal. X-ray irradiation and image reading are performed so as not to overlap.

  That is, the sequence of FIG. 4 is performed with “7.5 fps perspective and 15 fps accumulation”. Therefore, since X-ray irradiation is performed at 7.5 fps and image readout is performed at 15 fps, the sequence is one read-out with respect to one X-ray irradiation, and one X-ray non-irradiation. One image readout is performed.

  Note that one cycle of the synchronization signal is equal to or longer than a period obtained by adding an X-ray irradiation period TX for performing X-ray irradiation and an image reading period RD for performing image reading, as indicated by reference numeral T1 in FIG. Therefore, when the synchronization signal is given at 30 fps, an image of one frame can be acquired with 30 fps perspective and 30 fps accumulation. On the other hand, the sequence of FIG. 4 is performed at 7.5 fps fluoroscopy and 15 fps accumulation, so the rate is low. Note that one cycle T1 of the synchronization signal may theoretically coincide with the period obtained by adding the X-ray irradiation period TX and the image readout period RD, or the X-ray irradiation period TX and the image readout period RD are added. It may be longer than the period.

  Further, the image reading is performed after a preset period (time) has elapsed since the X-ray irradiation. For example, as shown in FIG. 4, X-ray irradiation is performed in synchronization with the synchronization signal so that the end point of the X-ray irradiation period substantially coincides with the synchronization signal. Image reading is performed based on the synchronization signal so that the start point of the image reading period substantially coincides with the synchronization signal. Thus, image reading is performed after the period of one cycle (about 33 ms) of the synchronization signal has elapsed after the X-ray irradiation. That is, the accumulation period AC is extended by one period of the synchronization signal. Note that one cycle T1 of the synchronization signal is not limited to about 33 ms.

  Next, the operation of the X-ray diagnostic apparatus 1 will be described. First, the overall operation of the X-ray diagnostic apparatus 1 will be described, and then the X-ray irradiation and image readout operations will be described.

<Overall operation of X-ray diagnostic apparatus>
As shown in FIG. 1, the X-ray tube 3 emits X-rays toward the subject M placed on the top 2, and the FPD 4 detects X-rays transmitted through the subject M. In the FPD 4 of FIG. 2, a common electrode 17 is provided on one surface of the semiconductor layer 16, and a preset bias voltage Vh is applied to the common electrode 17. The X-rays incident on the semiconductor layer 16 generate electric charges in response to the X-rays by the semiconductor layer 16. The generated charge is accumulated in the capacitor 21. The charge accumulated in the capacitor 21 is read out by driving the TFT 22.

  As shown in FIG. 3, the gate driver circuit 26 drives the TFTs 22 in turn for each gate line 24 (for each line). The gate driver circuit 26 drives the plurality of TFTs 22 connected to the gate line 24 by sequentially applying drive signals to the gate line 24 from the upper side in FIG. As a result, the electric charge accumulated in the capacitor 21 is sent from the capacitor 21 to the data line 25 through the TFT 22, and is sent to the array amplifier circuit 27 and the multiplexer 28 in order through the data line 25.

  The amplifier array circuit 27 amplifies the charge and converts it into a voltage signal, and the multiplexer 28 selects and outputs one voltage signal from the plurality of voltage signals. In this way, the FPD 4 outputs an image (X-ray detection signal) corresponding to the X-ray intensity (see FIG. 1). The A / D converter 7 converts the image from analog to digital, and the image processing unit 8 performs various necessary image processing on the digitally converted image. The image after image processing is displayed on the display unit 12 and accumulated in the storage unit 10.

<Operation of X-ray irradiation and image reading>
Next, operations of X-ray irradiation and image reading will be described.

  A synchronization signal is generated at an equal cycle by a synchronization signal generation unit (not shown) and is supplied to the X-ray tube control unit 6 and the FPD control circuit 29. The synchronization signal may be supplied to the X-ray tube control unit 6 and the FPD control circuit 29 through the main control unit 9, or may be directly supplied to the X-ray tube control unit 6 and the FPD control circuit 29.

  The X-ray tube control unit 6 performs X-ray irradiation at equal intervals at a rate of once every four synchronization signals. X-ray irradiation is performed based on an X-ray irradiation command, and is performed so that the end point of the X-ray irradiation period coincides with the synchronization signal so as not to overlap with the image reading period RD. The FPD control circuit 29 reads out images at equal intervals at a rate of once every two synchronization signals. The synchronization signal given at an equal period is 30 fps. Therefore, photographing is performed at a low rate of 7.5 fps fluoroscopy and 15 fps accumulation. Further, X-ray irradiation images with X-ray irradiation and non-irradiation images without X-ray irradiation are acquired alternately. The non-irradiated image is acquired to remove unnecessary charges accumulated in the capacitor 21 and is not used for image display.

  Further, for the purpose of suppressing the influence of the fluctuation of the bias voltage due to the X-ray irradiation, the image reading is performed after elapse of a preset period after the X-ray irradiation. In FIG. 4, the X-ray irradiation is performed with the end point of the X-ray irradiation period TX substantially matched with, for example, the synchronization signal S11. On the other hand, image reading is performed with the start point of the image reading period RD substantially coincided with the synchronization signal S12, for example. Therefore, the image reading is performed after a period of one cycle of the synchronization signals S11 to S12 has elapsed. As a result, a sufficient period from the X-ray irradiation to the image reading can be secured.

  According to the present embodiment, the X-ray tube control unit 6 and the FPD control circuit 29 perform X-ray irradiation and image reading based on the synchronization signal having the same period. X-ray irradiation is performed at equal intervals for every four synchronization signals so as not to overlap with the image readout period RD. On the other hand, image reading is performed at regular intervals for every two synchronization signals after elapse of a preset period after X-ray irradiation. If image reading is performed immediately after X-ray irradiation, it is affected by fluctuations in the bias voltage Vh applied to the common electrode 17 due to X-ray irradiation. Especially in low-rate continuous imaging, it is immediately before X-ray irradiation. The amount of charge such as leakage current accumulated in addition to the charge generated from the incident X-ray changes between the non-irradiated image readout, and the changed amount of charge affects the acquired X-ray irradiation image. Was giving. However, since the image reading is performed after a preset period has elapsed since the X-ray irradiation, it is possible to suppress the influence of fluctuations in the bias voltage Vh and to suppress the luminance unevenness generated in the image.

  Further, one cycle of the synchronization signal is equal to or longer than a period obtained by adding the X-ray irradiation period TX and the image readout period RD, and an image of one frame can be acquired in one cycle of the synchronization signal. However, image reading is performed at equal intervals for every two synchronization signals. For this reason, image reading is performed at a low rate. By performing image readout at a low rate, it is easy to ensure a period from X-ray irradiation to image readout. Further, since the image reading is performed at an equal cycle, it is not necessary to prepare offset data corresponding to a change in accumulation time as in Patent Document 2. Therefore, offset correction can be performed using existing offset data, so that image reading can be easily performed.

  Next, the sequence of FIG. 4 according to the first embodiment may be modified like the sequences of FIGS. 5, 6A, and 6B.

<Sequence of FIG. 5>
In the sequence of FIG. 4, X-ray irradiation is performed with the end point of the X-ray irradiation period TX being substantially coincident with the synchronization signal. On the other hand, image reading is performed after a period of one cycle has elapsed after X-ray irradiation. The start point of the period RD is made substantially coincident with the synchronization signal. In this regard, the image reading may be performed with the period of the synchronization signal next to the X-ray irradiation as shown in FIG. 5 and the end point of the image reading period RD substantially matching the synchronization signal.

  In this case, the period from the X-ray irradiation to the image reading is shorter than that in FIG. 4, but the image reading is not performed immediately after the X-ray irradiation, so that luminance unevenness can be suppressed. In addition, since the image is read out in the period of the synchronization signal next to the X-ray irradiation, the image can be acquired relatively quickly after the X-ray irradiation.

  Further, as shown in FIG. 5, the image reading is performed by making the end point of the image reading period substantially coincide with the synchronization signal, thereby ensuring a minimum period TD from the X-ray irradiation to the image reading. . That is, it is assumed that image reading may be performed with the synchronization signal S12 and the end point of the image reading period substantially coincident. In this case, the X-ray irradiation is performed so that the synchronization signal S10 and the start point of the X-ray irradiation period TX are substantially matched as indicated by the symbol J, or the synchronization signal S11 and the end point of the X-ray irradiation period TX are substantially matched. However, the period TD can be secured at a minimum.

  In addition, as indicated by reference numeral K in FIG. 5, when the X-ray irradiation is performed with the synchronization signal S21 and the start point of the X-ray irradiation period TX being substantially coincident, as indicated by reference numeral L, By making the synchronization signal S21 substantially coincide with the end point of the X-ray irradiation period TX, the period TD can be secured at a minimum. That is, by changing from the start point to the end point of the X-ray irradiation period TX, a period corresponding to the X-ray irradiation period TX can be secured.

<Sequence of FIGS. 6A and 6B>
Further, in the sequences of FIGS. 4 and 5, X-ray irradiation is performed with the end point of the X-ray irradiation period TX being substantially coincident with the synchronization signal. In this regard, the X-ray irradiation may be performed so that the start point of the X-ray irradiation period TX substantially coincides with the synchronization signal as shown in FIGS. 6 (a) and 6 (b).

  In FIG. 6A, image readout is performed with the period of the next synchronization signal after X-ray irradiation, and the start point of the image readout period RD is substantially coincident with the synchronization signal. In FIG. 6B, the image readout is performed with the period of the synchronization signal next to the X-ray irradiation, and the end point of the image readout period RD is substantially matched with the synchronization signal. The sequence of FIG. 5, FIG. 6 (a) and FIG. 6 (b) is “7.5 fps fluoroscopy and 15 fps accumulation” as in FIG.

  In FIG. 4 of the first embodiment, the X-ray tube control unit 6 performs X-ray irradiation by matching the end point of the X-ray irradiation period TX with the synchronization signal. As a result, as shown in FIG. 6A, it is possible to further secure a period until image reading, that is, a period until the bias voltage is stabilized, as compared with the case where the start point of the X-ray irradiation time TX is substantially coincident with the synchronization signal.

  That is, in FIG. 6A, for example, the synchronization signal S20 and the “start point” of the X-ray irradiation period TX are substantially matched. The period from X-ray irradiation to image readout at this time is a period TC obtained by subtracting the X-ray irradiation period TX from one cycle T1 of the synchronization signal. On the other hand, as shown in FIG. 4, for example, the synchronization signal S21 and the “end point” of the X-ray irradiation period TX are substantially matched. As a result, the period from the X-ray irradiation to the image readout becomes one cycle T1 of the synchronization signal, which can be secured more than the period TC in FIG.

  Next, Embodiment 2 of the present invention will be described with reference to the drawings. In addition, the description which overlaps with Example 1 is abbreviate | omitted. FIG. 7A and FIG. 7B are diagrams illustrating sequences such as X-ray irradiation and image reading according to the second embodiment.

  The sequence of the first embodiment is “7.5 fps perspective and 15 fps accumulation”, but is not limited thereto. The sequence of the second embodiment may be, for example, “3.75 fps perspective and 7.5 fps accumulation”.

  The X-ray tube control unit 6 performs X-ray irradiation at regular intervals at a rate of once every eight synchronization signals. X-ray irradiation is performed so as not to overlap with the image readout period RD. On the other hand, the FPD control circuit 29 reads out images at regular intervals at a rate of once every four synchronization signals. Since the synchronization signal is 30 fps, fluoroscopic imaging is performed at a lower rate of 3.75 (= 30/8) fps fluoroscopy and 7.5 (= 30/4) fps accumulation.

  In FIG. 7A, for example, X-ray irradiation is performed such that the end point of the X-ray irradiation period TX substantially coincides with the synchronization signal S11. On the other hand, the image reading is performed so that the start point of the image reading period RD substantially coincides with the synchronization signal S12. Therefore, image reading is performed after a period of one cycle has elapsed.

  In FIG. 7B, the X-ray irradiation is performed so that the start point of the X-ray irradiation period TX substantially coincides with the synchronization signal S10. On the other hand, the image reading is performed so that the end point of the image reading period RD substantially coincides with the synchronization signal S12. Therefore, image reading is performed after the elapse of a period obtained by subtracting the X-ray irradiation period TX from one cycle of the synchronization signals S10 to S11.

  According to the present embodiment, as in the first embodiment, the image reading is performed after a preset period has elapsed since the X-ray irradiation. Therefore, the influence of the fluctuation of the bias voltage Vh is suppressed, and the luminance unevenness generated in the image is reduced. Can be suppressed.

  Next, a modification of the second embodiment will be described. In FIG. 7A, in the period F, the image reading is performed so that the “start point” of the image reading period RD substantially coincides with the synchronization signal S12. However, the present invention is not limited to this. That is, in the periods E and F, as shown in FIG. 5, the image reading may be performed so that the “end point” of the image reading period RD substantially coincides with the synchronization signal. In the period G, the image reading may be performed so that any one of the “start point” and “end point” of the image reading period RD substantially coincides with the synchronization signal. In the period H, the image reading may be performed so that the “start point” of the image reading period RD substantially coincides with the synchronization signal. As a result, image readout can be performed after a period longer than one cycle of the synchronization signal after X-ray irradiation.

  In FIG. 7B, in the period E, the image reading is performed so that the “end point” of the image reading period RD substantially coincides with the synchronization signal S12. However, the present invention is not limited to this. That is, in the period E, the “starting point” of the image reading period RD may be performed so as to substantially coincide with the synchronization signal. Further, in the periods F and G, the “reading point” and the “ending point” of the image reading period RD may be performed so as to substantially coincide with the synchronization signal. Similarly, image readout can be performed after elapse of a period longer than one cycle of the synchronization signal after X-ray irradiation.

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

  (1) In each of the above-described embodiments, the X-ray tube control unit 6 performs X-ray irradiation at regular intervals and performs continuous imaging. However, the X-ray tube control unit 6 performs single imaging that performs X-ray irradiation only once. Also good. In this case, the FPD control circuit 29 performs image reading at equal intervals for every two or more synchronization signals. Thereby, it is possible to secure a period from the X-ray irradiation to the image reading without changing the rate of the synchronization signal, for example, 30 fps.

  (2) In each of the above-described embodiments and modification (1), photographing was performed with “7.5 fps fluoroscopy and 15 fps accumulation” or “3.75 fps fluoroscopy and 7.5 fps accumulation”. For example, “3.75 fps fluoroscopy and 15 fps accumulation” may be used.

  That is, in each of the above-described embodiments and modification (1), X-ray irradiation is performed for every four synchronization signals, and image readout is performed for every two synchronization signals. X-ray irradiation was performed for each synchronization signal, and image reading was performed for every four synchronization signals. In this respect, X-ray irradiation is performed at equal intervals for every 4 or more and multiples of 2 synchronization signals, that is, every 4 times, 6 times, 8 times, 10 times, 12 times,. It may be performed at equal intervals for each synchronization signal that is less than the number of synchronization signals (for example, 8 times) that divide the cycle of X-ray irradiation and is a multiple of 2 that can divide the number of periodic signals.

  For example, if the number of synchronization signals that engrave the X-ray irradiation cycle is 8 or 12, image readout is performed for each of the synchronization signals of 2 times or 4 times. Further, for example, if the number of synchronization signals that engrave the X-ray irradiation cycle is 6 or 10, the image is read out every two synchronization signals.

  In addition, although it has been described that X-ray irradiation is performed for each periodic signal of 4 or more and a multiple of 2, the X-ray irradiation rate may be lower than that for image reading.

DESCRIPTION OF SYMBOLS 1 ... X-ray imaging device 3 ... X-ray tube 4 ... FPD
6 ... X-ray tube controller 9 ... Main controller 16 ... Semiconductor layer 17 ... Common electrode 19 ... Active matrix substrate 21 ... Capacitor 22 ... TFT
29 ... FPD control circuit M ... Subject RD ... Image readout period TX ... X-ray irradiation period T1 ... 1 period of periodic signal

Claims (6)

An X-ray source that irradiates the subject with X-rays;
An X-ray detector for detecting X-rays transmitted through a subject, a conversion layer that generates charges in response to incident X-rays, and a bias voltage applied to one surface of the conversion layer The X-ray detector having a common electrode,
A readout circuit for accumulating the charge generated in the conversion layer and reading the accumulated charge;
A control unit for performing X-ray irradiation by the X-ray source based on a synchronization signal given at an equal period and performing image reading for reading out one frame image by the reading circuit;
One cycle of the synchronization signal is equal to or longer than a period obtained by adding an X-ray irradiation period for performing the X-ray irradiation and an image reading period for performing the image reading,
The control unit causes the X-ray irradiation so as not to overlap with the image readout period,
The control unit causes the image reading to be performed at equal intervals for each of two or more synchronization signals, and causes the image reading to be performed after a preset period has elapsed after X-ray irradiation. . The X-ray diagnostic apparatus according to claim 1,
The control unit performs the X-ray irradiation at equal intervals for each synchronization signal of 4 or more and a multiple of 2 so as not to overlap with the image readout period,
The control unit causes the image reading to be performed at equal intervals for each synchronization signal that is a multiple of 2 that is less than the number of synchronization signals that divide the period of the X-ray irradiation and is divisible by the number of synchronization signals. An X-ray diagnostic apparatus characterized by causing the image to be read after a preset period has elapsed. The X-ray diagnostic apparatus according to claim 1 or 2,
The X-ray diagnostic apparatus, wherein the control unit performs the X-ray irradiation by matching an end point of the X-ray irradiation period with a synchronization signal. In the X-ray diagnostic apparatus according to any one of claims 1 to 3,
The X-ray diagnostic apparatus, wherein the control unit performs the image reading by matching an end point of the image reading period with a synchronization signal. The X-ray diagnostic apparatus according to claim 4,
The control unit performs the X-ray irradiation by matching an end point of the X-ray irradiation period with a synchronization signal,
The X-ray diagnostic apparatus is characterized in that the control unit performs the image reading with a period of a synchronization signal next to X-ray irradiation and with an end point of the image reading period coincided with the synchronization signal. In the X-ray diagnostic apparatus according to any one of claims 1 to 4,
The X-ray diagnostic apparatus characterized in that the control unit causes the image reading to be performed after a period of one or more cycles of the synchronization signal has elapsed after X-ray irradiation.

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