JP2012200016A - Radiation imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate simple image processing display.SOLUTION: A radiation imaging apparatus comprises: a signal processing circuit for converting an electric charge signal imaged by an imaging device into a digital signal; a selector circuit for applying thinning control to converted signal data according to a thinning transfer rate; and a display control section for displaying image data subjected to dark current correction based on signal data with respect to dark current of the imaging device converted by the signal processing circuit and signal data subjected to the thinning control as a simple display image.

Description

  The present invention relates to a radiation imaging apparatus that forms a subject signal, which is a radiation intensity distribution that is transmitted through a subject by irradiating the subject with radiation, by an imaging device including a photoelectric conversion element.

  A method of irradiating an object with radiation, detecting an intensity distribution of the radiation transmitted through the object, and obtaining a radiation image of the object is widely used in industrial nondestructive inspection and medical diagnosis. The most common method for obtaining a radiographic image of an object. The most common method is to combine a so-called “fluorescent screen” (or intensifying screen) that emits fluorescence with radiation and a silver salt film to irradiate the object with radiation. In this method, a radiation image is converted to visible light with a fluorescent plate, a latent image is formed on the silver salt film, and then the silver salt film is chemically treated to obtain a visible image. The radiographic image obtained by this imaging method is a so-called analog photograph and is used for diagnosis, inspection, and the like.

  On the other hand, recently, a technique for acquiring a digital image by using a photoelectric conversion device in which pixels including minute photoelectric conversion elements, switching elements, and the like are arranged in a lattice form as an image receiving means has been developed. Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5 and the like are disclosed as radiation imaging apparatuses in which a phosphor is laminated on a CCD or amorphous silicon two-dimensional image sensor. These photographing devices can display acquired image data immediately, and can be directly called digital photographing devices.

  The advantages of digital photography devices over analog photography technology include:

  That is, filmless, expansion of acquired information by image processing, creation of a database, and the like. Further, the immediate digital imaging device has an advantage over the indirect digital imaging device in terms of immediacy. The ability to instantly display a captured image on the spot is advantageous in a medical site that requires urgent action.

US Pat. No. 5,418,377 US Pat. No. 5,396,072 US Pat. No. 5,381,014 US Pat. No. 5,132,539 U.S. Pat. No. 4,810,881

  However, regardless of the light receiving method such as CCD and amorphous silicon, the two-dimensional imaging device has a characteristic that dark current is accumulated even in the absence of a signal, which contributes to noise in shooting a small signal, and has a high gradation (= (Approx. 4096 gradations), it may cause a reduction in image quality. In addition, since this dark current changes depending on the ambient temperature and the like, it is necessary to perform imaging in a series of imaging sequences. For this reason, it takes about 3 to 4 seconds to display on the monitor from the start of shooting.

  FIG. 5 shows a configuration diagram of a radiation imaging apparatus that acquires this digital image. In FIG. 5, 1 is a radiation imaging means (hereinafter referred to as “sensor unit”), 2 is a control PC, 20 is a monitor, 21 is a printer, and 22 is a data storage device.

  Reference numeral 101 denotes a two-dimensional image sensor, and reference numeral 102 denotes an amplifier circuit that adjusts the gain of the image signal level output from the two-dimensional image sensor 101. Reference numeral 103 denotes an A / D converter that converts an analog imaging signal into digital. Reference numeral 104 denotes a line memory for storing one line of the digital signal output from the A / D converter 103. Reference numeral 105 denotes two line memories. This is a multiplex IC that converts the output of 104 into a serial signal output of one line.

  Further, a drive pulse required by the two-dimensional image sensor 101, a sampling pulse required by the A / D converter 103, and other necessary timing signals are supplied from the pulse generator. The pulse generator 108 is controlled by 109 MPUs. Reference numeral 107 denotes a communication IC for transferring the output of the multiplex IC 105 to the control PC 2. The control PC 2 performs image processing on the digital signal transferred from the communication IC 107, displays it on the connected monitor 20, prints it on the printer 21, and stores it in the data storage device 22.

  The imaging sequence will be described below with reference to FIGS.

  FIG. 6A shows the state transition of the two-dimensional image sensor, and FIG. 6B shows the operation of the control PC.

  When there is a request to start imaging, the two-dimensional imaging device is changed from the imaging standby state to a uniform state in which the imaging elements of the two-dimensional imaging device are reset, and X-ray exposure is performed and charge accumulation starts at the same time. This signal accumulation time PQ is proportional to the X-ray irradiation time. The accumulated signal charge is read as an S signal to the amplifier circuit 102, sequentially converted into a digital signal by the A / D converter 103, and transferred to the control PC 2 as image data SQ based on the S signal. The transfer time at this time is TSQ.

  When the reading of the S signal is completed (when the transfer of the S signal is completed), the state of the two-dimensional imaging device is reset, and dark current signal accumulation is performed in the same accumulation time PQ as in S signal imaging. The accumulated signal charge is read out as an F signal, processed in the same manner as the S signal, and transferred to the control PC 2 as image data FQ based on the F signal. The transfer time at this time is TFQ. After the transfer is completed, the two-dimensional image sensor stands by in a shooting standby state until the next shooting request is made.

  The control PC 2 receives the image data SQ based on the S signal imaged by the two-dimensional image sensor from the standby state from the sensor unit 1 and stores it. When this transfer ends, the standby state is restored.

  Similarly, the F signal corresponding to the dark current is also transferred from the sensor unit 1, and the control PC receives and stores it as the image data FQ. The transfer time at this time is TFQ.

  The transfer times TSQ and TFQ of the S signal and the F signal are the same as the signal read time, respectively.

  When the transfer of the F signal is completed, the control PC performs simple image processing for performing simple image display. First, dark current correction (dark current correction (QQ) = SQ−FQ) is performed by subtracting the image data FQ from the transferred image data SQ. In the conventional example, the total number of pixels of the two-dimensional image sensor is 2688 × 2688 pixels, and image processing is performed to display 336 × 336 pixels of each side 1/8 on the monitor. This image processing time is TPQ, the display image displayed on the monitor is QQ, and the time from X-ray exposure to monitor display is tQ.

  This simple image display is a display for confirming the dose of X-rays and the blurring and position of the photographed image, and does not perform inspection or diagnosis on this image, but merely displays an outline of the imaging result. Next, the image data subjected to dark current correction is used to perform optimal image processing for inspection and diagnosis (this is referred to as “main image processing”), and the result is stored in the data storage device 22.

  Further, the captured image file can be called up and displayed on the monitor 20 or printed on the printer 21 as necessary.

  In the configuration of the conventional example, since the sensor unit 1 does not have a frame memory, the image data of all the pixels must be transferred to the control PC 2 regardless of the simple image display, and the transfer rate is the signal reading rate. It is required to be the same as the rate. Therefore, when the simple image processing and the main image processing are compared from the viewpoint of monitor display, there is no difference. In such a configuration, in order to increase the display speed of a simple image, for example, when transferring 14-bit image data serially, the transfer rate is about 800 Mbps. Therefore, a special and expensive communication circuit is required.

  In order to solve the above problems, a radiation imaging apparatus according to the present invention mainly has the following configuration.

That is, the radiation imaging apparatus
Signal processing means for converting a charge signal imaged by the imaging means into a digital signal;
Frame image storage means for storing the signal data converted by the signal processing means as frame image data;
Communication means for transferring the data to display control means for displaying an image based on the frame image data stored in the frame image storage means;
The transfer rate of the communication means is slower than the signal readout rate from the imaging means.

Alternatively, the radiation imaging apparatus
Signal processing means for converting a charge signal imaged by the imaging means into a digital signal;
Selector means for controlling the thinning of the converted signal data in accordance with the thinning transfer rate;
Display control means for displaying image data subjected to dark current correction based on the signal data for the dark current of the imaging means converted by the signal processing means and the signal data subjected to the thinning control, as a simple display image; It is characterized by providing.

  In the above radiation imaging apparatus, a thinning transfer rate of the selector unit is slower than a signal reading rate of the imaging unit.

  In the radiation imaging apparatus, the frame image storage means stores frame image data for at least one frame of the imaging means.

  In the radiation imaging apparatus, the generation of the display image based on the dark current correction by the display control unit is signal data that is not subjected to thinning control, and is processed before reception of the charge signal by the imaging unit imaging. It is characterized by.

  According to the radiation imaging apparatus of the present invention, by providing the memory for storing the frame image data, the transfer rate of the image data to the display control unit can be made slower than the signal reading rate of the image sensor. .

  In synchronization with the storage of the frame image data, the selector circuit performs the thinning control of the image data, and the display control displays the simple image display in a short time from the X-ray exposure based on the thinned-out image data. Enable.

It is a block diagram explaining the structure of the radiography apparatus concerning embodiment of this invention. It is a figure explaining the imaging | photography sequence of the radiography apparatus concerning the 1st Embodiment of this invention. It is a figure explaining the imaging | photography sequence of the radiography apparatus concerning the 2nd Embodiment of this invention. It is a figure explaining the imaging | photography sequence of the radiography apparatus concerning the 3rd Embodiment of this invention. It is a block diagram explaining the structure of a prior art example. It is a figure which shows the imaging | photography sequence in a prior art example.

<Embodiment 1>
An embodiment of a radiation imaging apparatus according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram illustrating the configuration of the radiation imaging apparatus. Here, in FIG. 1, the same reference numerals are given to the same components as those in the configuration diagram of the conventional example of FIG. 5, and detailed description of those described in the conventional example is omitted.

  Further, in FIG. 1, there are two imaging signal output lines output from the two-dimensional imaging device 101, but this is for simplifying the drawing and defines the number of output lines of the imaging signal actually output. Not what you want.

  1 is a frame memory for storing at least one frame of signal output output from the multiplex IC 105, and 110 is a selector circuit for thinning and transferring the signal output for simple image display. .

  Hereinafter, the imaging sequence will be described with reference to FIGS.

  2A shows the state transition of the two-dimensional image sensor, FIG. 2B shows the state of the frame memory, and FIG. 2C shows the operation of the control PC.

  In the state of the two-dimensional image sensor, FIG. 2A, n in the figure represents the number of times of photographing. The contents of this processing sequence are the same as those in the conventional imaging sequence shown in FIG.

  When there is a request to start imaging in the imaging standby state, the two-dimensional imaging device 101 is in a uniform state in which each imaging element of the two-dimensional imaging device is reset from the imaging standby state, and X-ray exposure is performed. At the same time, charge accumulation begins. The signal accumulation time Pn is proportional to the X-ray irradiation time. The accumulated signal charge is read as an S signal by an amplifier (AMP) circuit 102, subjected to signal processing by an A / D converter 103, a line memory 104, and a multiplex IC 105, and the S signal converted into a digital signal is Are sequentially written in the frame memory 106 (FIG. 2B).

  When the two-dimensional imaging device finishes reading the S signal to the frame memory 106, it is reset to return to the uniform state, and then dark current signal accumulation is performed with the same accumulation time Pn as that during S signal imaging. The accumulated signal charge is read out as an F signal, processed in the same manner as the S signal, and written into the frame memory 106.

  When the readout of the F signal is completed, the two-dimensional image sensor returns to the imaging standby state until the next imaging request is made.

  Simultaneously with writing to the frame memory 106, the selector 110 sequentially performs signal thinning and transfer to the control PC 2 at a rate of one pixel per M pixel. Here, “M” is determined as a value suitable for a displayable pixel of the monitor 20. In the present embodiment, the total number of pixels of the two-dimensional image sensor is 2688 × 2688 pixels, and the displayable pixels of the monitor are 336 × 336 pixels, so that M = 8 (M = 2688/336). Accordingly, since the transfer rate to the control PC 2 can be transferred at a rate of 1 pixel per 8 pixels, the transfer rate is 1/8 of the signal read rate. The image data for the thinned S signal transferred to the control PC 2 is referred to as “image data SS” (FIG. 2C).

  The control PC 2 performs image processing using the transferred thinned image data SS and performs display control for simple image display. The dark current image data used in this image processing is subjected to dark current correction using the dark current image data (Fn-1) acquired in the previous photographing stored in the control PC. That is, the image data subjected to dark current correction is an image obtained by subtracting the dark current image data in the previous imaging from the thinned-out image data SS. If the display image subjected to dark current correction is Qn, Qn is expressed by the following equation. Defined by

Dark-current corrected image data (Qn) = SS−Fn−1
If this image processing time is TPn, the image processing time TPn is processed at a transfer rate of 1/8, so that the processing time in the entire two-dimensional image sensor is 1/64 compared with the conventional example. Thus, the processing time can be shortened (TPn (FIG. 2C)) <TPQ (FIG. 6B).

  Further, the time tn from the X-ray exposure to the monitor display is greatly shortened compared with the time tQ until the monitor display in the conventional example (tn <tQ).

  By using the dark current signal in the simple image processing that was acquired in the previous imaging, the simple image processing is performed in advance without waiting for the dark current signal accumulation, signal processing, and transfer to shorten the processing time. Can be achieved.

  The display image Qn is not equivalent when compared with the image QQ displayed in the conventional example, but the performance of the monitor (the monitor used in this embodiment has a resolution of 336 × 336, about 64 to 128 gradations) ), Or a simple image display, and an image that can be satisfactorily satisfied in view of the fact that the examination and diagnosis are not performed.

  When the simple image processing is completed in the control PC 2, the S signal image data and the F signal image data stored in the frame memory 106 are transferred to the control PC 2 at an arbitrary transfer rate, and the control PC 2 accepts the transfer of the S signal and the F signal. ,Store.

  Next, in this embodiment, since the frame memory 106 has a capacity of one frame, the transfer of the S signal is started before the F signal is written to the frame memory. Does not specify the order of transfer to the control PC. In addition, since the transfer rate is also provided with the frame memory, it can be made slower than the signal reading rate.

  Optimal image processing (main image processing) for performing inspection and diagnosis by subtracting the image data Fn for the F signal from the image data Sn for the S signal without thinning transferred from the frame memory 106 and performing dark current correction. ) And the result is stored in the data storage device 22, and the captured image file can be displayed on the monitor 20 and printed on the printer 21 as necessary.

  As described above, according to the radiation imaging apparatus according to the present embodiment, by providing a memory for storing frame image data, the transfer rate of image data to the display control unit is higher than the signal reading rate of the image sensor. It becomes possible to slow down.

  In synchronization with the storage of the frame image data, the selector circuit performs the thinning control of the image data, and the display control displays the simple image display in a short time from the X-ray exposure based on the thinned-out image data. Enable. According to this embodiment, the time taken for about 3 to 4 seconds in the conventional example can be reduced to about 2 seconds.

<Embodiment 2>
Next, a second embodiment according to the present invention will be described with reference to FIG. In FIG. 3, the same components as those in the imaging sequence of Embodiment 1 in FIG. 2 are denoted by the same reference numerals, and detailed description of overlapping portions is omitted.

  In the present embodiment, dark current correction processing for obtaining the display image QF in the simplified image processing of FIG. 3C is different from the first embodiment and dark current correction. The dark current correction signal used in the present embodiment uses dark current image data FF stored in advance in the control PC 2. Accordingly, the dark current corrected display image QF is defined by the following expression obtained by subtracting the dark current correction signal FF from the image data SS thinned out and transferred from the frame memory 106.

Dark current corrected image data (QF) = SS-FF
This dark current image data FF is an average value obtained by averaging a plurality of times of dark current image data, and a dark current that can ignore random noise that the image sensor has by taking the average of a plurality of times. It becomes image data. Note that the dark current image data FF to be actually subtracted is converted into a value proportional to the dark current accumulated during the S signal accumulation time Pn. The image QF displayed here is not the same as the image QQ displayed in the conventional example, but it is an image that is sufficiently satisfactory considering the performance of the monitor and simple image display.

  As described above, similarly in the radiographic apparatus according to the present embodiment, the transfer rate of the image signal to the control PC 2 can be made slower than the signal readout rate of the two-dimensional image sensor, and the system design can be improved. The degree of freedom is increased, and a special and expensive communication circuit is not required.

  In addition, it is possible to significantly reduce the time taken from the exposure of X-rays to the simple image display.

  As described above, in the radiation imaging apparatus according to the present embodiment as well, by providing a memory for storing frame image data, the transfer rate of image data to the display control unit is higher than the signal reading rate of the image sensor. It becomes possible to slow down.

  In synchronization with the storage of the frame image data, the selector circuit performs the thinning control of the image data, and the display control displays the simple image display in a short time from the X-ray exposure based on the thinned-out image data. Enable.

<Embodiment 3>
Next, a third embodiment according to the present invention will be described with reference to FIG. 4, the same reference numerals are given to the same components as those in the imaging sequence of the first embodiment in FIG.

  As shown in FIG. 4C, the present embodiment is different from the first and second embodiments in that the simple image processing is performed twice in the operation of the control PC2.

  In the simple image processing 1, as in the first embodiment, the dark current correction is performed using the thinned image data SS and the dark current image data Fn-1 acquired in the previous shooting. Here, the display image displayed on the monitor as a result of the simple image processing 1 is Qn, which is defined by the following equation.

Dark-current corrected image data (Qn) = SS−Fn−1
The image Qn displayed here is the same as the image displayed in the first embodiment, and the time tn from the X-ray exposure to the image display is also the same.

  After the simple image processing, the transfer of the S signal and the F signal for the main image processing is accepted from the frame memory 106, and the second simple image processing 2 starts after the F signal transfer. For the dark current correction performed in the simple image processing 2, dark current correction is performed using the image data Sn based on the S signal and the image data Fn based on the F signal transferred from the frame memory 106. Image data Rn subjected to this dark current correction is defined by the following equation.

Dark current corrected image data (Rn) = Sn−Fn
The image Rn displayed here is based on the S signal that has not been thinned out, and is a higher quality image than the first simple image processing 1.

  According to the radiation imaging apparatus of the present embodiment, the display from the X-ray exposure to the image display is shortened by the first process out of the two simple image processes, and the quality of the simple image is displayed by the second display. It is possible to display high-quality without dropping the image.

Claims (9)

A radiation imaging device comprising:
Signal processing means for converting a charge signal imaged by the imaging means into a digital signal;
Frame image storage means for storing the signal data converted by the signal processing means as frame image data;
Communication means for transferring the data to display control means for displaying an image based on the frame image data stored in the frame image storage means;
With
The radiation imaging apparatus, wherein a transfer rate of the communication unit is slower than a signal reading rate from the imaging unit. A radiation imaging device comprising:
Signal processing means for converting a charge signal imaged by the imaging means into a digital signal;
Selector means for controlling the thinning of the converted signal data in accordance with the thinning transfer rate;
Display control means for displaying image data subjected to dark current correction based on the signal data for the dark current of the imaging means converted by the signal processing means and the signal data subjected to the thinning control, as a simple display image; ,
A radiation imaging apparatus comprising:   The radiation imaging apparatus according to claim 2, wherein, in the dark current correction, the dark current signal is data stored as dark current data in the previous imaging.   The radiation imaging apparatus according to claim 1, wherein the imaging unit is a two-dimensional imaging device that is sensitive to radiation and outputs an electrical signal corresponding to an incident radiation dose.   The radiation imaging apparatus according to claim 1, wherein the frame image storage unit stores frame image data for at least one frame of the imaging unit.   3. The radiation imaging apparatus according to claim 2, wherein the thinning transfer rate is determined from a ratio between all pixel data of the imaging unit and minimum pixel data necessary for display as the display image.   3. The radiation imaging apparatus according to claim 2, wherein in the dark current correction, the dark current signal is data stored as an average value of dark current data in a plurality of times of imaging.   3. The display image generation based on the dark current correction by the display control unit is signal data that is not subjected to thinning control, and is processed before reception of a charge signal by the imaging unit. The radiation imaging apparatus described in 1. The display control means includes
A first display image that is signal data that is not subjected to thinning control, and that is subjected to dark current correction processing before reception of a charge signal by imaging of the imaging means;
The radiation imaging apparatus according to claim 2, wherein display control is performed on a second display image that is subjected to dark current correction processing after receiving a dark current signal for imaging by the imaging unit.

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