JP2009201587A - Radiographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic apparatus capable of executing afterimage correcting only in an image with afterimages by determining the presence of afterimages in the radiation image. <P>SOLUTION: The radiographic apparatus includes an image acquisition part which acquires afterimage data of the previous radiation image when radiation is not applied before the next radiography and acquires data of the next radiation image after the next radiography; an offset correction part which offset-corrects the afterimage data of the previous radiation image and data of the next radiation image; an afterimage determining part which determines the presence of afterimages in a specified region of the offset-corrected afterimage data; an afterimage correction part which executes afterimage correction by subtracting the afterimage data from the offset-corrected, next radiation image data if it is determined that an afterimage is present by the afterimage determining part; and a control part for controlling the operation of the radiographic apparatus. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiographic imaging apparatus that irradiates a subject with radiation, detects the radiation transmitted through the subject, converts the radiation into an electrical signal, and generates a radiation image based on the converted electrical signal.

  Radiographic imaging devices are used in various fields including, for example, medical diagnostic images and industrial nondestructive inspection. As a radiation detector for detecting radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) transmitted through a subject in a radiographic imaging apparatus, a flat panel that converts radiation into electrical signals at present There is a type using a flat panel detector (FPD). In a radiographic image capturing apparatus using FPD, an afterimage of a previously captured radiographic image becomes a problem as a cause of deterioration in the image quality of the radiographic image obtained by imaging the subject.

  In a radiographic imaging apparatus using an FPD, a subject is irradiated with radiation from a radiation source, the radiation transmitted through the subject is converted into an electrical signal by the FPD, and an electrical signal corresponding to the image data of the subject is read out from the FPD. Is generated. However, even after the electrical signal corresponding to the image data is read from the FPD, a part of the charge corresponding to the image data remains in the FPD. When the next subject is photographed in this state, the residual charge in the FPD is superimposed on the next radiation image as an afterimage, and the radiation image becomes an image affected by the afterimage.

  Therefore, in the radiographic image capturing apparatus, before capturing the next subject, an afterimage correction process is performed to remove the influence of the afterimage of the subject image captured before (before the next capturing). The afterimage correction process is usually performed by the following steps 1 to 4.

  In the following description, Offset (x, y) is offset correction data for correcting image data offset (deviation from the reference voltage level), and Xdata (x, y) is taken by irradiating radiation. The radiographic image data (corrected image data) of the next subject, Lagdata (x, y) is the afterimage data of the previous radiographic image read from the FPD without irradiation immediately before the next imaging. , Α is a correction coefficient for the afterimage amount for correcting a decrease in the afterimage amount (afterimage charge amount) from when the afterimage data is read until the next shooting is performed.

(Step 1)
As shown in the following formula (1), the offset correction data Offset (x, y) is subtracted from the afterimage data Lagdata (x, y) to offset the afterimage data Lagdata (x, y). Later image data Data1 (x, y) is obtained.
Data1 (x, y) = Lagdata (x, y)-Offset (x, y) (1)

(Step 2)
As shown in the following formula (2), the afterimage data Data1 (x, y) after the offset correction is obtained by multiplying the afterimage data Data1 (x, y) after the offset correction by a correction coefficient α of the afterimage amount. Correction is performed to obtain afterimage data after correction (image data for correction) Data2 (x, y).
Data2 (x, y) = α × Data1 (x, y) (2)

(Step 3)
As shown in the following equation (3), the correction image data Xdata (x, y) is offset corrected by subtracting the offset correction data Offset (x, y) from the correction image data Xdata (x, y). Thus, corrected image data Data3 (x, y) after offset correction is obtained.
Data3 (x, y) = Xdata (x, y)-Offset (x, y)… (3)

(Step 4)
As shown in the following equation (4), the corrected image data Data2 (x, y) is subtracted from the corrected image data Data3 (x, y) after the offset correction, and the corrected image data Data3 (x, y) is obtained. Afterimage correction is performed to obtain image data Data4 (x, y) after the afterimage correction.
Data4 (x, y) = Data3 (x, y)-Data2 (x, y) (4)

Since the afterimage data has a lot of noise components, the noise component of the image data Data4 (x, y) after the afterimage correction may partially increase by performing subtraction in the afterimage correction. Therefore, as shown in the following equation (5), the image data Data4 ′ (x, y) after the afterimage correction is calculated by subtracting the median-processed correction image data median (Data2 (x, y)) There is also.
Data4 '(x, y) = Data3 (x, y)-median (Data2 (x, y))… (5)

  Here, as prior art documents relevant to the present invention, for example, Patent Documents 1 and 2 can be exemplified.

  As a method for correcting afterimages, for example, Patent Document 1 discloses a method for calculating afterimages using arithmetic average values and performing afterimage correction based on the calculated afterimages. In Patent Document 1, before capturing a bright image (subject image), at least two dark images are acquired, an average value thereof is obtained, and a correction signal is calculated by subtracting the average value from the bright image.

  Patent Document 2 discloses that an FPN image is divided into a plurality of rectangles, and the presence / absence of an afterimage is determined using an average value of each pixel value obtained for each rectangle. Patent document 2 describes that afterimage determination is performed by such a method, and afterimage correction is performed when it is determined that there is an afterimage.

JP-A-10-85207 JP 2005-95578 A

However, in the conventional techniques such as Patent Documents 1 and 2, an afterimage is calculated by calculating an average value of pixel values. For this reason, it is suppressed to be smaller than the actual afterimage amount.
Further, in Patent Document 1, since the afterimage correction is performed in all regions in the image without determining the presence or absence of the afterimage, the processing takes time. In Patent Document 2, it is determined whether or not to perform afterimage correction based on the result of afterimage determination. Therefore, correction is also performed on unnecessary portions, which not only requires processing time but also leads to noise deterioration.

  An object of the present invention is to solve the problems of the prior art, and in radiographic imaging using a radiation solid-state detector (FPD), afterimage correction is performed only on a region that needs correction in the image. Accordingly, it is an object of the present invention to provide a radiographic imaging apparatus that can perform correction processing quickly and can perform accurate afterimage correction.

  In order to achieve the above object, the present invention irradiates a subject with radiation from a radiation source, detects the radiation transmitted through the subject with a flat panel radiation detector, and obtains a radiographic image obtained by photographing the subject. A radiographic image capturing device for generating afterimage data of a previous radiographic image read from the radiation detector at the time of non-irradiation of radiation before the next radiographing is performed, and the next radiographing is performed. An image acquisition unit that acquires data of the next radiographic image read from the radiation detector, an imaging menu setting unit that sets an imaging region of the subject in the next imaging, and the afterimage data In the region set according to the imaging region set by the imaging menu setting unit, there is an afterimage due to the previous radiographic image at the time of imaging the next radiographic image. A radiographic imaging device, comprising: an afterimage determination unit that determines an afterimage; and an afterimage correction unit that performs afterimage correction on data of the next radiation image when the afterimage determination unit determines that there is an afterimage It is to provide.

Here, the afterimage determination unit, when there is a predetermined number or more of pixel data having a pixel value equal to or greater than a determination threshold among pixel data corresponding to each pixel of the previous radiation image of the afterimage data, It is preferable to determine that there is an afterimage.
In addition, the afterimage determination unit includes pixel data having a pixel value equal to or greater than a determination threshold among pixel data corresponding to each pixel of the previous radiation image in the afterimage data, and the pixel data having 1% or more of the total number of pixels In this case, it is preferable to determine that the afterimage is present.

Furthermore, an afterimage amount correction unit that corrects a decrease in the afterimage amount of the afterimage data from when the afterimage data is read until the next shooting is performed,
The afterimage determination unit preferably performs afterimage determination on the afterimage data corrected by the afterimage amount correction unit.

Furthermore, an offset correction unit that performs offset correction of the afterimage data of the previous radiation image and the data of the next radiation image,
It is preferable that the afterimage correction unit performs afterimage correction of the next radiation image by subtracting the offset afterimage data from the offset-corrected next radiation image data.

Furthermore, it has a determination setting unit for setting the necessity of afterimage determination in the afterimage determination unit,
When afterimage determination is set to be unnecessary by the afterimage determination unit, it is preferable that afterimage correction is performed by the afterimage correction unit without performing afterimage determination by the afterimage determination unit.

According to the present invention having the above-described configuration, afterimage correction can be performed only on an image that requires afterimage correction by determining the presence or absence of an afterimage before performing afterimage correction. For this reason, it is possible to prevent the deterioration of noise caused by performing afterimage correction on an image that does not require correction, and it is possible to perform correction processing quickly.
In addition, since afterimage determination is performed by calculating the number of pixels with afterimages, it is possible to calculate an accurate afterimage amount compared to the conventional method of calculating an average value and performing afterimage determination based on the average value. Therefore, it is possible to perform afterimage determination with higher accuracy.

  Hereinafter, a radiographic imaging apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a block diagram of an embodiment showing a configuration of a radiographic image capturing apparatus of the present invention. A radiographic imaging apparatus (hereinafter also referred to as an imaging apparatus) 10 shown in the figure irradiates a subject (subject) H with radiation, detects the radiation transmitted through the subject H, and generates an electrical signal corresponding to image data. Based on the converted electrical signal, a radiographic image in which the subject H is captured is generated. The imaging device 10 includes an imaging unit 12, an imaging data processing unit 14, an image processing unit 16, an output unit 18, an imaging instruction unit 20, and a control unit 22.

  The imaging unit 12 is a part that shoots the subject H by irradiating the subject H with radiation and detecting the radiation transmitted through the subject H. The imaging unit 12 outputs data (analog data) of a radiographic image obtained by imaging the subject H. Details of the photographing unit 12 will be described later.

  The imaging data processing unit 14 is a part that performs data processing such as A / D (analog / digital) conversion on the radiation image data supplied from the imaging unit 12. The radiographic image data (digital data) after data processing is output from the imaging data processing unit 14.

  The image processing unit 16 is a part that performs image processing such as offset correction, afterimage amount correction, afterimage determination, and afterimage correction on the radiographic image data after data processing supplied from the imaging data processing unit 14. The image processing unit 16 is configured by a program (software) operating on a computer, dedicated hardware, or a combination of both. The image processing unit 16 outputs the radiation image data after the image processing. Details of the image processing unit 16 will be described later.

  The output unit 18 is a part that outputs radiographic image data after image processing supplied from the image processing unit 16. The output unit 18 is, for example, a monitor that displays a radiation image on a screen, a printer that prints out a radiation image, a storage device that stores radiation image data, and the like.

  The shooting instruction unit 20 is a part that sets a shooting menu, shooting conditions, a shooting mode, and the like and instructs shooting of the subject H. As the shooting instruction unit 20, a two-push type shooting button is used as an input key for setting a shooting menu, shooting conditions, and shooting modes, and shooting instructions. When the shooting button is pressed down to the first level (half-pressed), it is ready for shooting and when it is pressed down to the second level (fully pressed), shooting starts. The shooting instruction unit 20 outputs a shooting instruction signal indicating either the state where the shooting button is not pressed or the state where the first or second stage is pressed.

  Here, in the photographing apparatus 10 of the present invention, a photographing menu is input before photographing. The imaging menu is input for each object (imaging site) to be imaged, and includes menus such as chest imaging, lumbar imaging, and knee joint imaging. The shooting menu is input for each shooting before the shooting with the shooting device 10. The input shooting menu is used for afterimage determination in an afterimage determination unit 42 described later.

  In addition to the manual imaging mode in which imaging conditions such as radiation intensity and irradiation time (irradiation amount) are manually set as imaging modes, the imaging apparatus 10 has imaging conditions such as radiation intensity and irradiation time in advance. A set first shooting mode for shooting a still image and a second shooting mode for shooting a long image or the like are provided. In the first shooting mode, the accumulation time during shooting is set longer than in the second shooting mode.

  The accumulation time is the time during which radiation is converted into charges and accumulated in the radiation detector. In the imaging apparatus 10, for example, when the subject H is captured, image data (radiation image data) is read from the radiation detector after a predetermined accumulation time. In addition, during the period from when the radiation image data is read until the afterimage data of the previous radiation image is acquired, the idle reading of the image data (afterimage data) is performed at a predetermined accumulation time interval in order to reduce the amount of afterimage Done in Further, afterimage data is read out after a predetermined accumulation time from the last idle reading before the next shooting is performed.

  The control unit 22 is a part that controls the operation of the imaging apparatus 10 in accordance with the imaging instruction signal supplied from the imaging instruction unit 20. For example, the control unit 22 controls the photographing unit 12 so that photographing is performed with a predetermined photographing menu, photographing condition, or photographing mode. Further, control is performed so that afterimage data of the previous radiation image is read from the radiation detector after a predetermined accumulation time has elapsed. In addition, the control unit 22 controls the image processing unit 16 so that captured radiographic image data is acquired and image processing is performed.

  Next, the photographing unit 12 will be described.

  The imaging unit 12 includes an irradiation control unit 24, a radiation source 26, an imaging table 28, and a radiation detection unit 30.

  The irradiation control unit 24 drives the radiation source 26 to control the irradiation amount so that the radiation with the intensity set according to the imaging mode is irradiated for the set time. Radiation emitted from the radiation source 26 passes through the subject H on the imaging table 28 and enters the radiation detection unit 30.

  The radiation detection unit 30 detects the radiation transmitted through the subject H with the FPD 32 and converts it into an electrical signal (radiation image data). The radiation detection unit 30 outputs data (analog data) of a radiation image obtained by photographing the subject H. The FPD 32 can be either a direct FPD that directly converts radiation into electric charges, or an indirect FPD that converts radiation once into light and then converts the converted light into an electrical signal.

  The direct type FPD includes a photoconductive film such as amorphous selenium, a capacitor, a TFT (Thin Film Transistor) as a switch element, and the like. For example, when radiation such as X-rays is incident, electron-hole pairs (e-h pairs) are emitted from the photoconductive film. The electron-hole pair is accumulated in the capacitor, and the electric charge accumulated in the capacitor is read out as an electric signal through the TFT.

  On the other hand, an indirect FPD is composed of a scintillator layer made of a phosphor, a photodiode, a capacitor, a TFT, and the like. For example, when radiation such as “CsI: Tl” is incident, the scintillator layer emits light (fluoresces). Light emitted by the scintillator layer is photoelectrically converted by a photodiode and accumulated in a capacitor, and the electric charge accumulated in the capacitor is read out as an electrical signal through the TFT.

  Although not shown, the radiation source 26 and the radiation detection unit 30 are reciprocated along the longitudinal direction (left and right direction in FIG. 1) of the imaging table 28 for, for example, long imaging. It is configured as possible. On the other hand, you may comprise the imaging stand 28 so that a movement is possible.

  Next, the image processing unit 16 will be described.

  As shown in FIG. 2, the image processing unit 16 includes an image acquisition unit 34, an offset correction unit 36, an afterimage amount correction unit 40, an afterimage determination unit 42, and an afterimage correction unit 44.

  The image acquisition unit 34 acquires afterimage data of the previous radiographic image read from the FPD 32 at the time of non-irradiation where radiation is not applied before the next imaging. Further, the image acquisition unit 34 acquires data of the next radiation image read from the FPD 32 after the next imaging is performed. From the image acquisition unit 34, the afterimage data of the previous radiation image or the data of the next radiation image is output.

  Here, the control unit 22 may perform control so that the afterimage data of the previous radiation image is read from the FPD 32 at the timing when the imaging button is pressed to the first stage. Thereby, the time difference between the timing at which the afterimage data is acquired and the timing at which the next shooting is actually performed can be shortened. For this reason, it is possible to perform high-accuracy afterimage correction without giving the user (operator) of the photographing apparatus 10 the uncomfortable feeling of waiting time due to shot restriction.

  The offset correction unit 36 uses the predetermined offset data to offset-correct the afterimage data of the previous radiation image supplied from the image acquisition unit 34 or the data of the next radiation image. The offset correction unit 36 outputs afterimage data after offset correction or data of the next radiation image after offset correction.

  The offset data is calculated in advance based on the afterimage data and the accumulation time of the radiation image data at the next imaging. Various methods are known for calculating the offset data, and any method may be used for the calculation.

  The afterimage amount correction unit 40 corrects the amount of decrease in the afterimage amount from the afterimage data read-out until the next shooting (the amount of attenuation of the afterimage amount over time). There is a time difference between the reading of the afterimage data and the next shooting, although it is a very short time. Since the afterimage amount decreases with time, the afterimage amount correction unit 40 uses the offset supplied from the offset correction unit 36 so that the afterimage amount becomes a value corresponding to the afterimage amount when read at the next photographing time point. Correct the afterimage data after correction. The afterimage amount correction unit 40 outputs afterimage data after the afterimage amount correction.

  The afterimage amount correction unit 40 performs afterimage amount correction by multiplying the afterimage data read from the FPD 32 by an afterimage amount correction coefficient Rf (a constant equal to or less than 1, for example, 0.9). The correction coefficient Rf is a numerical value determined for each FPD 32 and is calculated in advance. In order to improve the accuracy of afterimage correction, it is desirable that the change in the amount of afterimage is reduced as the afterimage data readout timing is brought closer to the next shooting timing.

  The calculation method of the correction coefficient Rf is, for example, as follows. That is, a predetermined amount of radiation is irradiated, a radiographic image is read from the FPD 32 at regular time intervals to acquire an afterimage amount, and a graph showing the relationship of the afterimage amount with time as shown in FIG. 3 is obtained. The curve of this graph can be expressed by, for example, a function (exp (−t / τ)). Here, t is time and τ is a time constant. Therefore, the correction coefficient Rf is calculated from this function based on the afterimage data read timing and the next shooting timing. Rf is calculated in advance before actual use, for example, in shipping inspection or calibration.

  FIG. 3 is a graph showing the relationship between the elapsed time from the previous shooting and the afterimage amount. The vertical axis of the graph represents the afterimage amount of the previous radiation image, and the horizontal axis represents the elapsed time from the previous imaging. As shown in this graph, it can be seen that the afterimage amount of the previous radiation image decreases with time.

  By performing afterimage amount correction, it is possible to prevent the afterimage amount from decreasing after image data of the previous radiation image until the next subject is imaged, thereby preventing the accuracy of afterimage correction from decreasing. Can do.

  The afterimage determination unit 42 determines whether or not to perform afterimage correction on the afterimage data after the afterimage amount correction supplied from the afterimage amount correction unit 40 based on the shooting menu.

The afterimage determination method in the afterimage determination unit 42 will be described in detail below.
First, the afterimage determination unit 42 determines the afterimage on the afterimage data after the afterimage amount correction supplied from the afterimage amount correction unit 40 according to the shooting menu when the next shooting is performed, which is input by the shooting instruction unit 20. An area to be determined is set as a specified area (determination ROI (Region Of Interest)).
In the photographing apparatus 10 of the present invention, a determination ROI for performing afterimage determination is set in advance according to the photographing menu.

For example, when taking a knee joint image of a subject and making a diagnosis based on the captured image, it is desirable to accurately display the region around the joint, but other regions not related to the diagnosis or the subject For non-existing areas, the presence of an afterimage does not affect the diagnosis. Accordingly, the afterimage determination unit 42 determines that it is not necessary to perform afterimage correction when there is an afterimage only in a region that does not affect such diagnosis.
Specifically, the determination ROI is, for example, a portion excluding both ends of the imaging region when the imaging menu of the next imaging is knee joint imaging, or the entire imaging region when the imaging menu is chest imaging. In this case, it may be set to include an important area and exclude an unimportant part.
In the present invention, by performing afterimage determination only in the determination ROI set in this way, it is possible to prevent noise from deteriorating by performing correction on an image that does not require afterimage correction. Furthermore, the processing speed is increased by omitting unnecessary afterimage correction.

Next, in the afterimage data, the total number of pixels and the number of pixels having a pixel value equal to or greater than a predetermined threshold are calculated.
The threshold value of the pixel value is appropriately set according to the shooting menu, shooting conditions, shooting mode, and the like based on whether or not the afterimage amount value is at a level that can be visually recognized.

When the number of pixels having a pixel value equal to or greater than the predetermined threshold occupies a predetermined ratio or more of the total number of pixels, the afterimage determination unit 42 needs to correct afterimages when taking the next image. Judge that there is. In the present embodiment, it is assumed that afterimage correction is performed when the number of pixels having a pixel value equal to or greater than a predetermined threshold is 1% or more of the total number of pixels.
The afterimage determination unit 42 outputs the afterimage determination result and afterimage data after the afterimage amount correction.

  Only when it is determined that there is an afterimage according to the afterimage determination result supplied from the afterimage determination unit 42, the afterimage correction unit 44 uses the data of the next radiation image after the offset correction supplied from the offset correction unit 36. The afterimage data after the afterimage amount correction is subtracted to perform afterimage correction on the next radiation image and output to the output unit 18. If it is determined that there is no afterimage, the afterimage correction is not performed and the data of the next radiation image after the offset correction is output to the output unit 18 as it is.

  Next, the operation of the photographing apparatus 10 will be described. Here, referring to the graph of FIG. 3, an operation from the previous shooting to the next shooting will be described.

  As shown in the graph of FIG. 3, the amount of afterimage is reduced after the previous imaging is performed and the radiographic image data is read from the FPD 32 until the afterimage data of the previous radiographic image is acquired. For the purpose, idle reading of image data is performed at intervals of a predetermined accumulation time.

  When shooting conditions or shooting modes are set by the user in the shooting instruction unit 20 and the shooting button is pressed down to the first level, the shooting apparatus 10 is in a shooting ready state under the control of the control unit 22. As shown in the graph of FIG. 3, after the last empty reading is performed, the afterimage data of the previous radiation image is read from the FPD 32.

  The afterimage data read from the FPD 32 is subjected to processing such as A / D conversion by the photographing data processing unit 14 and supplied to the image processing unit 16. In the image processing unit 16, afterimage data supplied from the imaging data processing unit 14 is acquired by the image acquisition unit 34, subsequently offset-corrected by the offset correction unit 36, and afterimage amount correction is performed by the afterimage amount correction unit 40. The afterimage determination unit 42 determines whether there is an afterimage in the determination ROI.

  Subsequently, when the shooting button is pressed down to the second level, the next shooting is started as shown in the graph of FIG. When imaging is started, the imaging unit 12 emits radiation with intensity set according to imaging conditions or imaging modes from the radiation source 26 for a set time. The irradiated radiation passes through the subject H on the imaging table 28 and enters the FPD 32 of the radiation detection unit 30, and the radiation transmitted through the subject H is converted into an electrical signal (radiation image data).

  Similarly, captured radiographic image data is read from the FPD 32, processed by the imaging data processing unit 14 such as A / D conversion, and supplied to the image processing unit 16. In the image processing unit 16, when the radiation image data supplied from the imaging data processing unit 14 is acquired by the image acquisition unit 34, offset correction is performed by the offset correction unit 36, and afterimage determination unit 42 determines that there is an afterimage, The afterimage correction unit 44 automatically corrects afterimages using afterimage data whose afterimage amount has been corrected. If the afterimage determination unit 42 determines that there is no afterimage, the afterimage correction unit 44 does not perform afterimage correction.

  The radiographic image data after the afterimage correction is performed as necessary is supplied to the output unit 18. In the output unit 18, for example, the radiation image supplied from the afterimage correction unit 44 is displayed on a monitor, printed out from a printer, or stored in a storage device.

  In the above-described embodiment, the after-image determination is automatically performed after the after-image amount correction in the photographing apparatus 10, but the present invention is not limited to this, and the determination setting for setting whether or not the after-image determination is performed is set. A section (not shown) can be provided, and the user can determine whether to perform afterimage determination. When setting is made so that afterimage determination is not performed, the user arbitrarily determines whether or not to perform afterimage correction regardless of the presence or absence of the afterimage.

  The afterimage correction in the photographing apparatus 10 is performed by the following steps 1 to 5.

  In the following description, Offset (x, y) is offset data for offset correction of the afterimage data of the previous radiation image. Lagdata1 (x, y) is afterimage data of the previous radiation image, and Lagdata2 (x, y) is afterimage data for performing afterimage determination and afterimage correction. The corrected image data and the afterimage amount correction coefficient Rf are as described above.

(Step 1)
First, afterimage data for performing afterimage determination is calculated by the following equation (6). That is, as shown in Expression (6), after offset correction is performed by offset correcting the afterimage data Lagdata1 (x, y) by subtracting the offset data Offset (x, y) from the afterimage data Lagdata1 (x, y). Afterimage data is obtained. Further, the afterimage data after the offset correction is multiplied by the afterimage amount correction coefficient Rf to obtain the afterimage data Lagdata2 (x, y) after the afterimage complement correction by correcting the afterimage data after the offset correction.
Lagdata2 (x, y) = Rf x (Lagdata1 (x, y)-Offset (x, y)) (6)

(Step 2)
Next, residual data Lagdata2 (x, y) in the total number of pixels N _A, and calculates the number of pixels N _c with a predetermined threshold value iTh_Lag more pixel values in the determination ROI. In iTh_Lag, a threshold value is set as to whether or not the afterimage amount is at a level that is visible. In this embodiment, iTh_Lag is set to 18 as an example.

(Step 3)
Further, based on N _A and N _c calculated in step 2, if N _c is 1% or more of N _A , it is determined that there is an afterimage and that afterimage correction is necessary.
Alternatively, when N _A is a fixed value, 1% of the value of N _A is calculated as the reference number, the long at N _c is equal to or greater than the reference number, be determined that it is necessary to residual image correction Good.

(Step 4)
If it is determined in step 3 that there is an afterimage, afterimage correction is performed on the data of the next radiographic image.
As shown in the following equation (7), the correction image data Xdata (x, y) is offset corrected by subtracting the offset correction data Offset (x, y) from the correction image data Xdata (x, y). Thus, corrected image data Data1 (x, y) after offset correction is obtained.
Data1 (x, y) = Xdata (x, y)-Offset (x, y) (7)

(Step 5)
As shown in the following equation (8), by subtracting the afterimage complement correction image data Lagdata2 (x, y) calculated in step 1 from the corrected image data Data1 (x, y) after offset correction Then, afterimage correction is performed on the corrected image data Data1 (x, y) to obtain image data Data2 (x, y) after the afterimage correction.
Data2 (x, y) = Data1 (x, y)-Lagdata2 (x, y)… (8)

Since the afterimage data has many noise components, the noise component of the image data Data2 (x, y) after the afterimage correction may partially increase by performing subtraction in the afterimage correction. Therefore, as shown in the following formula (9), it is desirable to calculate the afterimage-corrected image data Data2 ′ (x, y) by subtracting the median-processed afterimage data median (Lagdata2 (x, y)). .
Data2 '(x, y) = Data1 (x, y)-median (Lagdata2 (x, y))… (9)

  In the present invention, as described above, a determination ROI to be subjected to afterimage determination is set according to the shooting menu, and afterimage correction is performed only when it is determined that there is an afterimage in the determination ROI. Thus, afterimage correction is not performed when there is an afterimage only in an area that is not affected in the image at the time of the next shooting, that is, unnecessary afterimage correction is not necessary. For this reason, noise deterioration due to unnecessary afterimage correction can be prevented. Further, the processing can be quickly performed by not performing unnecessary afterimage correction.

  In the present invention, the afterimage amount correction is not essential, but the afterimage amount correction can improve the accuracy of the afterimage amount (correction image data), so that the afterimage correction accuracy is improved. Is also desirable. In addition, the shooting modes in which shooting conditions are set in advance are not limited to two shooting modes as in the embodiment, and any number of shooting modes may be provided as long as there are one or more shooting modes.

The present invention is basically as described above.
The radiographic imaging apparatus of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications and changes may be made without departing from the gist of the present invention. It is.

It is a block diagram of one embodiment showing composition of a radiographic imaging device of the present invention. FIG. 2 is a block diagram illustrating a configuration of an image processing unit illustrated in FIG. 1. It is a graph showing the relationship between the elapsed time from the previous photographing and the afterimage amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation imaging device 12 Imaging unit 14 Imaging data processing unit 16 Image processing unit 18 Output unit 20 Imaging instruction unit 22 Control unit 24 Irradiation control unit 26 Radiation source 28 Imaging stand 30 Radiation detection unit 32 FPD
34 Image acquisition unit 36 Offset correction unit 40 Afterimage amount correction unit 42 Afterimage determination unit 44 Afterimage correction unit

Claims (6)

A radiation image capturing apparatus that irradiates a subject with radiation from a radiation source, detects radiation transmitted through the subject with a flat panel radiation detector, and generates a radiation image in which the subject is captured,
When radiation is not irradiated before the next imaging, afterimage data of the previous radiation image read from the radiation detector is acquired, and after the next imaging is performed, the afterimage data is read from the radiation detector. An image acquisition unit for acquiring data of the next radiation image that has been issued;
A shooting menu setting unit for setting a shooting part of the subject in the next shooting;
An afterimage that determines the presence or absence of an afterimage due to the previous radiographic image at the time of imaging the next radiographic image in an area set according to the imaging region set by the imaging menu setting unit of the afterimage data A determination unit;
A radiographic imaging apparatus comprising: an afterimage correction unit that performs afterimage correction on the next radiographic image data when the afterimage determination unit determines that there is an afterimage.   The afterimage determination unit determines that the afterimage is present when pixel data having a pixel value equal to or higher than a determination threshold among pixel data corresponding to each pixel of the previous radiation image of the afterimage data exists. The radiographic image capturing apparatus according to claim 1, wherein the radiographic image capturing apparatus is determined.   The afterimage determination unit is configured such that pixel data having a pixel value equal to or greater than a determination threshold among pixel data corresponding to each pixel of the previous radiation image in the afterimage data is 1% or more of the total number of pixels. The radiographic image capturing apparatus according to claim 1, wherein the afterimage is determined to be present. Furthermore, an afterimage amount correction unit that corrects a decrease in the afterimage amount of the afterimage data from when the afterimage data is read until the next shooting is performed,
The radiographic image capturing apparatus according to claim 1, wherein the afterimage determination unit performs afterimage determination on the afterimage data corrected by the afterimage amount correction unit. Furthermore, an offset correction unit that performs offset correction of the afterimage data of the previous radiation image and the data of the next radiation image,
The afterimage correction unit performs afterimage correction of the next radiological image by subtracting the afterimage data corrected by the offset from the data of the next radiographic image subjected to the offset correction. The radiographic imaging apparatus in any one of 1-4. Furthermore, it has a determination setting unit for setting the necessity of afterimage determination in the afterimage determination unit,
The afterimage correction by the afterimage correction unit is performed without the afterimage determination by the afterimage determination unit when the afterimage determination is set to be unnecessary by the afterimage determination unit. The radiographic imaging device described in any one of 1.

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