JP5526062B2 - Radiation imaging apparatus and defective pixel position information acquisition method - Google Patents

Description

  The present invention relates to a radiographic imaging apparatus, and more particularly to a radiographic imaging apparatus having a function of imaging a subject from a plurality of different directions.

  The present invention also relates to a method for acquiring defective pixel position information applied to the radiographic imaging apparatus as described above.

  Conventionally, for example, as disclosed in Patent Document 1, a subject is irradiated with radiation from a plurality of different directions, and a transmission radiation image of the subject is captured each time. Based on a plurality of pieces of radiation image information thus obtained, A radiation CT apparatus for reconstructing a three-dimensional image or a tomographic image of a subject is known. In this radiation CT apparatus, the two-dimensional radiation detector and the radiation source arranged opposite to the radiation detector are moved so as to rotate around the subject, and each time the rotational movement position is changed, for example, a cone beam-like shape is directed toward the subject. A radiation is irradiated, and the radiation that has passed through the subject at that time is detected by a two-dimensional radiation detector, and a plurality of radiation images are taken.

  For example, as shown in Patent Document 2, a radiation tomosynthesis apparatus that reconstructs a tomographic image or a three-dimensional image of a subject without moving the radiation detector is also known. In this radiation tomosynthesis apparatus, a radiation source facing a subject placed between a fixed two-dimensional radiation detector is moved along an arcuate trajectory, and each time the movement position changes, Radiation is emitted toward the object, and the radiation transmitted through the subject at that time is detected by the two-dimensional radiation detector, and a plurality of radiation images are taken.

  Furthermore, as disclosed in Patent Document 3, for example, a mammography imaging apparatus used for breast cancer screening or the like is known as one of radiographic imaging apparatuses. Many of these mammography imaging apparatuses basically have a two-dimensional radiation detector built-in to support a breast, which is an imaging part of a subject, and an opposition to the imaging table. It comprises a compression plate that presses against the radiation plate and a radiation source that exposes the breast with radiation via the compression plate.

  In the CT apparatus, tomosynthesis apparatus, and mammography imaging apparatus described above, as shown in Patent Document 2 and Patent Document 3, as a two-dimensional radiation detector, a minute pixel unit arranged in a two-dimensional matrix. Therefore, a radiation solid detector (so-called “Flat Panel Detector”, hereinafter referred to as “FPD”) that outputs a current corresponding to the intensity of incident radiation is often applied.

  In this FPD, there may be a defective pixel in which the correspondence relationship between the incident radiation intensity and the output current is specifically different from other normal pixels. In order to cope with this problem, for example, in Patent Document 4, the position of the defective pixel of the FPD is grasped in advance, and the image signal related to the defective pixel output by the FPD at the time of radiographic image capturing is the image signal related to the peripheral pixel. A signal correction method in which the average value is replaced is proposed.

JP 2000-152927 A JP 2008-110098 A JP 2008-264519 A JP 2008-229102 A

  According to the above signal correction method, when a radiographic image is reproduced from an image signal obtained by the radiographic imaging device, it is possible to prevent defective pixels from being generated in the reproduced image. However, in the conventional radiation CT apparatus, tomosynthesis apparatus, and mammography imaging apparatus, even if the above signal correction method is applied to the obtained image signal, the defective image (signal level is still in the radiation image carried by the image signal). Specific high or low pixels) may occur. If a three-dimensional image or a tomographic image is reconstructed from the radiation image in which the defective pixel is generated, an artifact is generated, resulting in an obstacle shadow at the time of interpretation, which may adversely affect the diagnosis.

  The present invention has been made in view of the above circumstances, and as described above, in a radiographic imaging apparatus having a function of imaging a subject from a plurality of different directions, the radiographic image carried by the output image signal is defective. The object is to reliably prevent the occurrence of pixels.

  It is another object of the present invention to provide a method capable of acquiring defective pixel position information applied to such a radiographic imaging apparatus, that is, information indicating a position on a radiation detection surface where an abnormality in radiation intensity occurs. .

A first radiographic image capturing apparatus according to the present invention includes:
A photographic stand that holds the subject,
A radiation source for irradiating the subject with radiation,
A radiation detector that has a radiation detection surface that receives the radiation transmitted through the subject and outputs an image signal carrying a transmitted radiation image of the subject;
An imaging unit driving means for moving the radiation source relative to the imaging table so that an angle formed between the radiation irradiation axis and the imaging table changes;
In the radiographic imaging apparatus in which the radiation source is driven each time the angle is set to any one of a plurality of different predetermined angles,
A position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector is stored in association with each of the plurality of predetermined angles. Storage means;
When radiation is performed with the angle set to a predetermined angle and an image signal is obtained from the radiation detector, an image related to the position based on the position stored in the storage means in association with the predetermined angle Correction means for correcting a signal defect is provided.

  The “position where an abnormality in radiation intensity occurs” refers to a position where the radiation intensity is specifically lowered or increased compared to the vicinity of the position.

  In addition, the “imaging unit driving means for moving the radiation source relative to the imaging table so that the angle formed between the radiation irradiation axis and the imaging table changes” means that the imaging table is fixed. This means all means for moving the radiation source, on the contrary, means for moving the imaging table while the radiation source is fixed, and means for moving both the radiation source and the imaging table.

  When the radiation detector has a plurality of pixels arranged in a two-dimensional matrix in a plane parallel to the radiation detection surface as in the FPD described above, the intensity of radiation is used as the storage means. What stored the position where the abnormality occurs as the position of the pixel can be suitably used.

In a preferred aspect of the present invention, the imaging table, radiation source, radiation detector and imaging unit driving means constitute a CT apparatus,
The imaging unit driving means is configured to rotate a radiation source and a radiation detector arranged opposite to the radiation source around the imaging table.

In another preferred embodiment of the present invention, the imaging table, the radiation source, the radiation detector, and the imaging unit driving means constitute a tomosynthesis device,
The imaging unit driving means is configured to move an opposing radiation source with an imaging table placed between the fixed radiation detector.

In another preferred embodiment of the present invention, the imaging table, the radiation source, the radiation detector, and the imaging unit driving means constitute a mammography imaging apparatus.
The imaging unit driving means is configured to move a radiation source facing the radiation detector with a compression plate interposed therebetween.

Furthermore, the second radiographic image capturing apparatus according to the present invention provides:
A photographic stand that holds the subject,
A radiation source for irradiating the subject with radiation,
A radiation detector that has a radiation detection surface that receives the radiation transmitted through the subject and outputs an image signal carrying a transmitted radiation image of the subject;
An imaging unit driving means for moving the radiation source relative to the imaging table so that the relative position in a direction perpendicular to or parallel to the radiation irradiation axis changes;
In the radiographic imaging device in which the radiation source is driven each time the relative position is set to any one of a plurality of different predetermined positions,
A position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector is stored in association with each of the plurality of predetermined positions. Storage means;
When irradiation is performed with the relative position as a predetermined position and an image signal is obtained from a radiation detector, the relative position is determined based on the relative position stored in the storage means in association with the predetermined position. Correction means for correcting a defect of the image signal related to the position is provided.

  Also in the second radiographic image capturing apparatus according to the present invention, the “position where the abnormality in the radiation intensity occurs” means that the radiation intensity is specifically lowered or increased compared to the vicinity of the position. It indicates the position that is.

  Also in the second radiographic imaging apparatus according to the present invention, the above-mentioned “the radiation source is moved relative to the imaging table so that the relative position in the direction perpendicular to or parallel to the radiation irradiation axis changes. “Imaging unit driving means” means means for moving the radiation source with the imaging table fixed, and means for moving the imaging table with the radiation source fixed, and moving both the radiation source and the imaging table. It refers to all of the means for making it happen.

  Also in the second radiographic imaging apparatus according to the present invention, the radiation detector has a plurality of pixels arranged in a two-dimensional matrix in a plane parallel to the radiation detection surface as in the FPD described above. In the case of a device, a device that stores a position where an abnormality in radiation intensity occurs as the position of the pixel can be suitably used as the storage unit.

On the other hand, the first defective pixel position information acquisition method according to the present invention includes:
In the first radiographic imaging device according to the present invention described above, a pixel position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between a radiation source and a radiation detector is obtained. A method for obtaining defective pixel position information to be obtained,
Placing the member between a radiation source and a radiation detector;
The radiation source is moved relative to the imaging table so that the angle formed by the radiation irradiation axis and the imaging table changes,
Each time the angle changes, a radiation source is driven to take a transmission radiation image of the member,
Among the plurality of radiographic images obtained by this imaging, when the pixel position that shows the same part of the member and the abnormality of the radiation intensity occurs is changed according to the change in the angle, Each pixel position is acquired in association with the angle when an image indicating the pixel position is captured.

  Note that “the radiation source is moved relative to the imaging table so that the angle between the radiation irradiation axis and the imaging table changes” means that the radiation source is moved while the imaging table is fixed. On the other hand, it means that the radiation source is fixed and the imaging table is moved, and that both the radiation source and the imaging table are moved.

In addition, the second defective pixel position information acquisition method according to the present invention includes:
In the second radiographic imaging apparatus according to the present invention described above, a pixel position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector is determined. A method for obtaining defective pixel position information to be obtained,
Placing the member between the radiation source and a radiation detector;
The radiation source is moved relative to the imaging table so that the relative position in a direction perpendicular to or parallel to the radiation irradiation axis changes.
Each time the relative position changes, a radiation source is driven to take a transmission radiation image of the member,
Among the plurality of radiographic images obtained by this imaging, when the pixel position that shows the same part of the member and the abnormality of the radiation intensity has occurred is changed according to the change in the relative position, Each of the pixel positions is acquired in association with the relative position when an image indicating the pixel position is captured.

  In this case as well, “to move the radiation source relative to the imaging table so that the relative position in the direction perpendicular to or parallel to the radiation irradiation axis changes” means that the imaging table is fixed. This means that the radiation source is moved, the radiation source is fixed and the imaging table is moved, and both the radiation source and the imaging table are moved.

  According to the research of the present inventor, even if the signal correction method shown in Patent Document 4 is applied to the obtained image signal in the conventional radiation CT apparatus, radiation tomosynthesis apparatus, and mammography imaging apparatus, the image signal is supported. It has been found that defective pixels are still generated in the image for the following reasons.

  In a radiographic imaging apparatus, a member such as an imaging stand exists between a radiation source and a radiation detector, and foreign matter that absorbs radiation may be mixed in such a member. Specifically, foreign objects in the imaging table (bubbles in the coating film on the bed, bubbles in the radiation shielding plate, metal pieces, defects, etc.), and the compression plate of the mammography device (this compression plate is also in a broad sense) And foreign matter in the scattered radiation removal grid, which constitute a part of the imaging stand). If such a foreign substance is present, the intensity of the radiation that reaches the radiation detection surface of the radiation detector through the presence of the foreign substance is specifically lowered or increased, thereby causing defective pixels. And, the position where the radiation passing through such a foreign substance reaches the radiation detection surface changes as the radiation source or the imaging table moves so that the angle formed by the radiation irradiation axis and the imaging table changes, Even if the signal correction method shown in Patent Document 4 described above is applied, correct correction cannot be performed.

  As described above, the position where the radiation that has passed through the foreign object reaches the radiation detection surface is the same as the movement of the radiation source or imaging table so that the relative position in the direction perpendicular or parallel to the radiation irradiation axis changes. This causes the same problem as described above.

  Based on the above knowledge, the first radiographic imaging device according to the present invention causes an abnormality in radiation intensity on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector. Storage means that stores the position in association with each of a plurality of predetermined angles (angles formed between the radiation irradiation axis and the imaging table), and radiation irradiation is performed with the above-mentioned angle as a predetermined angle, and an image signal is output from the radiation detector. Is obtained, based on the position stored in the storage means in association with the predetermined angle, the correction means for correcting the defect of the image signal related to the position is provided. Therefore, according to this radiographic imaging device, even if the position where the radiation that has passed through the foreign object reaches the radiation detection surface changes as the radiation source or the imaging table moves, It is possible to reliably prevent the occurrence of defective pixels in the radiographic image carried by the image signal.

On the other hand, according to the first defective pixel position information acquisition method of the present invention,
Placing the member between a radiation source and a radiation detector;
The radiation source is moved relative to the imaging table so that the angle formed by the radiation irradiation axis and the imaging table changes,
Each time the angle changes, a radiation source is driven to take a transmission radiation image of the member,
Among the plurality of radiographic images obtained by this imaging, when the pixel position that shows the same part of the member and the abnormality of the radiation intensity occurs is changed according to the change in the angle, Since each pixel position is acquired in association with the angle when the image indicating the pixel position is captured,
In the first radiographic imaging apparatus according to the present invention described above, the pixel position where the abnormality of the radiation intensity occurs on the radiation detection surface due to the defect of the member existing between the radiation source and the radiation detector is accurately determined. Can be acquired.

  Further, the second radiographic imaging device according to the present invention has a radiation intensity abnormality on the radiation detection surface due to a defect of a member existing between the radiation source and the radiation detector based on the above knowledge. Storage means for storing the generated position in association with each of a plurality of predetermined relative positions (relative positions of the radiation source and the imaging table in a direction perpendicular to or parallel to the radiation irradiation axis), and the relative position as the predetermined position When a position is irradiated with radiation and an image signal is obtained from the radiation detector, a correction for correcting a defect in the image signal related to the position based on the position stored in the storage means in association with the predetermined position Means. Therefore, according to this radiographic imaging device, even if the position where the radiation that has passed through the foreign object reaches the radiation detection surface changes as the radiation source or the imaging table moves, It is possible to reliably prevent the occurrence of defective pixels in the radiographic image carried by the image signal.

On the other hand, according to the second defective pixel position information acquisition method of the present invention,
Placing the member between a radiation source and a radiation detector;
Moving the radiation source relative to the imaging table so that the relative position in a direction perpendicular to or parallel to the radiation irradiation axis changes,
Each time the relative position changes, a radiation source is driven to take a transmission radiation image of the member,
Among the plurality of radiographic images obtained by this imaging, when the pixel position that shows the same part of the member and the abnormality of the radiation intensity has occurred is changed according to the change in the relative position, Since each of the pixel positions is acquired in association with the relative position when the image indicating the pixel position is captured,
In the second radiographic imaging apparatus according to the present invention described above, the pixel position where the abnormality of the radiation intensity occurs on the radiation detection surface due to the defect of the member existing between the radiation source and the radiation detector is accurately determined. Can be acquired.

The schematic side view which shows CT apparatus provided with the radiographic imaging apparatus by one Embodiment of this invention The block diagram which shows the structure in connection with the signal processing of the said CT apparatus A diagram for explaining the cause of defective pixels The figure explaining the acquisition method of a defective pixel correction table Schematic front view showing a tomosynthesis apparatus to which the radiographic imaging apparatus of the present invention can be applied. The schematic front view which shows another example of the tomosynthesis apparatus with which the radiographic imaging apparatus of this invention can be applied. The schematic front view which shows an example of the mammography imaging device with which this invention can be applied A diagram for explaining another cause of defective pixels The figure explaining another cause which a defective pixel generate | occur | produces

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of a radiation CT apparatus to which a radiographic imaging apparatus according to an embodiment of the present invention is applied. The radiation CT apparatus 1 includes a radiographic image capturing apparatus 3 including an image capturing unit 2 and the like, a computer 30 connected to the image capturing unit 2 and performing processing of an image obtained by controlling the image capturing apparatus and performing image capturing, The image display means 31 is connected to the computer 30.

  The radiographic imaging device 3 includes a radiation source 10 that emits conical (cone beam-like) radiation R, a radiation detector 11 that detects radiation R emitted from the radiation source 10 and transmitted through a subject P, and the radiation source 10. An imaging unit 2 including a C-arm 12 that holds the radiation detector 11, an imaging unit driving unit 15 that rotates the imaging unit 2, an arm 20 that holds the imaging unit driving unit 15, and an imaging that supports the subject P And a table 22. In addition to the above-described radiation source 10, a radiation source 10 that emits fan-shaped (fan beam-shaped) or linear (pencil beam-shaped) radiation may be used.

  The photographing unit 2 can rotate 360 ° around the rotation axis C. Moreover, the arm 20 provided with the movable part 20a is hold | maintained at the base 21 movably attached with respect to the ceiling. Note that the imaging unit 2 may be rotatable in an angle range other than 360 °, such as 180 °.

  The radiation source 10 and the radiation detector 11 are disposed to face each other with a predetermined distance therebetween with the rotation axis C interposed therebetween. The radiation detector 11 is made of FPD as an example, and pixels that are the minimum unit for detecting the radiation R are arranged in a two-dimensional matrix in a plane parallel to the radiation detection surface 11a. This type of FPD is also described in detail in Patent Document 2 described above.

  The computer 30 includes a central processing unit (CPU) (not shown), a storage device such as an HDD and an SSD, and operation input means such as a mouse and a keyboard. The CPU performs a function of image reconstruction on a plurality of image signals obtained by continuous imaging to obtain a three-dimensional radiation CT image or tomographic image of the subject P, and the operation of the radiation source 10. It has functions for performing control, control of the detection operation of the radiation detector 11 and image signal reading operation, and rotational movement control of the imaging unit 2 by the imaging unit driving means 15.

  Hereinafter, the basic operation of the radiation CT apparatus 1 will be described. First, the subject P is laid on the imaging table 22, and the radiation source 10 and the radiation detector 11 are arranged at symmetrical positions with the rotational axis C being the approximate center of the subject P's body. Then, the photographing unit 2 is positioned. The photographing unit 2 is moved based on the operation of the computer 30 by the photographer.

  When photographing is started, the photographing unit 2 is rotated around the rotation axis C. Thus, the radiation source 10 is driven each time the imaging unit 2 is rotated and the angle formed by the radiation irradiation axis O of the radiation source 10 and the imaging table 22 (that is, the radiation irradiation direction with respect to the subject P) becomes a predetermined angle. The Thus, the radiation R emitted from the radiation source 10 and transmitted through the subject P enters the radiation detector 11. The radiation detector 11 outputs an image signal indicating the intensity of incident radiation in units of the pixels described above, that is, carrying a transmitted radiation image of the subject P.

  As described above, image signals indicating a plurality of radiographic images obtained by photographing the subject P from different directions are acquired. These image signals are input to the computer 30, and after being subjected to first and second corrections described later, they are stored in the storage device.

  When the continuous imaging is completed, the CPU of the computer 30 performs an image reconstruction operation from the image signal stored in the storage device, generates a three-dimensional radiation CT image or a tomographic image, and displays these images as image display means. 31 is displayed.

  Next, the point of preventing the occurrence of defective pixels in the radiation image carried by the image signal will be described. First, the cause of such defective pixels will be described with reference to FIG. In FIG. 3, the same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted unless necessary (the same applies hereinafter).

  FIG. 3A illustrates how the level of the image signal obtained from the radiation detector 11 changes when the radiation detector 11 has a defective pixel Fd. Here, if the defective pixel Fd is a defective pixel due to, for example, a foreign substance that greatly absorbs radiation attached to the detector surface, the level of the image signal relating to that pixel is specifically lowered. Since the position of the defective pixel Fd in the radiation detector 11 is not changed, the signal level drop due to the defective pixel Fd shown in FIG. 1A similarly occurs in the cases of FIGS. .

  The defective pixel Fd of the radiation detector 11 may be generated by an abnormality of an X-ray conversion film such as a scintillator or a photoconductor or a photodiode, or a flaw on the detector surface. Then, the level of the image signal from the defective pixel Fd increases specifically or decreases on the contrary depending on the cause of the defect, but shows an abnormal value anyway, so that the defective pixel is based on the level of the signal. Fd can be identified.

  On the other hand, as shown in FIG. 2B, a case where a defect Fe that greatly absorbs radiation exists in a member located between the radiation source 10 and the radiation detector 11, here, for example, the imaging table 22 is considered. . In that case, the incident radiation intensity specifically decreases at a position on the radiation detector 11 where the radiation transmitted through the defect Fe enters. Therefore, the level of the image signal related to the pixel at that position is specifically lowered.

  Next, a state in which the radiation source 10 and the radiation detector 11 are rotationally moved as described above from the state shown in (2) of FIG. 3 is shown in FIG. When the angle formed between the radiation irradiation axis O and the imaging table 22 changes in this way, the position on the radiation detector 11 at which the radiation transmitted through the defect Fe on the imaging table 22 is incident is changed. The pixel position where the signal level decreases also changes.

  The defect Fe as described above is not limited to a foreign matter or the like that greatly absorbs radiation, and conversely, there can be one that transmits more radiation than usual. Specific examples of such a defect Fe include, for example, those composed of bubbles left on the imaging table 22. When such a defect Fe exists, the incident radiation intensity specifically increases at a position on the radiation detector 11 where the radiation transmitted through the defect Fe enters. Therefore, the level of the image signal related to the pixel at that position is specifically increased.

  Next, FIG. 2 shows a configuration related to signal processing of the radiation CT apparatus 1. In FIG. 2, each element shown as “XX section” in the computer 30 does not exist individually as hardware, but simply shows a configuration for executing each process based on software. Of course, each of the above elements may be constituted by individual hardware. In addition, as an example here, an imaging operation is performed every time the rotation angle of the imaging unit 2, that is, the rotation angle of the radiation source 10 changes by 1 °, and therefore a total of 360 radiation images are acquired in a series of imaging. To do.

  At the time of capturing a series of radiation images, the output of the radiation detector 11 is first input to the pre-processing unit 40, where it is subjected to processing such as amplification and A / D conversion to obtain an image signal of a predetermined standard. Is then input to the write / read unit 41. Each time an image signal for one radiation image is input, the writing / reading unit 41 temporarily stores it in the memory 42, adjusts the timing for correction processing to be described later, and reads the image signal from the memory 42. Is read as needed, and is input to the first correction unit 43.

  The first correction unit 43 refers to the table T1 stored in the internal memory of the computer 30, obtains the position of the defective pixel Fd existing in the radiation detector 11, and corrects the image signal related to the defective pixel Fd. . Note that since there are naturally one defective pixel in the radiation detector 11, only one table T1 is used. FIG. 4 (2) schematically shows such a table T1. Each square in the figure represents a pixel in the radiation detector 11, and a square filled in with black represents a defective pixel (defective pixel Fd shown in FIG. 3). That is, in this example, if the origin of the pixel matrix is the upper left corner, the pixel in the fifth row and the third column is a defective pixel.

  Specifically, the correction is performed by replacing the signal relating to the defective pixel with the average value or the median value of the signals relating to a predetermined number (a plurality of) pixels around the defective pixel. This correction is performed in common for the image signals carrying 360 radiation images. When another defective pixel exists in the predetermined number of pixels, it is desirable to obtain the average value, the median value, etc. after excluding the image signal relating to the other defective pixel. However, the correction of defective pixels is not limited to them, and may be performed by other methods.

The image signal subjected to the correction is then sent to the second correction unit 44. Second corrector 44 first selects one of the tables T2 ₁ to T2 ₃₆₀ and is for example 360 stored in the internal memory of the computer 30. Hereinafter, this selection will be described.

In this example, the first imaging is performed in a state where the radiation irradiation axis O is the first predetermined angle (for example, 90 °) with respect to the imaging table 22, and then the rotational position of the radiation source 10 is changed by 1 °. A total of 360 shots are taken every second, third,. Each of the ₃₆₀ tables T2 _{1 to} T2 ₃₆₀ is stored in association with the imaging order, that is, in association with the angle of the radiation irradiation axis O with respect to the imaging table 22.

(3) in FIG. 4 schematically shows such tables T2 _{1 to} T2 ₃₆₀ . Each square in the figure represents a pixel in the radiation detector 11, and the hatched square is incident radiation due to the defect Fe of the imaging table 22 shown in FIG. A pixel at a position where the intensity is specifically lowered or increased is shown. That the table T2 ₁ of this example, when the origin of the pixel matrix at the upper left corner, or the incident radiation intensity in the third row and third column of pixels and the second row 6 column of pixels is specifically low, Or higher. The second correction unit 44 selects the table T2 _n stored in association with the imaging order n, assuming that the image signal to be corrected relates to the nth radiographic image.

The second correction unit 44 refers to the selected table T2 _n , obtains the position of the pixel whose incident radiation intensity is specifically reduced or increased, and corrects the image signal related to the pixel. This correction is basically performed in the same manner as the correction performed by the first correction unit 43.

  The image signal that has undergone correction by the second correction unit 44 is then sent to the reconstruction processing unit 45, where it is temporarily stored in the storage device and then undergoes reconstruction processing. Since the image signal subjected to the reconstruction process in this way is corrected by the first correction unit 43 and the second correction unit 44 as described above, in the radiographic image carried by this image signal, the radiation detector 11 It is possible to prevent a defective pixel from being generated due to the defective pixel Fd or the defect Fe of the imaging table 22. According to the present invention, it is possible to surely prevent the occurrence of defective pixels due to the defect Fe of the imaging table 22, which could not be prevented by the prior art.

Next, the creation of the table T1 and the tables T2 _{1 to} T2 ₃₆₀ described above will be described with reference to FIGS. When these tables are created, so-called solid irradiation is performed in which the subject P is not placed on the imaging table 22 and the radiation R having a uniform intensity is emitted from the radiation source 10 toward the radiation detector 11. . This solid irradiation is also performed, for example, 360 times each time the rotational positions of the radiation source 10 and the radiation detector 11 are changed by 1 °. At this time, the output signal generated by the radiation detector 11 in FIG. 2 is stored in the memory 42 through the preprocessing unit 40 and the writing / reading unit 41 as in the case of the subject image photographing described above. Note that the pre-processing unit 40 may perform offset correction, gain and / or shading correction for moving the entire signal level on the output signal.

The table creation unit 46 performs threshold processing on an image signal carrying one radiation image, thereby extracting a pixel whose signal level is specifically high or low. The table creation unit 46 performs this process on all image signals carrying 360 radiation images. (1) in FIG. 4, the pixels extracted in this way, the photographing order is indicative for the first image D1,2 th image D2, · · · 360-th image D _360. Note that the squares in this figure mean the same as those described above for (2) and (3) in FIG. Further, the extracted pixels are both the pixels painted black in FIG. 4A and the pixels with diagonal lines.

Here, the positions of the pixels filled in black do not change even if the imaging order changes, that is, the angle formed between the radiation irradiation axis O and the imaging table 22 changes. On the other hand, the positions of the hatched pixels change as the shooting order changes. According to FIG. 3 described above, it is considered that the signal level relating to the former pixel is specifically increased or decreased due to the defective pixel Fd of the radiation detector 11. On the other hand, it is considered that the signal level related to the latter pixel is specifically increased or decreased due to the defect Fe of the imaging table 22. Therefore, the table creation unit 46 creates the table T1 of FIG. 2B based on the former pixel positions, and creates the tables T2 _{1 to} T2 ₃₆₀ of FIG. 3C based on the latter pixel positions. .

The table T1 and the tables T2 _{1 to} T2 ₃₆₀ created in this way are for obtaining the position of the pixel to be corrected in the correction performed by the first correction unit 43 and the correction performed by the second correction unit 44, as described above. Used.

  When only the table T1 is created, the radiation detector 11 is operated so as to perform so-called empty reading without solid radiation irradiation, and the table T1 is obtained from the output signal of the radiation detector 11 at that time. It is also possible.

Further, when the table T1 and the tables T2 _{1 to} T2 ₃₆₀ are created by performing solid radiation irradiation, every time the angle formed between the radiation irradiation axis O and the imaging table 22 is changed, at least solid irradiation with different radiation doses is performed. The linearity (relationship between the radiation detector output signal level and the radiation dose) between the plurality of images obtained in this manner is obtained for each pixel, and based on the magnitude relationship between it and a predetermined threshold, FIG. It is also possible to obtain the extracted pixels shown in (1). Furthermore, instead of performing the solid irradiation at least twice, the idle reading is performed at least twice by changing the gain, for example, and thereafter the extraction pixel shown in (1) of FIG. It is also possible to ask for it.

Further, when the table T1 and the tables T2 _{1 to} T2 ₃₆₀ are created in the same manner by performing solid radiation irradiation, every time the angle formed between the radiation irradiation axis O and the imaging table 22 is changed, the solid irradiation time is changed mutually. Irradiation is performed at least twice, and the linearity (relationship between the output signal level of the radiation detector and the radiation irradiation time) between the plurality of images obtained in this way is obtained for each pixel, and based on the magnitude relationship between it and a predetermined threshold It is also possible to obtain the extracted pixel shown in (1) of FIG.

  Although the defective pixels described above frequently appear, it is not preferable to reconstruct a three-dimensional image or a tomographic image in order to keep the image interpretation performance of these images high. Therefore, when the total number of extracted pixels shown in (1) of FIG. 4 exceeds a predetermined threshold, when the continuous length of those extracted pixels exceeds a predetermined threshold, and further, It is desirable to generate a warning when the group area (congestion degree) exceeds a predetermined threshold value so that necessary actions can be taken. Necessary measures include performing calibration for creating a new correction table, and requesting maintenance / repair of the radiographic imaging apparatus.

  According to the defective pixel position information acquisition method of the present invention, it can be determined whether the generation of the defective pixel in the radiation image is caused by the defective pixel Fd of the radiation detector 11 or the defective Fe of the imaging table 22. It is possible to immediately determine which treatment should be performed as a necessary treatment, and thus it can be prevented that it takes a long time to determine this treatment.

  Although the radiographic imaging apparatus applied to the radiographic CT apparatus has been described above, the radiographic imaging apparatus of the present invention can also be applied to configure the above-described radiographic tomosynthesis apparatus. FIG. 5 shows an example of such a radiation tomosynthesis apparatus. In this apparatus, the radiation source 10 is moved along an arcuate trajectory M centered on a point Q set in the subject P on the imaging table 22, and every time the movement position changes, that is, the radiation irradiation axis. A radiographic image is captured every time the angle formed by O and the imaging table 22 changes. Based on the plurality of radiographic images thus obtained, a three-dimensional image or tomographic image of the subject P can be reconstructed.

  FIG. 6 shows another example of the radiation tomosynthesis apparatus. In this apparatus, for example, the radiation source 10 held in an overhead traveling system (not shown) moves in a direction parallel to the imaging table 22, that is, along a linear locus N. Each time the movement position changes, the angle of the radiation source 10, that is, the angle formed between the radiation irradiation axis O and the imaging table 22 is changed, and a radiographic image is taken each time. In this case as well, a three-dimensional image or a tomographic image of the subject P can be reconstructed based on a plurality of radiographic images obtained by imaging.

  In such a radiation tomosynthesis apparatus, if the same correction processing as that performed in the radiation CT apparatus 1 of FIG. 1 is performed on the image signals each carrying a plurality of images taken as described above, The effect obtained in the radiation CT apparatus 1 can be similarly obtained.

  Next, an example of a mammography apparatus to which the present invention can be applied will be described with reference to FIG. In this apparatus, the radiation detector 11 as described above is arranged inside the imaging table 22, the breast Pm as a subject is arranged on the imaging table 22, and the breast Pm is formed thereon by the compression plate 50. It is pressed. While maintaining this state, the radiation source 10 is moved in the direction parallel to the imaging table 22 in the same manner as in the apparatus of FIG. The angle formed by O and the imaging table 22 is changed, and a radiographic image is captured each time.

  The compression plate 50 constitutes a part of the photographing stand in a broad sense, but foreign matter, bubbles, scratches, etc. may exist inside or on the surface. When such foreign matter, bubbles, scratches, etc. exist, the radiation that reaches the radiation detection surface (upper surface in the drawing) of the radiation detector 11 has a specific intensity lower or an increase. As a result, defective pixels are generated. The radiation source 10 moves at the position where the radiation that has passed through such a foreign substance reaches the radiation detection surface of the radiation detector 11 and the angle formed by the radiation irradiation axis O and the compression plate 50 changes. It changes with it.

  Even in such a mammography imaging apparatus, if the same correction processing as that performed in the radiation CT apparatus 1 of FIG. 1 is performed on the image signals each carrying a plurality of images captured as described above, The effect obtained in the radiation CT apparatus 1 can be similarly obtained.

  In the mammography apparatus shown in FIG. 7, the angle formed by the radiation irradiation axis O and the radiation detection surface of the radiation detector 11 changes every time a plurality of radiographic images are captured. It may be made constant through radiographic imaging. Even in such a case, the angle formed between the compression plate 50 and the radiation irradiation axis O in which foreign matter, bubbles, scratches, etc. may exist changes every time photographing is performed, so that a problem may occur that defective pixels are generated by changing the position. By applying the present invention, it is possible to prevent such defective pixels from occurring.

  As described above, the radiation detector 11 is disclosed in Patent Document 2, that is, a recording layer that receives an irradiation of radiation carrying image information and records the image as an electrostatic latent image, The recording layer is not limited to a scanning unit that scans the recording layer with reading light and generates a charge corresponding to the electrostatic latent image, and other known ones can be used as appropriate. For example, in JP 2009-212377, radiation carrying image information is converted into visible light by a scintillator, and the visible light is guided to a CCD or CMOS image sensor by a fiber plate, where the visible light is photoelectrically converted. An image sensor that obtains an image signal indicating a radiation image has been disclosed, but in the present invention, such an image sensor can be applied as a radiation detector. As a scintillator, it is preferable to use what was comprised by columnar crystals, such as CsI, as described in Unexamined-Japanese-Patent No. 2011-17683, for example. By using such a scintillator, a radiographic image with higher sharpness can be obtained, and the effect is particularly remarkable when a plurality of radiographic images are taken continuously.

  The embodiment has been described above in which the radiation source 10 is configured to move so that the angle between the radiation irradiation axis O and the imaging table 22 changes with respect to the fixed imaging table 22. In addition, the angle can be changed by moving the imaging table 22 with respect to the fixed radiation source 10. Furthermore, both the radiation source 10 and the imaging table 22 can be moved to change the angle. The present invention can also be applied to those cases, and when applied, the same effects as described above can be obtained.

  Furthermore, the present invention is also applicable to the case where either or both of the radiation source 10 and the imaging table 22 move so as to change the relative position in a direction perpendicular to or parallel to the radiation irradiation axis O. Hereinafter, these cases will be described with reference to FIGS. 8 and 9.

  FIG. 8 shows that the level of the image signal changes specifically due to the defective pixel Fe of the imaging table 22, as in FIG. 3 described above, and (1) and (2) are These are the same as those in FIG. After radiographic imaging is performed in the state shown in (2) of FIG. 8, when radiographic imaging is performed in the state of (3) in FIG. 8 in which the imaging table 22 is moved in a direction perpendicular to the radiation irradiation axis O, The positions where the incident radiation intensity specifically decreases on the radiation detector 11 during the two imaging operations are different from each other as illustrated. That is, if the relative position between the radiation source 10 and the imaging table 22 in the direction perpendicular to the radiation irradiation axis O changes, the pixel position at which the level of the image signal decreases due to the defect Fe in the captured radiographic image. Will be different.

Therefore, in this case, if the radiation image with the relative position changed is made 10 times, for example, a table (in the above embodiment) showing the pixel position where the level of the image signal specifically decreases or increases for each imaging. corresponds to the table T2 _n) is created 10, using those tables, for example, above the same correction processing in the second corrector 44 of FIG. 2 are performed. This reliably prevents defective pixels from being generated in the radiation image due to the defect Fe on the imaging table 22.

  The table can be created in the same manner as described above. That is, when creating this table, so-called solid irradiation is performed in which the subject P is not placed on the imaging table 22 and the radiation R is irradiated from the radiation source 10 toward the radiation detector 11. . In this solid irradiation, the relative positions of the radiation source 10 and the imaging table 22 along the direction perpendicular to the radiation irradiation axis O are changed to 10 types (the same as the relative positions set at the time of radiographic image capturing). Done. At this time, the output signal emitted from the radiation detector 11 is stored in the memory 42 through, for example, the preprocessing unit 40 and the writing / reading unit 41 in FIG. Based on this, 10 different tables are created.

  In the above description, the case where the imaging table 22 moves in a direction perpendicular to the radiation irradiation axis O with respect to the fixed radiation source 10 has been described. On the contrary, with respect to the fixed imaging table 22 By moving the radiation source 10, it is also possible to change the relative position in the direction perpendicular to the radiation irradiation axis O of both. Furthermore, both the radiation source 10 and the imaging table 22 can be moved to change the relative position. The present invention can also be applied to those cases, and when applied, the same effects as described above can be obtained.

  Next, the case where the relative position of the radiation source 10 and the imaging table 22 in the direction parallel to the radiation irradiation axis O can be changed will be described. FIG. 9 shows that the level of the image signal changes specifically due to the defective pixel Fe of the imaging table 22, as in FIG. 3 described above, and (1) and (2) are shown in FIG. Are the same as After radiographic imaging is performed in the state shown in (2) of FIG. 9, when radiographic imaging is performed in the state of (3) in FIG. 9 in which the imaging table 22 is moved in a direction parallel to the radiation irradiation axis O, The positions where the incident radiation intensity specifically decreases on the radiation detector 11 during the two imaging operations are different from each other as illustrated. That is, if the relative position between the radiation source 10 and the imaging table 22 in the direction parallel to the radiation irradiation axis O changes, the pixel position at which the level of the image signal decreases due to the defect Fe in the captured radiographic image. Will be different. Furthermore, in this case, the pixel range in which the level of the image signal decreases is also different. That is, the closer the relative position between the radiation source 10 and the imaging table 22 is, the wider the pixel range in which the level of the image signal decreases.

Therefore, in this case, if the radiographic image with the relative position changed is made 10 times, for example, 10 tables indicating pixel positions at which the level of the image signal specifically decreases or increases for each imaging are created. For example, the second correction unit 44 in FIG. 2 performs the same correction process as described above using these tables. This reliably prevents defective pixels from being generated in the radiation image due to the defect Fe on the imaging table 22. The table basically corresponds to the table T2 _n in the embodiment. In this case, the level of the image signal is indicated by indicating all the pixel positions where the level of the image signal changes specifically. A decreasing pixel range will also be shown.

  The table can be created in the same manner as described above. That is, when creating this table, so-called solid irradiation is performed in which the subject P is not placed on the imaging table 22 and the radiation R is irradiated from the radiation source 10 toward the radiation detector 11. . In this solid irradiation, the relative positions of the radiation source 10 and the imaging table 22 along the direction parallel to the radiation irradiation axis O are changed to 10 types (the same as the relative positions set at the time of radiographic image capturing). Done. At this time, the output signal emitted from the radiation detector 11 is stored in the memory 42 through, for example, the preprocessing unit 40 and the writing / reading unit 41 in FIG. Based on this, 10 different tables are created.

  In the above description, the case where the imaging table 22 moves in a direction parallel to the radiation irradiation axis O with respect to the fixed radiation source 10 has been described, but on the contrary, with respect to the fixed imaging table 22. By moving the radiation source 10, it is also possible to change the relative position in the direction perpendicular to the radiation irradiation axis O of both. Furthermore, both the radiation source 10 and the imaging table 22 can be moved to change the relative position. The present invention can also be applied to those cases, and when applied, the same effects as described above can be obtained.

DESCRIPTION OF SYMBOLS 1 Radiation CT apparatus 2 Imaging part 3 Radiographic imaging apparatus 10 Radiation source 11 Radiation detector 11a Detection surface of a radiation detector 12 C arm 15 Imaging part drive means 22 Imaging stand 30 Computer 31 Image display means 43 1st correction | amendment part 44 1st 2 correction unit 45 reconstruction processing unit 46 table creation unit O radiation irradiation axis R radiation T1, T2 ₁ , T2 ₂ , T2 ₃₆₀ table

Claims (9)

A photographic stand that holds the subject,
A radiation source for irradiating the subject with radiation,
A radiation detector that has a radiation detection surface that receives the radiation transmitted through the subject and outputs an image signal carrying a transmitted radiation image of the subject;
An imaging unit driving means for moving the radiation source relative to the imaging table so that an angle formed between the radiation irradiation axis and the imaging table changes;
In the radiographic imaging apparatus in which the radiation source is driven each time the angle is set to any one of a plurality of different predetermined angles,
A position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector is stored in association with each of the plurality of predetermined angles. Storage means;
When radiation is performed with the angle set to a predetermined angle and an image signal is obtained from the radiation detector, an image related to the position based on the position stored in the storage means in association with the predetermined angle A radiographic imaging apparatus, comprising: correction means for correcting a signal defect. The radiation detector has a plurality of pixels arranged in a two-dimensional matrix in a plane parallel to the radiation detection surface;
The radiographic image capturing apparatus according to claim 1, wherein the storage unit stores a position where the abnormality of the radiation intensity occurs as the position of the pixel. The imaging table, radiation source, radiation detector and imaging unit driving means constitute a CT apparatus,
The radiographic image capturing apparatus according to claim 1, wherein the imaging unit driving unit rotates a radiation source and a radiation detector arranged to face the radiation source around the imaging table. The imaging table, radiation source, radiation detector and imaging unit driving means constitute a tomosynthesis device,
3. The radiographic imaging according to claim 1, wherein the imaging unit driving unit is configured to move the opposing radiation source with the imaging table placed between the fixed radiation detector. 4. apparatus. The imaging table, radiation source, radiation detector and imaging unit driving means constitute a mammography imaging apparatus,
The radiographic image capturing apparatus according to claim 1, wherein the imaging unit driving unit moves a radiation source facing the radiation detector with a compression plate interposed therebetween. A photographic stand that holds the subject,
A radiation source for irradiating the subject with radiation,
A radiation detector that has a radiation detection surface that receives the radiation transmitted through the subject and outputs an image signal carrying a transmitted radiation image of the subject;
An imaging unit driving means for moving the radiation source relative to the imaging table so that the relative position in a direction perpendicular to or parallel to the radiation irradiation axis changes;
In the radiographic imaging device in which the radiation source is driven each time the relative position is set to any one of a plurality of different predetermined positions,
A position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector is stored in association with each of the plurality of predetermined positions. Storage means;
When irradiation is performed with the relative position as a predetermined position and an image signal is obtained from a radiation detector, the relative position is determined based on the relative position stored in the storage means in association with the predetermined position. A radiographic imaging apparatus, comprising: a correcting unit that corrects a defect in an image signal related to a position. The radiation detector has a plurality of pixels arranged in a two-dimensional matrix in a plane parallel to the radiation detection surface;
The radiographic image capturing apparatus according to claim 6, wherein the storage unit stores a position where the abnormality of the radiation intensity occurs as the position of the pixel. 6. The radiographic imaging apparatus according to claim 1, wherein an abnormality in radiation intensity occurs on the radiation detection surface due to a defect in a member existing between the radiation source and the radiation detector. A defective pixel position information acquisition method for obtaining a pixel position,
Placing the member between the radiation source and a radiation detector;
Moving the radiation source relative to the imaging table so that the angle formed between the radiation irradiation axis and the imaging table changes,
Each time the angle changes, a radiation source is driven to take a transmission radiation image of the member,
Among the plurality of radiographic images obtained by this imaging, when the pixel position that shows the same part of the member and the abnormality of the radiation intensity occurs is changed according to the change in the angle, A defective pixel position information acquisition method comprising: acquiring each pixel position in association with the angle when an image showing the pixel position is captured. 8. The radiographic imaging apparatus according to claim 6, wherein a pixel position where an abnormality in radiation intensity occurs on the radiation detection surface due to a defect of a member existing between a radiation source and a radiation detector is obtained. A defective pixel position information acquisition method comprising:
Placing the member between the radiation source and a radiation detector;
The radiation source is moved relative to the imaging table so that the relative position in a direction perpendicular to or parallel to the radiation irradiation axis changes.
Each time the relative position changes, a radiation source is driven to take a transmission radiation image of the member,
Among the plurality of radiographic images obtained by this imaging, when the pixel position that shows the same part of the member and the abnormality of the radiation intensity has occurred is changed according to the change in the relative position, A defective pixel position information acquisition method, wherein each of these pixel positions is acquired in association with the relative position when an image indicating the pixel position is captured.

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