JP4891292B2 - Radiation image reader - Google Patents

Description

  The present invention relates to a radiation image reading apparatus that reads a radiographic image of a photographed subject from a radiation conversion panel in which the radiation transmitted through the subject is received and a radiographic image of the subject is photographed.

  The radiation conversion panel converts irradiated radiation (X rays, α rays, β rays, γ rays, electron beams, ultraviolet rays, etc.) into electrical signals. As the radiation conversion panel, for example, a storage phosphor sheet that accumulates radiation energy and emits stimulated emission light corresponding to the radiation energy by irradiating excitation light, or the received radiation corresponds to the dose. A flat panel type radiation detector (FPD) that directly converts into an electrical signal is known.

  By the way, in the radiographic image reading apparatus, the geometrical positional relationship (direction and distance) between the radiation source and the radiation conversion panel generally differs between calibration and subject photographing. In that case, the amount and direction of radiation reaching the radiation conversion panel from the radiation source varies depending on the location (position) in the plane of the radiation conversion panel. As a result, density unevenness (geometric shading) occurred in the radiographic image of the photographed subject.

  In the conventional radiographic image reading apparatus, if the geometric positional relationship between the radiation source and the radiation conversion panel is different between calibration and subject shooting, density unevenness naturally occurs in the captured radiographic image. No particular measures were taken.

  Patent Documents 1 and 2 are prior art documents that the present applicant considers relevant to the present invention. Patent Document 1 discloses that shading correction is performed according to the angle of the reading optical system caused by the distortion of the radiation conversion panel itself due to gravity. Further, Patent Document 2 discloses that when creating a long image by partially overlapping a plurality of images, different shading correction is performed on pixels at the same position of the plurality of overlapping images. ing.

  However, Patent Documents 1 and 2 both correct the density unevenness in the radiation conversion panel surface, and the radiation changes due to the change in the geometrical positional relationship between the radiation source and the radiation conversion panel. It does not correct geometric shading that occurs in the image.

JP 2004-229735 A JP 2005-46444 A

  An object of the present invention is to eliminate the problems of the prior art and correct geometric shading generated in a radiographic image due to a change in the geometric positional relationship between the radiation source and the radiation conversion panel. An object of the present invention is to provide a radiation image reading apparatus capable of performing

In order to achieve the above object, the present invention provides radiation that reads a radiographic image of a photographed subject from a radiation conversion panel in which the radiation irradiated from the radiation source and transmitted through the subject is received and a radiographic image of the subject is photographed. An image reading device,
A position detection unit that detects position information of the radiation source and the radiation conversion panel at the time of calibration and photographing of the subject, and a radiation detection panel of the radiation conversion panel at the time of calibration and subject photographing based on the detected position information A position change calculation unit that calculates a change amount of a geometric position; a shading calculation unit that calculates shading based on the calculated change amount of the geometric position; and the radiation image based on the calculated shading. an image processing unit and an image correcting unit for correcting the geometric shading that occurs,
The geometric shading includes a shading generated by changing a length of radiation crossing the radiation conversion panel, and providing a radiation image reading apparatus.

  It is preferable that the geometric shading includes shading that is generated when the distance from the radiation source changes at the origin and each point that are the center position on the light receiving surface of the radiation conversion panel.

  Further, it is preferable that the geometric shading includes shading that is generated when the radiation irradiation angle changes at the origin and each point that are the center position on the light receiving surface of the radiation conversion panel.

  In addition, the image processing unit separates in-panel shading due to unevenness in the light receiving surface of the radiation conversion panel and radiation source shading caused by anisotropy of the radiation source, and individually performs shading correction. It is preferable.

  According to the present invention, the geometric shading generated in the radiographic image due to the change in the geometric positional relationship between the radiation source and the radiation conversion panel is corrected. As a result, the density of the part having the same thickness of the subject can be made almost constant regardless of the location. As a result, for example, even if the density of the region of interest is enhanced by gradation processing, there is an effect that white stripes and black stripes in other regions are less likely to occur.

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

  FIG. 1 is a perspective view of an embodiment showing a configuration of a radiation image reading apparatus of the present invention. The radiation image reading apparatus 10 shown in the figure irradiates the stimulable phosphor sheet S with excitation light and scans it in the main scanning direction (main direction) X, while the stimulable phosphor sheet S is substantially orthogonal to the main direction X. The image is conveyed in the sub-scanning direction (sub-direction) Y, scanned two-dimensionally, and the radiation image recorded on the stimulable phosphor sheet S is read. The reading apparatus 10 includes a main scanning optical unit 12, a sub-scanning transport unit 14, a stimulating light emission detection unit 16, and an image processing unit 18.

  The main scanning optical unit 12 is a part that polarizes excitation light in the main direction X and scans the stimulable phosphor sheet S. The main scanning optical unit 12 includes a laser light source 20 that emits laser light as excitation light, a polygon mirror 22 that is an optical deflector, a scanning lens group 24 including an fθ lens, an optical path changing mirror 26, An optical mirror 28 is used. These components are arranged in this order along the traveling direction of the laser beam.

  The sub-scanning conveyance unit 14 is a part on which the stimulable phosphor sheet S is placed and conveyed in the sub-direction Y that is substantially perpendicular to the main direction X. In the case of the illustrated example, a belt conveyor is used as the sub-scanning conveyance unit 14. The belt conveyor includes an endless belt 30 and two rollers 32 and 34 disposed in the endless belt 30 so as to stretch the endless belt 30. The endless belt is moved in the sub direction Y by rotating the rollers 32 and 34.

  The stimulating light detection unit 16 is a part that receives the stimulating light emitted from the stimulable phosphor sheet S when it is irradiated with excitation light, and photoelectrically converts it to an electrical signal. The stimulating light detection unit 16 includes a condensing guide 36, a photomultiplier (PMT) 38 that photoelectrically converts the stimulating light, and an A / D converter 42.

  The condensing guide 36 is made by molding a light guide material. The condensing guide 36 is disposed at a position facing the condensing mirror 28 so that the incident end face of the stimulated emission light extends along the main direction X, and is provided on the condensing end face (exit end face) of the stimulated emission light. The light receiving surface of the PMT 38 is coupled. The electrical signal (analog voltage) output from the PMT 38 is supplied to the A / D converter 42.

  The image processing unit 18 corrects the geometric shading generated in the radiographic image based on the position information of the radiation source and the stimulable phosphor sheet S in the radiographic imaging device during calibration and subject imaging. This is a part for performing various corrections including correction. The image processing unit 18 includes, for example, a personal computer (PC) having input means, display means, storage means, control means, and software (program) operating on the PC.

  As shown in FIG. 2, the image processing unit 18 detects and acquires the position information of the radiation source and the stimulable phosphor sheet S in the imaging apparatus during calibration and subject imaging, A position change calculation unit 46 for calculating a change amount of the geometric position of the stimulable phosphor sheet S during calibration and subject photographing based on the calculated position information, and a change amount of the calculated geometric position. A shading calculation unit 48 that calculates shading based on the image, and an image correction unit 50 that corrects geometric shading generated in the captured radiographic image based on the calculated shading.

  For example, in the case of an imaging device that uses an arm device or the like to move the radiation source and the stimulable phosphor sheet S together to move and image the subject, the position detection unit 44 communicates with the arm device to obtain position information. Can be obtained.

  Next, the operation of the reading device 10 will be described.

  The laser light emitted from the laser light source 20 enters the polygon mirror 22 and is reflected while being polarized in the main direction X according to the rotation of the polygon mirror 22. Subsequently, the focal point of the laser light is adjusted by the scanning lens group 24 so as to be focused on the stimulable phosphor sheet S, and the optical path is changed (reflected) by the optical path changing mirror 26 so that the optical path is directed toward the stimulable phosphor sheet S. ) And irradiated on the stimulable phosphor sheet S.

  On the other hand, the stimulable phosphor sheet S placed on the belt conveyor is conveyed in the sub-direction Y at a constant speed. That is, the stimulable phosphor sheet S is scanned two-dimensionally by being sub-scanned by the sub-scanning conveyance unit 14 while being main-scanned by the main-scanning optical unit 12.

  When the stimulable phosphor sheet S is irradiated with laser light, the stimulable phosphor sheet S emits stimulated emission light having a light amount corresponding to the radiation energy accumulated therein. This stimulated emission light is incident directly on the entrance of the condensing guide 36 or reflected by the condensing mirror 28 and enters the entrance of the condensing guide 36, and the PMT (photoelectric conversion circuit) 38 is incident on the condensing guide 36. Is propagated to. Thereafter, the photostimulated emission light is photoelectrically converted by the PMT 38 and converted into radiation image data (analog voltage).

  The radiation image data is converted into digital data corresponding to the analog voltage by the A / D converter 42 and supplied to the image processing unit 18.

  In the image processing unit 18, the position detection unit 44 detects the position information of the radiation source and the stimulable phosphor sheet S in the imaging device at the time of calibration and at the time of subject imaging. The position change calculation unit 46 calculates the amount of change in the geometric position of the stimulable phosphor sheet S during calibration and subject photographing based on the position information detected by the position detection unit 44. Subsequently, the shading calculation unit 48 calculates shading based on the change amount of the geometric position calculated by the position change calculation unit 46, and the image correction unit 50 uses the shading calculated by the shading calculation unit 48. Thus, the geometric shading generated in the radiographic image is corrected to generate a radiographic image in which density unevenness is greatly reduced.

  Next, with reference to the conceptual diagram shown in FIG. 3, the positional relationship between the radiation source and the stimulable phosphor sheet S in the imaging apparatus during calibration and subject imaging will be described.

  FIG. 3A is a side conceptual diagram showing the positional relationship between the radiation source and the stimulable phosphor sheet in the imaging device at the time of calibration and subject photographing, and FIG. 3B is the radiation source and the stimulable phosphor sheet. It is a perspective conceptual diagram showing these positional relationships. In the example of FIG. 3A, the stimulable phosphor sheet S is arranged at a position (left side) farther from the radiation source 52 at the time of calibration, and a position closer to the radiation source 52 (right side) at the time of subject photographing. ).

  As shown in FIG. 3, let s be the distance between the radiation source 52 and the center position of the light receiving surface of the stimulable phosphor sheet S. The center position of the stimulable phosphor sheet S is the origin (0, 0), and in FIG. 3, the direction perpendicular to the paper surface is the x axis, and on the light receiving surface of the stimulable phosphor sheet S, the direction perpendicular to the x axis is The y-axis is assumed (the x-axis and y-axis move with the inclination of the stimulable phosphor sheet S). Further, the distance between each point (x, y) on the light receiving surface of the stimulable phosphor sheet S and the radiation source 52 is z.

  At the time of calibration, the distance z of the radiation irradiated from the radiation source 52 to the point (x, y) on the light receiving surface of the stimulable phosphor sheet S is the same at the point target position with the origin (0, 0) as the center. Distance. In the case of the illustrated example, the upper end portion of the stimulable phosphor sheet S is inclined counterclockwise in FIG. In this case, the radiation has a different distance z at the upper and lower target positions of the origin (0, 0) (the distance z to the upper point in FIG. 3 becomes longer and the distance z to the lower point becomes shorter).

  Here, since z depends on x, y, s, and θ, it is also described as z = z (x, y, s, θ). x and y are pixel positions on the image, and s and θ are quantities directly obtained from communication with the arm. In FIG. 3, subscript 0 is attached to z and s during calibration, and subscript 1 is attached during subject photographing. z (0, 0, s, 0) = s.

  FIG. 3 shows an example of the positional relationship between the radiation source 52 and the stimulable phosphor sheet S in the imaging apparatus during calibration and subject imaging. The tilting direction of the stimulable phosphor sheet S is not limited to one direction with the x axis as the central axis, but may be tilted with the y axis as the central axis, or may be tilted in a combined direction. . Further, the distance s between the radiation source 52 and the stimulable phosphor sheet S is also appropriately changed.

  Next, geometric shading will be described.

  The amount by which the unit area on the light receiving surface of the stimulable phosphor sheet S receives radiation is proportional to the solid angle from which the unit area is expected from the radiation source 52. Therefore, as shown in FIG. 3, the amount of radiation that reaches the origin (0, 0) and the point (x, y) on the light receiving surface of the stimulable phosphor sheet S during calibration differs. This difference is conventionally corrected as shading (unevenness in the light receiving surface of the stimulable phosphor sheet S).

  On the other hand, the amount of radiation reaching the origin (0, 0) and the point (x, y) at the time of subject shooting is different from that at the time of calibration. For this reason, when the captured radiation image is corrected using the shading correction data acquired at the time of calibration, the density unevenness (shading) caused by the change in the geometrical positional relationship between the radiation source 52 and the stimulable phosphor sheet S. ) Remains. This remaining density unevenness is called geometric shading in the present invention.

Next, a method for calculating geometric shading will be described.
Geometric shading is calculated by dividing it into the following three effects (1) to (3).

(1) Distance effect With respect to a certain unit area on the light receiving surface of the stimulable phosphor sheet S, when the angle formed by the normal direction of the unit area and the incident direction of radiation is constant, the radiation source 52 is The solid angle for which the unit area is expected is inversely proportional to the square of the distance from the radiation source 52. The ratio of the amount of change in the distance from the radiation source 52 at the origin (0, 0) and point (x, y) on the light-receiving surface of the stimulable phosphor sheet S is shaded (shading that occurs when the distance changes). become. This is called a distance effect in the present invention.

  Comparing the time of calibration and subject photographing, the radiation dose at the origin (0, 0) on the light receiving surface of the stimulable phosphor sheet S is (s1 / s0) ^-2 times, and the point (x, y ) Will be (z1 / z0) ^-2 times. Therefore, the distance effect is calculated by the following formula (1).

(2) Angle effect The angle formed by the incident direction of the radiation with respect to a certain unit area on the light receiving surface of the stimulable phosphor sheet S is defined as φ. When the distance between the radiation source 52 and the stimulable phosphor sheet S is constant, the solid angle at which the radiation source 52 expects its unit area is proportional to cos φ. The ratio of the amount of change in the irradiation angle of radiation from the radiation source 52 at the origin (0, 0) and point (x, y) on the light-receiving surface of the stimulable phosphor sheet S is generated by shading (changed in angle). Shading). This is called an angle effect in the present invention. Since φ depends on x, y, s, and θ, φ = φ (x, y, s, θ) is described.

  At the time of calibration, cosφ (0,0, s0,0) = 1 and cosφ (x, y, s0,0) = s0 / z0, and at the time of shooting the subject, cosφ (0,0, s1, θ) ) = Cos θ, cos φ (x, y, s1, θ) = s1 / z1 × cos θ. Therefore, the angle effect is calculated by the following equation (2). In the following description, the angle effect is described as L (x, y).

(3) Thickness effect of the stimulable phosphor sheet S The length that the radiation crosses the stimulable phosphor sheet S is proportional to 1 / cos φ (x, y, s, θ), as can be seen from FIG. In the example of FIG. 4, when the thickness of the stimulable phosphor sheet S is Δ and the incident angle of radiation to the stimulable phosphor sheet S is φ, the length of the radiation that crosses the stimulable phosphor sheet S is Δ / cosφ. In the present invention, the shading generated when the length of the radiation that crosses the stimulable phosphor sheet S changes is called a thickness effect.

  When the radiation absorption rate of the stimulable phosphor sheet S is very small, the length of radiation that crosses the stimulable phosphor sheet S is proportional to the amount of radiation absorption. Therefore, L (x, y It can be seen that shading of ^ -1 occurs. On the other hand, when the radiation absorption rate of the stimulable phosphor sheet S is very large, the radiation absorption amount is constant (all on the surface of the stimulable phosphor sheet S) regardless of the length of radiation that crosses the stimulable phosphor sheet S. So shading does not occur.

  Since the radiation absorption rate of the actual stimulable phosphor sheet S is intermediate between them, the thickness effect in the case of the general stimulable phosphor sheet S is L (x, y) ^ (α-1) between the two. ) (0 <α <1). Further, in the actual stimulable phosphor sheet S, there is a fact that the efficiency of reading out signals due to radiation absorbed deep in the stimulable phosphor sheet S is small, but this is an effect of bringing the coefficient α closer to 1. The value of the coefficient α should be determined as appropriate. For example, the optimum value is determined by experiment.

  To summarize the above three types of effects, the geometric shading effect at the point (x, y) is L (x, y) ^ (2 + α). The geometric shading correction is performed by dividing the pixel value of the point (x, y) of the captured radiation image by this value.

  Note that the method of geometric shading correction is not limited to using the above three effects together. For example, it is also possible to store data for performing geometric shading correction under a plurality of fixed conditions and perform correction using this geometric shading data.

  In the reading device 10, as described above, the geometric shading generated in the radiographic image due to the change in the geometric positional relationship between the radiation source 52 and the stimulable phosphor sheet S is corrected. As a result, the density of the part having the same thickness of the subject can be made almost constant regardless of the location. As a result, for example, even if the density of the region of interest is enhanced by gradation processing, there is an effect that white stripes and black stripes in other regions are less likely to occur.

  Note that, in the region where the radiation image data is amplified by the geometric shading correction, not only the radiation image data but also the noise component is amplified, so it is desirable to perform noise reduction processing for reducing noise.

  Next, shading caused by anisotropy of the radiation source 52 and shading caused by uneven density in the light receiving surface of the stimulable phosphor sheet S will be described.

  As can be seen from FIG. 3, when attention is paid to the point (x, y), there are pixels that receive radiation radiated in different directions during calibration and during photographing of the subject. Therefore, the density unevenness that remains even if the above-described geometric shading correction is performed when a solid image is captured in the positional relationship at the time of subject shooting is referred to as shading (radiation source shading) due to the anisotropy of the radiation source 52. It can be determined separately.

  By removing the radiation source shading obtained by the above method from the shading obtained at the time of calibration, shading due to unevenness in the light receiving surface of the stimulable phosphor sheet S (in-panel shading) can be obtained (radiation source shading). And panel shading can be separated). The image processing unit 18 desirably corrects radiation source shading and in-panel shading individually.

  Further, by introducing the radiation source shading into the calculation of the geometric shading correction described above, that is, by correcting the geometric shading in consideration of the radiation source shading, the shading correction can be performed with high accuracy.

Hereinafter, a correction process for the radiation image performed by the image processing unit 18 will be described.
First, marker correction will be described.

  In particular, in a scanning reader, the physical position on the stimulable phosphor sheet S may differ from the pixel position on the captured radiation image. Japanese Patent Application Laid-Open No. 2004-117684 proposed by the applicant of the present application discloses a method of aligning using a marker when this misalignment becomes a problem in various corrections including shading correction. This method has problems such as in-plane displacement cannot be calculated unless the entire image is read, and calculation time for matrix calculation is required.

  FIG. 5 is a conceptual diagram showing a light receiving surface of a stimulable phosphor sheet with a marker, and FIG. 6 shows a parallel movement amount for correcting a shift in each cell of the stimulable phosphor sheet divided by the marker. FIG.

  In the example of FIG. 5, five markers 54 are linearly arranged in the main direction X along the lower side, and six markers 56 are along the left side at right angles to the arrangement of the lower side markers 54. They are arranged in a straight line at equal intervals in the sub-direction Y. As shown in FIG. 6, the light-receiving surface of the stimulable phosphor sheet S is divided into five regions corresponding to the respective lower side markers 54 in the main direction X, and the left side markers 56 are arranged in the sub direction Y. The area is divided into six regions with the position as the division position. Each of the 5 × 7 = 35 areas divided in a lattice shape is called a cell 58.

  Since the timing of scanning the stimulable phosphor sheet S is slightly shifted, the physical pixel position on the light receiving surface of the stimulable phosphor sheet S and the read from the stimulable phosphor sheet S are read as described above. There is a case where the pixel position of the radiation image is shifted. Therefore, the shift amount between the two is calculated for each cell two-dimensionally using the markers 54 and 56 on the lower side and the left side shown in FIG. 6, and the parallel movement amount for correcting the shift from the shift amount ( (Shown by a thick arrow in FIG. 6) is calculated, and the deviation between the two is corrected based on the amount of parallel movement.

  In FIG. 6, consider the case where the stimulable phosphor sheet S moves downward. When scanning is started, the five markers 54 on the lower side are read, and then the data of the pixels included in the five cells 58 arranged in the bottom main direction X are read. Thereafter, when the lowermost marker 56 on the left side is read, the lowermost marker 56 on the left side and the five markers 54 on the lower side are used to arrange the five cells in the bottom main direction X. The deviation at 58 is corrected. The subsequent operation is the same.

  Thereby, when the amount of positional deviation is small, even if there is rotation or expansion / contraction, the positional deviation can be easily approximated and corrected accurately. Further, with this method, even when the image is being read, if even the left side marker 56 for calculating the shift amount (movement amount) in the cell 58 is read, the cell 58 up to the marker 56 position is read each time. The position can be aligned by correcting the amount of deviation. Therefore, the aligned image portions can be calculated sequentially without waiting for the entire image to be read.

  The markers 54 and 56 are made of a material having a reflectance different from that of the light receiving surface of the stimulable phosphor sheet S. In addition, an image obtained by cutting out the marker region (the region in which the markers 54 and 56 are disposed in the light receiving surface of the stimulable phosphor sheet S) may be output as a radiographic image, and the imaging time, the operator's Character information such as an examiner's name may be written in the marker area and output.

  Next, the stain residual correction will be described.

  FIG. 7A is a conceptual diagram showing a defective pixel existing in the stimulable phosphor sheet S, and FIG. 7B is a conceptual diagram showing a state where the defective pixel position and the pixel position of the correction data do not match. C) is a conceptual diagram showing a state in which the defective pixel position and the pixel position of the correction data match.

  In the stimulable phosphor sheet S, as shown in FIG. 7A, there are defective pixels 60 that are independent or in which a plurality of pixels are connected. Normally, the position of the defective pixel 60 and correction data for correcting the defective pixel 60 are stored in a correction table or the like, aligned using the markers 54 and 56 described above, and defective using the correction data. Correct the pixels. However, there may be a local shift in the alignment by the markers 54 and 56, and the portion where the shift has occurred becomes a black-and-white pair correction residual (stain residual), so that the defective pixel correction is not performed. It will stand out.

  In this case, pixels where the defective pixel 60 and the pixel of the correction data do not overlap (in the case of the example shown in FIG. 7B), the upper and lower regions 62 where the defective pixel position and the pixel position of the correction data do not match. , 64 pixels, in other words, the number of pixels that are greater than or equal to the first threshold value than the pixel value of the overlapping central region 66 pixels) and the poorness of overlap (the pixel values of the regions 62 and 64). The sum of absolute values of differences from the pixel values in the region 66 is counted. If the count value is larger than the second threshold value, the shift amount is changed and the alignment is performed again, and the defective pixel position and the correction data pixel position are adjusted to coincide with each other as shown in FIG.

  Next, defect correction will be described.

  Pattern correction may be required for defect correction / correction. In particular, if the defect is large or the number of defective pixels is large, the calculation time increases. If the defect is too large / the number of defective pixels is too large, correction processing cannot be performed simultaneously with reading, and the processing may end abnormally. Normally, an upper limit (threshold value) of the total number of defects and the number of defective pixels that can be corrected is provided, and defect correction is stopped when the upper limit is exceeded.

  However, in the method of limiting the number of pixels, when there are many small defects, the correction is finished with the remaining power in the conversion of the number of pixels, and in the method of setting the upper limit in the number of pixels, the remaining power is calculated in the conversion of the number of defects when there are many large defects. The correction will be terminated. Therefore, points are set for each type (type), size (size), depth, and shape of the defect, and it is determined whether or not the correction is to be ended depending on whether the total point exceeds the upper limit.

  Table 1 below shows the maximum number of defective pixels that can be corrected in one line when there are defects of the same type and size in one line, with the number of points by defect type and size and the upper limit point being 700 points. Represents.

  Here, a spot defect and a point defect are illustrated as defect types. A spot defect has a depth shallower than a certain threshold. The spot defect is corrected by position adjustment and sensitivity correction (division). One point defect is deeper than the aforementioned threshold. The point defect is corrected by interpolating with surrounding pixels. Note that the meaning of shallower and deeper than the threshold is a difference when a spot defect and a point defect are compared.

  The defect size is a product of the width of the thickest place in the main direction (lateral direction) X and the width of the thickest place in the sub direction (vertical direction) (main direction size × sub-direction size). “A defect” on the line means that the defect start address (read first pixel position) is on the line. The upper limit point is appropriately determined as the maximum number of points that does not cause a problem in speed in order to correct simultaneously with reading (in parallel with reading).

  For example, if it is possible to correct up to 700 points (upper limit) per sub-scanning line, even if there are 14 spot defects of size 100 pixels in one line, all corrections can be made. When there are four spot defects of size 900 pixels and two point defects of size 36 pixels, the lines are corrected in the order in which they appear, but the last one is corrected because it exceeds the upper limit of 700 points. Can not.

  Finally, dark trend correction will be described.

  In a scanning reader, dark data (offset data) is acquired immediately before reading scanning, and the dark data is subtracted from the radiation image data, and then the above-described shading correction is performed. However, since dark data changes from moment to moment, appropriate offset data is subtracted on the leading end side (reading scanning start side) of the radiation image, but not appropriate on the trailing end side (ending end of reading scanning). Data will be subtracted.

  As described above, when appropriate offset data is not subtracted, the result of the shading correction is not appropriate. Therefore, when simultaneous reading correction is not required, dark data is acquired twice before and after the reading scan, and dark data at an arbitrary position in the radiation image is obtained by linear interpolation of the two dark data. Thereby, appropriate offset data can be subtracted from the radiation image data.

  In the above-described embodiment, the reader using a stimulable phosphor sheet is described as an example of the radiation conversion panel. However, the present invention can also be applied to a reader using an FPD. That is, the configuration of the reading device should be appropriately determined according to the radiation conversion panel to be used. Further, the reading device may be configured as an integrated type including both functions of the photographing device and the reading device.

The present invention is basically as described above.
Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and it is needless to say that various improvements and modifications may be made without departing from the gist of the present invention.

It is a perspective view of one embodiment showing composition of a radiographic image reading device of the present invention. It is a block conceptual diagram showing the structure of an image processing part. (A) is a side conceptual diagram showing the positional relationship between the radiation source and the stimulable phosphor sheet during calibration and subject photographing in the radiographic imaging device, and (B) is the radiation source and the stimulable phosphor. It is a perspective conceptual diagram showing the positional relationship of a sheet | seat. It is a conceptual diagram showing the change of the length in which radiation crosses a stimulable phosphor sheet. It is a conceptual diagram showing the light-receiving surface of the storage fluorescent substance sheet with a marker. It is a conceptual diagram showing the parallel displacement amount for correct | amending deviation | shift in each cell of the stimulable phosphor sheet | seat divided | segmented with the marker. (A) is a conceptual diagram showing a defective pixel existing in the stimulable phosphor sheet S, (B) is a conceptual diagram showing a state where the defective pixel position and the pixel position of the correction data do not match, (C) These are the conceptual diagrams showing the state in which the defective pixel position and the pixel position of correction data correspond.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation image reader 12 Main scanning optical part 14 Subscanning conveyance part 16 Detection part of stimulating emitted light 18 Image processing part 20 Laser light source 22 Polygon mirror 24 Scanning lens group 26 Optical path changing mirror 28 Condensing mirror 30 Endless belt 32 , 34 Roller 36 Condensing guide 38 Photomultiplier (PMT)
42 A / D Converter 44 Position Detection Unit 46 Position Change Calculation Unit 48 Shading Calculation Unit 50 Image Correction Unit 52 Radiation Source 54, 56 Marker 58 Cell 60 Defective Pixel 62, 64, 66 Region

Claims (4)

A radiation image reading device that reads a radiographic image of a photographed subject from a radiation conversion panel in which the radiation that has been irradiated from the radiation source and transmitted through the subject is received and a radiographic image of the subject is photographed,
A position detection unit that detects position information of the radiation source and the radiation conversion panel at the time of calibration and photographing of the subject, and a radiation detection panel of the radiation conversion panel at the time of calibration and subject photographing based on the detected position information A position change calculation unit that calculates a change amount of a geometric position; a shading calculation unit that calculates shading based on the calculated change amount of the geometric position; and the radiation image based on the calculated shading. an image processing unit and an image correcting unit for correcting the geometric shading that occurs,
The geometric image shading includes a shading generated by a change in the length of radiation crossing the radiation conversion panel .   2. The geometric shading includes a shading generated by a change in a distance from the radiation source at an origin and a point at a center position on a light receiving surface of the radiation conversion panel. The radiation image reading apparatus described.   The geometric shading includes shading that is generated by changing an irradiation angle of radiation at an origin and each point that are a central position on a light receiving surface of the radiation conversion panel. The radiation image reading apparatus described. The image processing unit separates in-panel shading due to unevenness in the light receiving surface of the radiation conversion panel and radiation source shading caused by anisotropy of the radiation source, and individually performs shading correction. radiation image reading apparatus according to any one of claims 1 to 3, characterized.

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