JP6122966B2 - X-ray equipment - Google Patents

Description

  The present invention relates to an X-ray imaging apparatus, and more particularly, to a general medical or dental X-ray imaging apparatus.

In general, in an image detector that detects X-rays such as a flat panel detector (FPD), the smaller the size of the pixel, that is, the larger the number of pixels per unit area, the obtained image. The resolution of the is increased. One method for obtaining a more easily viewable image is to reduce the pixel size of the image detector. However, an image detector with a small pixel size is expensive. Further, if the pixel size of the image detector is reduced, the light receiving sensitivity is lowered. Therefore, there is a limit to reducing the pixel size for use in medical X-ray imaging due to the problem of exposure dose.
Note that the resolving power of the medical X-ray imaging system, that is, the resolving limit or cut-off frequency, is the three elements of the pixel size of the image detector, the focal point size of the X-ray tube, and the magnification of the subject. Determined by

  Conventionally, the inventors of the present application have used the Nyquist frequency of the cut-off frequency of a modulation transfer function (MTF) by image processing using the Detector Moving and Frame Additional Technique (hereinafter referred to as the DEMOT method), which is a super-resolution technique. A method of pulling up twice has been proposed (see, for example, Patent Documents 1 and 2). Here, MTF is an absolute value of an optical transfer function (OTF), and is used as a numerical value representing the sharpness of an image. Note that OTF is a Fourier transform of a line spread function (LSF).

  In the technique described in Patent Document 1, the pixels are arranged so that the arrangement direction of the pixels on the light receiving surface of the image detector is inclined with respect to the moving direction of the image detector, and the signal obtained by the image detector is subjected to DEMOT. The image processing of law is performed. The technique described in Patent Document 2 provides a light receiving part area that receives X-rays and a dead part area that does not generate signal charges in pixels on the light receiving surface of an image detector. The image processing of the DEMOT method is performed.

Japanese Patent No. 4806433 Japanese Patent No. 4560098

  However, the techniques described in Patent Documents 1 and 2 have room for improvement. The technique described in Patent Document 1 can double the resolving power in the arrangement direction of the pixels on the light receiving surface of the image detector, but cannot increase the resolution more than twice. Patent Document 2 describes that a dead area is provided in a pixel group of one column of an image detector, and a signal obtained by the image detector is processed to increase the resolving power more than twice. However, specific image processing when pixels are arranged two-dimensionally is not described.

  The present invention has been made in view of the above circumstances, and in an image obtained by photographing a subject with an image detector in which pixels are two-dimensionally arranged, the cutoff frequency of the MTF is made larger than twice the Nyquist frequency. It is an object of the present invention to provide an X-ray imaging apparatus capable of performing the above.

In order to solve the above problems, an X-ray imaging apparatus according to the present invention includes an X-ray source and a pixel array in which pixels are two-dimensionally arranged on a light receiving surface that receives X-rays that have passed through a predetermined point of a subject. An image detector comprising a line image detection recording medium, driving means for moving the image detector in a direction orthogonal to the X-ray incident direction, and a frame image sent from the image detector at a predetermined frame rate are stored. A frame image storage means, and a recording area for each pixel that is aligned with each pixel in the pixel array of the image detector, and the recording area for each pixel is M rows horizontally (M is an integer of 2 or more) A large-capacity processed image storage in which an expanded memory space corresponding to a coordinate space obtained by expanding the frame image by M × N times by dividing the frame image into N columns (N is an integer of 2 or more) vertically X-ray imaging with means A pixel array direction of the pixel array of the image detector is inclined with respect to a direction in which the image detector is moved by the driving unit, and is arranged on the light receiving surface of the image detector. , A light receiving area and a dead area are provided for each pixel, the frame image is transferred to the large-capacity processed image storage means, and the number of pixels enlarged to M × N times one pixel of the frame image The shape of the light receiving surface of the pixel is recorded as a signal distribution in a plurality of corresponding memories, and the image detector is smaller than the pixel width with respect to the direction in which the vertical or horizontal pixel group in the pixel array is inclined. The output signal of the pixel of the image detector when it is moved minutely by the distance is M × N mem- bers corresponding to the position of the pixel in the expanded memory space according to the moving position of the image detector. Sequentially writing prorated to Li, characterized in that it comprises an image processing means for generating processed image signals to be written in the M × N memory of each pixel by adding on each memory.

  According to such a configuration, in the X-ray imaging apparatus, the light receiving area and the insensitive area are provided for each pixel on the light receiving surface of the image detector, and the arrangement of the pixels with respect to the direction in which the image detector is moved. The direction is inclined, and in the large-capacity processed image storage means, the light receiving surface shape of the pixel is recorded as a signal distribution in a memory expanded to the number of pixels M × N times that of one pixel of the input image. Since the image processing means performs image processing by the DEMOT method using a memory expanded to M × N times the number of pixels, the cutoff frequency of the MTF is made larger than twice the Nyquist frequency in the obtained image. Can do.

  In the X-ray imaging apparatus according to the present invention, in the pixels arranged in the image detector, the shape of the light-receiving surface of the insensitive area or the light-receiving area is the same as the shape of the light-receiving surface of the pixel. It is preferable that the shape of the overlapping portion formed when the two figures are shifted and overlapped is the same. Here, the shape of the light receiving surface of the pixel is, for example, a rectangle, a circle, a hexagon, or the like.

  In the X-ray imaging apparatus according to the present invention, in each pixel arranged in the image detector, the shape of the light-sensitive surface of the insensitive part area moves the shape of the light-receiving surface of the pixel to the image detector. It is preferable to include a symmetrical shape with respect to a center line that bisects the direction.

In the X-ray imaging apparatus according to the present invention, it is preferable that the shape of the insensitive part area or the light receiving part area is similar to the shape of the pixel.
In the X-ray imaging apparatus according to the present invention, it is preferable that the shape of the pixel and the insensitive part area is a square, and the insensitive part area is disposed at a corner of the pixel.

  If an insensitive part area is provided in the pixel of the image detector and the pixel arrangement direction is inclined with respect to the direction in which the image detector is moved, a two-dimensional artifact may occur in the image obtained by the X-ray imaging apparatus. . Therefore, in the X-ray imaging apparatus according to the present invention, the image processing means includes an angle of a pixel arrangement direction with respect to a direction in which the image detector is moved, the arrangement of the pixels, the insensitive part area, and the light receiving part. In the frame image enlarged by M × N in the memory space set in the large-capacity processing image storage unit, receiving input of each information about the area ratio to the area and the position of the dead area in the pixel By adding the signal intensity in the direction in which the image detector is moved, a sensitivity characteristic curve in a direction orthogonal to the direction in which the image detector is moved is obtained, and the signal value of the generated processed image is corrected by the sensitivity characteristic curve. Is preferred.

  According to such a configuration, variations in sensitivity on the light receiving surface of the image detector can be corrected by image processing, so that artifacts can be greatly reduced.

In the X-ray imaging apparatus according to the present invention, it is preferable that the pixel array of the image detector is an alternating array in which the positions of the pixels are shifted every other column.
According to this configuration, the sensitivity on the light receiving surface of the image detector can be averaged by shifting the pixel positions. Therefore, artifacts can be greatly reduced without obtaining a sensitivity characteristic curve.

  In the X-ray imaging apparatus according to the present invention, the image detector performs binning, which is processing for handling a plurality of adjacent pixels as a virtual unit pixel, and for each unit pixel, a predetermined part of the pixels It is preferable to form the dead area and the light receiving area for each unit pixel by reading the output signals of the remaining pixels without reading the output signal.

  According to such a configuration, although the spatial resolution is reduced when binning is performed, the number of pixels to be read is reduced, so that the frame rate is increased. A higher frame rate is advantageous for combination with the DEMOT method. Further, in the pixels arranged in the image detector, the resolving power can be improved by changing the area ratio or the shape of the light receiving area and the insensitive area.

  The X-ray imaging apparatus according to the present invention can make the cutoff frequency of MTF larger than twice the Nyquist frequency in an image obtained by imaging a subject with an image detector in which pixels are two-dimensionally arranged.

1 is a block diagram schematically showing an X-ray imaging apparatus according to an embodiment of the present invention. It is a figure which shows an example of an image detector and its moving direction. It is a schematic diagram which shows the state which shifted the pixel array by the half pixel in the X direction and the Y direction, and was piled up on the original pixel array. It is a schematic diagram which shows an example of FPD and the lead edge seen from the X-ray source side. It is a schematic diagram which shows an example of FPD and the lead edge seen from the side orthogonal to the irradiation direction of X-rays. It is a schematic diagram which shows an example of the signal value transferred from FPD to a high capacity | capacitance process image storage means. It is a schematic diagram which shows an example of the algorithm of the DEMOT method at the time of using FPD of FIG. 4B. It is a graph which shows an example of ESF calculated | required from FIG. It is a graph which shows an example of LSF calculated | required from FIG. It is a schematic diagram which shows the other example of the image detector seen from the X-ray source side, and a lead edge. It is a schematic diagram which shows the other example of the image detector seen from the side orthogonal to the irradiation direction of X-rays, and a lead edge. It is a schematic diagram which shows an example of the signal value transferred from an image detector to a mass storage image storage means. It is a schematic diagram which shows an example of the algorithm of the DEMOT method at the time of using the image detector of FIG. 8B. It is a graph which shows an example of ESF calculated | required from FIG. It is a graph which shows an example of LSF calculated | required from FIG. It is a graph which shows MTF calculated | required from FIG. 7B, and MTF calculated | required from FIG. 11B. FIG. 3 is a diagram illustrating a 2 × 2 pixel region in the image detector of FIG. 2. FIG. 3 is a schematic diagram in which a 2 × 2 pixel region is virtually divided in parallel with an X axis. FIG. 3 is a schematic diagram in which a 2 × 2 pixel region is virtually divided in parallel with a Y axis. It is a schematic diagram which shows an example of the signal strength written in the memory. It is a schematic diagram which shows an example of the signal strength apportioned on the memory with the movement to a X direction. It is a schematic diagram which shows an example of the signal strength apportioned on the memory with the movement to a Y direction. It is a schematic diagram which shows an example of the image detector of the X-ray imaging apparatus which concerns on embodiment of this invention. It is an image which shows the to-be-photographed object employ | adopted in the verification experiment which simulated the image detector of the X-ray imaging apparatus which concerns on embodiment of this invention with the FPD model. It is the image which image | photographed the to-be-photographed object in the state which made the FPD model of 100% of fill factors still in the verification experiment. It is an image obtained by photographing a subject before moving one pixel of an FPD model having a fill factor of 100% in a verification experiment. In the verification experiment, an image of the subject taken by the camera before moving the FPD model with a fill factor of 75% by one pixel. It is a figure which shows typically the sensitivity characteristic curve in the B-axis direction orthogonal to the A-axis in the extended image. 21 is an image obtained by correcting FIG. 20 by image processing. It is a schematic diagram of the image detector which arranged the pixel alternately. It is a schematic diagram which shows the modification of the shape of a pixel. It is a figure which shows an example of the image detector which arranged the pixel of the modification, and its moving direction. It is a schematic diagram which shows the other modification of the shape of a pixel. It is a conceptual diagram of pixel binning.

  An embodiment for implementing an X-ray imaging apparatus according to the present invention will be described in detail with reference to the drawings. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation.

(First embodiment)
The X-ray imaging apparatus 1 is, for example, a digital panoramic X-ray imaging apparatus, and as shown in FIG. 1, an X-ray source 2, an image detector 3, an arm 4, a turning drive unit 5, and A / D conversion. Means 6, large-capacity frame image storage means 7, large-capacity processing image storage means 8, all-image display storage means 9, image processing means 10, and output means 11 are provided.

  The X-ray source 2 applies a slit-shaped X-ray beam generated by irradiating X-rays through a slit (lead slit) provided in a housing (not shown) made of lead, for example, to the subject 12 at a predetermined timing. Irradiation.

  The image detector 3 includes an X-ray image detection recording medium having a pixel array in which pixels that receive X-rays that have passed through a predetermined point of the subject 12 are two-dimensionally arranged. The image detector 3 images the portion of the subject 12 through which the X-rays have passed at a predetermined frame rate. The image detector 3 is an X-ray image sensor, an X-ray detector, or a combination thereof.

  Here, the image sensor is, for example, a CCD (Charge Coupled Device) image sensor, a CMOS image sensor, a TFT (Thin Film Transistor) sensor, a CdTe sensor, or the like. The X-ray detector is an X-ray image intensifier (I.I.), a flat panel detector (FPD), or the like.

  In the present embodiment, the image detector 3 will be described as an FPD. In this case, the image detector 3 can be configured as one pixel having a pixel size of, for example, 100 μm × 100 μm and arranged in, for example, horizontal direction 1024 pixels × vertical direction 1024 pixels.

  The arm 4 holds the X-ray source 2 and the image detector 3 at a predetermined interval. This interval is set to, for example, 30 cm to 1 m so that the subject 12 is accommodated between the X-ray source 2 and the image detector 3. In addition, the irradiation part in which the X-ray tube of X-ray source 2 is arrange | positioned, and the light-receiving surface of the image detector 3 are arrange | positioned facing. The arm 4 is configured to be rotatable and slidable around the rotation center O. The arm 4 fixes and holds the image detector 3 via a base (not shown) on the image detector 3 side.

  The turning drive means 5 moves the image detector 3 in a direction orthogonal to the X-ray incident direction by rotating and sliding the X-ray source 2 and the image detector 3 around the subject 12. The turning drive means 5 includes a motor, an actuator, and the like, and turns the arm 4 so as to rotate at a predetermined angular velocity. In the present embodiment, the turning drive unit 5 rotates and slides the image detector 3 around the rotation center O by rotating the arm.

  An example of the image detector 3 and its moving direction is shown in FIG. The image detector 3a shown in FIG. 2 has a pixel array in which the pixels 20 are two-dimensionally arranged on the light receiving surface. The pixel array is a square array in which the pixels 20 are aligned vertically and horizontally. Here, a portion in which a pixel group composed of six pixels 20 arranged in the X direction (vertical) is arranged in six columns in the Y direction (horizontal) is illustrated.

  In addition to the pixel array, the image detector 3a includes a conventionally known electronic circuit (not shown). The electronic circuit includes, for example, a horizontal read control unit, a vertical read control unit, a timing generator that supplies a clock signal to each read control unit, an oscillator connected to the timing generator, and a vertical read control unit The amplifier includes an amplifier, an A / D converter connected to the amplifier, and a line driver connected to the A / D converter. Here, the horizontal reading control unit includes, for example, a vertical scanning register for row scanning. The vertical read control unit includes, for example, a horizontal shift register and a charge amplifier with a built-in CDS circuit.

  When an X-ray hits the pixel 20 on the light receiving surface, it is converted into an electric charge, and the electric charge is stored for each pixel 20. There are a direct conversion system and an indirect conversion system (scintillator system) as the conversion system to charge, but any conversion system may be used in the present invention. In the direct conversion method, X-rays are directly acquired as charges by an X-ray detection element typified by selenium (Se). In the case of the scintillator method, X-rays are absorbed by a scintillator such as cesium iodide (CsI), and fluorescence generated there is obtained as a charge by a photodiode. The accumulated charge is read out by horizontal reading control and vertical reading control by the horizontal reading control unit and the vertical reading control unit.

The pixel arrangement direction in the pixel array of the image detector 3a is inclined with respect to the direction 15 in which the image detector 3a is moved by the turning drive means 5.
This tilt angle is arbitrary, but it is preferable that the tilt angle is 45 degrees in order to improve the resolution in the vertical direction and the resolution in the horizontal direction equally in the obtained image. That is, assuming that the angle of the moving direction 15 of the image detector 3a is the reference azimuth (0 degree), the pixel groups arranged in the vertical column in the pixel array of the image detector 3a are arranged in a 45 degree direction, for example, It is preferable that the pixel groups arranged in this column are arranged in a direction of, for example, −45 degrees (135 degrees).

  The pixel 20 includes a light receiving area 21 and a dead area 22. The light receiving area 21 is an area for receiving X-rays and generating signal charges. The insensitive part area 22 is an area where no signal charge is generated or an area which is treated as having substantially no signal charge.

  The method of providing the insensitive part area may be a method of newly providing the insensitive part area for each pixel in the light receiving part area (fill factor 100%) of the normal image detector, or the light receiving part area on the light receiving surface of the image detector. And a method of providing a new pixel provided with a dead area. Examples of the method of providing the insensitive part area 22 include a method of providing a mask that physically covers a part of the pixel and a method of providing a wiring part that transfers signal charges generated in the light receiving part area. In addition to the method of providing the insensitive part area 22 in a fixed manner, the insensitive part area may be formed by applying binning, which is a process of handling a plurality of adjacent pixels as a virtual unit pixel. it can. This binning will be described in the fifth embodiment.

  As shown in FIG. 2, in the pixel 20, the dead area 22 is adjacent to the light receiving area 21. The shape of the insensitive part area 22 on the light receiving surface is a square similar to the shape of the pixel 20, and the insensitive part area 22 is disposed at the left corner of the pixel 20. Assuming that the pixel width is d, the value of the pixel width d is a total value of the width W of the insensitive area 22 and the width L of the light receiving area 21. Here, as an example, it is assumed that the width W and the width L are equal (W = L = 2 / d). That is, it is assumed that the fill factor is 75%.

  FIG. 3 is a schematic diagram illustrating a state in which the image detector 3 is shifted by 2 / d in the X direction and the Y direction, and is superimposed on the pixel array before the movement. As shown in FIG. 3, the shape of the light-sensitive surface of the insensitive area 22 is the same as the shape of the overlapping portion formed by shifting and overlapping two figures having the same shape as the shape of the light-receiving surface of the pixel. In other words, the shape of the insensitive part area 22 is the same as the shape of the overlapping part of two pixels formed when the two pixels are overlapped and then one of them is translated.

Returning to FIG. 1, the description of the configuration of the X-ray imaging apparatus 1 will be continued.
The turning drive means 5, the X-ray source 2, and the image detector 3 are controlled by a controller (not shown), and the X-ray source 2 emits X-rays while the turning drive means 5 rotates and slides the arm 4. The image detector 3 captures a frame image of the subject 12 and outputs it to the A / D conversion means 6 in synchronization with the X-ray irradiation timing.

  The A / D conversion means 6 acquires the output signal of the image detector 3, performs A / D conversion, and stores the output signal of the image detector 3 subjected to A / D conversion in the large-capacity frame image storage means 7. The output signal of the image detector 3 is an output signal of a plurality of pixels that are two-dimensionally arranged in the image detector 3, and is a frame image.

  The large-capacity frame image storage unit 7, the large-capacity processing image storage unit 8, the all-image display storage unit 9, and the image processing unit 10 can be realized by a general computer (computer), for example, (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), HDD (Hard Disk Drive), and an input / output interface.

  The output means 11 is comprised from CRT (Cathode Ray Tube), a liquid crystal display (LCD: Liquid Crystal Display), PDP (Plasma Display Panel), EL (Electronic Luminescence) etc., for example.

  The large-capacity frame image storage means 7 is composed of a general image memory, a hard disk or the like, and stores output signals (frame images) sent from the image detector 3 at a predetermined frame rate. The large-capacity frame image storage means 7 stores the A / D converted frame image.

  The large-capacity processed image storage means 8 is composed of a general image memory, a hard disk, and the like. In the present embodiment, the image processing means 10 uses the large-capacity processing image storage means 8 to perform image processing by the demott method or to perform panoramic tomographic image construction processing.

  The large-capacity processed image storage means 8 has a recording area for each pixel that matches the coordinate position of each pixel in an image (here, a frame image), and M rows (M is 2) An expanded memory space corresponding to a coordinate space obtained by enlarging the image M × N times is set by dividing the image into N columns (N is an integer of 2 or more). In the following, as an example, it is assumed that M and N have the same value. This expanded memory space is used for image processing by the DEMOT method.

  In the large-capacity processed image storage means 8, a memory space corresponding to each pixel in the frame image is set on a one-to-one basis. This one-to-one memory space is used for panoramic tomographic image construction processing. The storage means used for constructing the panoramic tomographic image may be a separate storage device.

  The all-image display storage unit 9 is composed of a general image memory or the like, and stores the panoramic tomographic image (image to be displayed) generated by the image processing unit 10. This panoramic tomographic image is represented by a luminance value, for example.

  The image processing means 10 reads out the frame image from the large-capacity frame image storage means 7 and transfers it to the large-capacity processing image storage means 8, and performs predetermined image processing on the large-capacity processing image storage means 8. That is, the image processing unit 10 acquires the frame image converted and output by the A / D conversion unit 6 and performs image processing. In the present embodiment, the image processing means 10 has an image processing function by the DEMOT method and a processing function for constructing a panoramic tomographic image.

  The function of the image processing means 10 is realized by the CPU developing and executing a predetermined program stored in the ROM or the like on the RAM. This program can be provided via a communication line, or can be provided by being written in a recording medium such as a CD-ROM.

  As processing for constructing a panoramic tomographic image, the image processing means 10 reads out a plurality of frame images subjected to image processing by the DEMOT method from the large-capacity processed image storage means 8. Then, the image processing means 10 has a predetermined shift width corresponding to a predetermined tomographic plane of the subject 12 in the memory space set in the large-capacity processing image storage means 8 (memory space corresponding to one-to-one pixel). A plurality of frame images are superimposed. Thereby, a panoramic tomographic image corresponding to a predetermined tomographic plane of the subject 12 is constructed. The process of constructing this panoramic tomographic image is known.

  Image processing by the DEMOT method is described in Patent Document 1 and Patent Document 2, and an image reconstruction algorithm of the DEMOT method will be described below with reference to the drawings.

  Taking an edge image as an example will be described with reference to FIGS. 4A and 4B. Here, a flat panel detector (FPD) that is a recording medium is used as the image detector 3 and imaging is performed by an edge method in which the subject 12 is a metal plate (lead edge).

FIG. 4A shows the arrangement of the FPD 13 and the lead edge 14. The FPD 13 is placed on a stage (not shown) capable of minute linear movement. Reference numeral 15 in FIG. 4A indicates the moving direction of the FPD 13. A lead edge 14 is placed close to the FPD 13. FIG. 4B shows a part of a cross-sectional pixel row along the alternate long and short dash line shown in FIG. 4A. It is assumed that the edge portion of the lead edge 14 coincides with the boundary line between the pixels of the FPD 13 at the initial state before the FPD 13 moves slightly and at the start. Pixels hidden lead edge 14 among the pixels of the FPD13 and P _1, the pixel is irradiated in the X-ray 16 and P _2.

The pixels P ₁ , P ₂ ,... Are one-dimensionally arranged on a one-dot chain line shown in FIG. 4A of the FPD 13 having a large number of pixels. Hereinafter, the FPD 13 will be described focusing on this one-dimensional line. First, it is assumed that the fill factor is 100%. That is, it is assumed that the pixel has only the light receiving area. At this time, a distance smaller than the pixel width is assumed. Specifically, assuming a minute distance in which the pixel width is divided into a plurality of distances, the operation of moving the FPD 13 by this minute distance and performing shooting is repeated as many times as the number of divisions, and finally the FPD 13 is changed to the pixel size. Shall be moved. Here, for example, assuming that the pixel size is d and the number of pixel divisions is 10, the operation of performing shooting by moving the FPD 13 slightly by d / 10 is repeated 10 times. As shown in FIG. 4B, the lead edge 14 is arranged slightly spaced from the surface of the FPD 13, and is fixed by a holder (not shown). Therefore, even if the FPD 13 moves, the lead edge 14 does not move in the initial arrangement.

And X-ray 16 is irradiated perpendicularly to FPD13, when shooting a lead edge image, an output signal corresponding to the incident X-ray amount from the pixel P ₂ is obtained. The two-dimensional image of the FPD 13 is transferred to the large-capacity processed image storage unit 8. In the memory space of the large-capacity processed image storage means 8, the size and position of the pixels of the FPD 13 are matched in advance, and corresponding to the number of divisions of the pixels of the FPD 13, ten times that of one pixel of the one-dimensional line of the FPD 13 The number of pixels is set. Accordingly, the number of pixels 100 times the total number of pixels of the two-dimensional FPD 13 is set in the memory space of the large-capacity processed image storage unit 8. The output signal of one pixel on the one-dimensional line of the FPD 13 is similarly transferred to 10 pixels on the memory space of the large-capacity processed image storage means 8 corresponding to the pixel position.

Here, the level of the output signal of the pixel will be described. The shooting at the start of the minute movement of FPD13 as shown in FIG. 4B, X-ray 16 is irradiated to the entire pixel in the pixel P _2. The level of the output signal of the pixel P _{2 at} this time is set to 10 for convenience, corresponding to the number of divided pixels. On the other hand, since the pixel P ₁ is blocked by the lead edge 14 and is not irradiated with the X-rays 16, the level of the output signal of the pixel P _{1 at} this time is set to zero.

The output signal (level 10) transferred from the pixel P _{2 of the} FPD 13 is written in 10 pixels corresponding to the position of the P ₂ pixel in the memory space of the large-capacity processed image storage means 8.
The output signal (level 0) transferred from the pixel P _{1 of the} FPD 13 is written in 10 pixels corresponding to the position of the P ₁ pixel in the memory space of the large-capacity processed image storage means 8.

Next, as indicated by reference numeral 15 in FIG. 5, the FPD 13 is slightly moved to the left in FIG. 5 by 1/10 of the pixel size. Then, by this first movement, the pixel P ₂ is shielded by the lead edge 14 in 1/10 of the pixel area. Therefore, the P ₂ pixel is irradiated with the X-ray 16 on an area of 90% of the entire pixel. Accordingly, the level of the output signal of the pixel P _{2 at} this time is 9. The output signal (level 9) is transferred to the large-capacity processed image storage means 8 and written is the numerical value shown in the middle of FIG. The output signal (level 9) shall be P ₂ pixels are transferred to the 10 pixels corresponding to the position after the fine movement only 1/10 of the pixel size in the memory space of the mass processed image storage means 8.

In FIG. 5, the position of the pixel P ₂ of the FPD 13 shown in the upper stage is the position at the start of the minute movement. In FIG. 5, the position of the pixel in the memory space of the large-capacity processed image storage means 8 shown in the middle stage indicates the position at the time of the first movement. In the memory space of the large-capacity processed image storage means 8, the leftmost pixel among the 10 pixels to which the level 9 output signal is written is the output signal (level 0) transferred from the pixel P ₁ at the start of the minute movement. Is the pixel that was written. That is, in the writing process associated with the first movement, level 9 is written in 10 pixels including a pixel shifted to the left by one pixel from the pixel in the memory space of the large-capacity processed image storage unit 8 at the start. . Accordingly, in the first movement, for example, the output signal (level 0) transferred from the pixel P ₁ is shifted to the left by one pixel from the pixel in the memory space of the large-capacity processing image storage means 8 at the start. Will be written into 10 pixels.

After the first movement of the FPD 13 and the writing of the output signal are completed, the FPD 13 is further moved slightly to the left in FIG. 5 by 1/10 of the pixel size to capture an edge image. Due to the second movement, the movement amount from the first position becomes 2/10 of the pixel size. Then, by this second movement, 2/10 of the pixel area of the pixel P ₂ is shielded by the lead edge 14. Therefore, the P ₂ pixel is irradiated with X-rays 16 on an area of 80% of the entire pixel. Accordingly, the level of the output signal of the pixel P _{2 at} this time is 8. The output signal (level 8) is transferred to the large-capacity processed image storage means 8 and written is the numerical value shown in the lower part of FIG.

  In this way, while the FPD 13 is moved and photographed, the process of transferring the output signal of each pixel to the large-capacity processed image storage means 8 is performed each time. At this time, the pixel position and the lead edge 14 in the memory space of the large-capacity processed image storage means 8 do not move from the initial set position. FIG. 6 shows a list of signal signals transferred to the large-capacity processed image storage means 8 that are output signals of the respective pixels in accordance with the minute movement of the FPD 13.

  In this case, since the movement is performed by 1/10 of the pixel size, the movement is completed by 10 movements, and returns at the start. That is, when the circuit is completed, the edge of the lead edge 14 coincides with the boundary line between the next pixels of the FPD 13. Output signals written to each pixel on the memory space of the large-capacity processed image storage means 8 during the movement until returning to the start are sequentially added. This process is a process of adding the signal levels in the table of FIG. 6 in the column direction.

  In FIG. 6, the final addition result is indicated as “0, 0, 0, 1, 3, 6,..., 100” under the large-capacity processing image storage unit 8. This numerical sequence is a photograph of the lead edge 14 and has a distance dimension. The curve represented by this numerical sequence is called an Edge Spread Function (ESF). The line spread function (LSF) calculated from the ESF distance differentiation is shown as “0, 0, 1, 2, 3,..., 0” at the bottom of FIG. A theoretically obtained ESF graph is shown in FIG. 7A. The theoretically obtained LSF graph is shown in FIG. 7B. The shape of the LSF is a triangular wave as a whole, but a shape obtained by combining two symmetrical sawtooth waves.

Next, imaging of the lead edge 14 during the minute movement of the image detector 30 will be described with reference to FIGS. 8A and 8B. FIG. 8B shows a part of the pixel column in the cross section taken along the alternate long and short dash line shown in FIG. 8A. The image detector 30 will be described focusing on this one-dimensional line. For example, assuming that the pixel size is d and the image detector 30 is slightly moved by d / 10 to perform photographing, the operation is repeated 10 times. The pixels P ₁ , P ₂ ,... Of the image detector 30 include a light receiving area 31 and a dead area 32. The value of the pixel width d is a total value of the width W of the insensitive area 32 and the width L of the light receiving area 31. Here, it is assumed that the width W and the width L are equal (W = L = 2 / d). That is, the description will be made assuming that the fill factor is 50% when viewed on a one-dimensional line. When viewed on a two-dimensional plane, the fill factor can be set to 75%, for example, according to the shape and area of the insensitive part area 32.

An X-ray 16 is irradiated perpendicularly to the image detector 30, when shooting a lead edge image, an output signal corresponding to the incident X-ray amount from the light receiving portion area 31 of the pixel P ₂ is obtained. The two-dimensional image of the image detector 30 is transferred to the large-capacity processed image storage means 8. In the memory space of the large-capacity processed image storage means 8, the size and position of the light receiving area 31 and the insensitive area 32 of the pixel of the image detector 30 are matched in advance, and one of the one-dimensional lines of the image detector 30 is stored. Ten times as many pixels as the number of pixels are set. In two dimensions, the number of pixels is set to 100 times.

Here, the level of the output signal of the pixel will be described. Shooting at the start of the minute movement of the image detector 30 as shown in FIG 8B, the light receiving portion area 31 of the pixel P ₂ is receiving the X-rays 16. The level of the output signal of the pixel P _{2 at} this time is 5 for convenience. On the other hand, the insensitive part area 32 of the pixel P ₂ does not generate signal charge, so the level of the output signal is set to zero. Image output signal of the light receiving portion area 31 of the detector 30 of the pixel P ₂ (Level 5), respectively, five pixels of the 10 pixels in the memory space of the mass processed image storage means 8 like corresponding to the pixel position Transferred to and written to. In the remaining five pixels, the output signal (level 0) of the dead area 32 is written.

Next, as indicated by reference numeral 15 in FIG. 9, the image detector 30 is slightly moved to the left in FIG. 9 by 1/10 of the pixel size. Then, by this first movement, the pixel P ₂ is shielded by the lead edge 14 in 1/10 of the pixel area. In this case, a part of the insensitive area 32 is shielded, and the light receiving area 31 is irradiated with the X-rays 16. Accordingly, the output signal level of the light receiving area 31 of the pixel P _{2 at} this time is 5. The output signal (level 5) is transferred to the large-capacity processed image storage means 8 and written to the corresponding five pixels, respectively, as shown in the middle part of FIG.

After the first movement of the image detector 30 and the writing of the output signal are completed, the image detector 30 is further moved slightly to the left in FIG. 9 by 1/10 of the pixel size to capture an edge image. The output signal (level 5) of the light receiving section area 31 of the pixel P _{2 at} this time is transferred to the large-capacity processed image storage means 8 and written is the numerical value shown in the lower part of FIG. In this way, while moving and photographing the image detector 30, a process of transferring the output signal of each pixel to the large-capacity processing image storage means 8 is performed. FIG. 10 shows a list of the output signals of each pixel in accordance with the minute movement of the image detector 30 as a signal sequence transferred to the large-capacity processed image storage means 8.

  Output signals written to each pixel in the memory space of the large-capacity processed image storage unit 8 during the movement until the image detector 30 is moved by d are sequentially added. This process is a process of adding the signal levels in the table of FIG. 10 in the column direction. The final addition result is shown below the large-capacity processed image storage unit 8 in FIG. The LSF calculated from the distance differentiation of the curve (ESF) represented by this numerical sequence is shown at the bottom of FIG. In this case, a theoretically obtained ESF graph is shown in FIG. 11A, and a theoretically obtained LSF graph is shown in FIG. 11B.

  From FIG. 7B, the MTF obtained when the shape of the LSF is a sawtooth wave is shown by a two-dot chain line in FIG. Similarly, the MTF obtained from FIG. 11B is shown by a solid line in FIG. As a comparison, the MTF obtained when the shape of the LSF is a rectangular wave is shown by a broken line in FIG. When the shape of the LSF is a rectangular wave, the cutoff frequency of the MTF is represented by 1 / (2d), that is, the Nyquist frequency, where d is the pixel size. On the other hand, when the DEMOT method is used without considering the dead area (when the fill factor is 100%), the cutoff frequency of the MTF is 1 / d, which is theoretically expressed as twice the Nyquist frequency. As a result, the resolution is improved. In addition, when the DEMOT method is used in consideration of the insensitive area (when the fill factor is 50%), the cutoff frequency of the MTF is 2 / d, which is theoretically expressed by four times the Nyquist frequency, and the resolving power is improves.

  In the image reconstruction algorithm using the DEMOT method in consideration of the insensitive area described above, the image detector 30 is described by focusing on the one-dot chain line shown in FIG. 8A to simplify the description. Pixels are two-dimensionally arranged in the image detector. Therefore, in the X-ray imaging apparatus 1 in FIG. 1, in order to increase the resolving power in two horizontal and vertical directions of the obtained image, the pixel group of an arbitrary column in the direction in which the image detector 3 is moved. The pixels are arranged so that the arrangement direction is inclined.

  Hereinafter, when the X-ray imaging apparatus 1 includes the image detector 3a, an image reconstruction algorithm using the DEMOT method will be described with reference to FIG. 2 and the like as appropriate. FIG. 13A is a diagram schematically illustrating an example of an arrangement of some of the pixels 20a, 20b, 20c, and 20d in the image detector 3a and a lead edge 14B as a subject. When the 2 × 2 pixel region shown in FIG. 13A moves to the lead edge 14B side, the movement can be divided into movement in the X direction and movement in the Y direction.

A 2 × 2 pixel region shown in FIG. 13A is divided into two equal parts by a boundary line parallel to the X axis, and a set of pixels 20a and 20b is assumed. Further, if the set of the pixels 20a and 20b is divided into two equal parts by a boundary line parallel to the X axis as shown in FIG. 13B, one of the pixels P ₁ and P ₂ having a dead area moves in the X direction. It can be regarded as a thing. The operation at this time is the same as the operation shown in FIG. 8B. In addition, the other of the two halves can be regarded as the pixels P ₃ and P ₄ having no dead area moving in the X direction. The operation at this time is the same as the operation shown in FIG. 4B. Therefore, ESF and LSF can be calculated by combining the DEMOT method considering the insensitive part area and the DEMOT method not considering the insensitive part area.

The same applies to the case of moving the 2 × 2 pixel region shown in FIG. 13A in the Y direction. In this case, as shown in FIG. 13C, the set of the pixels 20a and 20c is composed of pixels P ₅ and P ₆ having a dead area and pixels P ₇ and P ₈ having no dead area. It can be considered.

  FIG. 14 is a schematic diagram illustrating an example of the signal intensity written in the memory set in the large-capacity processing image storage unit 8 when the X-ray imaging apparatus 1 includes the image detector 3a. In FIG. 14, a bold rectangular frame represents a recording area for each pixel, is divided into 10 rows horizontally and 10 columns vertically, and has a total of 100 memories. Note that the entire display was tilted 45 degrees corresponding to the tilt angle in the arrangement direction of the pixel group.

  Here, for convenience, the level of the output signal when receiving X-rays in the entire light receiving area 21 of the pixel 20 of the image detector 3a is set to 5. On the other hand, since the dead area 22 does not generate signal charges, the level of the output signal is set to zero. In photographing at the start of the minute movement of the image detector 3a by the DEMOT method, the bold line shown in FIG. 14 corresponds to the area ratio (1/3) between the insensitive part area 22 and the light receiving part area 21 of the pixel 20 or the like. In the rectangular frame, signal level 0 is written in 25 memories, and signal level 5 is written in the remaining 75 memories.

  In the recording area of other pixels adjacent to the bold rectangular frame, the pixel output signal is similarly written in each memory. Therefore, in the row L1 along the A axis in FIG. 14, the signal level 0 is written in five consecutive memories. As viewed from the row L1, in the row one level up along the B axis in FIG. 14, the signal level 0 is written in four consecutive memories. In the second row above the row L1, the signal level 0 is written in three consecutive memories. Further, in the row L2 five above the row L1, the signal level 5 is written in ten consecutive memories. Similarly, in the row L4, the signal level 5 is written in ten consecutive memories. In rows L3 and L5, signal level 0 is written in five consecutive memories.

  As shown in FIG. 2, when the image detector 3a is moved in the moving direction 15 by 1.41 times a minute distance that is 1/10 of the pixel width d, the pixel group arranged in the image detector 3a is moved to the pixel in the X direction. It can be moved minutely by 1/10 of the width d. At the same time, the pixel groups arranged in the image detector 3a can be finely moved in the Y direction by 1/10 of the pixel width d.

When the moving direction 15 of the image detector 3a is decomposed in the X direction, as shown in FIG. 13B, a set of pixels 20a and 20b is virtually divided into pixels P ₁ and P ₂ having a dead area and a dead area. It can be considered that the pixel P ₃ is composed of pixels P ₃ and P ₄ that do not have In this case, the signal intensity written and finally added to each memory of a predetermined pixel set in the large-capacity processing image storage means 8 until the pixel width d is moved in the X direction by using the DEMOT method. An example is shown in FIG. 15A.

15A, the signal level “15, 19, 22, 24, 25” written in the five left half memories among the 10 hatched memories is the large-capacity processed image storage means 8 in FIG. Is the same as a part of the curve (ESF) represented by the numerical sequence described below, and corresponds to the position and size of the dead area of the pixel P ₂ shown in FIG. The signal level “90, 94, 97, 99, 100” written in the five memories on the right half is a curve represented by a numerical sequence described below the large-capacity processed image storage means 8 in FIG. This is the same as a part of (ESF) and corresponds to the position and size of the pixel P ₂ shown in FIG.

When the moving direction 15 of the image detector 3a is disassembled in the Y direction, as shown in FIG. 13C, a set of pixels 20a and 20c is virtually divided into pixels P ₅ and P ₆ having a dead area and a dead area. It can be regarded that the pixel P ₇ is composed of pixels P ₇ and P ₈ that do not have In this case, the signal intensity written and finally added to each memory of the predetermined pixel set in the large-capacity processing image storage means 8 until the pixel width d is moved in the Y direction by using the DEMOT method. An example is shown in FIG. 15B. A signal value that is a combination of the signal value shown in FIG. 15A and the signal value shown in FIG. 15B is written in each memory of this pixel.

  Here, another example of the image detector 3 will be described with reference to FIG. The image detector 3b has a pixel array in which the pixels 20 are two-dimensionally arranged. The pixel array is a square array in which the pixels 20 are aligned vertically and horizontally. Arrangement direction of an arbitrary pixel group is arranged so as to be inclined with respect to the moving direction 15 of the image detector 3b. The pixel 20 includes a light receiving area 21 and a dead area 22 and has a fill factor of 75%. Here, a pixel group composed of 10 pixels 20 arranged in the moving direction 15 (broken line L5) and a pixel group composed of nine pixels 20 arranged in the moving direction 15 (broken line L2) are alternately arranged. The arranged part is shown. The position of the broken line L2 corresponds to the position of the memory row L2 set in the large-capacity processing image storage unit 8 shown in FIG. Similarly, the position of the broken line L5 corresponds to the position of the row L5 shown in FIG.

In order to confirm the performance of the X-ray imaging apparatus 1 of the present invention, the following Experiment 1 and Experiment 2 were performed. This will be described with reference to FIG.
<Premise>
In each experiment, an FPD model simulating the image detector 3 was used. The FPD model is formed by providing a large number of windows simulating pixels in a rectangular frame with a predetermined thickness in a lattice shape and disposing diffusion plates on the front and back surfaces of the frame. Here, a rectangular window having a side of 10 mm divided by a 0.2 mm partition was provided in a rectangular frame having a length of 300 mm, a width of 300 mm, and a height of 20 mm. That is, the FPD model simulates an image detector in which pixels having a pixel width of 10.2 mm are arranged. By blocking a part of the window, the dead area can be simulated.

  In addition, FIG. 17 shows subjects commonly used in each experiment. The subject shown in FIG. 17 is a test pattern (star pattern chart). In this test pattern, a plurality of fan-shaped black and white striped patterns extending radially from the origin are formed. Thus, it can be seen that the more the radial black-and-white striped pattern is seen to the vicinity of the origin, the higher the resolving power by the photographing apparatus. The length of the pattern in the radial direction was about 100 mm.

<Experiment method>
The camera was fixed at a predetermined distance from the front side of the FPD model. By tilting the entire frame of the FPD model by 45 degrees from the horizontal direction, the arrangement direction of the windows was tilted by 45 degrees from the horizontal direction. A test pattern was fixed to the front half of the FPD model on the left half side as viewed from the camera. In this state, the FPD model was installed so that it could slide to the left and right when viewed from the camera. A surface-emitting backlight was fixed on the back side of the FPD model. The test pattern was photographed with the camera while the FPD model was illuminated with the backlight.

<Experiment 1>
Experiment 1 is a preliminary experiment for confirming that the resolving power is improved by the DEMOT method when a test pattern is photographed with a fill factor of 100%. For this reason, it was simulated that the dead area is not provided by opening all the windows of the FPD model. At this time, the test pattern was photographed while moving the FPD model minutely from right to left, for example. For comparison, a test pattern was photographed with the FPD model stationary.

The image shown in FIG. 18 is an image taken with the FPD model stationary. This image corresponds to an image output when the DEMOT method is not used for image processing. The fine square is the window of the FPD model. It can be seen that an image with this window as a pixel is obtained. Note that the vertically long rectangular image seen on the right side in FIG. 18 is irrelevant to the subject.
The image shown in FIG. 19 is an image taken while finely moving the FPD model by, for example, one window from right to left. This image corresponds to an image output when the DEMOT method is used for image processing. As shown in FIG. 19, it can be seen that an image of pixels smaller than the window of the FPD model is obtained.
In short, the image shown in FIG. 19 has a clearer black and white striped pattern of the test pattern than the image shown in FIG. Therefore, it was confirmed that when the DEMOT method was used with a fill factor of 100%, the resolving power theoretically improved twice as compared with the case where the DEMOT method was not used.

<Experiment 2>
In Experiment 2, a test pattern was taken with a reduced fill factor. For this reason, provision of the insensitive part area was simulated by shielding a part of the plurality of windows arranged in the FPD model. Specifically, a plurality of windows arranged on the left half side of the surface of the FPD model and their shielding portions were arranged as shown in FIG. 16, and the fill factor was 75%. Then, the test pattern was fixed on the surface of the FPD model where the dead area was provided, and the test pattern was photographed while moving the FPD model by one window from right to left. An image obtained at this time is shown in FIG.

  Although the image shown in FIG. 20 shows artifacts, it can be seen that the black and white striped pattern can be identified closer to the origin than the image shown in FIG. Therefore, it was confirmed that when the DEMOT method was used with a fill factor of 75%, the resolving power theoretically improved twice as compared with the case where the DEMOT method was used with a fill factor of 100%. That is, it was confirmed that the resolving power was theoretically improved by a factor of 4 compared with the case where the DEMOT method was not used.

  As described above, according to the X-ray imaging apparatus 1 according to the first embodiment, it is possible to obtain a resolution that is greater than twice the Nyquist frequency by image processing using the DEMOT method.

(Second Embodiment)
The X-ray imaging apparatus 1 according to the second embodiment reduces artifacts as shown in FIG. 20 by the image processing means 10. In the X-ray imaging apparatus 1 according to the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The X-ray imaging apparatus 1 according to the second embodiment includes, for example, an image detector 3b illustrated in FIG.

The image processing means 10 includes the angle of the arrangement direction of the pixels 20 with respect to the direction 15 in which the image detector 3 b is moved, the arrangement of the pixels 20, the area ratio between the insensitive area 22 and the light receiving area 21, The input of each information about the position of the insensitive part area 22 is received. Examples of arrangement information and pixel information of each pixel are described in the following (1) to (5).
(1) The angle of the arrangement direction of the pixels 20 with respect to the direction 15 in which the image detector 3b is moved is 45 degrees.
(2) The pixel array is a square array in which pixels are aligned vertically and horizontally.
(3) The area ratio between the insensitive area 22 and the light receiving area 21 is 1/3. That is, the fill factor is 75%.
(4) The position of the dead area 22 in the pixel 20 is the left corner of the rectangular pixel.
(5) The shape of the insensitive part area 22 is a rectangle like the shape of the pixel 20.

  These pieces of information may be input from a control device external to the image processing means 10, or the image processing means 10 may read out information stored in advance in the storage means. Thereby, the size and position of the pixel 20 of the image detector 3b are matched with the pixel space of the image detector 3b in the memory space of the large-capacity processed image storage means 8, and corresponding to the division number M of the recording area for each pixel, M × M times the number of pixels is set. For example, when the division number M = 10, as shown in FIG. 14, a total of 100 memories are provided for one pixel.

  When the image detector 3b shown in FIG. 16 is used, a two-dimensional artifact as shown in FIG. 20 occurs. The reason why such an artifact has occurred is considered to be due to variations in sensitivity on the light receiving surface of the image detector 3b. The pixel array of the image detector 3b shown in FIG. 16 is a square array. In this case, the sensitivity in the pixel group arranged along the moving direction 15 varies depending on the column position. Specifically, as shown in FIG. 16, for example, only the light receiving area 21 is arranged on the broken line L <b> 2. For example, the ratio of the insensitive area 22 is equal to the light receiving area 21 on the broken line L <b> 5. (Insensitive area area occupation rate 50%).

  Therefore, in order to correct the sensitivity variation on the light receiving surface, in this embodiment, the image processing means 10 detects the sensitivity from the frame image enlarged 100 times in the memory space set in the large-capacity processing image storage means 8. A characteristic curve was obtained, and the signal value of the generated processed image was corrected by the sensitivity characteristic curve. The image processing means 10 obtains a sensitivity characteristic curve in the direction orthogonal to the moving direction by adding the signal intensity in the direction 15 in which the image detector 3b is moved in the enlarged frame image.

  Specifically, an enlarged frame image is assumed in which the signal value of the image detected by the image detector 3b is recorded in 100 memories for each pixel as shown in FIG. The direction of the A axis in FIG. 14 corresponds to the moving direction 15 of the image detector 3b. In FIG. 14, for example, in rows L1 and L5, signal values are written in 100 memories corresponding to 10 pixel groups, and the total is 250, for example. In the rows L2 and L4, signal values are written in 95 memories, and the total is 475, for example. In the row L3, signal values are written in 90 memories corresponding to 9 pixel groups, and the total is 225, for example. The sensitivity characteristic curve shown in FIG. 21 is obtained in this way. The sensitivity characteristic curve shown in FIG. 21 has a higher relative intensity as the signal level is higher, that is, as the image density is lower. A sensitivity characteristic curve may be employed in which the relative intensity increases as the image density increases.

  In the experiment 2, a test pattern was photographed while moving the FPD model provided with the insensitive area by a small amount from the right to the left by one window, and the signal value of the processed image generated by the image processing means 10 is expressed as a sensitivity characteristic. An image was obtained by correcting with a curve. The obtained image is shown in FIG. In the image shown in FIG. 22, the artifact can be greatly reduced as compared with the image shown in FIG. 20.

(Third embodiment)
The X-ray imaging apparatus 1 according to the third embodiment reduces artifacts as shown in FIG. 20 without obtaining a sensitivity characteristic curve. In the X-ray imaging apparatus 1 according to the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate. Assume that the X-ray imaging apparatus 1 according to the third embodiment includes, for example, an image detector 3c illustrated in FIG.

  The individual pixels 20 arranged in the image detector 3c are the same as the individual pixels 20 arranged in the image detector 3b shown in FIG. However, the pixel array of the image detector 3c is an alternating arrangement in which the positions of the pixels are shifted every other column. The shift width is arbitrary, but here, as an example, the pixel positions are shifted by half a pixel every other column.

  As shown in FIG. 23, in the case of the alternating arrangement, the sensitivity in the pixel group arranged along the movement direction 15 is constant regardless of the column position. Specifically, the ratio of the insensitive part area 22 on the broken line L6 is approximately 1/3 of the ratio of the light receiving area 21 (the insensitive part area occupancy rate of 33%). Further, even at a position where the broken line L6 is shifted up and down, the ratio occupied by the insensitive area 22 and the ratio occupied by the light receiving area 21 are unchanged. Therefore, it is considered that artifacts as shown in FIG. 20 can be greatly reduced.

(Fourth embodiment)
The X-ray imaging apparatus 1 according to the fourth embodiment is the same as the X-ray imaging apparatus 1 according to the first embodiment except that the shape of the insensitive area of the pixel is different on the light receiving surface of the image detector 3. . Therefore, the shape of the insensitive area of the pixel and its modification will be described with reference to the drawings.

  A pixel 40 shown in FIG. 24A includes a light receiving area 41 and a dead area 42. The dead area 42 includes the center point of the pixel 40 and is surrounded by the light receiving area 41. The shape of the insensitive area 42 is a square that is similar to the shape of the pixel 40. The fill factor of the pixel 40 is 75%.

  A pixel 50 shown in FIG. 24B includes a light receiving area 51 and a dead area 52. The shape of the insensitive part area 52 is a square similar to the shape of the pixel 50, and the insensitive part area 52 is disposed at the right corner of the pixel 50. The fill factor of the pixel 50 is 75%.

  A pixel 60 shown in FIG. 24C includes a light receiving area 61 and a dead area 62. The shape of the insensitive part area 62 is a rectangle, and the insensitive part area 62 includes one side of the outline of the pixel 60 and a part of each side of both ends thereof. The fill factor of the pixel 60 is 75%.

A pixel 70 shown in FIG. 24D includes a light receiving area 71 and a dead area 72. The insensitive part area 72 has a rectangular shape, and the insensitive part area 72 includes the left corner of the pixel 70 and a part of two sides sandwiching the corner. The fill factor of the pixel 70 is 62.5%.
In each pixel shown in FIGS. 24 (a) to 24 (d), the shape of the light-receiving surface of the insensitive area is an overlap formed when two shapes having the same shape as the shape of the light-receiving surface of the pixel are shifted and overlapped. The shape of the part is the same.

A pixel 80 shown in FIG. 24E includes a light receiving area 81 and a dead area 82. The shape of the light receiving surface of the light receiving portion area 81 is the same as the shape of the overlapping portion formed when two figures having the same shape as the shape of the light receiving surface of the pixel are shifted and overlapped. The shape of the light receiving area 51 is a square that is similar to the shape of the pixel 80, and the light receiving area 51 is disposed at the right corner of the pixel 80. The fill factor of the pixel 80 is 25%.
In each of the pixels shown in FIGS. 24A to 24E, the shape of the light-receiving surface of the insensitive area is relative to the center line C that bisects the shape of the light-receiving surface of the pixel in parallel with the moving direction 15. And symmetric shapes.

  FIG. 25 is a diagram illustrating an example of the image detector 3d in which the pixels 60 illustrated in FIG. The image detector 3d shown in FIG. 25 has a pixel array in which the pixels 60 are two-dimensionally arranged. The pixel array is a square array in which the pixels 60 are aligned vertically and horizontally. Assuming that the pixel width is d, the value of the pixel width d is the total value of the width W of the insensitive area 62 and the width L of the light receiving area 61. Here, as an example, the width L is assumed to be three times the width W. That is, the fill factor is 75%. In this case, theoretically, the resolving power in the X direction in the image detector 3d is represented by 40 [cycles / mm], and is improved to 8 times the Nyquist frequency.

  Next, the relationship between the area of the insensitive area and the resolving power will be described with reference to FIGS. 26 (a) to 26 (d). Here, some specific examples will be given in which one pixel on the light receiving surface of the image detector 3 is focused on, has a dead area at the corner of the pixel, and moves the image detector in the diagonal direction of the pixel. Will be described.

  Since the pixel 100 shown in FIG. 26A is not provided with a dead area, the fill factor of the pixel 100 is 100%. When image processing by the DEMOT method is performed using the image detector 3 in which the pixels 100 are arranged, the resolving power is theoretically expressed by twice the Nyquist frequency.

  A pixel 120 shown in FIG. 26C includes a light receiving area 121 and a dead area 122. The fill factor of the pixel 120 is 75%. Since the shape of the light receiving portion area 121 on the light receiving surface is an L shape of the alphabet, the pixel 120 is also referred to as an L-shaped pixel. When image processing by the DEMOT method is performed using the image detector 3 in which the pixels 120 are arranged, the resolving power is theoretically expressed by four times the Nyquist frequency as described above. In the case of such a relatively high resolution (in the case of a high resolution type), it is preferable to set the fill factor value.

  A pixel 110 illustrated in FIG. 26B is an L-type pixel, and includes a light receiving area 111 and a dead area 112. The fill factor of the pixel 110 is 93.75%. When image processing by the DEMOT method is performed using the image detector 3 in which the pixels 110 are arranged, the resolving power is theoretically expressed by three times the Nyquist frequency. According to this, an image having high resolution compared to the case where the pixel 100 shown in FIG. 26A is used and an excellent graininess compared to the case where the pixel 120 shown in FIG. 26B is used. Is obtained. Therefore, when it is intended to obtain a high-resolution image while emphasizing the graininess of the image (in the case of a high-resolution type emphasizing graininess), the value of the fill factor is preferable.

  A pixel 130 illustrated in FIG. 26D is an L-type pixel, and includes a light receiving area 131 and a dead area 132. The fill factor of the pixel 130 is 43.75%. When image processing by the DEMOT method is performed using the image detector 3 in which the pixels 130 are arranged, the resolving power is theoretically expressed by 8 times the Nyquist frequency. According to this, a much higher resolving power can be obtained as compared with the case where the pixel 100 shown in FIG. Therefore, when it is desired to obtain an ultra-high resolution image (in the case of an ultra-high resolution type), the value of the fill factor is preferable.

  Next, modification examples of the shape of the pixel will be described with reference to FIGS. 26 (e) to 26 (g). Here, paying attention to one pixel on the light receiving surface of the image detector 3, the shape of the pixel is a circle as an example, the radius of the circle is r, and the left direction in FIGS. 26 (e) to 26 (g) Several specific examples will be described as moving the image detector.

  A pixel 140 shown in FIG. 26E includes a light receiving area 141 and a dead area 142. The shape of the light-sensitive surface of the insensitive area 142 is the same as the shape of the overlapping portion formed when the same two circles as the shape of the light-receiving surface of the pixels are shifted and overlapped. The maximum width of the overlapping portion of the two circles is 3r / 2. The fill factor of the pixel 140 is 31.5%. Since the shape of the light-receiving portion area 141 is a crescent moon, the pixel 140 is also referred to as a crescent moon-shaped pixel.

  A pixel 150 illustrated in FIG. 26F is a crescent moon-shaped pixel, and includes a light receiving area 151 and a dead area 152. The shape on the light receiving surface of the insensitive part area 152 is the same as the shape of the overlapping portion that is formed when the same two circles as the shape on the light receiving surface of the pixel are shifted and overlapped. The maximum width of the overlapping part of the two circles is r. The fill factor of the pixel 150 is 60.9%.

A pixel 160 illustrated in FIG. 26G is a crescent moon-shaped pixel, and includes a light receiving area 161 and a dead area 162. The shape of the light-sensitive surface of the insensitive part area 162 is the same as the shape of the overlapping portion formed when the same two circles as the shape of the light-receiving surface of the pixel are shifted and overlapped. The maximum width of the overlapping portion of the two circles is r / 2. The fill factor of the pixel 160 is 85.6%.
In each pixel shown in FIGS. 26 (e) to 26 (g), the shape of the light-receiving surface of the insensitive area is a center line that bisects the same circle as the shape of the light-receiving surface of the pixel in parallel with the moving direction. It contains a symmetrical shape.

  26 (b) to 26 (d) show an L-shaped pixel in which a light-sensitive surface area of a rectangular pixel is provided, and FIGS. 26 (e) to 26 (g) show a circular shape. Although the crescent-shaped pixel in which the insensitive part area is provided on the light receiving surface of the pixel is shown, the shape of the pixel is not limited to a rectangle or a circle, and may be, for example, a hexagon. When the shape of the pixel is a regular hexagon, the pixels can be arranged without gaps to form a so-called honeycomb structure.

The present invention can be applied to pixels having any shape as long as a pixel including a light receiving area and a dead area satisfies the following conditions (1) and (2).
(1) The shape of the light-receiving surface in the insensitive area is the same as the shape of the overlapping portion formed when two figures having the same shape as the shape of the light-receiving surface of the pixel are shifted and overlapped. In this case, the insensitive part area may be surrounded by the light receiving part area.
(2) The shape of the light-receiving surface of the light-receiving portion area is the same as the shape of the overlapping portion formed when two figures having the same shape as the shape of the light-receiving surface of the pixel are shifted and overlapped. In this case, it is not preferable that the light receiving area is surrounded by the insensitive area because the sensitivity is poor.

  According to the present invention, in the large-capacity processed image storage means 8, the shape of the light-receiving surface of a pixel is recorded as a signal distribution in a memory expanded to the number of pixels M × M times that of one pixel, and an image is obtained based on the DEMOT method. By synthesizing, the cut-off frequency of MTF can be made larger than twice the Nyquist frequency in the obtained image.

(Fifth embodiment)
The X-ray imaging apparatus 1 according to the fifth embodiment is similar to the X-ray imaging apparatus 1 except that the insensitive part area 22 and the light receiving part area 21 are formed in each pixel 20 by the image detector 3 performing binning. This is the same as the line imaging apparatus 1. Hereinafter, binning when the FPD 13 shown in FIG. 27A is used as an example of the image detector 3 of the X-ray imaging apparatus 1 will be described.

  For example, in the case of a general FPD, in addition to a pixel array for accumulating charges, a vertical scanning register for row scanning and a plurality of charge amplifier arrays are included, and the charge amplifier array is a charge amplifier with a built-in CDS circuit of several tens of channels. And a horizontal shift register. In the present embodiment, for example, the image processing means 10 outputs a control command to the FPD 13 to electrically turn off the charge amplifier array corresponding to the pixel P to be made into the dead area in the pixel array. As a result, the output signals of the remaining pixels can be read without reading the output signals of the corresponding pixels. By performing binning in this way, a dead area and a light receiving area can be formed for each unit pixel. As a method for freely setting and controlling the position and size of a local area on the light receiving surface of the FPD, for example, a method similar to the method described in Japanese Patent Application Laid-Open No. 2010-42121 can be used.

In the FPD 13 shown in FIG. 27A, normal rectangular pixels P are squarely arranged. When 2 × 2 pixels including, for example, the pixels P ₁₁ , P ₁₂ , P ₂₁ , and P _{22 of the} FPD 13 are collectively handled as the unit pixel 210, for example, without reading the output signal of the pixel P ₂₁ , the remaining pixels P ₁₁ , Read the output signals of P ₁₂ and P ₂₂ . The light receiving area 211 can be formed by reading the output signals from the pixels P ₁₁ , P ₁₂ , and P ₂₂ , and the dead area 212 can be formed by not reading the output signal from the pixel P ₂₁ .

When 2 × 2 pixels composed of the pixels P ₁₁ , P ₁₂ , P ₂₁ , and P ₂₂ are collectively handled as a unit pixel, any pixel may correspond to the insensitive area. For example, the unit pixel 220 shown in FIG. 27B forms the light receiving area 221 by reading the output signals of the pixels P ₁₁ and P ₁₂ and is insensitive by not reading the output signals of the pixels P ₂₁ and P _22. A partial area 222 is formed. The unit pixel 230 shown in FIG. 27C forms a light receiving area 231 by reading output signals from the pixels P ₁₁ , P ₂₁ , and P ₂₂ , and insensitive area by not reading the output signal from the pixel P _12. 232 is formed.

  Since the number of pixels decreases when binning, the spatial resolution is lowered. However, the binning increases the frame rate (frame / second) because the number of pixels to be read decreases. For example, when the pixel size of the FPD 13 is 100 [μm] × 100 [μm] and arranged in a horizontal direction of 1024 pixels × vertical direction of 1024 pixels, the unit pixel size of 2 × 2 pixels is 200 [μm]. × 200 [μm]. In the case of this unit pixel, if the other conditions are the same, the frame rate is doubled compared to the normal pixel. Image processing by the DEMOT method is more advantageous as the frame rate is higher. Further, when the subject is a dentition, practically, for example, about 60 to 80 pixels are sufficient in the vertical direction of the pixel array, and when using a mode in which only a part of the pixel array is used as described above, It is possible to further increase the frame rate by a dozen times.

  In the binning process, the number of pixels handled together is not limited to four pixels. For example, 3 × 3 pixels may be collectively handled as a unit pixel. In the unit pixel 240 shown in FIG. 27D, the insensitive part area 242 is formed by not reading the output signal of the central one pixel, and the light receiving part area 241 is formed by reading the output signal of the peripheral eight pixels. Is. The unit pixel 250 shown in FIG. 27E forms the insensitive part area 252 by not reading the output signals of the four corner pixels, and forms the light receiving part area 251 by reading the output signals of the five neighboring pixels. It is a thing.

  In the present embodiment, the fill factor of the unit pixel is not limited to that illustrated, and can be changed as appropriate. Further, a control command may be output to the FPD 13 from a controller (not shown) different from the image processing means 10.

[Modification]
The present invention is not limited to the above-described embodiments. For example, the horizontal division number M and the vertical division number N of the recording area for each pixel set in the large-capacity processed image storage unit 8 have been described as being equal, but the values of M and N may be different. . For example, the division number M is not limited to 10 and is arbitrary.
When the DEMOT method is used, the number of horizontal divisions and the number of vertical divisions of one pixel of the image detector 3 may be different, but if they are equal, the vertical resolution and the horizontal resolution are the same in the obtained image. Therefore, it is preferable. Further, the number of pixel divisions is not limited to 10 and is arbitrary. Considering the processing load and processing time of the apparatus, for example, it is preferably 3-20, and more preferably 5-10.

  In each embodiment, the dental X-ray imaging apparatus 1 has been described. However, the present invention is not limited to dental X-ray imaging and can be used for general medical images. For example, it may be applied to a chest X-ray imaging apparatus for internal medicine. In the present invention, the subject is not limited to the human body, and may be, for example, a naturally occurring object such as a mineral or a product of various industries. In this case, various types of analysis and inspection for damage can be performed.

DESCRIPTION OF SYMBOLS 1 X-ray imaging apparatus 2 X-ray source 3,3a, 3b, 3c, 3d, 30 Image detector 4 Arm 5 Turning drive means 7 Large capacity frame image memory | storage means 8 Large capacity processed image memory means 9 All image display memory means 10 Image processing means 11 Output means 12 Subject 13 FPD
14 Lead edge 15 Movement direction 16 X-ray 20, 20a, 20b, 20c, 20d Pixel 21, 31, 41, 51, 61, 71, 81 Light receiving area 22, 32, 42, 52, 62, 72, 82 Insensitive area Area 40, 50, 60, 70, 80 Pixels 100, 110, 120, 130, 140, 150, 160 Pixels 111, 121, 131, 141, 151, 161 Light receiving area 112, 122, 132, 142, 152, 162 Insensitive area 210, 220, 230, 240, 250 Unit pixel 211, 221, 231, 241, 251 Light receiving area 212, 222, 232, 242, 252 Insensitive area d Pixel width w Insensitive area L Light receiving area Width O Center of rotation

Claims (8)

An X-ray source;
An image detector comprising an X-ray image detection recording medium having a pixel array in which pixels are two-dimensionally arranged on a light-receiving surface that receives X-rays passing through a predetermined point of a subject;
Driving means for moving the image detector in a direction orthogonal to the X-ray incident direction;
Frame image storage means for storing a frame image sent at a predetermined frame rate from the image detector;
It has a recording area for each pixel whose position is aligned with each pixel in the pixel array of the image detector, and the recording area for each pixel is divided into M rows (M is an integer of 2 or more) and N columns vertically. A large-capacity processing image storage means in which an expanded memory space corresponding to a coordinate space obtained by dividing the frame image by M × N times by dividing into N (N is an integer of 2 or more) is set. A radiography apparatus,
With respect to the direction in which the image detector is moved by the driving means, the arrangement direction of the pixels in the pixel array of the image detector is arranged to be inclined,
In the light receiving surface of the image detector, a light receiving area and a dead area are provided for each pixel,
The frame image is transferred to the large-capacity processed image storage means, and the shape of the light receiving surface of the pixel is signaled to a plurality of memories corresponding to the number of pixels expanded by M × N times for one pixel of the frame image. Recorded as a distribution, the pixel of the image detector when the image detector is moved minutely by a distance smaller than the pixel width with respect to the direction in which the vertical or horizontal pixel group in the pixel array is inclined. Output signals are proportionally written in M × N memories corresponding to the position of the pixel in the expanded memory space according to the moving position of the image detector and sequentially written, and M × N pieces for each pixel. An X-ray imaging apparatus comprising image processing means for generating a processed image by adding signals to be written in each memory on each memory.   In the pixels arranged in the image detector, the shape of the light-receiving surface of the insensitive area or the light-receiving area is an overlap that is formed when two shapes having the same shape as the shape of the light-receiving surface of the pixel are shifted and overlapped. The X-ray imaging apparatus according to claim 1, wherein the X-ray imaging apparatus has the same shape as the portion.   In each pixel arranged in the image detector, the shape of the light-receiving surface of the dead area is symmetric with respect to a center line that bisects the shape of the light-receiving surface of the pixel in the direction in which the image detector is moved. The X-ray imaging apparatus according to claim 1, wherein the X-ray imaging apparatus includes an arbitrary shape.   The X-ray imaging apparatus according to claim 3, wherein a shape of the insensitive area or the light receiving area is similar to the shape of the pixel.   The X-ray imaging apparatus according to claim 3 or 4, wherein the shape of the pixel and the insensitive part area is a square, and the insensitive part area is disposed at a corner of the pixel.   The image processing means includes an angle of a pixel arrangement direction with respect to a direction in which the image detector is moved, an arrangement of the pixels, an area ratio between the insensitive area and the light receiving area, and the insensitivity in the pixel. The signal intensity in the direction in which the image detector is moved in the frame image enlarged by M × N in the memory space set in the large-capacity processed image storage means is received. 6. The sensitivity characteristic curve in a direction orthogonal to the moving direction is obtained by adding, and the signal value of the generated processed image is corrected by the sensitivity characteristic curve. The X-ray imaging apparatus as described in any one of Claims.   The X-ray imaging apparatus according to any one of claims 1 to 5, wherein the pixel array of the image detector is an alternating array in which the positions of the pixels are shifted every other column.   The image detector performs binning, which is a process of handling a plurality of adjacent pixels as a virtual unit pixel, and for each unit pixel, the remaining pixels without reading an output signal of a predetermined part of the pixels The X-ray imaging apparatus according to claim 1, wherein the insensitive part area and the light-receiving part area are formed for each unit pixel by reading the output signal.

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