JP4560098B2 - X-ray imaging apparatus and signal processing method thereof - Google Patents

Description

  The present invention relates to an X-ray imaging apparatus and a signal processing method thereof, and more particularly, to an X-ray imaging apparatus and a signal processing method thereof for improving the resolution of tomographic images taken for general medical use and dental use.

2. Description of the Related Art Conventionally, as a dental X-ray tomography apparatus, a panorama imaging apparatus in which a rotation operation and a slide operation are combined is known (see, for example, Patent Document 1 and Patent Document 2). The devices disclosed in Patent Document 1 and Patent Document 2 acquire a tomographic image in the vertical plane direction (Z direction) of the dentition at the position of the dentition aligned on the horizontal plane (XY plane).
JP-A-10-2111200 (0033-0040, FIG. 4) Japanese Utility Model Publication No. 4-48169 (pages 3 to 4 and FIG. 4)

  Since the tomographic image (panoramic tomographic image) is generated by superimposing a plurality of simple X-ray images captured while the X-ray imaging unit rotates and slides, the image tends to become unclear. Therefore, it is desired to generate a clearer image. However, for example, in order to realize a high resolution, an X-ray imaging unit having a high number of pixels is necessary. Since the X-ray imaging means having a high number of pixels is expensive, there is a problem that the manufacturing cost becomes high when such an expensive X-ray imaging means is used.

  Accordingly, an object of the present invention is to provide an X-ray imaging apparatus and a signal processing method thereof that can solve the above-described problems and can generate a high-resolution image at low cost.

  In order to solve the above problems, an X-ray imaging apparatus according to claim 1 generates a signal charge by receiving an X-ray source that irradiates a subject with X-rays and X-rays that have passed through a predetermined point of the subject. An X-ray imaging unit in which a plurality of pixels having a light receiving unit and a non-sensitive unit that does not generate a signal charge adjacent to the light receiving unit are arranged, and the X-ray imaging unit is moved in a direction orthogonal to the X-ray incident direction A driving unit; an image signal processing unit that generates a frame image by processing a signal output from the X-ray imaging unit; and a frame image storage unit that stores a frame image generated as the signal processing result. In the tomography apparatus, the frame image storage unit corresponds to a region in which the pixel is divided more finely than the pixel width, with the total value of the width of the light receiving unit and the width of the insensitive portion being a pixel width in the pixel. There are several memory areas for each of the pixels, and the image signal processing means moves the predetermined pixels of the X-ray imaging means by the pixel width as the X-ray imaging means moves. The value of the signal output from the predetermined pixel is apportioned according to the position of the light receiving unit during the movement of the predetermined pixel, integrated in each memory area for the predetermined pixel, and X-rays passing through the predetermined point Each memory area for the predetermined pixel is divided according to the position of the light receiving unit during the movement of the adjacent pixel adjacent to the predetermined pixel that receives light next to the predetermined pixel and is output from the adjacent pixel. The frame image is generated by accumulating to the above.

  According to a fourth aspect of the present invention, there is provided a signal processing method comprising: an X-ray source that irradiates a subject with X-rays; a light-receiving unit that receives X-rays that have passed through a predetermined point of the subject and generates a signal charge; An X-ray imaging unit in which a plurality of pixels having an insensitive portion that does not generate a signal charge is arranged adjacent to the X-ray imaging unit; a driving unit that moves the X-ray imaging unit in a direction orthogonal to an X-ray incident direction; Image signal processing means for generating a frame image by processing a signal output from a line imaging means; and a total value of a width of the light receiving portion and a width of the insensitive portion as a pixel width of the pixel Signal processing in an X-ray imaging apparatus comprising a plurality of memory areas corresponding to areas divided more finely than the pixel width for each of the pixels and frame image storage means for storing a frame image generated as a result of the signal processing In the way Thus, the value of the signal output from the predetermined pixel within the time during which the predetermined pixel of the X-ray imaging unit moves by the pixel width as the X-ray imaging unit moves by the image signal processing unit. According to the position of the light receiving unit during movement of the predetermined pixel, the predetermined pixel is accumulated and accumulated in each memory area for the predetermined pixel, and X-rays passing through the predetermined point are received next to the predetermined pixel. The frame image is generated by distributing the values of the signals output from the adjacent pixels to the memory areas for the predetermined pixels according to the position of the light receiving unit during movement of the adjacent pixels adjacent to the pixel. It is characterized by doing.

  According to the X-ray imaging apparatus having such a configuration and the signal processing method therefor, the X-ray imaging apparatus includes a plurality of memories corresponding to areas obtained by dividing the pixels included in the X-ray imaging unit finely than the pixel width in the frame image storage unit. Each pixel has a region, and the image signal processing means outputs a value of a signal output from a predetermined pixel that receives X-rays passing through a predetermined point of the subject and a signal output from an adjacent pixel that receives light next Are proportionally distributed according to the position of the light receiving portion of each pixel and integrated in each memory area for a predetermined pixel. After a predetermined pixel has moved by a predetermined pixel width, the adjacent pixel moves as a new predetermined pixel while receiving X-rays passing through a predetermined point of the subject in the same manner as the original predetermined pixel. It will be. However, the value of the signal output from the new predetermined pixel and the value of the signal output from the new adjacent pixel are accumulated in each memory area for the new predetermined pixel. The same applies hereinafter.

  Therefore, in the X-ray imaging apparatus and the signal processing method thereof configured as described above, in the frame image storage means, the signal accumulated in each memory area for each pixel has an X-ray intensity signal waveform obtained from a predetermined point of the subject as a triangular wave. It becomes. The length of the base of the sawtooth waveform obtained by cutting this triangular wave along a line-symmetric axis is shorter than the pixel width and becomes the width of the light receiving portion. On the other hand, if the X-ray intensity signal is not accumulated in each memory area, the X-ray intensity signal obtained from a predetermined point of the subject has a rectangular waveform for the output signal of each pixel or the signal accumulated according to the elapsed time. . The length of this rectangle is the pixel width. Since the resolving power is obtained from the reciprocal of the waveform period, if both the length of the base of the sawtooth waveform and the length of the rectangle are pixel widths, the spatial frequency of the sawtooth waveform is 2 of the spatial frequency of the rectangular waveform. Doubled. However, according to the present invention, since the length of the base of the sawtooth waveform is the width of the light receiving portion shorter than the pixel width, a resolution larger than twice as compared with the case where X-ray intensity signals are not integrated can be obtained. Can do. In general, when the LSF is a triangular wave, the cutoff frequency value is higher in the spectral region than when the LSF (Line Spread Function) is a rectangular wave. That is, it is known that the resolution is increased. Therefore, according to the X-ray imaging apparatus and the signal processing method with such a configuration, it is possible to generate a high-resolution image without changing the X-ray imaging unit to a high-resolution one.

  The X-ray imaging apparatus according to claim 2 is the X-ray imaging apparatus according to claim 1, wherein the X-ray imaging unit includes a mask that covers a part of the pixels as the insensitive part. Features.

  According to such a configuration, in the X-ray imaging apparatus, the pixel included in the X-ray imaging unit is partially covered with the mask to form the insensitive part, so that the proportion of the insensitive part occupied by the pixel is appropriately changed in design. can do.

  The X-ray imaging apparatus according to claim 3 is the X-ray imaging apparatus according to claim 1 or 2, wherein the X-ray imaging unit is configured such that the width of the insensitive portion is the pixel width in the pixel. It is comprised so that it may become 10 to 40%.

  According to such a configuration, in the X-ray imaging apparatus, the pixels included in the X-ray imaging unit can suppress the pixels of the displayed image from becoming coarse while increasing the ratio occupied by the insensitive part.

  According to the present invention, the X-ray imaging apparatus can generate a high-resolution tomographic image at a low cost.

  Hereinafter, the best mode for carrying out the X-ray imaging apparatus of the present invention (hereinafter referred to as “embodiment”) will be described in detail with reference to the drawings.

[Configuration of Digital Panorama Camera]
FIG. 1 is a configuration diagram schematically showing a digital panorama photographing apparatus according to an embodiment of the present invention. The digital panoramic imaging apparatus (X-ray imaging apparatus) 1 uses a panoramic X-ray tomography method to photograph an X-ray image on a predetermined tomographic plane along the dentition of the maxilla / mandible of a subject (person) K for dental As shown in FIG. 1, an X-ray source 2, an X-ray imaging unit 3, an arm 4, a turning drive unit 5, an A / D conversion unit 6, and a large capacity are generated. A frame image storage means 7, a large-capacity processed image storage means 8, an all-image display storage means 9, an image signal processing means (frame image processing) 10, and an output means 11 are provided.

  The X-ray source 2 has a slit (not shown), and irradiates the subject K with a slit beam (X-ray beam) generated by irradiating X-rays through the slit at a predetermined timing. .

  The X-ray imaging means 3 receives X-rays emitted from the X-ray source 2 and transmitted through the subject K, and images a portion of the subject K where X-rays are transmitted at a predetermined frame rate. The X-ray imaging means 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 X-ray imaging unit 3 will be described as a CCD image sensor. In this case, one pixel size can be set to 100 μm, for example. The X-ray imaging means 3 includes a plurality of pixels having a light receiving portion that receives X-rays that have passed through a predetermined point of a subject and generates a signal charge, and a dead portion that does not generate a signal charge adjacent to the light receiving portion. Has been. Here, it is assumed that the insensitive portion is a wiring portion that transfers signal charges generated in the light receiving portion.

  The arm 4 holds the X-ray source 2 and the X-ray imaging means 3 at a predetermined interval. This interval is set to, for example, 30 cm to 1 m so that the subject K is accommodated between the X-ray source 2 and the X-ray imaging means 3. In addition, the irradiation part of the X-ray source 2 and the light-receiving surface of the X-ray imaging means 3 are arranged to face each other. Further, the arm 4 is configured to be capable of rotating and sliding around the rotation center O. Accordingly, the X-ray imaging unit 3 can capture a tomographic image in an arbitrary direction around the subject K while maintaining a predetermined distance between the X-ray source 2 and the X-ray imaging unit 3.

  The turning drive means (drive means) 5 moves the X-ray imaging means 3 in a direction orthogonal to the X-ray incident direction. 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. The turning drive means 5, the X-ray source 2 and the X-ray imaging means 3 are controlled by a controller (not shown), and the X-ray source 2 emits X-rays while the turning drive means 5 turns the arm 4. The imaging is repeated, and the X-ray imaging unit 3 captures an X-ray image (simple X-ray imaging image) of the subject K in synchronization with the X-ray irradiation timing and outputs it to the A / D conversion unit 6. The A / D conversion unit 6 acquires the output signal of the X-ray imaging unit 3, performs A / D conversion, and outputs it to the image signal processing unit 10.

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

The large-capacity frame image storage means 7 stores X-ray radiography integrated images (frame images) for a plurality of frames generated as a result of integration processing by the image signal processing means 10, and is a general image memory, hard disk, etc. Consists of The large-capacity frame image storage means 7 includes a plurality of pixels corresponding to regions obtained by dividing the pixels into smaller pixels than the pixel width, using the total value of the width of the light receiving portion and the width of the insensitive portion in the pixels of the X-ray imaging means 3. Memory area for each pixel. Specific examples will be described later.
The large-capacity processed image storage means 8 is a storage means used for processing such as image synthesis by the image signal processing means 10 and is composed of a general image memory or the like.

  The all-image display storage unit 9 stores a tomographic image (a tomographic image corresponding to a tomographic plane to be displayed) generated as a result of the synthesis processing by the image signal processing unit 10 and displayed on the output unit 11. A typical image memory. This tomographic image is represented by a luminance value, for example. Note that the output unit 11 includes, for example, a CRT (Cathode Ray Tube), a liquid crystal display (LCD), a PDP (Plasma Display Panel), an EL (Electronic Luminescence), and the like.

[Tomographic image]
Here, the tomographic image stored in the all-image display storage unit 9 will be described with reference to FIG. FIG. 2 is a plan view of the dentition. In the state shown in FIG. 2, the X-ray source 2 emits X-rays from the front tooth portion P side of the dentition of the person who is the subject K (see FIG. 1). Although the imaging unit 3 receives light, the X-ray source 2 and the X-ray imaging unit 3 rotate and slide during imaging. Here, the tomographic plane F is taken at the center in the front-rear direction of the dentition.

  The tomographic image (panoramic tomographic image) on the tomographic plane F shown in FIG. 2 is formed by superimposing a plurality of frame images (X-ray imaging integrated images) at a predetermined interval. An actual panoramic tomographic image is constructed by combining several hundred to several thousand frame images. Further, all the X-ray imaging integrated images may be formed by being overlapped at equal intervals, or may be overlapped by changing the shift width.

Returning to FIG. 1, the description of the configuration of the digital panorama photographing apparatus 1 will be continued.
The image signal processing means 10 acquires the output signal of the A / D conversion means 6, generates an X-ray imaging integrated image different from the simple X-ray imaging image of the subject K as a frame image, and generates frame images for a plurality of frames. It is used to synthesize tomographic images. The image signal processing means 10 includes control means including a CPU that executes various processes described later by developing a predetermined program stored in a ROM, an HDD, or the like in a RAM.

The image signal processing means 10 has a function as a signal integration means and a function as an image composition means.
The image signal processing means 10 is output from a predetermined pixel as a function of the signal integrating means within a time during which the predetermined pixel of the X-ray imaging means 3 moves by a predetermined pixel width as the X-ray imaging means 3 moves. The signal value is apportioned according to the position of the light receiving unit during movement of the predetermined pixel, integrated in each memory area for the predetermined pixel, and X-rays passing through the predetermined point of the subject are received next to the predetermined pixel. A frame image is generated by dividing the value of a signal output from an adjacent pixel into each memory area for a predetermined pixel according to the position of the light-receiving unit during movement of the adjacent pixel adjacent to the pixel. . Specific examples will be described later.

  The image signal processing means 10 acquires, as a function of the image synthesizing means, a plurality of X-ray imaging integrated images of a predetermined tomographic plane of the signal-processed dentition, and acquires the acquired frame image (X-ray imaging integrated image). Are superimposed with a predetermined shift width to synthesize an image (panoramic tomographic image) corresponding to a tomographic plane to be displayed. The tomographic plane to be displayed may be determined in advance, or may be specified by information from an input device (not shown). The combined tomographic image is output to the output unit 11.

[Concrete example]
Next, the function of the signal integration means for the image signal processing means 10 will be specifically described. Hereinafter, the memory area will be described with reference to FIG.

FIG. 3 is an explanatory diagram of the large-capacity frame image storage means shown in FIG. 1. FIG. 3A schematically shows an example of a method for obtaining the LSF of the recording system that is convolved with a predetermined point of the subject. (B) shows a memory area for each pixel. Here, in order to simplify the explanation, the X-ray imaging means 3 is a CCD image sensor of one line of vertical 1 pixel × horizontal 12 pixels, and has pixels (pixels) G ₁ ,..., G ₁₂ . The pixel width is d. Each pixel G ₁ ,..., G ₁₂ includes a light receiving unit 101 and a wiring unit 102. The light receiving unit 101 receives X-rays, generates signal charges, and stores them. The wiring part 102 is disposed adjacent to the light receiving part 101 and is a part for transferring the signal charge generated in the light receiving part 101 to the outside of the X-ray imaging means 3, and does not generate a signal charge even when receiving X-rays. The insensitive part. As schematically shown in FIG. 3A, the value of the pixel width d is a total value of the width L of the light receiving unit 101 and the width W of the wiring unit 102. In the pixel, the width W of the insensitive portion is configured to be 10 to 40% of the pixel width d. In this example, for example, it is assumed that the light receiving unit 101 is configured to occupy 70% of the entire pixel and the wiring unit 102 is configured to occupy, for example, 30% of the entire pixel.

At a certain point in time, as shown in the upper side in FIG. 3A, the pixel G ₁ is arranged inside (left side) the edge E of the subject, and the pixel G ₂ is arranged outside (right side) the edge E. In FIG. 3, the X-ray imaging means 3 moves in a direction approaching or moving away from the edge E. In this example, it is assumed that the X-ray imaging unit 3 moves in a direction approaching the edge E. The large-capacity frame image storage means 7 has a plurality of memory areas corresponding to areas obtained by dividing each pixel finer than the pixel width d for each pixel. This is called an address group. For example, the address group A ₁ corresponding to the pixels G _1, address group A ₂ or the like corresponding to the pixel G ₂ is provided. In this example, each pixel is virtually divided into ten in the moving direction of X-ray imaging means 3 (the direction from right to left in FIG. 3). Then, corresponding to the divided area where the pixel is virtually divided, the memory area (address group) for the pixel is divided into 10 storage areas (addresses). In FIG. 3, when each pixel is outside (right side) the edge E of the subject, the identification information (area ID) of the address corresponding to the divided area closest to the edge E is R ₁ , and R ₂ ,. , and R _10. Hereinafter, a predetermined pixel is referred to as a first pixel, and an adjacent pixel adjacent to a predetermined pixel that receives X-rays passing through a predetermined point of the subject next to the predetermined pixel is referred to as a second pixel. In this case, the large-capacity frame image storage means 7 has 10 memory areas corresponding to the areas IDR ₁ ,..., R ₁₀ for every 12 pixels, as shown in FIG. In FIG. 3B, the numbers described in the address group A ₁ to the address group A ₃ indicate an example of signal strength.

  The image signal processing means 10 sets the value (for example, luminance value) of the signal output from the first pixel to the position during movement of the first pixel according to the elapsed time until the first pixel moves by the pixel width. Accordingly, the value is accumulated in each memory area for the first pixel, and the value of the signal output from the second pixel is accumulated in each memory area for the first pixel according to the moving position of the second pixel. Here, the image signal processing means 10 may add and average the values of the signals output from the first pixel and the second pixel in each memory area for the first pixel. For example, when signals output from the first pixel and the second pixel are added 10 times in total, a value obtained by dividing the added value (integrated value) by 10 may be stored. By the processing of the image signal processing means 10, the above-described X-ray imaging integrated image is formed based on the value of the signal integrated in each memory area for each pixel for each frame. The image signal processing means 10 outputs an X-ray integrated image of a predetermined tomographic surface of the dentition as a processing result to the large-capacity frame image storage means 7 as a frame image.

  The function of the image signal processing means 10 is realized by the CPU developing and executing a predetermined program stored in the ROM or the like on the RAM. Therefore, the image signal processing means 10 can also be realized by executing a signal processing program that causes a general computer to execute the functions of the image signal processing means 10 described above. This program can be distributed via a communication line, or can be written on a recording medium such as a CD-ROM for distribution.

[Operation of Digital Panorama Camera]
The operation of the image signal processing means 10 will be described mainly with reference to FIG. 4 (refer to FIG. 1 as appropriate) as the operation of the digital panorama photographing apparatus shown in FIG. FIG. 4 is a flowchart showing the operation of the digital panorama photographing apparatus shown in FIG. First, the digital panoramic imaging apparatus 1 performs A / D conversion on a signal that is imaged by the X-ray imaging unit 3 on a predetermined tomographic surface of the dentition and output from each pixel by the A / D conversion unit 6 (step S1). ). Then, the digital panorama photographing apparatus 1 uses the image signal processing unit 10 to output the output signal of the first pixel and the output signal of the second pixel according to the position of the light receiving unit of the moving pixel of the X-ray imaging unit 3 with a large capacity. Integration is performed in the memory area for the first pixel in the frame image storage means 7 (step S2). Then, the digital panorama photographing apparatus 1 stores the signal integrated in each memory area for each pixel for each frame by the image signal processing unit 10 in the large-capacity frame image storage unit 7 as a frame image. Here, the signals accumulated while the pixels of the X-ray imaging means 3 move by a predetermined width of the pixels are stored. Then, the digital panorama photographing apparatus 1 obtains a plurality of frame images (X-ray photographing integrated images) from the large-capacity frame image storage means 7 by the image signal processing means 10 (step S3), and obtains each frame image. Are expanded in the large-capacity processed image storage means 8 and overlapped with a predetermined shift width (step S4), and the combined tomographic image is stored in the all-image display storage means 9. The digital panorama photographing apparatus 1 reads the synthesized tomographic image from the all-image display storage unit 9 and outputs it to the output unit 11 (step S5).

[Specific example of operation of digital panorama camera]
FIG. 5 is a diagram illustrating an example of signal strength in the vicinity of an edge. FIG. 5 shows the time when each pixel moves in the direction approaching the edge E (left side in FIG. 5) in 10 stages in the vertical direction in the figure in time series. Here, the pixel G ₁ inside the edge E (left side in FIG. 5) is defined as a first pixel, and the pixel G ₂ adjacent thereto is defined as a second pixel. Further, the intensity of the signal received by the pixel G ₁ on the inner side from the edge E (left side in FIG. 5) is set to “0”. Therefore, in this case, the signal output from the first pixel (pixel G ₁ ) is “0”, and this value is integrated. Further, the intensity of the signal received by each of the pixels G ₂ and G ₃ outside the edge E (right side in FIG. 5) is set to “70”. Then, the region of the light receiving unit 101 (see FIG. 3) corresponding to a length of 10% of the pixel width d of the pixel G ₂ (hereinafter referred to as the light receiving unit region) has moved inward (left side in FIG. 5) from the edge E. In this case, the intensity of the signal received by the pixel is “60”. Hereinafter, similarly, if the receiving unit region corresponding to alpha% of the length of the pixel width d of the pixel G ₂ is moved inwardly (left side in FIG. 5) from the edge E is a signal which the pixel G ₂ is received The intensity is “70-α”. Further, the intensity of the signal received by the wiring portion 102 (see FIG. 3) of each of the pixels G _{1 to} G ₃ (the strength of the signal received by the width W portion of the wiring portion 102) is set to “0”.

For example, when the intensity of the signal received by the pixel G ₂ is “60”, that is, the image signal processing means 10 has a light receiving area corresponding to 10% of the pixel width d of the pixel G ₂ from the edge E. When moving inward (left side in FIG. 5), the signal strength is set to “6 (===) in the address of the area ID“ R ₁₀ ”in the ₁₀ memory areas of the address group A ₁ of the large-capacity frame image storage means 7. 60/10) ". Further, the image signal processing means 10 is configured such that, for example, when the intensity of the signal received by the pixel G ₂ is “50”, that is, the light receiving area corresponding to 20% of the pixel width d of the pixel G ₂ has an edge. When moving to the inner side (left side in FIG. 5) from E, signals are sent to the addresses of the area IDs “R ₁₀ ” and “R ₉ ” in the ₁₀ memory areas of the address group A ₁ of the large-capacity frame image storage means 7. As an intensity of “5”, only “5 (= 50/10)” is added. The same applies hereinafter.

Further, the image signal processing means 10 performs the same processing using the pixel G ₂ as the first pixel and the adjacent pixel G ₃ as the second pixel. Specifically, the image signal processing means 10 is configured such that when the light receiving region corresponding to, for example, 20% of the pixel width d of the pixel G ₂ moves inward (left side in FIG. 5) from the edge E, Of the 10 memory areas of the address group A ₂ , the signal intensity is added by “ ₅ ” to the addresses of the area IDs “R ₁ ” to “R ₅ ”. In the section example shown in FIG. 5, the intensity of the signal received by the pixel G ₃ remains unchanged at “70”. Therefore, the image signal processing unit 10, for example, 20% of pixel width d of the pixel G ₃ When the light receiving region corresponding to the length is moved to the left side in FIG. 5, the address group A ₂ 10 pieces of Of the memory area, “7” is added as the signal strength to the addresses of the area IDs “R ₁₀ ” and “R ₉ ”.

The image signal processing means 10 proposes the output signal of the pixel G ₁ out of the change in signal intensity shown in FIG. 5 and the light receiving part region moved to the inside (left side in FIG. 5) of the edge E of the pixel G ₂ . The divided output signal of the pixel G ₂ is integrated in each memory area of the address group A ₁ of the large-capacity frame image storage means 7. The pixel image signal processing unit 10, among the changes in the signal intensity shown in FIG. 5, which is prorated to the light receiving region arranged outside (right side in Fig. 5) from the edge E of the pixel G ₂ The output signal of G _{2 and} the output signal of the pixel G ₃ divided in the light receiving area disposed outside the edge E (right side in FIG. 5) up to the pixel width d of the pixel G _3. Then, it accumulates in each memory area of the address group A ₂ of the large-capacity frame image storage means 7. Further, the image signal processing unit 10, among the changes in the signal intensity shown in FIG. 5, are arranged in a range of outside (right side in Fig. 5) from the edge E of the pixel G ₃ from the pixel width d to 2d located in the range of the output signal of the pixel G ₃ is prorated to the light receiving region, the pixel width d on the outer (right side in Fig. 5) from the edge E of the pixel G ₄ (not shown) adjacent to the pixel G ₃ to 2d The output signal of the pixel G ₄ that is allocated to the received light receiving area is integrated into each memory area of the address group A ₃ of the large-capacity frame image storage means 7. The same applies hereinafter. FIG. 6 shows changes in signal strength stored in the address group A ₁ , the address group A _2, and the address group A ₃ at this time. In FIG. 6, the ten stages of the time series shown in FIG.

The signal strength of each of the ten memory areas in the address group A ₁ shown in FIG. 6 at time t = 10 and the signal strength of each of the ten memory areas in the address group A ₂ at time t = 10. The strength is shown in FIG. The horizontal axis of the graph of FIG. 7 is obtained by normalizing the distance from the edge E corresponding to the region ID to d = 10.
Specifically, the signal strengths of the distances “−9” to “0” from the edge E indicate the signal strengths of the addresses of the area IDs “R ₁ ” to “R ₁₀ ” of the address group A ₁ , respectively. The signal intensity of the distance "1" to "10" from the edge E shows the region ID "R _1" ~ address group A ₂ the signal strength of the address of the "R _10" respectively. FIG. 7 is a graph showing an ESF (Edge Spread Function) for the signal strength example shown in FIG.

  8 is obtained when a difference is obtained with respect to the symmetrical signal intensity around the “distance“ 0 ”from the edge” shown in FIG. 7. This FIG. 8 differentiates the ESF shown in FIG. 8 is a graph showing the LSF that can be obtained by dividing the distance from the edge E. Here, Δ = 7 corresponds to the width L of the light receiving portion. Δ = −7 indicates the difference between the signal intensity at the distance “−8” from the edge E and the signal intensity at the distance “−7” from the edge E. Δ = −6 indicates a difference between the signal intensity at the distance “−7” from the edge E and the signal intensity at the distance “−6” from the edge E. Δ = −5 indicates the difference between the signal intensity at the distance “−6” from the edge E and the signal intensity at the distance “−5” from the edge E. The same applies hereinafter. As shown in FIG. 8, the X-ray intensity signal obtained from the difference between the symmetrical signal intensities about the distance “0” from the edge has a triangular waveform. According to the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 of the present embodiment, the shape of the X-ray intensity signal obtained from the edge E is a triangular wave. This means that the shape of the X-ray intensity signal obtained from the difference in the signal intensity in one direction away from the edge becomes a sawtooth waveform. Note that the length of the base of the sawtooth waveform is shorter than the pixel width d and becomes the width L of the light receiving portion.

[Resolution of generated image]
Here, the resolution of an image generated by the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 of the present embodiment will be described with reference to FIGS. 9 is an explanatory diagram of the LSF shown in FIG. 8, where (a) shows a triangular wave, (b) shows a function obtained by Fourier transform of (a), and FIG. 10 shows the function shown in FIG. It is explanatory drawing of LSF, (a) is a rectangular wave, (b) has each shown the function which carried out the Fourier transform of (a). FIG. 11 is an explanatory diagram of the spatial frequency, where (a) shows a stationary state, and (b) and (c) show a signal processing time. FIG. 12 is a graph showing the MTF obtained from the LSF shown in FIG.

First, a triangular wave corresponding to the LSF generated by the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 of the present embodiment will be described with reference to FIG.
At the edge E, when the triangular wave A (x) shown in FIG. 9A is LSF, the MTF is obtained in the real space region by the calculation represented by the equation (1). “*” In the equation (1) indicates an operation symbol of convolution integration. In addition, the triangular wave A (x) in Formula (1) is shown by Formula (2). Further, the function f (x) indicating the edge E is expressed by Expression (3).

  In order to perform the calculation of the above-described equation (1) in the frequency domain, when the triangular wave A (x) shown in FIG. 9A is Fourier transformed, equation (4) is obtained. In Expression (4), ω represents a spatial frequency. If the complex part shown by the right side of this Formula (4) is performed and the real part is calculated | required, Formula (5) will be obtained. The waveform shown by Formula (5) is shown in FIG.9 (b). Thereby, when the calculation of the above-described equation (1) is performed in the frequency domain, the equation (6) is obtained.

  Next, a comparative example with the LSF generated by the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 of the present embodiment will be described with reference to FIG. At the edge E, the MTF having the rectangular wave C (x) shown in FIG. 10A as an input is obtained in the real space region by the calculation represented by Expression (7). In addition, the rectangular wave C (x) in Formula (7) is shown by Formula (8). The function f (x) indicating the edge E is expressed by the above-described equation (3).

  In order to perform the calculation of Equation (7) in the frequency domain, Equation (9) is obtained by Fourier transform of the rectangular wave C (x) shown in FIG. If the complex part shown by the right side of this Formula (9) is performed and the real part is calculated | required, Formula (10) will be obtained. The waveform shown by Formula (10) is shown in FIG.10 (b). Thus, when the calculation of the above-described equation (7) is performed in the frequency domain, the equation (11) is obtained.

  Here, the spatial frequency ω will be described with reference to FIG. If the X-ray imaging means 3 (see FIG. 3) of the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 is still, the LSF of the recording system that is convolved with a predetermined point of the subject is shown in FIG. As shown to (a), it becomes a rectangular wave. In the area 201 shown in FIG. 11A, the width of the rectangle is the same as the pixel width d (see FIG. 3). When forming a light and dark line pair having the same width (line pair) using two consecutive pixels of the displayed image, the region 201 and the region 202 having the same width as the region 201 are combined. The portion corresponds to one period (2d) of the rectangular wave. In this case, the spatial frequency ω is expressed by Expression (12). For example, if the pixel width d is 0.1 [mm] = 100 [μm], the spatial frequency ω is 5 [cycles / mm]. In FIG. 11, L indicates the width of the light receiving unit 101 (see FIG. 3), and W indicates the width of the wiring unit 102.

Further, when the graph is created by using the transition of the signal strength illustrated in FIG. 6, instead of using the signal strength of all the memory areas of the address group A ₁ and the address group A ₂ , the time t = 10 The pixel width outside the edge E (right side in FIG. 5) based on the signal strength of the address of the area ID “R ₁₀ ” in the address group A ₁ and the signal strength of all the memory areas of the address group A ₂ . Graphs can also be created using signal intensities in the range up to d. In this case, in the graph showing the ESF shown in FIG. 7, it is possible to create a graph only in the right range from the position of the distance “0” from the edge E. According to this, the LSF graph can create a sawtooth waveform graph only in the right range from the position of the distance difference “0” from the edge E in the LSF graph shown in FIG. The graph created at this time is shown in FIG. The waveform shown in FIG. 11B corresponds to a single pixel of the displayed image. Note that the broken line corresponds to the LSF shown in FIG.

  A waveform formed by connecting the waveforms shown in FIG. 11B corresponds to continuous pixels in the displayed image. The graph created at this time is shown in FIG. Regions 211, 212, and 213 shown in FIG. 11C correspond to three consecutive pixels in the displayed image. Regions 211, 212, and 213 correspond to one period (L) of the sawtooth wave. In this case, the spatial frequency ω is expressed by Expression (13). For example, if the pixel width d is 0.1 [mm] = 100 [μm] and the width L of the light receiving unit 101 (see FIG. 3) is 70 [μm], the spatial frequency ω is approximately 14.3 [cycles / mm]. This is a value when the width W of the insensitive portion is 30% of the pixel width d. Therefore, when the width W of the insensitive portion is 10% of the pixel width d, the spatial frequency ω is approximately 11.1 [cycles / mm], and the width W of the insensitive portion is 40% of the pixel width d. In this case, the spatial frequency ω is approximately 16.6 [cycles / mm].

  Further, in the case of a structure in which the pixel shape is a square, the square light receiving part is located at the center of the pixel, and the insensitive part is arranged around the pixel, the ratio of the width W of the insensitive part to the pixel width d and the light receiving part The relationship with the area is as follows. That is, when the width W of the insensitive portion is 10 to 40% of the pixel width d, the area occupied by the light receiving portion 101 in the pixel is 36 to 81%. Therefore, in this case, a decrease in the X-ray dose that can be received by the light receiving unit 101 can be effectively suppressed while increasing the spatial frequency. In addition, the arrangement of the light receiving part and the insensitive part in the pixel can be changed as appropriate.

Next, the MTF of an image generated by the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 of the present embodiment will be described with reference to FIG.
In the above equation (6), when the amplitude at the origin of ω = 0 is normalized to 1, an MTF is obtained. As indicated by a solid line in FIG. 12, the value of ω when the MTF value is “0” is “1 / L”. On the other hand, the MTF obtained by normalizing the amplitude at the origin of ω = 0 to 1 in the above equation (11) is ω when the MTF value is “0” as shown by the broken line in FIG. The value of is 1 / (2d). That is, the image generated by the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 of the present embodiment is compared with a case where such signal processing is not performed at all in the spectral region as shown in FIG. The value of the cutoff frequency becomes higher than twice. That is, the image generated by the image signal processing means 10 is a high resolution image. In the waveform after Fourier transforming the sawtooth wave shown in FIG. 11 (b), the position of the intersection with the ω axis (horizontal axis) is the same position as in FIG. 9 (b) and FIG. 10 (b). Become. Therefore, also in this case, the value of the cut-off frequency is higher in the spectral region than in the case of the rectangular wave, so that the resolution of the image can be improved.

  According to the present embodiment, the digital panoramic imaging apparatus (X-ray imaging apparatus) 1 can generate a high-resolution image by signal processing without changing the X-ray imaging unit 3 to a high-resolution one. . Therefore, a high-resolution tomographic image can be generated at low cost.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can implement in the range which does not change the meaning. For example, in the present embodiment, the X-ray imaging unit 3 is configured such that the insensitive part of the pixel is the wiring part of the pixel, but the present invention is not limited thereto, and a mask that covers a part of the pixel is provided as the insensitive part. You can also According to this, it is possible to appropriately change the design of the ratio occupied by the insensitive part in the pixel. For example, when the ratio occupied by the insensitive part increases, the width of the triangular wave that is the waveform of the X-ray intensity signal integrated in the large-capacity frame image storage unit 7 decreases. Therefore, the length of the base of the sawtooth waveform obtained by cutting the triangular wave becomes shorter. Therefore, a greater resolution can be obtained. Here, the mask preferably covers at least the wiring portion.

  In the present embodiment, the X-ray imaging unit 3 is described as moving in the horizontal direction (horizontal direction) in panoramic imaging, but may be continuously moved in the vertical direction (vertical direction). Also, a two-dimensional high-resolution image can be obtained by moving in the vertical direction while rotating in the horizontal direction.

In the present embodiment, each pixel is described as being virtually divided into 10 pixels. However, for example, the pixels may be divided into 3, 4, 5,.
Further, in the present embodiment, each pixel is virtually equally divided, but if the waveform of the triangular wave shown in FIG. 8 or the waveform similar to the sawtooth wave shown in FIG. 11B can be generated, It is not always necessary to divide equally. In this case, since it is not necessary to make the moving speed of the X-ray imaging unit 3 constant, various images can be obtained by moving the X-ray imaging unit 3 with a complicated movement.

  In the present embodiment, the image signal processing means 10 synthesizes a tomographic image on a predetermined tomographic plane as a function of the image synthesizing means. However, the present invention is not limited to this. You may make it synthesize | combine the multi-tomographic image which shows the image in a some tomographic plane. This multi-tomographic image can be generated, for example, by a method disclosed in Japanese Patent Laid-Open No. 2006-180944. Note that the function as the image synthesizing unit may be separated from the image signal processing unit 10 and provided separately.

  In the present embodiment, the dental digital panoramic imaging apparatus 1 has been described. However, the present invention is not limited to panoramic imaging, and is not limited to dental X-ray imaging. If an X-ray imaging unit that can move in a direction orthogonal to the incident direction of X-rays that have passed through a predetermined point of the subject is provided, it can be used for general medical purposes. 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.

1 is a configuration diagram schematically illustrating a digital panorama photographing apparatus according to an embodiment of the present invention. It is a top view of a dentition. FIGS. 2A and 2B are explanatory diagrams of the large-capacity frame image storage unit illustrated in FIG. 1, in which FIG. 1A illustrates a subject photographing possible area and FIG. 1B illustrates a memory area for each pixel. 2 is a flowchart showing the operation of the image signal processing means shown in FIG. It is a figure which shows an example of the signal strength of the edge vicinity. It is a figure which shows the signal strength integrated | accumulated in the memory area according to time. It is a graph which shows ESF about the example of the signal strength shown in FIG. It is a graph which shows LSF calculated | required from ESF shown in FIG. It is explanatory drawing of LSF shown in FIG. 8, Comprising: (a) has shown the triangular wave, (b) has each shown the function which carried out the Fourier transform of (a). It is explanatory drawing of LSF shown in FIG. 8, Comprising: (a) is a rectangular wave, (b) has each shown the function which carried out the Fourier transform of (a). It is explanatory drawing of a spatial frequency, Comprising: (a) at the time of a stillness, (b) and (c) have each shown at the time of signal processing. It is a graph which shows MTF calculated | required from LSF shown in FIG.

Explanation of symbols

1 Digital panoramic radiography equipment (X-ray radiography equipment)
2 X-ray source 3 X-ray imaging means 4 Arm 5 Turning drive means (drive means)
7 Large-capacity frame image storage means (frame image storage means)
8 Large-capacity processing image storage means 9 All image display storage means 10 Image signal processing means 11 Output means 101 Light-receiving part 102 Wiring part

Claims (4)

An X-ray source that irradiates the subject with X-rays, a light-receiving unit that receives X-rays passing through a predetermined point of the subject and generates a signal charge, and an insensitive portion that does not generate a signal charge adjacent to the light-receiving unit An X-ray imaging unit in which a plurality of pixels are arranged; a driving unit that moves the X-ray imaging unit in a direction orthogonal to the X-ray incident direction; and a signal output from the X-ray imaging unit An X-ray imaging apparatus comprising: an image signal processing unit that generates a frame image; and a frame image storage unit that stores a frame image generated as the signal processing result,
The frame image storage means includes a plurality of memory areas corresponding to areas obtained by dividing the pixel more finely than the pixel width, with the pixel width being a total value of the width of the light receiving portion and the width of the insensitive portion in the pixel. For each pixel,
The image signal processing means outputs a value of a signal output from the predetermined pixel within the time during which the predetermined pixel of the X-ray imaging means moves by the pixel width as the X-ray imaging means moves. Proportionally according to the position of the light-receiving unit during movement of the light-receiving unit and integrated in each memory area for the predetermined pixel, and adjacent to the predetermined pixel that receives X-rays passing through the predetermined point next to the predetermined pixel The frame image is generated by distributing the value of the signal output from the adjacent pixel in accordance with the position of the light receiving unit during the movement of the adjacent pixel and adding the value of the signal output from the adjacent pixel to each memory area for the predetermined pixel. A featured X-ray imaging apparatus.   The X-ray imaging apparatus according to claim 1, wherein the X-ray imaging unit includes a mask that covers a part of the pixels as the insensitive part.   3. The X-ray imaging according to claim 1, wherein the X-ray imaging unit is configured such that a width of the insensitive portion is 10% to 40% of the pixel width in the pixel. apparatus. An X-ray source that irradiates the subject with X-rays, a light-receiving unit that receives X-rays passing through a predetermined point of the subject and generates a signal charge, and an insensitive portion that does not generate a signal charge adjacent to the light-receiving unit An X-ray imaging unit in which a plurality of pixels are arranged; a driving unit that moves the X-ray imaging unit in a direction orthogonal to the X-ray incident direction; and a signal output from the X-ray imaging unit A plurality of image signal processing means for generating a frame image, and a plurality of regions corresponding to a region obtained by dividing the pixel more finely than the pixel width, with a total value of the width of the light receiving portion and the width of the insensitive portion as the pixel width of the pixel A signal processing method in an X-ray imaging apparatus, comprising a frame image storage means for storing a frame image generated as the signal processing result having a memory area for each pixel,
The value of a signal output from the predetermined pixel is calculated by the image signal processing unit within a time during which the predetermined pixel of the X-ray imaging unit moves by the pixel width as the X-ray imaging unit moves. Proportionally according to the position of the light-receiving unit during movement of the light-receiving unit and integrated in each memory area for the predetermined pixel, and adjacent to the predetermined pixel that receives X-rays passing through the predetermined point next to the predetermined pixel The frame image is generated by distributing the value of the signal output from the adjacent pixel in accordance with the position of the light receiving unit during the movement of the adjacent pixel and adding the value of the signal output from the adjacent pixel to each memory area for the predetermined pixel. A characteristic signal processing method.

Images