JP2008242178A - Radiographic image reading apparatus and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic image reading apparatus wherein a scanning means, such as a resonance mirror and a polygon mirror, can be operated at a high speed, even when the response speed of an electric circuit or a recording medium is low, and to provide a scanning method. <P>SOLUTION: The radiographic image reading apparatus includes an irradiating means to two-dimensionally scan while intermittently irradiating the recording medium with the excitation light, and a light receiving means to receive the stimulable luminescence light emitted from the recording medium in reply to the irradiation. The radiographic image reading apparatus also includes a control means, provided that the sizes of the reading pixels in a main scanning direction and a subscanning direction are expressed by X and Y, respectively, M ≥1 and N≥integer 2 are established (M≠N), to control the irradiating means to irradiate the recording medium with the stimulable light for every N-reading pixels in the main scanning direction, and also, to control the irradiating means so that the irradiation position on the main scanning line and the irradiation position on the preceding main scanning line may deviate by M×X in the main scanning direction, and a feed pitch by the irradiating means in the sub scanning direction may become Y/N. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiographic image reading apparatus that reads a radiographic image by scanning and irradiating a recording medium on which a radiographic image is recorded with excitation light and receiving excited stimulating light, and a scanning method for excitation light.

  Radiation images typified by X-ray images have been widely used for disease diagnosis and the like.

  In the field of radiographic images, a latent image is formed by irradiating the photostimulable phosphor sheet as a recording medium with radiation that has passed through the subject in order to reduce exposure dose and improve consistency with digital image processing systems. In many cases, a technique for reading the radiation image by receiving the stimulated emission light output by irradiating the latent image with the excitation light is used.

  In general, the reading of the latent image is performed by using an image reading unit including a laser light source, a polygon mirror, a lens, a mirror, and the like, and a light receiving unit that receives the stimulated emission light as a recording medium. This is done by relatively moving along the surface of the phosphor sheet.

  Since the excited emission light that is excited is weak, an optical device that eliminates the influence of the excitation light is used for photometry.

  For example, a filter is provided at the receiving port of the stimulated emission light to separate the excitation light and the stimulated emission light, and the excitation light is pulsed to eliminate the influence of the stimulated emission light that is harmful to the measurement. There is also a proposal for prohibiting irradiation of excitation light when receiving stimulated emission light after irradiation (see, for example, Patent Document 1).

  There is also a proposal of excitation light irradiation means that arranges spots so as to remove the influence between irradiation spots while sufficiently ensuring the size of the irradiation spot of the laser beam that is excitation light (see, for example, Patent Document 2). .

  In addition to the above-described optical devices, the photometric signal is stably amplified, the measurement data is processed while ensuring the required number of digits, and the necessary response speed is ensured. Ingenuity is also important for improving the processing speed of the apparatus.

  However, the response speed of the electrical circuit described above, for example, the response speed of the logarithmic conversion amplifier used for quantifying and handling the dynamic range of the measurement result to about four digits, or the stimulated emission emitted from the stimulable phosphor sheet Depending on the response characteristics of light, there are cases where the scanning speed of scanning means capable of scanning at a higher speed, such as a resonant mirror or a polygon mirror, is limited.

In general, when a resonant mirror or a polygon mirror is used at a low speed, the performance may be reduced, or the cost may be increased to adapt to the speed used.
Japanese Patent No. 19012297 Japanese Patent No. 3016631

  The present invention has been made in view of the situation as described above, and its purpose is to use a scanning means such as a resonant mirror and a polygon mirror at high speed even when the response speed of an electric circuit or a recording medium is low. An object of the present invention is to provide a radiological image reading apparatus and a scanning method that can perform the above-mentioned.

The above-mentioned subject is achieved by realizing the following invention.
1. Irradiation means for two-dimensionally scanning a recording medium on which a radiographic image is recorded as a latent image while intermittently irradiating with excitation light, and light reception for receiving stimulated emission light emitted from the recording medium by the irradiation A radiological image reading apparatus comprising:
When the sizes of the read pixels in the main scanning direction and the sub-scanning direction are X and Y, respectively, and M is an integer of 1 or more and N is an integer of 2 or more, provided that M ≠ N.
Irradiation of the excitation light to the recording medium by the irradiation unit is performed for every N read pixels in the main scanning direction, and the irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are the main. In order to shift M × X in the scanning direction,
The radiation image reading apparatus further includes a control unit that controls the irradiation unit such that a feed pitch of the irradiation unit in the sub-scanning direction is Y / N.
2. 2. The radiation image reading apparatus according to claim 1, further comprising calculation means for calculating read data of a read pixel at a predetermined position from read data of a read pixel at another position.
3. The calculating means includes
The read data of the read pixel at the predetermined position is at least read data of the read pixel adjacent to the read pixel in the sub-scanning direction, or read data of the read pixel located closest to the read pixel in the main scanning direction. The radiation image reading apparatus according to item 2, wherein the radiation image reading apparatus is calculated from the following.
4). Irradiation means for two-dimensionally scanning a recording medium on which a radiographic image is recorded as a latent image while intermittently irradiating with excitation light, and light reception for receiving stimulated emission light emitted from the recording medium by the irradiation A method for controlling a radiological image reading apparatus comprising:
When the sizes of the read pixels in the main scanning direction and the sub-scanning direction are X and Y, respectively, and M is an integer of 1 or more and N is an integer of 2 or more, provided that M ≠ N.
Irradiation of the excitation light to the recording medium by the irradiation unit is performed for every N read pixels in the main scanning direction, and the irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are the main. In order to shift M × X in the scanning direction,
The method of controlling a radiation image reading apparatus, wherein the irradiation unit is controlled so that a feed pitch in the sub-scanning direction of the irradiation unit becomes Y / N.

  According to the present invention, it becomes possible to use a scanning means such as a high-speed resonant mirror and polygon mirror by the radiographic image reading apparatus, so that the scanning performance and life of the scanning means can be improved, and a low-cost scanning means can be selected. Become.

  As a result, performance improvement and cost reduction of the radiation image reading apparatus are realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an external view of the radiation image reading apparatus D.

  As shown in the figure, the radiation image reading device D has a box shape, and an operation display unit 21 and an opening 23 are provided on the exterior portion 20 on the upper surface thereof. The opening 23 is an insertion opening for a cassette that houses a photostimulable phosphor sheet as a recording medium.

  FIG. 2 is a conceptual diagram showing the inside of the radiation image reading apparatus D.

  The cassette inserted from the opening is separated into two surfaces.

  A magnet is affixed to the front surface (arrow f) of the back plate holding plate 201, and this magnet holds one surface of the cassette holding the separated photostimulable phosphor sheet. The surface of the phosphor sheet is exposed in front of the drawing.

  The image reading unit 300 is covered with a rectangular parallelepiped exterior, is fixed to the upper portion of the base 351, and moves in the direction of the arrow g.

  The pedestal 351 is movable along the guide rail 352, and is constituted by a linear motor 360 including a circular shaft-shaped magnet unit 361 having both ends fixed and a columnar movable coil 362 fixed to the pedestal 351. Movement is controlled.

  Such movement control using the linear motor 360 is preferable as control of the sub-scanning means of laser beam scanning because high-precision low-speed movement is realized.

  The separation and holding of the cassette and the movement of the image reading unit 300 as described above are known techniques as described in, for example, WO 2006/064636 or WO 2006/043425.

  FIG. 3 is a conceptual diagram of the inside of the image reading unit 300.

  Inside the exterior of the image reading unit 300 are housed an excitation light irradiating means 310 as an irradiating means, a stimulating light receiving means 320 as a light receiving means, an erasing lamp 308 as an image erasing means, and the like. Note that optical parts, mechanical parts, electrical parts, and mechanisms that combine them are all known techniques.

  The excitation light irradiation means 310 includes a laser diode LD as a light emitting element, a collimator lens (not shown), a cylindrical lens (not shown), a scanning lens (not shown) such as a polygon mirror 314 and an fθ lens, mirrors 302 and 303, and the like. Is done.

  The laser beam LB as excitation light is swung by a polygon mirror 314 as scanning means, guided to the mirrors 302 and 303, and emitted from the slit 307 toward the photostimulable phosphor sheet K.

  The scanning means may be a resonant mirror instead of the polygon mirror. At that time, as a matter of course, the scanning lens is changed to a suitable one.

  The entire surface of the photostimulable phosphor sheet K is two-dimensionally scanned by scanning the laser beam LB by rotating the polygon mirror 314 (main scanning) and scanning by moving the image reading unit 300 at a constant speed (sub scanning). Is done.

  The photostimulated light receiving means 320 includes a light guide 321 that is a light guiding means and a light collecting tube 322 that is a light collecting means, such as a light receiving element PD that uses a photodiode or a photomultiplier tube.

  From the photostimulable phosphor sheet K irradiated with the laser beam LB as excitation light, stimulating light having an intensity (light quantity) corresponding to the recorded radiation image is emitted.

  The stimulated emission light is guided to the light collecting tube 322 by the light collecting mirror 306 and the light guide 321, and is repeatedly reflected by the light collecting tube 322, and the light receiving surface of the light receiving element PD attached to the end of the light collecting tube. The light is condensed and photoelectrically converted.

  The electrical signal after the photoelectric conversion is subjected to processing such as amplification, current-voltage conversion, logarithmic conversion, A / D conversion, etc., and becomes read data.

  FIG. 4 is a top view of the image reading unit 300.

  The image reading unit 300 moves within the reading movement range indicated by the arrow y in the drawing, finishes reading the image recorded on the photostimulable phosphor sheet K, and temporarily stops at the dotted line position. Thereafter, the erasing lamp 308 is turned on, and again returns to the home position before the start of scanning.

  The entire surface of the photostimulable phosphor sheet K is irradiated by the erasing lamp 308 by this returning operation, and all the recorded images are erased.

  FIG. 5 is a block diagram showing the control relationship of the radiation image reading apparatus D.

  The control means C is a computer system having a CPU, a memory, an input / output interface, a communication interface, and various other circuits. Each control is performed by executing a predetermined program stored in the memory.

  The speed of the photostimulable phosphor K in the main scanning direction is controlled by the speed control of the polygon mirror as a scanning means, and the feed pitch in the sub-scanning direction is controlled by the speed control of the linear motor.

  The excitation light that performs intermittent irradiation is controlled by controlling lighting of the laser diode LD that is a light source.

  These controls are all known techniques. In the figure, the description of blocks not directly related to the embodiment of the present invention is omitted.

  FIG. 6 is a block diagram of the reading circuit.

  The reading circuit is one of various circuits included in the control means C.

  The intermittent irradiation of the photostimulable phosphor sheet K is a pulse signal generated by a timing generation unit based on a signal from a scanning start position reference sensor (not shown) that determines the main scanning start position of the laser beam LB. The laser diode LD, which is a light source of excitation light, is intermittently driven in response to the above.

  The stimulated light emitted from the photostimulable phosphor sheet K, which is a recording medium, when excited by intermittent excitation light is received by the stimulated light receiving means 320 and subjected to photoelectric conversion.

  An electric signal obtained by photoelectric conversion is subjected to current-voltage conversion and amplification, logarithmic conversion, A / D conversion, and read data.

  In some cases, the electrical signal after photoelectric conversion is not voltage-voltage conversion but voltage-voltage conversion. Further, all of the circuit techniques relating to the irradiation of the excitation light and the reception of the emitted light are known techniques.

  FIGS. 7A, 7B, and 7C are diagrams illustrating the shape and arrangement of the irradiation spot on the recording medium of the laser beam LB that is excitation light.

  FIG. 7A shows a state in which the image surface of the photostimulable phosphor sheet K which is a recording medium is divided by read pixels whose size in the main scanning direction is X and whose size in the sub-scanning direction is Y.

  It should be noted that the size of the read pixel and the number of divisions shown in the figure are appropriate sizes and numbers for easy understanding of the description, and generally X = Y in many cases.

  FIG. 7B shows an array of irradiation spots formed when each pixel is intermittently irradiated with a laser beam LB having a substantially circular irradiation spot shape. Such an arrangement of irradiation spots is the most commonly performed arrangement.

  The stimulated light excited by the excitation light shown in FIG. 7B is received by the light receiving means for each irradiation spot, that is, every time the laser beam LB travels a distance X in the main scanning direction. Therefore, the photoelectrically converted electrical signal must be processed in accordance with this reading speed to be read data.

  Since it is desirable to handle the read data in a dynamic range of about four decimal digits, usually, the electrical signal that has been converted and amplified is subjected to logarithmic conversion and then subjected to A / D conversion processing to obtain read data.

  However, in the logarithmic conversion circuit, the response characteristic is limited in a low signal range due to the influence of the parasitic capacitance of the transistors constituting the circuit, and the stimulable phosphor sheet K is caused by the response characteristic that emits the stimulated emission light. Since it is necessary to consider the influence of response delay, it is necessary to capture the read signal while suppressing the operation speed of the polygon mirror or the resonance mirror that determines the main scanning speed of the laser beam.

In FIG. 7C, the size of the read pixel in the main scanning direction and the sub-scanning direction is X and Y, respectively, and M is 1 or more and N is an integer of 2 or more, provided that M ≠ N. The irradiation means irradiates the recording medium with the excitation light for every N read pixels in the main scanning direction, and the irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are the main scanning. So as to shift M × X in the direction,
Further, it is a diagram illustrating an example in which the irradiation unit is controlled so that the feed pitch of the irradiation unit in the sub-scanning direction becomes Y / N.

  In the example shown in the figure, M = 1, N = 3, that is, the irradiation spot pitch in the main scanning direction is tripled, and the irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are in the main scanning direction. Are arranged so that they are shifted by X and the feed pitch in the sub-scanning direction is 1/3.

  In the case of N = 1, the control is the same as the control generally adopted conventionally, and the effect of the present invention is not exhibited. Therefore, N is an integer of 2 or more.

  If reading of the entire surface of the recording medium is completed within the same time as in the case of FIG. 7B with such a spot arrangement, the number of main scanning lines is tripled, and photoelectric conversion is performed. Assuming that the processing speed of the circuit that uses the electrical signal as read data that is digital data and the response characteristics of the photostimulable phosphor sheet K are the same, it is necessary to increase the main scanning speed up to three times.

  In other words, the scanning speed of the polygon mirror or the resonant mirror can be increased up to 3 times, so that the polygon mirror or the resonant mirror is operated at a higher speed, or a higher speed polygon mirror or the resonant mirror is used. Will be possible.

  FIG. 7C illustrates a case where the pitch of irradiation spots in the main scanning direction is tripled and the feed pitch in the sub-scanning direction is 1/3. The irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are shifted by M × X in the main scanning direction, and the feed pitch in the sub scanning direction is set to 1 / N. It is also adapted when reading control is performed.

  However, if M = N, the irradiation spots overlap in the sub-scanning line direction, and reading data cannot be obtained for each reading pixel. Therefore, it is necessary to set M ≠ N.

  FIG. 8 is a diagram showing the arrangement of irradiation spots when M = 2 and N = 5.

  As is apparent from the figure, even under this condition, each irradiation spot is arranged on the entire surface so as not to overlap each other.

  That is, by controlling the irradiation means so as to realize the spot arrangement as described above, the entire surface of the photostimulable phosphor sheet K as a recording medium is scanned so that the irradiation spots do not overlap.

  Note that the lack of the irradiation spot at the upper end of the image plane is not a problem because it is an area that can be ignored as a read image.

  FIG. 9 is a diagram for explaining a calculation method by the calculation unit 500.

  The calculation unit 500 is a program stored in the memory M of the control unit C that calculates read data of a read pixel at a predetermined position from read data corresponding to an irradiation spot adjacent at the position of the read pixel.

  The arrangement of the irradiation spots shown in FIG. 9 is the same as the arrangement shown in FIG. Assume that digitized read data A1-4, B1-4, and C1-4 are obtained corresponding to these irradiation spots a1-4, b1-4, and c1-4.

In the embodiment of the present invention, read data X2Y2 and X3Y2 corresponding to irradiation spots x2y2 and x3y2 indicated by dotted lines in FIG.
X2Y2 = 1/3 (A2 + 2 × B2)
X3Y2 = 1/3 (2 × A3 + B3)
The above equation is a weighting that is inversely proportional to the size of the overlap of two irradiation spots adjacent to each other in the sub-scanning direction with respect to the pixel at the required position, that is, the distance between the center of the read pixel pixel and the center of the irradiation spot. To obtain an average value of the data of the two irradiation spots.

  In the example described, read data of a predetermined pixel is calculated from an irradiation spot adjacent in the sub-scanning direction (vertical direction in the figure), but the same concept is applied to the main scanning direction (horizontal direction in the figure). Then, weighting inversely proportional to the distance between the center of the read pixel pixel and the center of the irradiation spot is performed, and two irradiations before and after being positioned closest to the main scanning direction, for example, X2Y2 = 1/3 (2 × B1 + A4). The read data of a predetermined pixel may be calculated from the spot.

  In addition, the values obtained from the two front and rear irradiation spots closest to the main scanning direction and the irradiation spots adjacent in the sub-scanning direction are calculated with the same weighting, and the read data of a predetermined pixel is also obtained. Good.

  As described above, the size of the read pixel obtained by dividing the recording medium in the main scanning direction and the sub-scanning direction is X and Y, respectively, M is an integer of 1 or more, and N is an integer of 2 or more. However, when M.noteq.N, the recording medium is irradiated with excitation light every N read pixels in the main scanning direction, and the irradiation position on the next main scanning line and the preceding main scanning line. By controlling the irradiation unit such that the irradiation position is shifted by M × X in the main scanning direction and the feed pitch of the irradiation unit in the sub-scanning direction is Y / N, the entire surface of the recording medium is controlled. (All read pixels) are scanned and irradiated.

  Further, data corresponding to a read pixel at a predetermined position is calculated from data obtained corresponding to the scanning irradiation.

  Accordingly, it is possible to use N times faster scanning means than when reading pixel by pixel in the main scanning direction.

  As described above, according to the present invention, the conventional technique in the radiation image reading apparatus in which the scanning speed of the excitation light must be kept low by the response speed of the light receiving circuit of the stimulated emission light and the response characteristics of the stimulated emission light. The above restrictions can be removed.

  As a result, the high-speed stability inherent in the polygon mirror or the resonant mirror is utilized, the reliability of the radiation image reading apparatus is improved, and the cost is reduced.

It is an external view of a radiographic image reading apparatus. It is a conceptual diagram which shows the inside of a radiographic image reading apparatus. It is a conceptual diagram inside an image reading part. It is a top view of an image reading unit. It is a block diagram which shows the control relationship of a radiographic image reading apparatus. It is a block diagram of a reading circuit. It is a figure explaining the irradiation spot shape and arrangement | positioning on a recording medium. It is a figure which shows arrangement | positioning of the irradiation spot in case M = 2 and N = 5. It is a figure explaining the calculation method by a calculation means.

Explanation of symbols

C Control means D Radiation image reader K Stimulable phosphor sheet (recording medium)
LB Laser beam 310 Excitation light irradiation means (irradiation means)
320 Stimulated light receiving means (light receiving means)
500 Calculation means

Claims (4)

Irradiation means for two-dimensionally scanning a recording medium on which a radiographic image is recorded as a latent image while intermittently irradiating with excitation light, and light reception for receiving stimulated emission light emitted from the recording medium by the irradiation A radiological image reading apparatus comprising:
When the sizes of the read pixels in the main scanning direction and the sub-scanning direction are X and Y, respectively, and M is an integer of 1 or more and N is an integer of 2 or more, provided that M ≠ N.
Irradiation of the excitation light to the recording medium by the irradiation unit is performed for every N read pixels in the main scanning direction, and the irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are the main. In order to shift M × X in the scanning direction,
The radiation image reading apparatus further includes a control unit that controls the irradiation unit such that a feed pitch of the irradiation unit in the sub-scanning direction is Y / N. The radiation image reading apparatus according to claim 1, further comprising a calculation unit that calculates read data of a read pixel at a predetermined position from read data of a read pixel at another position. The calculating means includes
The read data of the read pixel at the predetermined position is at least read data of the read pixel adjacent to the read pixel in the sub-scanning direction, or read data of the read pixel located closest to the read pixel in the main scanning direction. The radiation image reading apparatus according to claim 2, wherein the radiation image reading apparatus is calculated from: Irradiation means for two-dimensionally scanning a recording medium on which a radiographic image is recorded as a latent image while intermittently irradiating with excitation light, and light reception for receiving stimulated emission light emitted from the recording medium by the irradiation A method for controlling a radiological image reading apparatus comprising:
When the sizes of the read pixels in the main scanning direction and the sub-scanning direction are X and Y, respectively, and M is an integer of 1 or more and N is an integer of 2 or more, provided that M ≠ N.
Irradiation of the excitation light to the recording medium by the irradiation unit is performed for every N read pixels in the main scanning direction, and the irradiation position on the next main scanning line and the irradiation position on the preceding main scanning line are the main. In order to shift M × X in the scanning direction,
The method of controlling a radiation image reading apparatus, wherein the irradiation unit is controlled so that a feed pitch in the sub-scanning direction of the irradiation unit becomes Y / N.

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