JPH05313264A - Radiation image reader - Google Patents

Abstract

PURPOSE:To perform correction with higher accuracy without complicating a constitution by correcting irregularity by means of the specification of each surface of a polygon mirror and a sub-scanning position. CONSTITUTION:A black mark for specifying and detecting a referential surface is put on the upper surface of the polygon mirror 91, and a reflection type sensors LD1, PD1 detect that the mark is on a specified position. The detected signal IT is Supplied to a sub-scanning motor controlling mechanism 110 with a signal outputted from an encoder 92. An origin position in the sub-scanning direction of a moving and reading unit is detected by using origin position detecting sensors LD2, and PD2, a detection signal is transmitted to the sub- scanning motor controlling mechanism 110, and the stopping position of the unit 90 is controlled. Thus, besides the two-dimensional irregularity information of shading/fading/plate, the information of a polygonal surface used are superimposed, and the absolute positions of a beam and a phosphor plate 3 are aligned, so that the correction is performed with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image reader for optically reading radiation image information, and more particularly, it is necessary to accurately reproduce fine grayscale information as in a reader using a stimulable phosphor. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a correction technique of read image data in a certain reader.

[0002]

2. Description of the Related Art FIG. 7 is a diagram showing a method of recording an image (for example, a disease diagnosis image) on a stimulable phosphor plate. The X-rays emitted from the X-ray source 100 are focused on by the diaphragm 200 and then radiated on the subject 300. The X-rays that have passed through the subject 300 are incident on a stimulable phosphor plate (hereinafter, simply referred to as plate) 400, whereby a latent image of the image of the subject 300 is formed on the plate.

This latent image is imaged by scanning a laser beam to excite the plate, radiating the accumulated latent image energy as fluorescence, and condensing the fluorescence by a condenser to obtain a photoelectron image multiplier. After being detected by a photodetector equipped with (photomultiplier, hereinafter simply referred to as "photomul"), the obtained analog electric signal is A / D converted and digitized,
This is performed by subjecting the data to predetermined signal processing.

[0004]

SUMMARY OF THE INVENTION The present inventor has examined a correction technique of read image data in order to reproduce an image with higher accuracy, and as a result, the following matters have been clarified. This will be described with reference to FIG. (1) For example, when a light beam is scanned using a polygon mirror 100 (having surfaces A to H as reflecting surfaces) as shown in FIG. 6A, as shown in FIG. ,
There is a difference in reflectance between the A surface and the E surface. As a result, even if the same position of the plate is scanned, the laser power reaching the plate is different between when the A surface is used and when the E surface is used. However, the detected signal levels are different. Therefore, it is necessary to make a correction in consideration of the polygon surface to be used. (2) In that case, the characteristics of the polygon surface are stored for each surface,
Although it may be used for creating correction data, it causes problems such as an increase in memory capacity and complicated signal processing for correction. (3) Further, as shown in FIG. 6C, the plate 3 has two-dimensional unevenness in sensitivity (or unevenness caused by unevenness in X-rays). It is important to correct not only the direction but also the sub-scanning direction.

The present invention has been made on the basis of such consideration, and an object thereof is to provide a radiographic image reading apparatus which can perform more accurate correction without complicating the structure.

[0006]

The outline of the typical one of the present invention is as follows. (1) When actually reading an image, the image data of the pixel is read using the same polygonal surface, and the correction data is added to or subtracted from the image data for correction. The correction may be performed immediately after reading the image data, or may be performed after once storing all the image data in the memory. That is, each surface of the polygon mirror and the sub-scanning position of the light beam are specified, and the specific relationship is that when the uneven correction data is created and when the actual read image is corrected using the correction data. In any case, the two-dimensional condition is established in common. As a result, the characteristic information of the polygon surface used for the correction data for each pixel is superimposed. (2) The unevenness correction data is stored in the storage means in advance, and when the image data to be read is obtained, the timing in which the specific surface of the rotating polygon mirror reaches a predetermined position is used as a reference in the sub-scanning direction of the light beam. The correction data is read from the storage means in synchronization with the start of the scanning and the timing as a reference, and the correction data is added to or subtracted from the image data to execute the unevenness correction. In this case, the sub-scanning direction of the light beam with respect to the plate is set so that the specific relationship between each surface of the polygon mirror and the sub-scanning position of the light beam is always accurately established two-dimensionally (along the sub-scanning direction). It is better to strictly control the scanning accuracy of. The required accuracy is within 1/2 of the scan pitch in the sub-scanning direction.

[0007]

(1) Since the scanning of the light beam is always started on the basis of the specific surface of the polygon, the usage surface of the polygon for each pixel is always uniquely determined. Therefore, in the correction data and the read image data, The difference in reflectance does not occur due to the difference in the polygon surface used. This improves the correction accuracy. (2) In order to achieve high accuracy by controlling the timing in the light beam scanning, the storage of reflection characteristic data of each surface of the polygon, the calculation for masking the adverse effect of the dispersion of the reflectance based on the data, etc. (that is, No need for signal processing). Therefore, the signal processing circuit does not become complicated. (3) The scanning accuracy of the light beam in the main scanning direction is naturally improved by the synchronous control with the position of the polygon specific surface, which is a feature of the present invention. Therefore, if the scanning accuracy in the sub-scanning direction is guaranteed, the scanning position of the light beam with respect to the plate is specified, and the scanning is repeated while tracing substantially the same locus on one plate that is repeatedly used. .. Therefore, even if the position where the correction data is obtained and the actual image read position are almost the same (that is, the absolute position is the same) and the plate has two-dimensional sensitivity (X-ray) unevenness, the absolute position The correction error due to the deviation is reduced. That is, in addition to shading and fading, unevenness in sensitivity (X-ray unevenness) of the plate itself can be corrected with high accuracy.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. (1) Configuration around the movable reading unit FIG. 1 is a diagram showing a configuration of a main part of an embodiment of a radiation image reading device of the present invention. In this device, the phosphor plate 3 is fixed to the left side wall and is repeatedly used. The moving reading unit 90 moves along the guide shaft 71 by driving the ball screw 72 by the sub-scanning motor (stepping motor) 80, and scans the scanning line (light beam 50) in the sub-scanning direction. The scanning in the main scanning direction is performed by the polygon scanning mechanism 60. The operation of the sub-scanning motor 80 is controlled by the sub-scanning motor control mechanism 110. The fluorescence is collected by the light collector 4a and converted into an electric signal by the photomultiplier 4b.

(2) Polygonal Surface Detection Mechanism As shown on the right side of FIG. 1, a black mark for identifying and detecting the index surface (reference surface) is provided on the upper surface of the polygon mirror 91. The arrival of this mark at a predetermined position is detected by a reflection type sensor (consisting of LD1 and PD1). The detection signal IT is provided to the sub-scanning motor control mechanism 110 together with the FG signal and the PG signal output from the encoder 92. In addition, a transmissive sensor or an optical encoder can be used to detect the polygon surface.

(3) Mechanism for improving the origin position accuracy of the moving reading unit in the sub-scanning direction In this embodiment, the movement of the reading unit 90 is started by using the polygon surface as a trigger, so that the phosphor plate 3 and the reading unit 90 are separated from each other. It is important to keep the absolute position accuracy high in the initial stage (at standby). Therefore, the origin (0) position of the moving reading unit in the sub-scanning direction is detected using the origin position detection sensor (transmission type sensor including the laser light source LD2 and the photosensor PD2) (origin position detection signal SD
Is sent to the sub-scanning motor control mechanism 110), and controls the stop position of the moving reading unit.
As shown on the left side of FIG. 1, the stop position of the moving reading unit is controlled by decelerating by trapezoidal driving to prevent overrun when the unit returns. The accuracy of the origin position is within 1/2 of the sub-scanning pitch. That is, in the case of 100 μm, it is necessary to stand by with an accuracy within about 50 μm. When it is difficult to achieve accuracy with a transmissive sensor, it is preferable to provide a slit in the sensor to improve the resolution.

(4) Sub-scanning of the reading unit The sub-scanning of the reading unit 90 is controlled by the pulse signal UP supplied to the sub-scanning motor (stepping motor) 80 as shown in the upper part of FIG. That is, when returning, the pulse is stopped when reaching the origin position, and in the case of going, control is performed so that the head of the image comes after entering a certain speed range after acceleration.

(5) Features of this Embodiment In this embodiment, the polygonal surface A is used as a reference surface, and light beam scanning is started by using the position of this surface as a trigger. Therefore, in the correction data, as shown in FIG. 2, in addition to shading / fading / plate two-dimensional unevenness information,
Information on the polygon surface used is also superimposed. Further, even during reading, the relationship between the polygon surface used and the pixels is maintained, and the absolute positions of the beam and the plate match, so that highly accurate correction can be performed.

(6) Configuration Example of Signal Processing Circuit FIG. 3 shows a configuration example of the signal processing circuit. In this apparatus, X-rays generated from the radiation source 1 are transmitted through the subject 2 and are incident on the stimulable phosphor plate 3 to form a latent image. When reading the latent image, the plate 3
The laser beam scans the upper part (laser light source 12, optical scanning mechanism 1
The generated fluorescence is collected by the condenser 4a and photoelectrically converted by the photomultiplier 4b.

Reference numeral 5 is a power supply for supplying a photomultiplier tube voltage, 6 is a linear amplifier, 7 is a logarithmic amplifier, 9 is a sample hold circuit, and 10 is an A / D converter. The switch 14 plays a role of switching between a correction data acquisition path and a path when an actual image is read, and is switched to the A side when acquiring the correction data and to the B side when reading the image. Reference number 1
Reference numeral 5 is a frame memory, 25 is a controller, and 26 is a peripheral device such as a printer or an automatic developing device. A timing circuit 11 supplies a timing clock to each circuit.

The real number type correction means 24 includes a correction (addition) circuit 16 for correcting the read image data, a correction data generation means 17, a shading data memory 18, and
Fading data memory 19, thinning data memory 20, interpolation data creating means 21, addition (and integerizing means) 24, and correction memory 2 for storing correction data.
3 and 3. Each of the correction data (real number type data with decimal precision and a-bit precision) created by the correction data creating means 17 is stored in the memory 18, 19,
Stored in 20. The interpolation data creation means 21 performs linear interpolation on the basis of the thinned-out data to create interpolation data for each pixel. The correction data are added all at once by the adder circuit 22 to round the a bits below the decimal point to an integer, and the correction data is stored in the correction memory 23 corresponding to each pixel. At the time of image reading, correction data corresponding to each pixel is output and added to the read data by the correction (addition) circuit 16 to correct the read image data.

(7) Contents of Correction FIG. 4 is a diagram showing a method of creating shading correction data and fading correction data, and a state of adding these to generate correction data for one pixel (G _{i, j} ). is there. In FIG. 7, original data is obtained by emitting X-rays in the absence of a subject.

The shading correction data is m in the Y direction.
It is obtained by averaging pixels and obtaining the difference between the MAX value and each average value. When precision of a bits after the decimal point is required, at least 2 ^a pixels are required as the value of m. In order to eliminate the adverse effect of noise, the value of m is preferably large, and it is desirable to perform arithmetic mean for all pixels in the Y direction (one column). Similarly, the fading correction data is obtained by averaging the n pixels in the X direction and obtaining the difference from the MAX value. These real number type data are added, and the addition result is rounded to be an integer. Since the correction data is created from each data having the precision of the decimal point or less, the step variation position of the correction data does not become linear, and more accurate digital correction can be performed.

FIG. 5 is a diagram for explaining an interpolation data generation method based on thinned data. Thinned pixels (B1 to
The thinned-out data for B5) is obtained by averaging the data of the surrounding N pixels and smoothing. As a result, the influence of plate defects and dust can be eliminated. Next, the interpolation level at each pixel position is obtained by linear interpolation, and the difference from the MAX value is used as interpolation data. According to a study made by the present inventor, it has been found that the thinning-out pixel can be maintained at a considerable interpolation accuracy by obtaining only one thinning-out pixel per 32 pixels in the main scanning direction. By this interpolation, it is possible to correct the effect of gentle unevenness peculiar to the plate.

In the case of the present invention, the original data is obtained by X-ray exposure in the state where there is no subject, and the correction data is created. Therefore, even when the polygon mirror is exchanged in a hospital or the like where the apparatus of the present invention is actually installed, correction data is not calculated from the data of the polygon itself but correction data from the data obtained by the actual X-ray exposure. Thus, highly accurate correction data can be obtained every time.

[0020]

As described above, according to the present invention, by configuring each surface of the polygon and the sub-scanning position to perform the unevenness correction, the following effects can be obtained. (1) The difference in reflectance between the correction data and the read image data is not affected by the difference in the polygon surfaces used, and the correction accuracy is improved. (2) In order to achieve high accuracy by controlling the timing in the light beam scanning, the storage of reflection characteristic data of each surface of the polygon, the calculation for masking the adverse effect of the dispersion of the reflectance based on the data, etc. (that is, (Signal processing) is not required and the signal processing circuit does not become complicated. (3) A plate having two-dimensional sensitivity (X-ray) unevenness in which the position where the correction data is obtained and the actual image reading position (absolute position) substantially match (that is, the absolute position matches). Also, the correction error due to the deviation of the absolute position is reduced. That is, in addition to shading and fading, unevenness in sensitivity (X-ray unevenness) of the plate itself can be corrected with high accuracy. (4) In the present invention, since it is possible to correct each pixel of the plate including the information of the polygon surface to be used, it is most effective when the correction is performed for all pixels, and highly accurate correction can be performed. (5) As a result, the radiation image reading apparatus can be made highly functional.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration around a moving reading unit of an embodiment of a radiation image reading apparatus of the present invention.

FIG. 2 is a diagram for explaining features of the embodiment of FIG.

FIG. 3 is a diagram illustrating a configuration example of a signal processing system according to an embodiment.

FIG. 4 is a diagram illustrating a method of creating shading correction data and fading correction data, and adding these to obtain one pixel (G
It is a figure which shows a mode that the correction data about _{i, j} ) are produced | generated.

FIG. 5 is a diagram for explaining an interpolation data generation method based on thinned-out data.

6A, 6B, and 6C are views for explaining matters that have been studied and clarified by the present inventor before the present invention.

FIG. 7 is a diagram for explaining an outline of photographing a medical diagnostic image using a stimulable phosphor plate.

[Explanation of symbols]

 1 X-ray source 2 Subject 3 Photostimulable phosphor plate 4a Concentrator 4b Photomal 5 Tube power supply 6 Linear amplifier 7 Logarithmic amplifier 8 Filter 9 Sample / hold circuit 10 A / D converter 11 Timing circuit 12 Laser light source 13 Light Scanning mechanism 15 Frame memory 24 Real number type correction means 25 Controller 26 Peripheral equipment such as printer and automatic developing device 27 Laser beam scanning start position detecting sensor 60 Polygon scanning mechanism 71 Guide shaft 72 Ball screw 80 Sub scanning motor 90 Reading unit 110 Sub scanning Motor control mechanism

Claims (2)

[Claims] 1. A radiation image reading apparatus for scanning a light beam on a stimulable phosphor plate, detecting the resulting fluorescence, and reading an image recorded on the stimulable phosphor plate. The scanning of the light beam in the main scanning direction is performed using a polygon mirror, and each surface of the polygon mirror and the sub-scanning position of the light beam are specified. A radiation image reading apparatus, which is commonly established in both cases of creating correction data and correcting an actual read image using the correction data. 2. The non-uniformity correction data is stored in the storage means, and when obtaining image data to be read, the light beam is scanned in the sub-scanning direction with reference to the timing when the specific surface of the rotating polygon mirror reaches a predetermined position. The correction data is read out from the storage means in synchronization with the timing of starting scanning and using the timing as a reference, and the correction data is calculated into the image data to perform unevenness correction.
The radiographic image reading device described.