JP3305749B2 - Radiation image reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiographic image reading apparatus for optically reading radiographic image information, and more particularly to a reading apparatus such as a hard copy apparatus for medical images, which needs to accurately reproduce fine density information. In the technology for correcting read image data.

[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 X-ray detector. X-rays emitted from the X-ray source 100
After being stopped down by 0, the object 300 is irradiated. The X-ray transmitted through the subject 300 enters a stimulable phosphor X-ray detector (hereinafter simply referred to as a detector) 400,
As a result, a latent image of the image of the subject 300 is formed on the detector.

In order to image the latent image, a laser beam is scanned to excite a detector, the stored latent image energy is emitted as fluorescent light, and the fluorescent light is condensed by a light concentrator to form a photomultiplier tube. (A photomultiplier, hereinafter simply referred to as a photomultiplier) is detected by a photodetector, and the obtained analog electric signal is subjected to A / D conversion. For example, a half-size detector is divided into 2048 × 2464 pixels.
After digitizing each pixel into 10 bits (1024 gradations), the data is subjected to predetermined signal processing to perform the processing. Thereby, a high-quality X-ray image can be obtained.

[0004]

The inventor of the present invention has studied a technique for correcting read image data in order to reproduce images with higher accuracy. As a result, the following matters have become clear. (1) As a type of correction, in addition to correcting unevenness (shading) of the light collector and the photodetector, it is necessary to correct fading in which the emission intensity of the phosphor attenuates with time.

Further, when high image quality is required, it is necessary to correct sensitivity unevenness (two-dimensional gradual unevenness) peculiar to the phosphor detector to be used. (2) When performing shading correction and fading correction, an integer-type digital correction (a correction performed on the basis of digital data obtained by rounding bits after the decimal point and obtaining an integer) when calculating correction data is performed. As shown in FIG. 6, streak-like noise is likely to occur in the reproduced image. That is, even though the actual image level changes linearly, for example, several pixels are collectively regarded as the same level by comparing with a threshold value to generate correction data, and when the correction data is added, the DC level in the electric signal conversion is obtained. Is flattened, but in the actual linear signal superimposed on the DC level, discontinuous edges occur in each range regarded as the same level, which causes the occurrence of streak-like noise. (3) As a method of suppressing the generation of the streak-like noise, it is conceivable to increase the accuracy of data used for correction. In this case, a high-precision D / A converter or A / D converter is required. As a result, the circuit becomes complicated and the cost increases. In addition, by adding a random component to the corrected read signal, it is possible to make steep edges inconspicuous and reduce streak-like unevenness. However, on the other hand, the noise component is increased, which does not directly lead to an improvement in image quality. .

The present invention has been made based on the above considerations, and an object of the present invention is to provide a radiation image reading apparatus capable of performing more accurate correction with a simple circuit without deteriorating the image quality. It is in.

[0007]

The outline of a typical embodiment of the present invention is as follows. (1) Correction of a real number type is performed. First, correction data (shading correction data and fading correction data) with higher resolution than the read image data are acquired in the main and sub-scanning directions from the reference image read without a subject. Increasing the resolution of the data in this case does not increase the accuracy of circuit components (such as A / D converters) in the data reading path, but instead uses a conventional precision component to read the detector once exposed to X-rays. Then, all pixel data is stored in a frame memory as a reference image, and arithmetic processing such as averaging is performed on the reference image data to improve the accuracy of the arithmetic processing. For example, an averaging operation is performed on data of ^2a or more pixels on the main scanning line (on the same row) and on the sub-scanning line (on the same column) of the detector, and the division result is obtained with a bit precision below the decimal point. Is stored as correction data.

Next, at the time of normal photographing, high-resolution shading correction data and fading correction data (average data of each row and each column) are added to the read image data, and the sum thereof is expressed by a value after the decimal point. Rounding is performed to obtain an integer, and correction is performed for each pixel. (2) In addition to the above correction, the following correction is performed.

Based on the thinning-out correction data, interpolation data for each pixel is generated by an interpolation process, and this interpolation data is added together with the above-mentioned shading correction data and fading correction data to perform rounding. Make corrections. The thinning-out correction data is, in principle, from all pixels.
It refers to data about a specific pixel extracted according to a certain rule, but more preferably, it is not simply extracting image data of a specific pixel, but also averaging and smoothing including a plurality of pixels around the specific pixel. It is preferable to create thinning correction data from data extracted as data of pixels representing the smoothing area. Also in this case, the correction data is in the form of a real number. The interpolation processing is generally linear interpolation, but is not limited thereto, and various interpolation processings are allowed. This correction is ideal for correcting unevenness that changes slowly, such as uneven sensitivity of the detector.The same unevenness always occurs at the same reading position, such as when the detector and reading mechanism are integrated. Suitable for you. In addition, in a configuration in which a plurality of detectors are used repeatedly, thinning correction data is stored for each detector, and can be used without any problem as long as the data matches the reading detector.

[0010]

[Action]

(1) Circuit components (A / D
Rather than increasing the accuracy of the converter, etc., all the pixel data of the X-ray-exposed detector is once read into the frame memory using parts of the conventional accuracy, and the stored data is averaged, etc. By increasing the accuracy of the arithmetic processing, the resolution of the correction data in both the main scanning direction and the sub-scanning direction is improved to the reading accuracy or more. For this reason, a high-precision A / D converter or D / A converter is not required for improving the resolution. On the other hand, the improvement of the calculation accuracy is easily achieved by the calculation capability of the ALU of the computer. Therefore, high-resolution data can be obtained easily at low cost. Further, the number of data used for averaging may be a number that can obtain desired accuracy, and the memory for correction processing may be small. The data of the decimal point precision (real number type data) in each of the main and sub scanning directions is added to obtain correction data for one pixel. Even if the correction data is finally converted to an integer, the step-like steps due to the correction do not line up in a straight line,
No streak-like unevenness occurs.

(2) By shading correction and fading correction, steep unevenness existing on the detector is almost removed, but two-dimensional slow unevenness (sensitivity unevenness) unique to the detector to be used is:
Will remain. In addition, the effect of high-frequency noise superimposed on all pixels on the detector (due to X-ray mottle, detector defects, presence of dust, etc.) still remains. For these, countermeasures are taken by interpolation processing based on the thinning correction data and smoothing (averaging processing of surrounding pixels) at the time of obtaining the thinning correction data.

That is, the representative value of the image level in a local area on the detector is detected by smoothing while eliminating the influence of high frequency noise. The difference between the representative value of the image level at the thinned pixel position and the largest value (MAX value) in the data including other representative values is calculated as thinned correction data.

A gradual change tendency (distribution) of the image level of the entire detector is grasped from the thinning correction data, and interpolation (linear interpolation) is performed based on the gradual change tendency.
The adverse effect of slow unevenness is removed for each pixel. In addition, since a representative value is obtained by performing smoothing, and thinning correction data is created based on the representative value, the amount of memory to be stored can be reduced, and at the same time, highly accurate correction data can be created. I have. By adding together the interpolation data together with the shading correction data and the fading correction data, correction data for each pixel corrected for the two-dimensional unevenness of the shading / fading / detector can be obtained at once. After this summation (addition), the bits below the decimal point are rounded and converted to an integer, so that the correction data of each pixel does not match and stepwise correction is not performed, and fine correction can be performed for each pixel ( No unevenness on the streaks).

[0014]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of the radiation image reading apparatus of the present invention.

(1) Overall Configuration In this apparatus, X-rays generated from a radiation source 1 pass through a subject 2 and enter a stimulable phosphor X-ray detector 3 to form a latent image. I have. At the time of reading the latent image, the laser beam scans the detector 3 (by the laser light source 12 and the optical scanning mechanism 13), and the generated fluorescent light is collected by the light collector 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 and hold circuit, and 10 is an A / D converter. The switch 14 serves to switch between a correction data acquisition path and a path at the time of actual image reading, and is switched to the A side at the time of correction data acquisition and to the B side at the time of image reading. Reference number 1
Reference numeral 5 denotes a frame memory, 25 denotes a controller, and 26 denotes peripheral devices such as a printer and 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 generating means 17, a shading data memory 18,
It includes a fading data memory 19, a thinning data memory 20, an interpolation data creation unit 21, and an addition (and integer conversion unit) 24. Each correction data (following the decimal point,
The real-type data with a-bit precision) is stored in the memories 18, 19, and 20 according to the type. The interpolation data creation unit 21 performs linear interpolation based on the thinning correction data, and creates interpolation data for each pixel. The correction data are added all at once by the addition circuit 22, rounded to a bit below the decimal point, converted to an integer, added to the read data by the correction (addition) circuit 16, and the read image data is corrected.

(2) Content of Correction FIG. 2 is a diagram showing a method of generating shading correction data and fading correction data, and generating correction data for one pixel (G _{i, j} ) by adding them. is there. The shading correction data is obtained by averaging m pixels in the Y direction and calculating the difference between the MAX value and each average value. When precision of a bits below 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, it is preferable that the value of m is large, and it is preferable to perform averaging 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 calculating the difference from the MAX value. These real type data are added, and the result of the addition is rounded to be converted to an integer. Since the correction data is created from each data having the precision of the decimal point or less, the step change position of the correction data does not become linear, and digital correction with higher precision can be performed.

FIG. 3 is a diagram for explaining a method of generating interpolation data based on thinning correction data. This thinning correction data is created based on data obtained by adding the shading and fading correction data obtained earlier to the reference image data.

The image level data for the thinned pixels (B1 to B5) is obtained by averaging the data of the surrounding N pixels and smoothing. As a result, it is possible to eliminate the influence of high frequency noise due to defects in the X-ray mottle or detector, dust, and the like. Next, the difference from the MAX value is used as thinning correction data. According to the study of the present inventor, sharp unevenness components are removed by correction of shading and fading, so that the thinned pixels are 3 pixels in both the main scanning direction and the sub-scanning direction.
It has been found that considerable interpolation accuracy can be maintained only by obtaining one pixel per two pixels. By this interpolation, the influence of the gradual unevenness inherent to the detector can be corrected. Therefore, thinning correction data is 1 for all image data.
/ 1000 is sufficient. Actually, 5K words of the image data of 5M words are thinned-out correction data, which is very inexpensive.

(3) Procedure for Obtaining Correction Data FIG. 4 is a flowchart showing a procedure for obtaining correction data. It consists of steps 30-34. FIG. 5 is a flowchart showing a procedure for performing correction using correction data at the time of actual image reading. Step 40 ~
Step 43 is executed.

The correction method of the present invention exhibits the greatest effect when the detector and the reading device are integrally formed. That is, since the detector is integrated, there is almost no dust or damage to the detector, and irregularities in the defect are extremely unlikely to occur. Further, since the detectors are always the same, there is almost no change in the irregularities. In other words, once the correction data is obtained, it can usually be used without any awareness at all.

[0023]

As described above, according to the present invention, the correction data in the main scanning direction and the sub-scanning direction are obtained by averaging a plurality of pixels, obtaining a higher resolution than the read signal, adding them, and finally obtaining an integer. Into correction data, and
The following effects can be obtained by performing an interpolation process based on the thinning-out correction data and performing the correction in consideration of the interpolation data. (1) No streak-like unevenness due to correction occurs. (2) Two-dimensional unevenness of shading / fading / detector can be corrected. (3) Noise does not increase. (4) Since high-precision A / D converters, D / A converters, etc. are unnecessary and the conversion accuracy is not affected by the conversion accuracy, high-precision correction can be performed easily and inexpensively with a simple circuit. I can do it. (5) These make it possible to enhance the functionality of the radiation image reading apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a radiation image reading apparatus according to an embodiment of the present invention.

FIG. 2 shows a method of creating shading correction data and fading correction data, and adding these to one pixel (G
FIG. 11 is a diagram illustrating a state in which correction data for ( _{i, j} ) is generated.

FIG. 3 is a diagram for explaining a method of generating interpolation data based on thinned data.

FIG. 4 is a flowchart illustrating a procedure for acquiring correction data.

FIG. 5 is a flowchart illustrating a procedure for performing correction using correction data at the time of actual image reading.

FIG. 6 is a diagram for explaining the cause of the occurrence of streak-like unevenness when performing integer-type correction.

FIG. 7 is a diagram for explaining an outline of imaging of a medical diagnostic image using a stimulable phosphor X-ray detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray source 2 Subject 3 Stimulable phosphor detector 4a Condenser 4b Photomultiplier 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 device such as printer, automatic developing device 27 Laser beam scanning start position detection sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification code FI H04N 5/30 G06F 15/66 355C (58) Field surveyed (Int.Cl. ⁷ , DB name) G03B 42/02 A61B 6 / 00 G06T 1/00 G06T 3/40 G21K 4/00 H04N 5/30

Claims (1)

(57) [Claims] 1. A radiation image reading apparatus for reading an image recorded on a stimulable phosphor X-ray detector, wherein a calculation process is performed on reference data obtained via a reading system, and the calculation is performed in the main scanning direction and the sub-scanning direction. main scanning direction Ru to obtain a compensation data of higher resolution than standard de <br/> over data-
A sub-scanning Direction correction data acquisition means, with respect to the reference data, the main scanning direction and the sub scanning direction
Correction is performed using the correction data, and the
Thinning correction data to obtain thinning correction data from
Data acquisition means, and interpolating the thinning-out correction data to obtain the base data.
Interpolation to create interpolation data with higher resolution than quasi-data
Data creation means and correction data in the main scanning direction having a higher resolution than the reference data.
Data, interpolation data in the sub-scanning direction, and interpolation data for each pixel.
After each addition, the resolution is higher than that of the reading system.
Addition adjustment to create each pixel correction data by rounding the high part
Digitizing means, and the read image data is supplemented by the pixel correction data.
A radiation image reading apparatus , comprising : a correction unit that corrects the radiation image.