JPH021081A - Method for deciding correction of contour candidate points of radiation irradiating field - Google Patents

Abstract

PURPOSE:To accurately recognize a radiation irradiating field and to optimally set picture processing conditions by examining whether a pair of detected contour candidate points are respectively and mutually equidistant from the edge of a recording medium or not and whether both the candidate points are non-equally close with each other or not. CONSTITUTION:The contour candidate point signal detecting part 223 obtains contour candidate points E1 and E2 from information Sm to indicate a difference obtained by differentiation processing and information Sth to indicate a set threshold and outputs information Se to indicate picture element positions corresponding to first-read picture signals Sp. A correction deciding part 224 decides whether the points E1 and E2 are respectively positioned on irradiat ing field contours B1 and B2 from the information Se. In this case, an distance l1 from a left side 103L of an accumulative fluorescent material sheet 103 to the point E1, a distance l2 from a right side 103R of the sheet 103 to the point E2, and a distance l3 between the points E1 and E2 are obtained, thresholds are made into alpha and beta, and it is determined whether relations ¦l1-l2¦<alpha, l3>beta are satisfied or not. Further, when both relations are satisfied, the information Se is regarded as effective one. In this manner, the prescribed number of correct candidate points are obtained and sent to an operation part 225 to obtain information to indicate a radiation irradiating area B.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a method for preventing radiation irradiation on the recording medium when reading radiation image information from a recording medium such as a stimulable phosphor sheet on which radiation image information is recorded. The present invention relates to a method for determining whether a contour candidate point detected as being located on a contour portion of an irradiation field is correct in order to recognize the field.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain an image signal, perform appropriate image processing on the image signal, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which it is recorded and converted into an electrical signal. By performing image processing on this electrical signal (image signal) and then reproducing it as a visible image in a photocopy, etc., it is possible to obtain a reproduced image with good image quality performance such as contrast, sharpness, and graininess. A system has been developed (see Japanese Patent Publication No. 81-5193).

The applicant has also proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image of the subject can be recorded on recording materials such as photographic materials, CRTs, etc. A radiation image recording and reproducing system that outputs a visual image has already been proposed (Japanese Patent Application Laid-Open No. 1983-1989)
No.-12429, No. 5G-11395.

55-103472, 5B-104645, 55-116340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

In the above system, the stimulable phosphor sheet is scanned in advance with a low-level light beam before obtaining an image signal by reading it under optimal reading conditions depending on the dose of radiation applied to the stimulable phosphor sheet. Pre-reading is performed to read the outline of the radiation image recorded on this sheet, the pre-read image signal obtained by this pre-reading is analyzed, and then the above sheet is irradiated with a light beam of a higher level than the light beam used during the above-mentioned pre-reading. There is also a system configured to perform main reading to obtain an image signal by scanning the radiation image and reading it under the optimum reading conditions for the radiation image (Japanese Patent Application Laid-open Nos. 58-67240, 5g-67241, 5g-67242). No. etc.).

Here, reading conditions are a general term for various conditions that affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading, such as reading gain, scale factor, or , the power of excitation light during reading, etc.

Also, the high level and low level of the light beam are, respectively.
If the intensity of the light beam irradiated per unit area of the sheet or the intensity of stimulated luminescence light emitted from the sheet depends on the wavelength of the light beam (has a wavelength sensitivity distribution), It refers to the weighted intensity after weighting the intensity of the light beam irradiated per unit area of the sheet with the wavelength sensitivity.As a method of changing the level of the light beam, it is possible to methods to use, methods to change the intensity of the light beam itself emitted from a laser light source, methods to change the intensity of the light beam by inserting or removing an ND filter, etc. on the optical path of the light beam, methods to change the beam diameter of the light beam. How to change the scanning density,
Various known methods can be used, such as a method of changing the scanning speed.

In addition, regardless of whether the system performs this pre-reading or the system that does not, the obtained image signal (including the pre-read image signal) is analyzed and the optimal image processing conditions are determined when applying image processing to the image signal. Some systems let you decide. The method of determining the optimal image processing conditions based on this image signal is not limited to systems using stimulable phosphor sheets, and for example, image signals are obtained from radiation images recorded on a recording medium such as a conventional X-ray film. It is also applied to the system.

Various methods have been proposed to analyze the above-mentioned image signals (including pre-read image signals) and find optimal reading conditions and image processing conditions, but one known method is to create a histogram of the image signal. (For example, Japanese Patent Application No. 59-12658). By calculating the histogram of the image signal, for example, the maximum value, minimum value, etc. of the image signal can be determined.
The value of the image signal at the point where the frequency is maximum can be known, and from these points, the characteristics of the radiation image recorded on a recording medium such as a stimulable phosphor sheet or an X-ray film can be understood. Therefore, by determining the optimal reading condition 1 image processing condition based on this histogram, it becomes possible to reproduce and output a radiation image that is highly suitable for observation.

On the other hand, when capturing and recording radiation images on a recording medium, it is important to avoid irradiating radiation to parts of the subject that are not necessary for observation, or to prevent radiation from being irradiated to parts unnecessary for observation. Scattered rays may enter some areas, reducing image quality. Therefore, use an irradiation field aperture to limit the radiation irradiation area so that only the necessary parts of the subject and part of the recording medium are irradiated with radiation. Often.

However, when analyzing the image signal to determine the reading condition 2 image processing conditions as described above, if the image signal used for analysis is an image signal obtained from a recording medium photographed using an irradiation field aperture, Even if you ignore the existence of this irradiation field and analyze the image signal, the radiographic image taken and recorded will not be understood correctly, and incorrect reading conditions and image processing conditions will be required, resulting in a radiographic image that is suitable for observation being reproduced and recorded. There may be cases where this is not done.

In order to solve this problem, before determining the reading condition 1 image processing conditions, it is necessary to recognize the irradiation field and determine the reading condition 9 image processing conditions based on the image signal within the irradiation field.

The applicant has already proposed several methods for recognizing radiation fields (for example, Japanese Patent Application Laid-Open No. 61-39039).
The above-mentioned problems can be overcome by recognizing the irradiation field using such a method and determining the reading conditions and image processing conditions based on the image signal corresponding only to the recognized area.

In many cases, in the method of recognizing the radiation irradiation field as described above, first, points that are considered to be on the contour of the irradiation field,
In other words, several contour candidate points are determined.

Once we have found several such contour candidate points, we can then find straight lines or curves along those points.
The area inside these straight lines or curves can be recognized as the radiation irradiation field.

The above-mentioned irradiation field can be narrowed down to various shapes. For example, in the case of recording a radiation image on a stimulable phosphor sheet, as shown in FIG. 2 or 3, a stimulable phosphor sheet is used. 103 is often narrowed down to a rectangle with two contours located approximately equidistant from the opposite sides toward the center of the sheet and approximately parallel to each other, and if this is known as a premise. The irradiation field can be recognized relatively easily. That is, in this case, taking FIG. 2 as an example, first, the stimulable phosphor sheet 10 is determined based on the image signal obtained by reading the stimulated luminescence light.
3, calculate the digital image data at each position on the sheet 103, then differentiate this image data along one line on the sheet 103 perpendicular to the above two sides, and calculate the absolute value of the differential value obtained by this process. It is sufficient to detect two points whose values exceed a predetermined threshold as contour candidate points (for example, as disclosed in
115989). Then, if such processing is performed for a large number of lines in the above direction, and out of the many contour candidate points obtained thereby, straight lines that respectively follow a group of points on the left side of the sheet 103 and a group of points on the right side of the sheet 103 are obtained.
The area between these two straight lines can be recognized as the irradiation field. In addition, when recognizing the irradiation field B as shown in FIG. 3, the above differential processing is performed in the horizontal and vertical directions of the stimulable phosphor sheet 103, and a total of four straight lines, two in each case, are obtained. The enclosed area may be recognized as the irradiation field.

(Problem to be Solved by the Invention) By the way, when detecting contour candidate points using the method described above, there are parts in the image where the density changes rapidly, similar to the irradiation field contour parts, such as the edges of bones. If the energy of scattered radiation is accumulated in the irradiation field, points in these areas may be erroneously detected as irradiation field contour candidate points. Although it is difficult to completely eliminate such false detections, if it is accurately determined that a certain contour candidate point is falsely detected, that contour candidate point can be canceled or a contour candidate detected by other methods can be used. By correcting to a point, it is possible to avoid misrecognizing the irradiation field.

Therefore, an object of the present invention is to provide a method that can accurately determine whether the contour candidate points detected as described above are correct or incorrect.

(Means and effects for solving the problem) The radiation field contour candidate point correctness determination method according to the present invention is based on the radiation image information obtained by applying a rectangular irradiation field aperture as shown in FIG. 2 or TS3. Image information is read from the rectangular recording medium on which it is recorded, digital image data on the center side of the recording medium is obtained from this image information, and this image data is differentiated along one line as described above. In the method of detecting two contour candidate points for each line based on the obtained differential value, the distance from one of the two sides of the recording medium that the above lines intersect at right angles to the contour candidate point that is closer to that side is calculated. fLx, the distance from the other of the two sides to the contour candidate point closer to the side is 2, the distance between both contour candidate points is l3, and the predetermined thresholds are α and β, ll-l21 Check whether the relationship <α l3> β holds, and if at least one of these relationships is not satisfied, replace these two contour candidate points with falsely detected points that do not exist on the irradiation field contour. The feature is that it is determined that there is.

As mentioned above, a rectangular irradiation field diaphragm is placed on a rectangular recording medium with two contours located approximately equidistant from the opposite sides toward the center of the recording medium and approximately parallel to each other. When radiographic image information is recorded over one line, the two outline candidate points found for one line are supposed to be located approximately the same distance from each other from the side of the recording medium that is close to each of them. Therefore, 1λ1
If -λ21<α, then the distance is considered to be 1. If they are far apart from each other, at least one of the two contour candidate points can be considered to be an erroneously detected point.

On the other hand, as described above, the front edge or the like in the recorded image may be detected as a contour candidate point, and in that case, it may happen that ltlzl<α. However, in such a case, the distance between the two detected contour candidate points is smaller than the distance between the two correct contour candidate points, so unless 9.3〉β holds, the two contour candidate points The points can be considered to be false positive points.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a radiation image information recording and reproducing system that determines whether a radiation field contour candidate point is correct or incorrect by the method of the present invention. This radiation image information recording and reproducing system basically includes a radiation image capturing section 20, a pre-reading reading section 30, a main reading reading section 40, and an image reproducing section 5.
Consists of 0.

In the radiographic imaging unit 20, a radiation source 100 such as an X-ray tube is directed toward a subject (subject) 101, for example.
Radiation 102 is irradiated. At the position where the radiation 102 that has passed through the subject 101 is irradiated, there is a stimulable phosphor sheet 10 that accumulates radiation energy as described above.
3 is arranged, and transmitted radiation image information of the subject lot is stored and recorded on this stimulable phosphor sheet 103. Note that there is a radiation 102 between the radiation source 100 and the subject 101.
A diaphragm 104 is arranged to narrow down the irradiation field.

The stimulable phosphor sheet 103 on which the radiation image information of the subject 101 has been recorded in this manner is sent to the pre-reading reading section 30 by sheet transport means 110 such as a transport roller. In the pre-reading reading section 30, the pre-reading laser light source 2
The laser beam 202 emitted from the laser beam 2
A filter 2 that cuts the wavelength range of stimulated luminescence light emitted from the stimulable phosphor sheet 103 by excitation of 02
03, it is linearly deflected by an optical deflector 204 such as a galvanometer mirror, and is reflected by a plane reflection Vt 205.
The light is incident on the stimulable phosphor sheet 103 through the stimulable phosphor sheet 103. Here, the laser light source 201 uses laser light 202 as excitation light.
is selected so that the wavelength range does not overlap with the wavelength range of the stimulated luminescent light emitted by the stimulable phosphor sheet 103. On the other hand, the phosphor sheet 103 is transported in the direction of an arrow 206 by a sheet transport means 210 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the phosphor sheet 103 is irradiated with laser light 202. Here, the laser light source 20
Emission intensity of 1, beam diameter of laser beam 202, laser beam 2
The scanning speed of 02 and the transport speed of the stimulable phosphor sheet 103 are selected so that the energy of the excitation light (laser light 202) for pre-reading is smaller than that for main reading performed in the reading section 40 for main reading, which will be described later. ing.

When irradiated with the laser beam 202 as described above, the stimulable phosphor sheet 103 emits stimulated luminescent light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light is transmitted to the pre-reading light guide 207. incident on . The stimulated luminescence light is guided through the light guide 207, exits from the exit surface, and is received by a photodetector 208 such as a photomultiplier. The light receiving surface of the photodetector 208 is equipped with a filter that transmits only light in the wavelength range of stimulated luminescence light and cuts light in the wavelength range of excitation light, and detects only stimulated luminescence light. I'm starting to get it. The detected stimulated luminescence light is converted into an electrical signal carrying accumulated recording information, and is sent to an amplifier 2.
09. The signal output from the amplifier 209 is digitized by the A/D converter 211 and inputted to the main reading control circuit 314 of the main reading reading section 40 as a pre-read image signal Sp. This book reading control circuit 314 is
Based on the accumulated recording information indicated by the pre-read image signal Sp, the reading gain setting value a1 recording scale factor setting value b1
Determine reproduction image processing condition setting value C. The pre-read image signal Sp is also input to an irradiation field recognition circuit 220, which will be described in detail later.

The stimulable phosphor sheet 1 has completed pre-reading as described above.
-103 is transferred to the reading unit 40 for main reading.

In the main reading reading section 40, the main reading laser light source 3°I
The laser beam 302 emitted from this laser beam 302
A filter 303 that cuts the wavelength range of stimulated luminescent light emitted from the stimulable phosphor sheet 103 by excitation of the stimulable phosphor sheet 103.
After passing through the stimulable phosphor sheet 103, the beam diameter is strictly adjusted by a beam expander 304, linearly deflected by an optical deflector 305 such as a galvanometer mirror, and passed through a flat reflecting mirror 306 to the stimulable phosphor sheet 103. incident on the top. There is f between the optical deflector 305 and the plane reflecting mirror 30B.
A θ lens 307 is arranged so that the beam diameter of the laser light 302 scanning over the stimulable phosphor sheet 1O3 is made uniform. On the other hand, the stimulable phosphor sheet 1o3 is transported in the direction of the arrow 308 by a sheet transport means 320 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the stimulable phosphor sheet 103 is irradiated with laser light. When irradiated with the laser beam 302 in this manner, the stimulable phosphor sheet 103 emits stimulated luminescence light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light enters the main reading light guide 309. do. The stimulated luminescent light guided through the main reading light guide 309 while repeating total reflection is emitted from its exit surface, and is emitted from the photomultiplier.
The light is received by a photodetector 310 such as. Photodetector 31
A filter that selectively transmits only the wavelength range of the stimulated luminescence light is attached to the light receiving surface of the photodetector 310 so that the photodetector 310 detects only the stimulated luminescence light.

The output of the photodetector 310 that photoelectrically detects the stimulated luminescent light representing the radiation image recorded on the stimulable phosphor sheet 103 has a read gain based on the read gain setting value a determined by the control circuit 314. The electric signal is amplified to an appropriate level by the amplifier 311 set to . The amplified electrical signal is input to the A/D converter 312, and based on the recording scale factor setting value, it is converted into a digital signal with a recording scale factor suitable for the signal fluctuation width, and the digital signal is input to the signal processing circuit 313. . The above digital signal is
In this signal processing circuit 3H, the reproduction image processing condition setting value C is
Signal processing (image processing) is performed based on the data and output.

The read image signal (actual read image signal) So output from the signal processing circuit 313 is transmitted to the optical modulator 401 of the image reproducing unit 50.
is input. In this image reproducing section 50, a laser beam 403 from a recording laser light source 402 or a light modulator 40 is used.
1, the reading image signal So input from the signal processing circuit 313 is modulated based on the scanning mirror 404.
The light beam is deflected by the light beam and scans over a photosensitive material 405 such as photographic film. The photosensitive material 405 is then transported in a direction perpendicular to the scanning direction (arrow 406 direction) in synchronization with the scanning, and a radiation image based on the actual reading image signal So is output onto the photosensitive material 405. In addition to this method, various other methods can be used to reproduce the radiographic image, such as the above-mentioned CRT display.

Next, even when the radiation irradiation field B is narrowed down in the stimulable phosphor sheet 103 as shown in FIG. 2, the reading gain setting value a1 recording scale factor setting value b1 image processing condition setting value C A mechanism for appropriately determining is explained with reference to FIG. As shown in FIG. 5, the control circuit 314 includes a signal extraction section 35
0, a histogram analysis section 351, a reading section 352, and a storage section 353. The pre-read image signal Sp is input to the signal extraction section 350, and in the signal extraction section 350,
A pre-read image signal Sp' is extracted for only the designated area as will be described later. This signal extraction section 35
The pre-read image signal Sp' output from 0 is input to the histogram analysis section 351. Histogram analysis section 35
1 creates a histogram of the pre-read image signal Sp',
For example, the maximum value, minimum value, maximum frequency value, etc. are determined and information S' indicating these values is sent to the reading unit 352.
The optimum reading gain setting value a1 recording scale factor setting value and image processing condition setting value C corresponding to these maximum values, minimum values, etc. are stored in the reading unit 53.
2 reads setting values a, b, and c corresponding to the information Sr from the storage section 353, and inputs them to the amplifier 3 as described above.
11, A/D converter 312 and signal processing circuit 313
send to

Next, signal extraction in the signal extraction section 350 will be explained. The irradiation field recognition circuit 220 includes a differential processing section 2211, a threshold value setting section 222, a contour candidate point signal detection section 223, a correctness determination section 224, and a calculation section 225. In this irradiation field recognition circuit 220, the pre-read image signal Sp is input to a differential processing section 221 and a contour candidate point signal detection section 223. The differential processing unit 221 first performs differential processing on this digitized pre-read image signal Sp along one line D1 shown in FIG.
...Perform differential processing along Dn. In this example, it is known that radiation image information is recorded on the stimulable phosphor sheet 103 by applying a rectangular irradiation field aperture as shown in FIG. 2, and the line D!
, D2, D3, . Ru. The method of differentiation may be one-dimensional first-order differentiation or higher-order differentiation, or two-dimensional first-order differentiation or higher-order differentiation. Furthermore, in the case of discretely sampled images, differentiation is equivalent to finding the difference between adjacent image data, and in this example, this difference is found. Regarding such differential processing, please refer to the above-mentioned Japanese Patent Application Laid-open No. 62
A detailed description is given in No.-115989.

The information Sm indicating the difference is provided by the contour candidate point signal detection unit 22
Sent to 3. The contour candidate point signal detecting section 223 determines the contour BISBZ of the radiation irradiation field B on the sheet 103 based on the information Sm indicating the difference and the information sth indicating the threshold Th output by the threshold setting section 222. Find contour candidate points that are considered to be. That is, since the level of the image signal within the irradiation field B is clearly higher overall than the level of the image signal for the area outside the irradiation field B, the pre-read image signal Sp along a certain line Di The value of has a distribution as shown in FIG. 4(a). Therefore, as shown in FIG. 4(b), the value of the above-mentioned difference varies greatly specifically at the edge of the irradiation field.

Therefore, the contour candidate point signal detection unit 223 detects points where the absolute value of this difference exceeds the predetermined threshold Th, and
Find two contour candidate points. Note that, as described above, the energy of the scattered radiation accumulated outside the radiation irradiation field B is detected at the time of look-ahead, so that the distribution of the look-ahead image signal Sp along the line Di becomes, for example, as shown in FIG. 6(a). , as a result, the distribution of differences may become as shown in FIG. 6(b). Furthermore, in the case of the stimulable phosphor sheet I03 on which the bone region is recorded, the distribution of the pre-read image signal Sp along the line Di that crosses the front edge is as shown in FIG. 7(a), for example. The distribution of the resulting differences may be as shown in FIG. 7(b). In such a case, three or more points exceeding the threshold Th may be detected, so for example, by selecting two points in descending order of the difference value, two points are always detected for one line Di. Detect contour candidate points.

The contour candidate point signal detection unit 223 extracts the pre-read image signals Sp for the two contour candidate points obtained as described above, determines the pixel position corresponding to each extracted pre-read image signal Sp, and Information Se indicating the position is sent to the correct/incorrect determining section 224. The pre-read image signal Sp extracted as described above is mostly an image signal responsible for the contour B1%B2 of the radiation irradiation field B (see FIG. 2) on the stimulable phosphor sheet 103, that is, a contour candidate point signal. becomes. In this example, the pixel position is expressed in an x-y orthogonal coordinate system on the stimulable phosphor sheet 103, as shown in FIG.

The correctness determination unit 224 determines whether the contour candidate points at the pixel positions indicated by the information Se are really located on the contours B1 and B2 of the irradiation field, as described below. As shown in FIG. 8, the correct/incorrect determination unit 224
When the two outline candidate points for each line are El and EZ, the distance from the left side 103L of the stimulable phosphor sheet 103 to the left outline candidate point E1 is 9. s and the right side 10
Distance 2 from 3R to the right contour candidate point E2, and distance 2 between both points E1 and B2. and set the predetermined threshold value to α
, as β, 9.1 −21〈α ・・・・・・(1) l3
>β...Check whether the following relationship (2) holds. If contour candidate points E1, B2
If point 11■ in Figure 6(b) is detected, the difference between the two becomes large, even though there should be almost no difference between the two. The relationship is not established. Furthermore, if points I and II in FIG. 7(b) are detected as contour candidate points E1 and B2, the two points E1 and Ez should originally be sufficiently far apart, but this is not the case. Therefore, the relationship (2) does not hold. Therefore, if even one of the relationships (1) and (2) above is not satisfied, the correctness/incorrect determination unit 224 considers that the contour candidate points E1 and B2 are erroneously detected, and changes the pixel position information Se. Information about the contour candidate points El and E2 is deleted from among them. On the other hand, if the relationships (1) and (2) above are both satisfied, the pixel position information regarding the outline candidate points E1 and B2 is utilized as is.

The correct/incorrect judgment section 224 performs the above judgment processing and, if necessary, the above deletion processing on all detected contour candidate points, and sends the processed pixel position information Se' to the calculation section 225.

In this example, when contour candidate points E1 and E2 are determined to be erroneously detected points, these points are canceled, but such points are replaced with more appropriate points derived from other contour candidate points. It may also be corrected.

The calculation unit 225 calculates two straight lines along these contour candidate points based on information Se' indicating the correct pixel position of the contour candidate points. As mentioned above, such a straight line forms the outline of the irradiation field.

A line along this contour candidate point can be formed by, for example, connecting the remaining points after smoothing those points, or adding contour candidate points El and E2 in the y direction as shown in FIG. The number of candidate points for each coordinate is determined), and a straight line parallel to the y-axis passing through the peak positions X1 and x2 of the added numbers is determined. The calculation unit 225 generates information S indicating the radiation irradiation field B recognized as described above.
t is sent to the signal extraction section 350 of the control circuit 314. The signal extraction unit 350 extracts this information St from the pre-read image signal sp.
Only the signals for the region indicated by are extracted and sent to the histogram analysis section 351. Therefore, the histogram analysis in the histogram analysis unit 351 is performed only on the area on the stimulable phosphor sheet 103 that is actually irradiated with radiation, so the above-mentioned set values a, b, and C are based on the actual accumulated It is optimal for recorded information.

In the embodiments described above, the differential processing is performed only on the in-line parallel to the , perform differential processing on several lines parallel to the y-axis to detect contour candidate points, find two straight lines along those contour candidate points, and combine these straight lines with the above-mentioned method. What is necessary is to recognize the rectangular area surrounded by the two straight lines found as the irradiation field.

In addition, "pre-reading" as explained above is usually called "book-reading".
This is done on a coarser pixel basis than in . The above-mentioned differential processing may be performed on the image data itself obtained by such a relatively coarse reading operation, or the image data may be interpolated to obtain finer image data and then the images may be It may also be performed on data. Furthermore, the above differential processing may be performed on image data obtained by averaging image signals of a plurality of pixels.

The apparatus shown in FIG. 1 has separate reading sections for main reading and reading sections for pre-reading.
As shown in No. 87242, the reading system for main reading and the reading system for pre-reading are used together, and when the pre-reading is completed, the stimulable phosphor sheet is returned to the reading system by the sheet transport means and the main reading is performed. The energy adjustment means may be used to adjust the excitation light energy to be smaller than that during main reading, and the method of the present invention is also applicable when reading radiation image information using such an apparatus.

Furthermore, in the embodiments described above, the radiation irradiation field is recognized from the pre-read image signal, but the actual reading image signal or the image signal obtained by directly performing reading equivalent to the actual reading without performing pre-reading is used. Of course, it is also possible to use the method of the present invention to recognize irradiation field contour candidate points. In such a case, the recognized irradiation field information can be used, for example, to appropriately set the image processing condition setting value C.

Furthermore, in the embodiments described above, a stimulable phosphor sheet is used as a recording medium for radiographic image information, but the method of the present invention is capable of producing radiation from conventionally known silver halide photographic film for X-ray photography. The same method can be used when reading an image to obtain an image signal.

(Effects of the Invention) As explained in detail above, in the radiation field contour candidate point correctness determination method of the present invention, a pair of contour candidate points detected based on differential processing are located at a distance from each other from the edge of the recording medium. In addition to checking whether the contour candidate points are located at equal distances from each other, we also check whether the contour candidate points are unduly close to each other. It is now possible to accurately determine whether the contour candidate points found for the contour are correct or incorrect. Therefore, according to this method, it is possible to prevent incorrect contour candidate points from being used for irradiation field recognition, accurately recognize the radiation irradiation field, correctly grasp information about the subject, and adjust the reading conditions for main reading and image processing. Conditions can be set optimally. Therefore, according to the method of the present invention, it is possible to always reproduce radiographic images with excellent suitability for observation and interpretation.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an apparatus for reading radiation image information by determining whether irradiation field contour candidate points are correct or incorrect using the method of the present invention; FIG. 2 is an explanatory diagram illustrating the direction of differential processing according to the present invention; FIG. 3 is an explanatory diagram showing the recording state of radiation image information on the stimulable phosphor sheet according to the present invention, and FIG. 4 is a graph showing the distribution state of image signals and the distribution state of image signal difference values according to the present invention. FIG. 5 is a block diagram showing in detail a part of the apparatus shown in FIG. 1, and FIGS. 6 and 7 show other examples of the distribution state of image signals and the distribution state of image signal difference values according to the present invention. FIG. 8 is an explanatory diagram illustrating a method for determining whether a contour candidate point is correct or incorrect according to the present invention, and FIG. 9 is an explanatory diagram illustrating a method for extracting a region surrounded by a straight line along a contour candidate point. 20...Radiation image capturing unit 30...Reading unit for pre-reading 40...Reading unit for main reading 100...
Radiation source 101...Subject 102...
- Radiation 103...Stormable phosphor sheet 103L...Left side of the sheet 103R...Right side of the sheet 104...Aperture 201...Laser light source for pre-reading 202...Laser light for pre-reading 204... Pre-reading optical deflector 208... Pre-reading photodetector 210... Pre-reading sheet transport means 220.250... Irradiation field recognition circuit 221... Differential processing section 222... Threshold setting section 223 ... Contour candidate point signal detection section 224, 251 ... Correctness determination section 225 ... Calculation section 301 ... Laser light source for main reading 302 ... Laser light for main reading 305 ... Optical deflector for main reading 310 ... Photodetector for main reading 311 ... Amplifier 312 ... A/D converter 313 ... Signal processing circuit 314 ... Control circuit 320 ... Sheet transport means for main reading B ... Radiation irradiation Field B1, B2・
...Irradiation field contour a...Reading gain setting value b...Recording scale factor setting value C...Reproduction image processing condition setting value D1-Dn...Direction of differential processing El, B2...Contour candidate Point 0, P...Point that is the starting point of differential processing So...Actual reading image signal Sp...Pre-reading image signal Se...Information indicating contour candidate points Se'...Contour candidate points after correctness determination Information showing Kamezemi

Claims (1)

[Scope of Claims] A rectangular irradiation field is formed with respect to a rectangular recording medium, with two contours located approximately equal distances toward the center of the recording medium from two opposing sides and approximately parallel to each other. When radiation image information is recorded on the recording medium by irradiating radiation with an aperture, reading the image information from the recording medium and determining digital image data at each position on the recording medium from this image information, This image data is differentiated along a line perpendicular to the two sides, and two contour candidate points that are considered to be located on the two contours are determined based on the differential values obtained. In the detection method, the distance from one of the two sides to the contour candidate point closer to the side is l_1, and the distance from the other of the two sides to the contour candidate point closer to the side is l_2. , the distance between both contour candidate points is l_3, and the predetermined thresholds are α and β, it is investigated whether the following relationship holds: |l_1−l_2|<α, l_3>β, and at least one of these relationships is If one of the conditions is not satisfied, the two contour candidate points are determined to be erroneously detected points that are not located on the contour.