JPH0690412B2 - Irradiation field recognition method and image processing condition determination method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention recognizes an irradiation field when radiation image information is recorded by narrowing the irradiation field on a recording medium such as a stimulable phosphor sheet. The present invention relates to a method and a method for determining an image processing condition for processing an image signal read from the recording medium, the method using the irradiation field recognition method.

(Prior Art) When a certain kind of phosphor is irradiated with radiation (X-ray, α-ray, β-ray, γ-ray, electron beam, ultraviolet ray, etc.), a part of this radiation energy is accumulated in the phosphor, It is known that when a phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated emission depending on the stored energy, and a phosphor having such a property is called a stimulable phosphor. .

Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded on a sheet-shaped stimulable phosphor, and then the stimulable phosphor sheet is scanned with excitation light such as laser light. Generate stimulated emission light, photoelectrically read this stimulated emission light to obtain an image signal, perform image processing on this image signal, and photograph a radiation image of the subject based on the image signal subjected to this image processing The applicant has already proposed a radiation image information recording / reproducing system for outputting a visible image on a recording material such as a photosensitive material or a display device such as a CRT.
(JP-A-55-12429, JP-A-56-11395, etc.) In addition, in the above system, in order to improve the observation and interpretation suitability of a visible image, when the above stimulated emission light is photoelectrically read, It is desirable to perform the reading based on the optimum reading condition determined according to the captured image. From this viewpoint, as one aspect of the above system, a stimulable phosphor sheet in which radiation image information of a subject is stored and recorded. Scanning with excitation light, prior to the "main reading" to obtain an electrical image signal for reproducing the diagnostic visible image by reading the stimulated emission light emitted from the sheet by this scanning by photoelectric reading means, Pre-reading is performed by scanning the sheet with excitation light of a lower level than the excitation light used for the main reading in advance and reading the outline of the image information accumulated and recorded on this sheet. The reading conditions when performing the main reading are determined based on the obtained image signal, the main reading is performed according to the reading conditions, and the image signal obtained by the main reading is input to the image processing means, and the image processing means There is known a system in which an image signal is processed so that an output image suitable for a diagnostic purpose is obtained according to a region to be imaged, a photographing method, and the like, and the image signal is reproduced as a visible output image on a photographic light-sensitive material. This is disclosed in Japanese Patent Application Laid-Open No. 58-67240, which was filed by the applicant of the present invention and which has already been published.

Here, the reading condition is related to the output of the reading means, for example, in the above, the input (light amount of stimulated emission light) and the output (electrical image signal level) of the photoelectric reading means.
Is a general term for various conditions that affect the relationship with, for example, the read gain (sensitivity) that determines the relationship between input and output,
It means a scale factor (latitude) or the power of excitation light in reading.

Further, the excitation light used for pre-reading is at a lower level than the excitation light used for main reading means that the effective energy of the excitation light that the stimulable phosphor sheet receives per unit area during pre-reading is that during the main reading. Means less than.

In this way, by grasping the outline of the image information accumulated and recorded in advance on the sheet prior to the main reading and performing the main reading according to the reading condition determined based on the outline of the image information, the fluctuation of the subject or the imaging region or It is possible to eliminate the inconvenience caused by the fluctuation of the radiation energy level range accumulated and recorded in the stimulable phosphor sheet on the sheet due to the fluctuation of the radiation exposure amount and the like, and it is possible to always obtain a visible image excellent in observation and interpretation.

(Problems to be solved by the invention) However, in the above system, in order to prevent radiation from being applied to a portion which is not required for humanitarian diagnosis, or when radiation is applied to a portion which is unnecessary for diagnosis, the portion needs to be diagnosed. The scattered radiation enters in a certain portion, and the contrast resolution is lowered. For the reason such as preventing it, the radiation irradiation field may be narrowed at the time of recording the radiation image information (at the time of photographing). In this way, when shooting is performed with the irradiation field narrowed down, there will be a part inside the irradiation field and a part outside the irradiation field within the stimulable phosphor sheet. In that case, is it somewhere inside the irradiation field? In other words, it is convenient if it is possible to know where the contour of the irradiation field exists.

This is because, for example, when the pre-reading of the stimulable phosphor sheet is performed and the reading conditions for the main reading are determined based on the image signal obtained by the pre-reading, the sheet is used when the irradiation field is narrowed down. This is because it is preferable to determine the reading condition based only on the pre-read image signal within the irradiation field range above.

This point will be described in more detail below. That is, as a specific method for determining the reading condition in the main reading based on the image information obtained by the pre-reading,
For example, the histogram of the level of the image signal obtained by pre-reading is obtained, and the maximum image signal level Pmax and the minimum image signal level Pmin of the desired image signal range in this histogram are obtained from this histogram.
ax and Pmin, respectively, of the main reading so as to correspond to the maximum signal level Qmax and the minimum signal level Qmin of the desired input signal range in the image processing means determined by the maximum density Dmsx and the minimum density Dmin of the appropriate density range in the visible output image, respectively. A method for determining the reading conditions has been filed by the present applicant (Japanese Patent Laid-Open No. 60-156055).

However, when imaging is performed with the radiation field narrowed down as described above, normally, scattered radiation generated from a subject in the irradiation field is incident outside the irradiation field on the stimulable phosphor sheet, resulting in high sensitivity storage. Since the phosphor sheet also accumulates and records the scattered rays, the image signal level based on the scattered rays is also included in the histogram of the preread image signal level. Since the image signal level outside the irradiation field on the sheet may be higher than the image signal level inside the irradiation field based on the scattered rays, the image signal level inside and outside the irradiation field is distinguished from the obtained histogram. Is difficult. Therefore, as described above, when Pmax and Pmin are obtained from the histogram, and when the reading conditions are determined from this, the minimum value of the image signal level in the irradiation field should originally be Pmin. It may happen that the minimum value is Pmin. When the minimum value of the image signal level outside the irradiation field is set to Pmin in this way, since that value is generally lower than the minimum value of the image signal level inside the irradiation field, the scattered radiation unnecessary for diagnosis in the main reading is reduced in concentration. Therefore, the density of the image of the portion necessary for diagnosis becomes too high, and as a result, the contrast decreases and it becomes difficult to make a satisfactory diagnosis.

That is, when shooting is performed with the irradiation field narrowed down, scattered rays generated from the subject enter the outside of the irradiation field on the sheet,
Since the pre-reading image signal also includes the one based on this scattered radiation, it is difficult to determine the optimum reading condition even if the reading condition is determined based on such a pre-reading image signal. As a result, it is difficult to obtain a visible image with excellent aptitude for interpretation.

Therefore, when trying to determine the reading conditions based on the pre-reading image signal by the above method, the exposure field is accurately recognized when the image is taken with the irradiation field stopped down, and the pre-reading image signal in the irradiation field is detected. It is desirable to determine it based on this, and to eliminate the above-mentioned adverse effects of scattered radiation outside the irradiation field.

The above is an explanation of the necessity of irradiation field recognition when deciding the reading conditions when the stimulable phosphor sheet is used for imaging, but this irradiation field recognition is not limited to such a case, and is generally applied to the recording medium. This may be necessary due to various circumstances when the radiation image information is recorded by narrowing the field.

On the other hand, in the above system, image processing is performed on the read image signal as described above. This image processing is generally performed on the basis of image processing conditions determined on the basis of the imaged region or method so that an output image suitable for a diagnostic purpose can be obtained for each image. For example, it is conceivable that the determination is made based on the image signals obtained by the pre-reading or the actual reading instead of the imaged region or the imaged method, or based on both the image signals and the imaged region / imaged method.

However, when an image is taken with the irradiation field stopped down, even if the image processing conditions are determined based on the pre-reading or main-reading image signal as described above, the information due to scattered rays outside the irradiation field is included in the image signal as described above. Since (noise) is included, it is difficult to obtain a preferable image processing condition that is expected to be obtained by initially determining the image signal.

Therefore, when the image processing condition is determined based on the image signal as described above, when the image is captured with the irradiation field stopped, it is not determined simply based on the read image signal itself, but by some method. It is desirable to make the determination based on the image signal with less noise, which is obtained by eliminating the information due to.

The problem in determining such image processing conditions is not only in the case of photographing using the above-mentioned stimulable phosphor sheet, but generally in the case where radiation image information is recorded by narrowing the irradiation field on the recording medium. It can happen.

The image processing conditions collectively refer to various conditions that affect the relationship between input and output in the image processing means, and mean, for example, gradation processing conditions and spatial frequency processing conditions.

In view of the above circumstances, the first object of the present invention is to provide a method of recognizing an irradiation field when radiation image information is recorded by applying an irradiation field stop on a recording medium such as a stimulable phosphor sheet. To do.

In view of the above circumstances, the object of the present invention in FIG. 2 is to provide scattered radiation information outside the irradiation field when the radiation image information is recorded on the recording medium such as a stimulable phosphor sheet with the irradiation field narrowed. An object of the present invention is to provide a method for determining an image processing condition based on an image signal with less noise removed.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the irradiation field recognition method according to the first aspect of the present invention is a stimulable phosphor sheet on which radiation image information has been captured by narrowing down the irradiation field. An image signal is read from a recording medium such as, and from the image signal, a sample image signal relating to an arbitrary pixel row extending from the recording region end portion of the recording medium toward the center side is extracted, and the end indicated by the sample image signal is extracted. Image density change between a certain number of pixels near the
Expressed by an approximate expression that is substantially a linear equation, the difference between the assumed image density and the actual image density indicated by the sample image signal is obtained by this approximate expression, and the difference is calculated from the end portion toward the center. It is characterized in that the area until the predetermined value is reached is recognized as the area outside the irradiation field and the area inside the area is recognized as the irradiation field.

In order to achieve the above-mentioned object, the image processing condition determining method according to the second aspect of the present invention reads an image signal from a recording medium such as a stimulable phosphor sheet on which radiation image information is photographed by narrowing the irradiation field. , An image between a predetermined number of pixels near the end portion indicated by the sample image signal is extracted from the image signal by extracting a sample image signal regarding an arbitrary pixel row extending from the end portion of the recording area of the recording medium toward the center side. The density change is substantially expressed by an approximate expression consisting of a linear equation, and the difference between the assumed image density and the actual image density indicated by the sample image signal is obtained by this approximate expression, and the difference is calculated from the end to the center side. The image within the recognized irradiation field among the image signals read from the recording medium by recognizing the area until the difference reaches a predetermined value as the irradiation field and the area inside the irradiation field as the irradiation field. And determines the image processing conditions based on No..

The "recording medium" in the above means a medium on which radiation image information can be recorded, and the above-mentioned stimulable phosphor sheet can be mentioned as a specific example, but it is not necessarily limited thereto.

Further, the "image signal read from the recording medium" in the above means an image signal obtained by reading the image information recorded on the recording medium by some method, for example, in the above-mentioned stimulable phosphor sheet. It means an image signal obtained by pre-reading or main reading, but is not necessarily limited thereto.

Of course, the method of using the irradiation field recognized by the above method is not limited to any particular one.

In the image processing condition determining method, it does not matter whether the image signal for recognizing the irradiation field is the same as the image signal for determining the image processing condition. For example, the irradiation field may be recognized from the main reading image signal, and the image processing condition may be determined based on the main reading image signal in the irradiation field. Alternatively, the irradiation field may be recognized from the pre-reading image signal and the pre-reading or main reading in the irradiation field may be performed. The image processing condition may be determined based on the image signal.

Further, the above-mentioned "determining the image processing condition based on the image signal in the irradiation field" means not only determining based on such an image signal but also such an image signal and other ones, for example, the above-mentioned It is also meant to include the case where the determination is made based on the imaged part, the imaged method, and the like.

The image processing condition may be determined based on the image signal in the irradiation field, that is, any method may be used as long as the image signal is used, and the specific method is not limited at all. .

Further, the image processing condition determination to be made can also include the gradation processing condition as a typical one, but is not necessarily limited thereto.

(Effect of the Invention) As described above, the irradiation field recognition method according to the first aspect of the present invention extracts a sample image signal relating to an arbitrary pixel row extending from the end portion of the recording area of the recording medium toward the center side, and the sample image signal is extracted. The image density change between a predetermined number of pixels near the edge indicated by the image signal is substantially expressed by an approximate expression consisting of a linear equation, and the assumed image density by this approximate expression and the actual image density indicated by the sample image signal are expressed. The area where the difference reaches a predetermined value from the end portion toward the center side is recognized as the outside field of the irradiation field, and the area inside the irradiation field is recognized as the irradiation field.

The image density variation indicated by the sample image signal extracted as described above is generally relatively high in the irradiation field, and changes in accordance with the image information, and is lower in the irradiation field portion than in the irradiation field. Then, the scattered radiation from the subject is also radiated to the outside portion of the irradiation field, and the scattered dose gradually decreases as the distance from the irradiation field increases. Therefore, the image density in the outside portion of the irradiation field becomes higher toward the center side, and moreover, at the end of the recording area. In the vicinity, it is relatively gentle and increases linearly, and increases rapidly as it approaches the irradiation field.

Therefore, the density change in the vicinity of the end of the recording area is approximated by a substantially linear equation (equation expressed by a straight line) based on the sample image signal, and the assumed density and the actual density by the sample image signal are calculated by this approximate expression. If the difference is obtained, the difference increases as it goes to the center side in the outer part of the irradiation field, that is, as it approaches the irradiation field, and exceeds the predetermined density difference δ at the edge part of the irradiation field. If experimentally and empirically obtained in advance, the area from the edge of the recording area toward the center side until the difference reaches δ should be judged as the outside area of the irradiation field, and the area inside it as the irradiation field. You can

Therefore, according to the first aspect of the present invention configured as described above, it is possible to accurately recognize the irradiation field.

As described above, the image processing condition determining method according to the second aspect of the present invention recognizes the irradiation field by the irradiation field recognition method according to the first aspect of the present invention, and performs image processing based on the recognized image signal in the irradiation field. It determines the conditions.

If the irradiation field is obtained and only the image signal in the irradiation field is extracted, the extracted image signal is the image signal read from the entire recording medium from which the image signal due to scattered rays outside the irradiation field is excluded, that is, such scattering. It can be said that it is a true image signal that does not include lines / noise.

Therefore, according to the present invention, the image processing condition can be determined based on a true image signal that does not include such scattered ray noise, and as a result, an appropriate image processing condition can be determined. You can

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

First, an embodiment of the irradiation field recognition method according to the first aspect of the present invention will be described. In this embodiment, the present invention is applied to the case of recognizing an irradiation field from a preread image signal in a stimulable phosphor sheet which is photographed with a rectangular irradiation field diaphragm.

FIG. 1 is a radiation image provided with a process for recognizing an irradiation field using one embodiment of the present invention, and the irradiation field recognized by this process is used when determining reading conditions and image processing conditions. 1 illustrates an example of an information recording / reproducing system. This radiation image information recording / reproducing system basically includes a radiation image capturing unit 20 and a read-ahead reading unit 3
0, a main reading reading unit 40, and an image reproducing unit 50. In the radiation image capturing unit 20, radiation 102 is emitted from a radiation source 100 such as an X-ray tube toward a subject (examinee) 101. At the position where the radiation 102 transmitted through the subject 101 is irradiated, the stimulable phosphor sheet 103 for accumulating the radiation energy is arranged as described above, and the transmitted radiation of the subject 101 is placed on the stimulable phosphor sheet 103. Image information is accumulated and recorded. Between the radiation source 100 and the subject 101, a diaphragm 10 that narrows down the irradiation field of the radiation 102.
4 are arranged.

The stimulable phosphor sheet 103 on which the radiation image information of the subject 101 is recorded in this manner is sent to the prereading reading unit 30 by the sheet transfer means 110 such as a transfer roller. The laser light 202 emitted from the laser light source 201 for pre-reading in the pre-reading reading section 30 passes through the filter 203 that cuts the wavelength region of the stimulated emission light emitted from the stimulable phosphor sheet 103 by the excitation of this laser light 202. After that, it is linearly deflected by an optical deflector 204 such as a galvanometer mirror, and is incident on the stimulable phosphor sheet 103 via a plane reflecting mirror 205. Here, the laser light source 201 is selected so that the wavelength range of the laser light 202 as the excitation light does not overlap with the wavelength range of the stimulated emission light emitted by the stimulable phosphor sheet 103. On the other hand, the stimulable phosphor sheet 103 is transferred in the direction of arrow 206 by the sheet transfer means 210 such as a transfer roller to be sub-scanned, and as a result, the laser beam 202 is irradiated over the front surface of the stimulable phosphor sheet 103. . Here, the emission intensity of the laser light source 201, the beam system of the laser light 202, the laser light
The scanning speed of 202, the transfer speed of the stimulable phosphor sheet 103,
The energy of the pre-reading excitation light (laser light 202) is selected to be smaller than that of the main reading performed by the main reading reading unit 40 described later.

When the laser light 202 is irradiated as described above, the stimulable phosphor sheet 103 emits stimulated emission light of a light amount corresponding to the radiation energy stored and recorded in the stimulable phosphor sheet 103. Incident on. The stimulated emission light is guided through the light guide 207, emitted from the emission surface, and received by a photodetector 208 such as a photomultiplier.
On the light receiving surface of the photodetector 208, a filter that transmits only light in the wavelength range of stimulated emission light and cuts light in the wavelength range of excitation light is attached, and detects only stimulated emission light. Is ready to go. The detected stimulated emission light is converted into an electric signal (image signal) carrying the accumulated record information, and the amplifier 20
Amplified by 9. The signal output from the amplifier 209 is A /
The pre-read image signal Sp is digitized by the D converter 211.
Is input to the main reading control circuit 314 of the main reading reading unit 40 and the irradiation field recognition circuit 220 described in detail later. The main reading control circuit 314 determines a read gain a, a recording scale factor b, and an image processing condition c based on the preread image signal in the irradiation field recognized by the irradiation field recognition circuit 220 among the preread image signals Sp. .

The stimulable phosphor sheet that has been read ahead as described above
103 is transferred to the reading unit 40 for main reading. Book reader 4
The laser light 302 emitted from the main reading laser light source 301 at 0 passes through the filter 303 that cuts the wavelength region of the stimulated emission light emitted from the stimulable phosphor sheet 103 by the excitation of the laser light 302, and then the beam The beam diameter is strictly adjusted by the expander 304, is linearly deflected by the optical deflector 305 such as a galvanometer mirror, and the stimulable phosphor sheet 1 is passed through the plane reflecting mirror 306.
03 incident on. An fθ lens 307 is arranged between the light deflector 305 and the plane reflecting mirror 306 so that the beam diameter of the laser light 302 scanning the stimulable phosphor sheet 103 becomes uniform. On the other hand, the stimulable phosphor sheet 103 is transferred in the direction of arrow 308 by the sheet transfer means 320 such as a transfer roller to be sub-scanned, and as a result, the stimulable phosphor sheet 10 is transferred.
The entire surface of 3 is irradiated with laser light. When the laser light 302 is irradiated in this manner, the stimulable phosphor sheet 1
03 emits stimulated emission light of a light amount corresponding to the radiation energy stored and recorded, and this emission light is guided through the light guide 309 for reading while repeating total reflection, and the emission light is the emission surface. And is received by a photodetector 310 such as a photomultiplier. A filter that selectively transmits only the wavelength region of stimulated emission light is attached to the light receiving surface of the photodetector 310 so that the photodetector 310 detects only the stimulated emission light.

The output of the photodetector 310, which photoelectrically detects stimulated emission light showing a radiation image recorded on the stimulable phosphor sheet 103, is more suitable for the amplifier 311 based on the reading gain a determined by the control circuit 314. It is amplified to a level electric signal. The amplified electric signal is input to the A / D converter 312, is also converted into a digital signal having an appropriate signal level width based on the recording scale factor b determined by the control circuit 314, and is input to the signal processing circuit 313. It In the signal processing circuit 313, the digital signal is subjected to signal processing (image processing) on the basis of the image processing condition c determined by the control circuit 314 so that a radiographic image excellent in observation and interpretation suitability can be obtained.

The read image signal (main read image signal) So output from the signal processing circuit 313 is input to the optical modulator 401 of the image reproducing unit 50. In the image reproducing section 50, the recording laser light source
The laser light 403 from 402 is modulated by the optical modulator 401 based on the main reading image signal So input from the signal processing circuit 313, deflected by the scanning mirror 404, and scanned on the photosensitive material 405 such as photographic film. . And photosensitive material 4
Reference numeral 05 is transferred in a direction (arrow 406 direction) orthogonal to the scanning direction in synchronization with the scanning, and a radiation image based on the main reading image signal So is output onto the photosensitive material 405. As a method for reproducing the radiation image, various methods such as the above-described CRT display can be adopted in addition to such a method.

Here, when the radiation image information is stored and recorded (photographed) on the stimulable phosphor sheet 103, the aperture 104 is operated to apply an illumination field aperture as shown in FIG. An irradiation field (image recording portion) 103B is formed in a part of the recording area 103A. Then, as described above, the irradiation field recognition circuit 220 recognizes this radiation irradiation field 103B based on the look-ahead image signal Sp, sends information St indicating the irradiation field 103B to the control circuit 314, and this control circuit 314 performs the irradiation. Field information St
The read gain a, the recording scale factor b, and the image processing condition c are determined based on the preread image signal Sp in the irradiation field 103B.

Hereinafter, the irradiation field recognition by the irradiation field recognition circuit 220 will be described in detail. This irradiation field recognition circuit 220 is an A / D converter
From the total pre-reading image signal Sp input from 211, the stimulable phosphor sheet 103 as shown by X ₁ -X ₁ line in FIG.
The image signal of an arbitrary pixel column (for example, a pixel line in the main scanning direction) extending from the end of the recording area toward the center is extracted. The change in the image density d indicated by the sample image signal thus extracted is generally as shown in FIG. That is, the irradiation field 103B has a relatively high concentration,
The change is shown according to the image information, and the concentration is lower in the portion outside the edge portion of the irradiation field 103B, that is, in the portion outside the irradiation field than in the irradiation field 103B. Here, the scattered radiation from the subject is also radiated to the outside field of the irradiation field, and the scattered dose gradually decreases with distance from the irradiation field 103B. Therefore, the image density d in the outside field of the irradiation field changes as shown in the figure. Show. FIG. 3 is an enlarged view of the density change in this portion. As shown in the figure, the image density d changes relatively gently and linearly in the vicinity of the end of the recording area.
It rapidly increases as it approaches the irradiation field 103B.

As shown in FIG. 3, the irradiation field recognition circuit 220 calculates a linear density change between a predetermined number N of images near the edge of the recording area.
It is represented by a known method, for example, by an approximate expression composed of a linear equation of y = ax + b. Note that this approximation formula may be another higher-order equation as long as it is a formula that substantially represents a straight line.

Next, the irradiation field recognition circuit 220 obtains an assumed image density d ′ for each pixel of the pixel array based on the above approximation formula, and obtains a difference | d−d ′ | with the actual density d for each pixel. Next, the irradiation field recognition circuit 220 sequentially compares the density difference | d−d ′ | and the predetermined density difference δ from the pixels on the end side of the recording area. In the vicinity of the edge of the recording area, the density difference | d
Although −d ′ | is small, the pixel density X _{0 at} the edge portion of the irradiation field 103B exceeds the predetermined density difference δ for the first time. Therefore, the irradiation field recognition circuit 220 calculates the density difference | d
The pixel X ₀ whose −d ′ | exceeds the predetermined density difference δ for the first time is recognized as the irradiation field edge point pixel. The preferable value of the predetermined density difference δ can be experimentally or empirically determined. By performing the above analysis also on the end portion on the opposite side of the recording area 103A, two irradiation field edge point pixels X ₀ can be detected for the pixel rows X ₁ -X ₁ (see FIG. 2 (a)).

The irradiation field recognition circuit 220 uses the above-mentioned analysis, for example, the pixel row X
Pixel row X ₂ −X ₂ parallel to ₁ −X ₁ and orthogonal pixel row Y ₁ Y
_{Also for 1} and Y ₂ −Y ₂ (see FIG. 2A), other irradiation field edge point pixels X ₀ and Y ₀ are obtained. Then, the portion outside the edge point pixels X ₀ and Y ₀ is recognized as the outside portion of the irradiation field and the inside portion is recognized as the irradiation field 103B, and the irradiation field information St indicating the recognized irradiation field 103B is controlled as described above. Circuit 31
Send to 4. If the control circuit 314 determines the reading gain a, the recording scale factor b, and the image processing condition c based on the preread image signal Sp in the irradiation field 103B indicated by the information St,
These conditions are not affected by the stored record information outside the irradiation field, and may be optimum for the radiation image information actually recorded in the irradiation field 103B.

The pixel columns for extracting the sample image signal are the example shown in FIG. 2, that is, the two columns (X in the horizontal direction of the stimulable phosphor sheet 103).
_1- X ₁ and X ₂ -X ₂ ) and two vertical rows (Y ₁ -Y ₁ and Y _2-
It is not limited to Y ₂ ). The method of extracting the sample image signal shown in FIG. 2 is such that, for example, the irradiation field 103B is narrowed to a quadrangle on the stimulable phosphor sheet 103, and the irradiation field recognition circuit 220 is also based on this premise. It is effective when it is configured to recognize. If the shape of the irradiation field is not determined, the sample image signal is extracted for a large number of pixel rows that are relatively close to each other, and the calculated large number of edge point pixels are determined. The inside of the bounded boundary line may be recognized as the irradiation field, and thus the present invention is applicable even in the case of a circular or other irradiation field other than a quadrangle, or the direction of the quadrangle irradiation field is unknown. .

Further, even in the case of so-called divided photographing in which one recording medium, in the above-described embodiment, one sheet is divided and photographing is performed in each division, for example, information that the divided photographing is performed is acquired in advance. Therefore, the present invention can be applied to each of the sections.

Further, the system shown in FIG. 1 has a reading system for main reading and a reading system for pre-reading separately.
As shown in No. 58-67242, the reading system for main reading is also used as the reading system for pre-reading, and when the pre-reading is completed, the sheet transport means returns the stimulable phosphor sheet to the reading system to perform the main reading. The excitation light energy adjusting means may adjust the excitation light energy so as to be smaller than that at the time of actual reading, and the present invention can be adopted in such a system.

The irradiation field recognized as described above can be used for various purposes. For example, as described above, it can be used to extract only the image signal of the pre-reading image signal and determine the reading condition based on it. It can be used not only when extracting only the signal and determining the image processing condition based on it, but also when extracting only the image signal in the irradiation field from the main reading image signal and determining the image processing condition based on it. , And for other purposes, for example, by recognizing the irradiation field from the pre-reading image signal, during the main reading,
As disclosed in Japanese Patent Application Laid-Open No. 60-120346 filed by the applicant of the present application, the present invention can also be used when the reading area is limited to the irradiation field. In this way, by limiting the reading area of the main reading to the inside of the irradiation field, noise components due to scattered rays stored outside the irradiation field of the stimulable phosphor sheet are not read, and an excellent final image can be obtained. Further, by narrowing the reading area, it is possible to shorten the reading time or increase the reading density.

Of course, the recognition of the irradiation field in the present invention is not limited to the pre-reading image signal as in the above-mentioned embodiment, but may be performed based on another image signal, for example, the main reading image signal.

Next, an example of the image processing condition determining method according to the second aspect of the present invention will be described.

As described in the radiation image information recording / reproducing system shown in FIG. 1, the present invention recognizes the irradiation field from the pre-reading image signal and determines the image processing condition based on the recognized pre-reading image signal in the irradiation field. However, the embodiment described below recognizes the irradiation field from the main reading image signal, and based on the recognized main reading image signal in the irradiation field, the gradation which is one of the image processing conditions. The present invention is applied when the processing conditions are determined.

In the present embodiment, first, the stimulable phosphor sheet that has been photographed by narrowing down the irradiation field is actually read to obtain an image signal.

The main reading to obtain an image signal means that the stimulable phosphor sheet is scanned by the pre-reading excitation light, and the stimulated emission light emitted from the sheet by the scanning is read by the photoelectric reading means. The obtained image signal is an electric signal corresponding to the stimulated emission light amount for each scanning point (that is, each pixel) on the sheet.

Next, a sample image signal relating to an arbitrary pixel row extending from the edge of the recording area of the sheet toward the center side is extracted from the image signal thus obtained, and a sample image signal near the edge indicated by the sample image signal is extracted. The change in image density between a predetermined number of pixels is represented by an approximate expression that is substantially a linear equation, and the difference between the assumed image density and the actual image density indicated by the sample image signal is obtained by this approximate expression, and the edge portion is calculated. From that to the center side, the area until the difference reaches a predetermined value is recognized as the outside area of the irradiation field, and the area inside thereof is recognized as the irradiation field.

The method for recognizing such an irradiation field is the same as the method for recognizing an irradiation field according to the first aspect of the present invention described above, and thus a detailed description thereof will be omitted.

Next, the gradation processing condition is determined based on the recognized image signal in the irradiation field among the actual reading image signals read from the recording medium. Any method may be used for this determination, but the following method can be given as an example.

Such a method obtains the histogram of the main reading image signal in the irradiation field (image signal level) and obtains the maximum image signal level Pmax and the minimum image signal level Pmin of the desired image signal range in this histogram from this histogram, and these Pmax and Pmin are The gradation processing conditions are determined so as to correspond to the maximum signal level Rmax and the minimum signal level Rmin of the desired input signal range in the image reproducing means, which are determined by the maximum density Dmax and the minimum density Dmin of the appropriate density range in the visible output image, respectively. To do.

This method will be described below in detail with reference to FIG. In FIG. 4, not the histogram of the electrical image signal obtained by photoelectrically reading the stimulated emission light by the photoelectric reading means, but the histogram of the stimulated emission light before the photoelectric reading is shown. As shown, this stimulated emission light is converted into an electrical image signal according to the fixed and linear reading conditions shown in the figure, so the amount of stimulated emission light and the image signal level are fixed. , And the histogram of the stimulated emission light is substantially the same as the histogram of the image signal. Therefore, in the following description, the explanation will be given by regarding it as the stimulated emission light histogram image signal histogram in FIG.

It should be noted that in the present embodiment, the image signal used for the creation of the histogram is not necessarily limited to the one read under the linear reading condition as described above, and the point is that there is some correspondence with the stimulated emission light amount. Any image signal may be used as long as the image signal is included, and may be an image signal read under a non-linear reading condition, for example.

First, a histogram of the main reading image signal in the irradiation field is obtained, and a desired image signal range (range of stimulated emission light amount) is obtained from this histogram. Since the pattern of the histogram is determined to some extent by the imaged region and the image capturing method, the desired image signal range is obtained from the histogram with reference to these imaged region and image capturing method. For example, the histogram in the case of chest radiography has a pattern as shown in FIG. 4, of which J is the mediastinum, K is the heart, L is the lung field,
Since it is possible to know that M is the skin and soft parts, and N is the outside of the subject, the maximum image signal level Pmax (maximum stimulated emission light amount Sm) that is the range of the desired image signal can be obtained from this histogram.
ax) and minimum image signal level Pmin (minimum stimulated emission light amount Sm
in) can be obtained. For example, in the case of FIG. 4, if the information on the skin and the soft part M and the non-subject N is unnecessary, the range from Pmax to Pmin including the desired image signal ranges J, K, and L is shown. As a method of obtaining Pmax and Pmin, for example, a method of determining constant threshold values T ₁ and T ₂ according to a desired image signal range and then obtaining from these T ₁ and T ₂ is conceivable. It may be obtained from the histogram with.

On the other hand, in the radiation image information recording / reproducing system, an electric image signal is usually obtained from the stimulated emission light by the photoelectric reading means as described above, and various signal processing, especially gradation processing, is performed on this signal by the image processing means. Then, the signal is reproduced and recorded as a visible output image on the photographic light-sensitive material or the like by the image reproducing means. In this output image, there is a density range suitable for observation and interpretation. Generally, this proper density is within the range (Dmax to Dm
in) The reproduction conditions in the image reproduction means (conditions that determine the relationship between the input to the reproduction means and the output from the reproduction means) are also predetermined, so that the appropriate density range ( The input signal level range (Rmax to Rmin) to the image reproducing means corresponding to (Dmax to Dmin) is
It is uniquely determined according to this image reproduction condition.

Therefore, the gradation processing conditions in the gradation processing are determined so that Pmax and Pmin obtained as described above correspond to Rmax and Rmin determined as described above.

The gradation process is a process of converting the level of each image signal input to the image processing unit (gradation processing unit) according to a certain condition and then outputting the converted signal. The certain condition is called a gradation processing condition. , Usually represented by a non-linear tone curve.

Such gradation processing is intended to obtain a preferable visible output image suitable for a diagnostic purpose in accordance with imaging conditions such as an imaging site such as a head and chest and a simple imaging method such as contrast enhancement. In general, a basic form of a non-linear gradation processing condition having a most preferable pattern for each photographing condition is set in advance, and the gradation processing of each image is appropriate in accordance with the photographing condition of the image. It is preferable to select a basic form of different gradation processing conditions and perform gradation processing using the basic form.

Also in the present embodiment, in this way, an appropriate one is selected from the basic forms of the gradation processing conditions that are predetermined according to the image capturing conditions, and is corrected based on the irradiation field image signal. That is, as shown in the second quadrant of FIG. 4, that basic form is vertically shifted or rotated about a predetermined center point O so that Pmax, Pmin, etc.
Gradation processing conditions to be used by positioning are determined so as to correspond to max and Rmin.

It should be noted that it is conceivable that a linear one is used as the gradation processing condition without being limited to the non-linear one determined by the above-mentioned photographing condition. In that case, one predetermined straight line is used as in the above case. Similarly, rotate or shift
By positioning so that Pmax, Pmin, etc. correspond to Rmax, Rmin, the gradation processing conditions to be used are determined. By this method, the gradation processing condition is determined based on only the image signal in the irradiation field, not on the imaging part or the imaging method as in the former case.

As described above, if the gradation processing of the image signal is performed in accordance with the gradation processing condition set according to each photographed image (image signal), for example, in the photographing of each image, the subject, the photographed part, or the radiation Even if the radiation energy level range accumulated and recorded on each photographed sheet fluctuates due to fluctuations in the irradiation amount, the necessary subject image information is always observed and interpreted in any visible output image regardless of the fluctuation. It is convenient because it can be displayed in a suitable concentration range suitable for.

Further, in that case, according to the present invention, since the determination can be made based on the image signal that does not include the scattered radiation information noise, the desired image signal range can be more accurately obtained from the image signal histogram, and as a result, the necessary subject image can be obtained. The effect that information is displayed in the proper density range is more prominent.

Such a method of determining the gradation processing condition processes the image signal read based on the read condition determined without considering the variation of the recorded radiation energy level range in the individual imaging as described above. It is useful if used in some cases.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a radiation image information recording / reproducing system using one embodiment of the first and second inventions, and FIG. 2 is a state of irradiating a radiation field on a stimulable phosphor sheet in the above system, Explanatory diagram showing an example of image density change of one pixel row of the sheet, FIG. 3 is an explanatory diagram explaining a method for recognizing an irradiation field in the first and second inventions, and FIG. 4 is a second book. It is explanatory drawing explaining an example of the method of determining a gradation process condition in invention. 30 ... Read-ahead reading unit, 40 ... Main-reading reading unit 50 ... Image reproducing unit, 100 ... Radiation source 101 ... Subject, 102 ... Radiation ray 103 ... Accumulable phosphor sheet (recording medium) 104 ... Aperture, 201 ... Look-ahead Laser light source 202 ... Pre-reading laser light 204 ... Pre-reading light deflector 208 ... Pre-reading light detector 210 ... Pre-reading sheet transfer means 220 ... Irradiation field recognition circuit 301 ... Main reading laser light source 302 ... Main reading laser light 305 ... Main reading Light deflector 310 ... Main reading photodetector, 311 ... Amplifier 312 ... A / D converter, 314 ... Control circuit, 320 ... Main reading sheet transfer means a ... Read gain b ... Recording scale factor c ... Image processing condition Sp … Pre-read image signal, So… Main read image signal St… Irradiation field information

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G06F 15/70 335 Z 9071-5L H04N 1/04 E 7251-5C

Claims (2)

[Claims] 1. A method of recognizing the irradiation field when radiation image information is recorded by applying an irradiation field stop on the recording medium, the method comprising recognizing an image signal read from the recording medium from the recording medium. A sample image signal relating to an arbitrary pixel row extending from the end of the recording area toward the center is extracted, and a change in image density between a predetermined number of pixels near the end indicated by the sample image signal is substantially a linear equation. The difference between the assumed image density and the actual image density indicated by the sample image signal is obtained by this approximate expression, and the difference from the end to the center side until the difference reaches a predetermined value. An irradiation field recognition method characterized in that an area is recognized as an area outside the irradiation field and an area inside the irradiation field is recognized as an irradiation field. 2. A method of determining an image processing condition when processing an image signal read from a recording medium on which radiation image information is recorded by narrowing an irradiation field, the image signal read from the recording medium. From this, a sample image signal relating to an arbitrary pixel row extending from the end of the recording area of the recording medium toward the center side is extracted, and a change in image density between predetermined pixels near the end indicated by the sample image signal is substantially The difference between the assumed image density and the actual image density indicated by the sample image signal is calculated by an approximate expression consisting of a linear equation, and the difference is predetermined from the end toward the center. The area up to the value is recognized as the outside area of the irradiation field, and the area inside the irradiation area is recognized as the irradiation field, and based on the recognized image signal in the irradiation field among the image signals read from the recording medium. Image processing condition determining method characterized by determining the image processing conditions are.