JPH0464227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method for determining reading conditions for radiographic image information used in a radiographic image information recording and reproducing system using a stimulable phosphor used for medical diagnosis and the like.

(Technical Background of the Invention and Prior Art) Certain phosphors are exposed to radiation (X-rays, α-rays, β-rays,
When irradiated with γ-rays, electron beams, ultraviolet rays, etc., a portion of this radiation energy is accumulated in the phosphor, and when the phosphor is irradiated with excitation light such as visible light, the phosphor increases depending on the accumulated energy. is known to exhibit stimulated luminescence, and phosphors exhibiting this property are called stimulable phosphors (stimulable phosphors).

Using this stimulable phosphor, radiation image information of a subject such as a human body is recorded on a sheet of stimulable phosphor, and then the stimulable phosphor sheet is scanned with excitation light such as a laser beam. Generates stimulated luminescent light, reads this stimulated luminescent light photoelectrically to obtain an image signal, and based on this image signal, a radiation image of the subject is made visible on a recording material such as a photographic light-sensitive material or a display device such as a CRT. The applicant has already proposed a radiation image information recording and reproducing system that outputs the information as an image. (JP-A-55-12429, No. 56-11395, etc.) As one aspect of the radiation image information recording and reproducing system described above, a stimulable phosphor material in which radiation image information of a subject is stored and recorded using radiation energy level as a medium. Prior to "book reading", the sheet is scanned with excitation light, and the stimulated luminescence light emitted from the sheet is read by a photoelectric reading means to obtain an electrical image signal for reproducing a diagnostic visible image. , "Pre-reading" is performed in advance by scanning the sheet with excitation light at a lower level than the excitation light used for this main reading and reading the outline of the image information accumulated and recorded on this sheet, and the image information obtained by this pre-reading is performed. The reading conditions for performing the main reading are determined based on the reading conditions, the main reading is performed according to the reading conditions, the image signal obtained by this main reading is input to the image processing means, and the image processing means determines the imaged area and The image signal is processed to obtain an output image suitable for diagnostic purposes according to the imaging method, etc.
A system for reproducing this image signal as a visible output image on a photographic light-sensitive material is known.
It is disclosed in Japanese Patent No. 58-67240.

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 (sensitivity) that determines the relationship between input and output, It means the scale factor (latitude) or the power of excitation light during reading.

In addition, the fact that 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 equal to that during main reading. means smaller than. As a method to make the excitation light of the pre-reading at a lower level than the excitation light of the main reading, there is a method of reducing the output of the excitation light source such as a laser light source, and a method of passing the excitation light emitted from the light source to an ND filter, AOM, etc. in its optical path. There are methods to attenuate the excitation light, and methods to provide a light source for pre-reading and a light source for main reading separately and make the output of the former smaller than the output of the latter.Furthermore, there are methods of increasing the beam diameter of the excitation light. Examples include a method of increasing the scanning speed of excitation light, and a method of increasing the transport speed of the stimulable phosphor sheet.

In this way, by grasping the outline of the image information stored on the sheet before the actual reading and performing the actual reading in accordance with the reading conditions determined based on the outline of this image information, it is possible to It is possible to eliminate inconveniences caused by fluctuations in the range of radiation energy levels accumulated and recorded on the sheet due to fluctuations or fluctuations in the amount of radiation exposure, etc., and to always perform main reading under desirable reading conditions.

A specific method for determining the reading conditions for main reading based on the image information obtained by such pre-reading is, for example, to obtain a histogram of the amount of stimulated luminescence in pre-reading, and to obtain desired image information in this histogram from this histogram. Maximum stimulated light amount Smax and minimum stimulated light amount of the range
Find Smin, and these Smax and Smin are respectively
Maximum density of appropriate density range in visible output image
The applicant has filed an application for a method for determining reading conditions for main reading so as to correspond to the maximum signal level Qmax and minimum signal level Qmin of a desired input signal range in an image processing means determined by Dmax and minimum density Dmin. (Unexamined Japanese Patent Publication No. 59-12658)
issue).

On the other hand, in order to avoid irradiating radiation to areas that are not necessary for humane diagnosis, or if radiation is applied to areas that are unnecessary for diagnosis, scattered radiation will enter the areas necessary for diagnosis from that area, reducing contrast resolution. To prevent this, it is often preferable to narrow down the radiation irradiation field when recording radiation image information. However, when the radiation irradiation field is narrowed down in this way, the scattered radiation generated from the subject in the irradiation field usually enters the irradiation field on the stimulable phosphor sheet, and the highly sensitive stimulable phosphor sheet Since these scattered rays are also accumulated and recorded, the histogram of the amount of stimulated luminescence obtained by pre-reading also includes the amount of stimulated luminescence based on these scattered rays. Since the amount of stimulated luminescence outside the irradiation field on the sheet based on this scattered radiation may be larger than the amount of stimulated luminescence inside the irradiation field, it is possible to distinguish between the amount of stimulated luminescence inside and outside the irradiation field from the obtained histogram. It is difficult to do so. Therefore, as mentioned above, find Smax and Smin from the histogram,
When determining the reading conditions from this, the minimum value of the stimulated luminescence light amount in the irradiation field should be Smin, but the minimum value of the stimulated luminescence light amount due to scattered radiation outside the irradiation field may be set as Smin. and,
In this way, the minimum value of the amount of stimulated luminescence outside the irradiation field is
When it is set as Smin, the value is generally lower than the minimum value of the amount of stimulated luminescence within the irradiation field, so in the main reading, scattered radiation unnecessary for diagnosis will be recorded in the low concentration area, and therefore the part necessary for diagnosis will be recorded. The density of the image becomes too high, resulting in reduced contrast and difficulty in making a satisfactory diagnosis.

In other words, when shooting with a narrowed irradiation field, scattered rays generated from the subject enter the irradiated field on the sheet, and the image information obtained by pre-reading includes information based on these scattered rays. Therefore, even if reading conditions are determined based on such pre-read image information, it is difficult to determine optimal reading conditions, and as a result, it is difficult to obtain visible images that are suitable for observation and interpretation. becomes.

(Object of the Invention) In view of the above-mentioned circumstances, the object of the present invention is to provide a method for determining reading conditions for main reading based on image information obtained by pre-reading. The object of the present invention is to provide a method that eliminates the above-mentioned inconvenience caused by narrowing the irradiation field and can determine optimal reading conditions.

(Structure of the Invention) In order to achieve the above object, the reading condition determining method according to the present invention obtains digital image data at each position on the stimulable phosphor sheet from image information obtained by pre-reading, and obtains digital image data at each position on the stimulable phosphor sheet. Processing in which the data is subjected to differential processing to determine the difference between the image data to create a differential image consisting of differential values, a predetermined threshold value Th is prepared, and predetermined processing is performed on the differential image or the differential image. The completed difference image is scanned in at least two directions, and for each scanning direction, +Th on each scanning line in that direction is scanned.
A predetermined range formed by a set of predetermined sections sandwiched between the above difference value and the difference value below -Th is detected, and the irradiation is determined based on each predetermined range detected for each scanning direction. The present invention is characterized in that reading conditions for the main reading are determined based on image information obtained by the pre-reading in the field area.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The embodiment described below is a method of determining reading conditions when reading a stimulable phosphor sheet 10 photographed with a rectangular irradiation field aperture, as shown in FIG. Note that the X-axis and Y-axis in FIG. 1 are set along two adjacent sides of the outline of the rectangular irradiation field 12, and generally in the case of a rectangular irradiation field, each side of the rectangular irradiation field outline Since the irradiation field is apertured to be parallel to each side of the sheet 10, the X-axis and Y-axis can be considered to be set along two adjacent sides of the sheet 10.

In this embodiment, first, the image information stored and recorded on the stimulable phosphor sheet 10 shown in FIG. 1 is read by pre-reading as described above.

Reading image information from the stimulable phosphor sheet 10 by pre-reading means reading the stimulated luminescence light emitted from the sheet 10 by scanning the sheet 10 with the pre-read excitation light using a photoelectric conversion means. This means obtaining information consisting of electrical signals corresponding to the amount of stimulated luminescence light for each scanning point (that is, each pixel) on the top 10.

Next, digital image data at each position on the sheet is obtained from the image information read as described above. In obtaining this digital image data, it may be obtained directly from the image information read by the above-mentioned pre-reading, or it may be obtained by performing preprocessing such as spatial filter processing on the image information. .

In the case of direct determination, for example, the position on the sheet may be set in units of pixels, and the pre-read image information of the pixels corresponding to each position may be digitized and used as digital image data at that position.

When calculating by performing preprocessing such as spatial filter processing, for example, multiple pixels in a certain relationship are set as one position, and based on the pre-read image information of the pixels included in this position, for example, they are The digital image data at the position may be calculated by averaging, or the position on the sheet may be set in units of pixels, and the digital image data at the position may be calculated by calculating the digital image data at the position and its surrounding positions. It may be calculated based on pre-read image information of pixels.

In this embodiment, positions on the sheet are set pixel by pixel, and pre-read image information of pixels corresponding to each position is digitized as digital image data at that position.

Figure 2 is an enlarged view of part A of the stimulable phosphor sheet in Figure 1. Each square in the figure represents one pixel (position), and the f (1,1), f(1,2), . . . indicate the digitized image information at each pixel (1, 1), (1, 2), .

After obtaining digital image data at each position as described above, the image data is then subjected to differential processing to create a differential image consisting of differential values.

The above-mentioned difference processing refers to a process of calculating a difference value at a predetermined position based on the difference between digital image data that have a predetermined relationship, such as adjacent or nearby digital image data, and is a one-way difference process. (It is a process of calculating the difference value between image data in only one direction, for example, a process of calculating the difference value using a difference operator as shown in FIGS. 3a to 3d described below), or 2
Difference processing in one direction or more directions (processing to find the difference value between image data in two or more directions, for example, as shown in Fig. 3 e and f described below)
It may also be a process of calculating a difference value using a difference operator as shown in FIG. Further, the difference image created by performing difference processing in a plurality of directions is not necessarily one, but may be composed of a plurality of difference images. For example, when creating a difference image by performing difference processing in two directions, you may create a single difference image using a difference operator such as e or f in Figure 3, or a in Figure 3a. Two images may be created, one using the difference operator shown in FIG. 3 and the other using the difference operator shown in FIG. 3c.

The difference processing shown in the difference operators shown in FIGS. 3a to 3f above is as follows.

Difference processing using the operator shown in FIG. 3a is performed by subtracting digital image data at adjacent positions in the X-axis direction and using the result as a difference value. For example, in FIG. 2, positions (3, 4) digital image data f(3,4) to position(3,3)
The digital image data f (3, 3) is subtracted and the result is used as the difference value at the position (3, 3).

In addition, the difference processing using the operator shown in FIG. Digital image data f at position (3, 4) in Figure 2
The digital image data f(3,2) at position (3,2) is subtracted from (3,4) and the result is subtracted from position (3,4).
3) is the difference value.

Difference processing using the operator shown in FIG. 3c subtracts digital image data at adjacent positions in the Y-axis direction and uses the result as a difference value. For example, in FIG. 2, position (4, 3) digital image data f(4,3) to position (3,3)
The digital image data f (3, 3) is subtracted and the result is used as the difference value at the position (3, 3).

Difference processing using the operator shown in FIG. 3d involves subtracting digital image data at positions on both sides of a predetermined position in the Y-axis direction and using the result as the difference value for the predetermined position, for example, as shown in FIG. Digital image data f(4, 3) at position (4, 3) in
3) to position (2, 3) digital image data f
Subtract (2, 3) and put the result at position (3, 3)
This is the difference value of .

The differential processing using the operator shown in FIG. 3e is a process performed by simultaneously using the operator shown in FIG. 3a and the operator shown in FIG.
In the figure, the result of subtracting digital image data f(3,3) at position (3,3) from digital image data f(3,4) at position (3,4) and
The result of subtracting the digital image data f (3, 3) at position (3, 3) from the digital image data f (4, 3) at position (3, 3) is added to the digital image data f (4, 3) at position (3, 3).
3) is the difference value.

The differential processing using the operator shown in FIG. 3f is a process performed by simultaneously using the operator shown in FIG. 3b and the operator shown in FIG.
In the figure, the result of subtracting digital image data f(3,2) at position (3,2) from digital image data f(3,4) at position (3.4) and position (4,
The result of subtracting the digital image data f (2, 3) at position (2, 3) from the digital image data f (4, 3) at position (3) is added to the digital image data at position (3, 3).
3) is the difference value.

The above-mentioned difference value may be obtained for all of the above-mentioned positions, or may be obtained for some appropriately selected positions.

In this embodiment, a difference image is created by performing difference processing in two directions, and in creating the difference image, the operator shown in FIG. 3a is used to calculate difference values at all the positions. Using the operator shown in FIG. 3c, a difference image (X-axis difference image) consisting of the difference values at all the positions is created (Y-axis difference image).

Next, a predetermined threshold value Th is prepared, and at least two differential images created as described above or processed differential images obtained by performing appropriate processing on the differential images are generated.
(the directions are not parallel to each other but preferably orthogonal), and for each scanning direction, a difference value of +Th or more and a difference value of −Th or less on each scanning line in that direction are sandwiched. A predetermined range formed by a set of predetermined intervals is detected.

In this embodiment, the predetermined range is detected using the processed difference image. That is, the X-axis direction difference image and the Y-axis direction difference image obtained as described above are subjected to threshold processing using the above-mentioned predetermined threshold Th, and a difference value of +Th or more is set to +1, The difference values less than or equal to -Th are encoded as -1, and the other difference values, that is, the difference values smaller than +Th and greater than -Th, are encoded as 0, and the threshold-processed difference values encoded in this way are used. The threshold-processed X-axis direction and Y-axis direction difference images are scanned in the X-axis direction and Y-axis direction, respectively, and a set of predetermined sections sandwiched between +1 and -1 on each scanning line in the X-axis direction is obtained. Detected as a predetermined range in the X-axis direction,
A set of sections sandwiched between +1 and -1 on each scanning line in the axial direction is detected as a predetermined range in the Y-axis direction.

Figure 4 is an arbitrary line in the X-axis direction in Figure 1.
FIG. 5 is a diagram showing the digital image data on lx, and FIG. 5 shows the difference value obtained by processing the digital image data in FIG. 4 using the difference operator shown in FIG. Figure 6 is a diagram showing how threshold processing is performed.
The thresholded difference values (-1, 0, +
1) is a diagram showing a threshold-processed X-axis direction difference image in the present embodiment, and FIG. It is a figure which shows the value-processed X-axis direction difference image. However, in Figures 6 and 7, the +
represent 1 and −1 simply as and,
The portion where the thigh is not displayed is the portion where the threshold-processed difference value is 0.

Since the digital image data at each position on the stimulable phosphor sheet corresponds to the energy level of the radiation incident on the sheet, for example, as shown in FIG. level, and the image data within the radiation field 12 will generally be at a high quantum level. Therefore, as shown in FIG. 5, for example, the difference value between the image data in the part where the irradiation field contour is located is much larger or smaller than the difference value in other parts, and there are places where the difference value is extremely large and places where the difference value is extremely large. By detecting the small position using an appropriately set threshold value Th, it is possible to detect the position of the irradiation field outline and, furthermore, the section within the irradiation field sandwiched between the two positions. Therefore, by scanning the X-axis direction difference image in the X-axis direction, each scanning line LX ₁ , LX ₂ ,
The difference value on LX ₃ , ...LXi, ...LXn is +
Detecting a predetermined range consisting of a set of predetermined sections (shaded areas in the figure) sandwiched between positions above Th and positions below -Th means ultimately detecting the range corresponding to the irradiation field. It means that.
Furthermore, by scanning the above Y-axis direction difference image in the Y-axis direction, each scanning line LY ₁ , LY ₂ ,
The same goes for detecting a predetermined range consisting of a set of predetermined intervals on LY ₃ , ...LYi, ...LYn.

Note that in FIGS. 6 and 7, since the scanning lines LX ₁ , LX ₂ and LY ₁ , LY ₂ , LY ₃ are located in the outside irradiation area 14, naturally there is a difference value of +Th or more or -Th or less does not exist. Also, like line LXi in Figure 6,
Even for a line located on the irradiation field 12, there may be cases where there is no combination of a position where the difference value is +Th or more and a position where the difference value is -Th or less. It is treated as if the specified section was not detected.

The above embodiment creates two difference images using the difference operators shown in FIGS. 3a and 3c,
By scanning each difference image in one direction, the difference image is scanned in two directions, and two predetermined ranges are detected.

In this case, the two difference images may be created using the difference operators shown in FIGS. 3b and 3d, for example. If the difference values are obtained using the difference operators shown in Figures 3b and 3d, and the same threshold processing as above is performed on them, the results will be the same as in Figures 6 and 7, respectively. A difference image is obtained, and therefore both difference images may be scanned in the X-axis direction and the Y-axis direction to detect a predetermined range, as in the above embodiment.

Alternatively, only one difference image may be created and the difference image may be scanned in two directions to detect two predetermined ranges. For example, create a difference image using the difference operator shown in FIG. 3 e or f above,
When the difference image is threshold-processed using the method described above, a threshold-processed difference image as shown in FIG. 8 is obtained. It is sufficient to detect a predetermined range.

Note that the arrows in the X-axis and Y-axis directions in FIG. 8 are predetermined sections on each scanning line when scanning in the X-axis and Y-axis directions, respectively. The set is a predetermined range detected by scanning in the X-axis direction, and the set of predetermined sections indicated by arrows in the Y-axis direction is a predetermined range detected by scanning in the Y-axis direction.

In short, the above embodiment performs threshold processing on the difference image to encode all of the difference values so that difference values of +Th or more, difference values of -Th or less, and other difference values can be distinguished, and The threshold-processed difference image consisting of the threshold-processed difference values (+1, 0, -1) created by the processing was scanned to detect a predetermined range, but other processing, For example, the difference value between +Th and -Th is set to 0, and the other difference values are left unchanged. Only a part of the difference value is encoded, threshold processing is applied, and the other difference values are left unchanged. A predetermined range may be detected by scanning a threshold-processed difference image consisting of threshold-processed difference values obtained by .

Next, after detecting the predetermined ranges in each scanning direction as described above, the irradiation field area is determined based on each of the predetermined ranges. As a method for determining the irradiation field area, the following two methods can be considered, for example.

One method is to determine the sum of the predetermined ranges as the irradiation field area, and the other method is to determine the common part of the predetermined ranges as the irradiation field area.

The summation part of each predetermined range means a part formed by putting together each predetermined range, and a part that corresponds only to any of the predetermined ranges is also treated as an irradiation field area. Specifically, for example, in this embodiment, a predetermined range in the X-axis direction indicated by diagonal lines in FIG. 6 and a predetermined range in the Y-axis direction indicated by diagonal lines in FIG. 7 are detected. In this step, the range formed by bringing together both predetermined ranges (the shaded area in FIG. 9) is determined to be the irradiation field area. if,
If the irradiation field area is determined only from the predetermined range detected by unidirectional scanning, if there is a line in which a predetermined section is not detected, such as line LXi in FIG. 6 or line LYi in FIG. The problem arises that the section is not recognized as an irradiation field area even though it should originally be recognized as an irradiation field area.
If the sum of the predetermined ranges detected by scanning in two directions is determined as the irradiation field area as in this method, the above problem will be solved, and the line as shown in Fig. 9 will be solved.
Although the intersection between LXi and LYi is missing, it is possible to determine as the irradiation field area a range that sufficiently covers almost the entire area that is originally the irradiation field area.

On the other hand, the common part of each predetermined range means a part that corresponds to all of the predetermined ranges, and a part that only applies to any one of the predetermined ranges is not treated as an irradiation field area. This method can be suitably used, for example, in the case of so-called divided imaging, in which the stimulable phosphor sheet 10 is divided into two parts and the irradiation field aperture is applied to each division. It's a method. That is,
In the case of such divided shooting, for example, the eighth
As shown in Figure 11, the threshold-processed difference image created using the same method as the one shown in the figure may have an incomplete shape, that is, the position D that should originally be, may not be. In this case, the predetermined section (predetermined range) obtained by scanning this differential image in the X-axis direction is as shown by the double-headed arrow in the X-axis direction (in this case, scanning from left to right in the X-axis direction, and → section Extrude only as a predetermined section, →
The predetermined section (predetermined range) obtained by scanning in the Y-axis direction is as shown by the double-headed arrow in the Y-axis direction, and if the set of both predetermined ranges is determined as the irradiation field area as described above, the original Portion that is not the irradiation field area (portion sandwiched by both positions D above)
However, if only the common part of a predetermined range in both scanning directions is determined as the irradiation field area as in this method, such non-irradiation field areas will be eliminated, and the irradiation field It is possible to determine only that part as the irradiation field area.

After determining the irradiation field area as described above, next, the pre-read image information within this irradiation field area is appropriately extracted from the above-mentioned pre-read image information, and the main reading is performed based on the extracted pre-read image information. Determine the reading conditions.

This reading condition can be determined in various ways, but for example, as described above, a histogram of the amount of stimulated luminescence within the irradiation field is created, and from this histogram, a predetermined maximum amount of stimulated luminescence Smax and minimum stimulated luminescence are determined. The light amount Smin is determined, and the reading conditions can be determined based on Smax and Smin.

Note that the determination of reading conditions is not limited to the case where the reading conditions are determined based only on the pre-read image information within the above-mentioned irradiation field. , a photographing method such as enlarged photographing, etc. can also be taken into account when determining the photographing method.

After determining the reading conditions as described above, the actual reading is performed according to the reading conditions, but this actual reading is as disclosed in Japanese Patent Application Laid-Open No. 120346/1989, which was previously filed by the applicant. Preferably, the reading area is limited to the irradiation field determined based on the above method. By limiting the reading area for the main reading within the irradiation field in this way, noise components due to scattered radiation recorded outside the irradiation field of the stimulable phosphor sheet are not read, making it possible to obtain an excellent final image. . In addition, by narrowing down the reading area,
It is possible to shorten reading time or maximize reading density.

FIGS. 12a and 12b are threshold-processed difference images created in the same manner as FIGS. 6 and 7, respectively, and show a case where the irradiation field is circular. As can be easily understood from this figure, the present invention is also applicable to cases where the irradiation field is other than rectangular.

FIG. 13a is a diagram showing the stimulable phosphor sheet 10 photographed with a diagonal aperture in a rectangular irradiation field. In this case, for example, the differential plate shown in FIG. A difference image is created by calculating the difference image, and by applying threshold processing to it in the same way as in the case of Fig. 6, a threshold-processed difference image as shown in Fig. 13b is obtained, and this difference image is By scanning in the X'-axis and Y'-axis directions in the figure, a predetermined range in each axis direction can be determined.

In the case of the divided photographing, the present invention can be applied to each section on the sheet by obtaining information in advance that it is divided photographing.

The concept of a difference value and a difference process in the present invention also includes the concepts of a differential value and a differential process that are substantially the same.

Note that image processing conditions for performing the image processing can also be determined based on pre-read image information within the irradiation field region determined according to the present invention.

(Effects of the Invention) As described above, the radiation image information reading condition determination method according to the present invention provides digital image information (pre-read image information) at each position on the stimulable phosphor sheet.
Create a difference image by performing difference processing, and create a difference image (or a processed difference image processed by a prescribed method)
is scanned in at least two directions, and for each scanning direction,
detecting a predetermined range consisting of a set of predetermined sections sandwiched between a difference value greater than or equal to a predetermined threshold value +Th and a difference value less than or equal to a predetermined threshold value on each scanning line in that direction;
The reading conditions are determined from pre-read image information within the irradiation field area determined based on these predetermined ranges.

Since the method according to the present invention detects the irradiation field area in this way and determines the reading conditions based on the pre-read image information in that area, it is possible to eliminate the adverse effects of scattered radiation incident on the irradiation field as described above. Optimum reading conditions can always be determined.

Furthermore, as described above, the predetermined sections on each scanning line are sections within the irradiation field on each scanning line, and therefore, the predetermined range that is a collection of the predetermined sections originally corresponds to the true irradiation field; Reality does not always match exactly for various reasons. The method according to the present invention uses the predetermined range obtained by scanning in at least two different directions as described above and appropriately combines them to determine the irradiation field area, so the irradiation field is closer to the true irradiation field. It is possible to determine the area.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the stimulable phosphor sheet photographed with the irradiation field apertured, Figure 2 is an enlarged view of section A in Figure 1, showing digital image data at each position, Figure 3 4 is a diagram showing the digital image data on the line lx in FIG. 1, and FIG. 5 is a difference value obtained by performing differential processing on the digital image data in FIG. 4. Figures 6, 7, and 8 are threshold-processed difference images obtained by thresholding the difference images created using the difference operators shown in Figures 3a, c, and e, respectively. Figure 9 is a diagram showing the irradiation field area, Figure 10 is a diagram showing a stimulable phosphor sheet that has been photographed in sections, and Figure 11 is a threshold-processed difference image of the sheet shown in Figure 10. Figures 12a and 12b are diagrams showing threshold-processed difference images when the irradiation field is circular, and Figure 13a is a stimulable phosphor photographed with a diagonal aperture in a rectangular irradiation field. A diagram showing the sheet, Figure 13b is the 13th
FIG. 3 is a diagram showing a threshold-processed difference image on the sheet shown in FIG. 10... stimulable phosphor sheet, 12... irradiation field.

Claims (1)

[Scope of Claims] 1. Radiation images stored on a stimulable phosphor sheet by irradiating excitation light onto a stimulable phosphor sheet on which radiation image information is stored and recorded by applying an irradiation field aperture. Prior to main reading, in which information is emitted as stimulated luminescence light and this stimulated luminescence light is read photoelectrically to obtain an electrical image signal for outputting a visible image, the energy of the excitation light used in the main reading is Radiation that performs pre-reading to read the radiation image information stored and recorded on the stimulable phosphor sheet using low-energy excitation light, and determines reading conditions for the main reading based on the image information obtained by this pre-reading. In the image information reading condition determination method, digital image data at each position on the stimulable phosphor sheet is obtained from the image information obtained by the pre-reading, and a difference process is performed to obtain a difference between the image data. to create a difference image consisting of difference values, prepare a predetermined threshold Th, scan the difference image or a processed difference image obtained by processing the difference image in a predetermined manner in at least two directions, and scan each difference image in at least two directions. For each scanning direction, + on each scanning line in that direction.
A predetermined range formed by a set of predetermined sections sandwiched between a difference value greater than or equal to Th and a difference value less than or equal to -Th is detected, and determined based on each predetermined range detected for each scanning direction. A method for determining reading conditions for radiation image information, characterized in that reading conditions for the main reading are determined based on image information obtained by the pre-reading within an irradiation field area. 2. A processed difference image obtained by performing predetermined processing on the difference image is such that the difference value of the difference value can be discriminated from the difference value of +Th or more, the difference value of -Th or less, and other difference values with respect to the difference image. 2. The reading condition determining method according to claim 1, wherein the image is a threshold-processed difference image that has been subjected to threshold processing to encode all or part of the image. 3. The reading condition determining method according to claim 1 or 2, wherein the total sum of each predetermined range detected in each scanning direction is determined as the irradiation field area. 4. The reading condition determining method according to claim 1 or 2, wherein a common portion of each predetermined range detected in each scanning direction is determined as the irradiation field area.