JPH0584504B2 - - 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 part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor changes depending on the accumulated energy. is known to exhibit stimulated luminescence, and phosphors exhibiting this property are called 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 this 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 present applicant has already proposed a radiation image information recording and reproducing system that outputs the information as an image (Japanese Patent Application Laid-open No. 12429/1982, No. 11395/1986, etc.).

As one aspect of the radiation image information recording and reproducing system, a stimulable phosphor sheet in which radiation image information of a subject is stored and recorded using radiation energy levels as a medium is scanned with excitation light, and as a result of this scanning, the radiation image information emitted from the sheet is scanned. Prior to "main reading" in which stimulated luminescence light is read by a photoelectric reading means to obtain an electrical image signal for reproducing a visible image for diagnosis, excitation light of a lower level than the excitation light used for this main reading is used in advance. "Pre-reading" is performed in which the sheet is scanned to read the outline of the image information accumulated and recorded on this sheet, and the reading conditions for performing the main reading are determined based on the image information obtained by this pre-reading. The main reading is performed according to the conditions, and the image signal obtained from this main reading is input to an image processing means, so that the image processing means can obtain an output image suitable for diagnostic purposes according to the imaging site, imaging method, etc. A system is known that processes an image signal and reproduces this image signal as a visible output image on a photographic light-sensitive material, etc.
-Disclosed in Publication No. 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 lower 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 in advance before the actual reading, and performing the actual reading according to the reading conditions determined based on the outline of this image information, it is possible to understand the subject and the part to be photographed. 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. The maximum amount of stimulated light emission Smax and the minimum amount of stimulated light emission Smin of the range are determined, and Smax and Smin are determined by the maximum density Dmax and minimum density Dmin of the appropriate density range in the visible output image, respectively. The present applicant has filed an application for a method of determining reading conditions for main reading so as to correspond to the maximum signal level Qmax and minimum signal level Qmin of the desired input signal range (Japanese Patent Application No. 1983-
No. 12658).

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 in the irradiated 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 the 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 determination method according to the present invention obtains digital image data at each position on a stimulable phosphor sheet from image information obtained by pre-reading, In the differential image made up of the obtained differential values, first find an arbitrary position where the differential value is the maximum or a predetermined value or more, and use this as the first point of interest,
Next, search for a position whose differential value is greater than or equal to a predetermined value from among the surrounding positions adjacent to this first point of interest, define this as the second point of interest, and then Search for a position where the differential value is greater than or equal to a predetermined value from among the positions excluding the previous point of interest, that is, the first point of interest, define this as the third point of interest, and repeat the process of searching for this third point of interest. When a position adjacent to the first point of interest is found as a new point of interest, that is, when the point of interest is sequentially searched using the above method and the point of interest is returned to the first point of interest, The present invention is characterized in that the inside of a closed curve formed by sequentially connecting the previous points of interest is recognized as an irradiation field, and the reading conditions for main reading are determined based on the pre-read image information within this irradiation field.

Note that the above-mentioned "surrounding positions adjacent to the attention point" do not necessarily have to be all of the surrounding positions adjacent to the attention point. For example, if the contour of the irradiation field is known in advance, a part of the position may be determined according to the shape of the contour.

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

The embodiment described below is a reading condition determination method when reading a stimulable phosphor sheet 12 having one irradiation field 10 photographed with a rectangular irradiation field diaphragm, as shown in FIG. . The x-axis shown in the figure indicates the main scanning direction when scanning the sheet 12 and pre-reading image information, and the y-axis indicates the sub-scanning direction.

First, the image information stored and recorded on the stimulable phosphor sheet 12 shown in FIG. 1 is read by pre-reading as described above.

Reading image information from the stimulable phosphor sheet 12 by pre-reading means reading the stimulated luminescence light emitted from the sheet 12 by scanning the sheet 12 with the pre-read excitation light with 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 12.

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. Median filter processing can be cited as one of the latter calculation methods. This median filter processing refers to processing in which the median value (median value) of the image information (quantization level) of a predetermined pixel (position) and its surrounding pixels (position) is used as the image information of the predetermined pixel (position).

A specific example of this median filter processing will be explained with reference to FIG. FIG. 2a is a diagram showing the original image 14 consisting of the pre-read image information for each pixel, and each square in the figure represents one pixel. FIG. 2b is a diagram showing a median filter processed image 16 consisting of digital image data at each position obtained by applying the above median filter processing to the image information of each pixel in the original image. Note that in this specific example, the position is set in pixel units, so the processed image 16
Each position therein is also called a pixel.

First, a mask 18 of a predetermined size, for example, a 3×3 size mask 18 having a width of 3 pixels in the vertical and horizontal directions.
, the mask 18 is arranged in the original image 14 so that a predetermined pixel (the pixel indicated by diagonal lines in the figure) is located in the center of the mask, and then the image of the nine pixels included in the mask is The median value of the information is digitized and used as digital image data for that predetermined pixel, and this processing is applied to all pixels in the original image 14 (however, it cannot be applied to the pixels located at the outermost circumference, so those digital image data at that pixel is obtained, and a median filtered image 16 consisting of this data is obtained. Note that if a 3×3 size mask is used, the median filter processing cannot be applied to the outermost pixels as described above, so the processed image 16 will be smaller than the original image 14 by 17 pixels on the outermost circumference. The outermost pixel portion 17 has a quantization level of 0 (zero).
can be substituted as image data.
The size of the mask is not limited to 3×3. Also,
In order to prevent the processed image 16 from becoming smaller,
For example, median filter processing may be performed on the assumption that there are pixels around the original image 14 that have the same quantization level as the outermost pixels of the original image. By performing the median filter processing described above, it is possible to remove noise when the quantization level is extremely high or low compared to surrounding pixels, and the advantage is that the irradiation field contour information is not blurred. be.

Note that the above preprocessing is not limited to the median filter processing described above, but can be any spatial filter processing that has the characteristics of leaving necessary information such as the contour of the irradiation field and removing unnecessary information such as noise. Anything is fine.

After obtaining digital image data at each position on the sheet as described above, the image data is then subjected to differential processing to create a differential image consisting of differential values. Differential processing may be performed by any method.

FIGS. 3a and 3b are views showing processed images, and each square in each figure represents one position.

For example, as shown in FIG. 3a, when differentiating digital image data at a predetermined position 20 in a processed image 16, a mask 22 with a pixel size of 2×2 is used, and the mask 22 is placed in the upper left corner of the mask. The mask 2 is placed so that the predetermined position 20 is located in the
If the digital image data at four positions included in 2 are a, b, c, and d as shown in the figure, then a'=√(-) ² +(-) ² is calculated and a' is converted to the above value. Differential processing may be performed by using a differential value at a predetermined position 20 and performing this differential calculation for each position. Further, instead of the above formula, the differential processing may be performed by performing the operation a'=√(-+-) ² +(-+-) ² .
Of course, differential expressions other than these may be used.

Furthermore, although the above example is a first-order differential process, the third
As shown in FIG.
The digital image data at nine positions included in the mask are set as a, b, c, d, e, f, g, h, i as shown in the figure, and e'=|e- It is also possible to use various types of second-order differential processing such as performing the calculation a+b+c+d+f+g+h+i/8| and using the result e' as the differential value at the predetermined position 26.

Next, the contour of the irradiation field is detected based on the differential image created as described above. Since the digital image data corresponds to the energy level of the radiation incident on the sheet, the image data outside the irradiation field will generally have a low quantum level, and the image data within the irradiation field will generally have a high quantum level. Therefore, the differential value of the image data at the position where the irradiation field contour exists generally has a higher quantum level than the differential value of the image data at other positions, and as a result, the position where the differential value is maximum or a predetermined value in the differential image When set appropriately, a position where the value is greater than or equal to a predetermined value can be said to be a position where an irradiation field contour exists.

The method according to the present invention detects the irradiation field outline by finding and tracking the positions where the irradiation field outline exists in the differential image one after another based on the above facts, and the tracking starts. The process consists of two steps: a step of detecting a first point of interest, which is a point, and a tracking step of tracking the position of the contour from the first point of interest.

First, the differential image is scanned to find an arbitrary position where the differential value is maximum or greater than a predetermined value, and this is set as the first point of interest.

As mentioned above, the differential value at the position where the irradiation field contour exists is larger than that at other positions. Therefore, if an appropriately set predetermined value is used, the position where the differential value is greater than or equal to the predetermined value will be the irradiation field. It can be determined that this is the position where the contour exists, and of course, the position where the differential value is the maximum can also be determined to be the position where the irradiation field contour exists. Therefore, first, one of the positions where the irradiation field outline exists is detected by the method described above, and that position is set as the first point of interest.

Next, the contour of the irradiation field is tracked from this first point of interest, and the irradiation field is recognized. This tracking first searches for a position whose differential value is greater than or equal to a predetermined value among the surrounding positions adjacent to the first point of interest, sets this as the second point of interest, and then Search for a position whose differential value is greater than or equal to a predetermined value among positions excluding the previous point of interest (first point of interest), define this as the third point of interest, and repeat the process of searching for this third point of interest. This is done by repeatedly finding new points of interest one after another. When a position adjacent to the first point of interest is found as a new point of interest, the inside of the closed curve connecting the previous points of interest is recognized as the irradiation field.

In the above tracking, if there is only one position whose differential value is equal to or greater than a predetermined value among the adjacent surrounding positions, that one position should be the next point of interest; if there are two or more, then is the position with the highest priority according to a certain priority given in advance to the adjacent surrounding positions, or any position among those two or more positions, or the maximum differential value. The position of etc. should be the next point of attention,
If there is none, the next point of interest may be the one with the largest differential value among the adjacent surrounding positions.
Of course, the position to become the next point of interest is selected from positions excluding the previous and current points of interest.

The above tracking can be performed using a mask as shown in FIG. 4 or FIG. 5, for example.

The mask shown in FIG. 4 is a mask with a 3×3 position size as shown, and an example of tracking performed using this mask will be described with reference to FIG. 6.

FIGS. 6a to 6e each show a differential image 28 having a rectangular irradiation field contour and explain a method for tracking the contour step by step.

First, as shown in Fig. 6a, the first point of interest A existing on the irradiation field contour obtained as described above is located at the center of the mask (the shaded area in Fig. 4). The mask is placed at , and the position within this mask where the differential value is equal to or greater than a predetermined value (excluding the first point of interest A, of course) is set as the next second point of interest. If the differential values of a plurality of positions are greater than or equal to a predetermined value, any of them may be selected as the second point of interest, but for example, the position with the maximum differential value among them may be selected. In the illustrated example, parts a and e of the mask correspond to the irradiation field contour positions, so the differential values of the positions of parts a and e are greater than a predetermined value, and the differential value of part e is larger, so is selected as the second point of interest B.

Next, as shown in Figure 6b, this second point of interest B
Move the mask so that it is located in the center, and similarly move the position in this mask where the differential value is greater than or equal to the predetermined value (of course excluding the current second point of interest B and the immediately preceding first point of interest A) to the next position. This is the third point to note. If the differential values of a plurality of positions are greater than or equal to a predetermined value, the position that is earliest in the priority order is set as the next third point of interest according to a predetermined priority order. There are various ways to give priority, but in this specific example, as shown in FIG. For example, if we call it part a,
Counterclockwise from this part a, that is, b,
Priorities are given in the order of c, d, e, f, g, and h. Therefore, in the example of Figure 6b, the new third
Of the portions that can be points of interest, portions e and f have differential values greater than or equal to a predetermined value, and the position of portion e, which has the highest priority, is selected as the third point of interest C.

Next, in the same way, by setting the position where the differential value is above a predetermined value, or if there are multiple positions where the differential value is above the predetermined value, as a new point of interest, the position with the earlier priority as described above, As shown in Fig. 6c and d, the fourth point of interest D and the fifth point of interest E are selected, and thereafter, new points of interest are sequentially selected in the same manner, and the sixth point of interest is selected.
As shown in Figure e, if the position adjacent to the first point of interest A is selected as the new point of interest,
Closed curve 3 connecting the point of interest A to the nth point of interest F
The inside of 0 is recognized as the irradiation field 10.

Note that the arrow in FIG. 6 indicates the tracking direction of the irradiation field contour, and in this specific example, since the above priority order is set in a counterclockwise direction, the tracking direction is also counterclockwise. However, the priority order may be set in a clockwise direction, in which case the tracking direction will also be clockwise.

The mask shown in Fig. 5 covers all positions (8 positions) surrounding the position of interest, whereas the mask shown in Fig. 4 covers only a portion (4 positions) of the surrounding positions. This mask is configured to cover only the target position), and this mask is used by changing its orientation depending on the tracking direction. In addition,
The arrows shown at the bottom of FIG. 4 indicate the tracking direction when using each mask.

A case will be described in which a rectangular radiation field is tracked using this mask.

First, determine the initial tracking direction. To do this, for example, if the differential image is scanned to find the position where the differential value is maximum and that position is set as the first point of interest A, then as shown in Figure 7a, four adjacent positions in the x and y axis directions,
, , the position with the maximum differential value is found, and tracking is started from the first point of interest A toward the position of the maximum differential value. In the illustrated case, assuming that the position has the maximum differential value, tracking is started in the left direction toward that position.

In this case, the tracking direction is to the left, so
Using a mask oriented as shown in FIG. 5a, place the mask so that the first point of interest A is located in the shaded part of the mask, that is, as shown in FIG. 7b,
Among the positions in the mask, a position (excluding the first point of interest A) whose differential value is equal to or greater than a predetermined value is found and is set as the next second point of interest. In the illustrated example, only portion b of the mask has a differential value greater than or equal to the predetermined value, so the position of portion b is selected as the second point of interest B.

Next, as shown in FIG. 7c, move this mask to position the second point of interest B in the shaded area of the mask. (The first and second points of interest from the previous
(excluding points of interest A and B) and set it as the third point of interest. In this case, in the illustrated example, part b and part c have a differential value greater than a predetermined value, and the priority order is a, b, c, as shown by the long arrow in Fig. 5a.
Since they are assigned in the order of d, b has the earliest priority.
The position of the part is selected as the next third point of interest C.

Next, we will select the fourth point of interest.
Since the tracking from the point of interest B to the third point of interest C is still in the left direction, similarly use the mask shown in FIG. While moving, the position shown in FIG. 7d is searched for a position where the differential value is greater than a predetermined value, and this is set as the next fourth point of interest. In the illustrated example, only portion d has a differential value greater than or equal to a predetermined value, and the position of portion d is selected as the fourth point of interest D.

Next, the fifth point of interest E is selected, but since the tracking from the third point of interest C to the fourth point of interest D is downward, the mask in Figure 5b is used to select the Move the mask so that the fourth point of interest D is located in the shaded area of the mask, search for a position where the differential value is greater than a predetermined value in the state shown in Figure 7e, and set this as the next fifth point of interest. . In the illustrated example, only portion b has a differential value greater than a predetermined value, and the position of portion b is selected as the fifth point of interest E.

Thereafter, new points of interest are sequentially searched for in the same manner, and when the lower left corner position is selected as a new point of interest F, a mask is placed as shown in Figure 7e, and the next point of interest is searched. . In this case, as shown in the figure, only the d part of the mask has a differential value greater than a predetermined value, and the position of the d part is selected as the next point of interest G, and when searching for the next point of interest, the tracking direction is changed. Since it will be on the right, use the mask shown in Figure 5c, place the mask so that the point of interest G is located in the diagonally shaded part of the mask, that is, as shown in Figure 7f, and use the same method as above. The next point of interest H is selected.

Thereafter, we will continue to detect points of interest using the mask shown in Figure 5c in the same way, and when the position of the lower right corner becomes a new point of interest as shown in Figure 7f, we will move on to the next point of interest. Since the point J is at the position of the d part of the mask, the tracking direction changes upward, and next, as shown in Fig. 7g, tracking is continued using the mask of Fig. 5d, and the same point is shown in Fig. 7g. As shown in FIG. 7, when the position of the upper right corner becomes the new point of interest K, the next point of interest L becomes the position of the d part of the mask, so the tracking direction changes to the left, and next, as shown in Figure 7h, the tracking direction changes to the left. Continue tracking using the mask shown in Figure 5a.

Then, as shown in FIG. 7h, when the position adjacent to the first point of interest A is selected as the new nth point of interest M, the closed curve connecting the first point of interest A to the nth point of interest M 30 is recognized as the irradiation field 10.

In the above specific example, it is assumed that a plurality of points whose differential value is equal to or greater than a predetermined value appear in the mask in the corner portion of the irradiation field contour, and one point whose differential value is equal to or greater than the predetermined value appears in the straight portion of the contour. And, as mentioned above, we have proceeded with the discussion assuming that it appears in part b of the mask, but in any case, there is a possibility that multiple points whose differential value is greater than a predetermined value appear in the mask, and in that case, Also, the item with the highest priority above is always the next point of attention. Then, when the next point of interest appears in sections a, b, and c, the tracking direction remains the same and the mask used is not changed, and only when the point appears in section d, the mask is changed and tracking is continued. Note that this point also applies to the case where the mask shown in FIG. 4 is used. However, the mask shown in FIG. 4 differs from the mask shown in FIG. 5 in that the same mask is always used.

In the above specific example, the position with the maximum differential value in the differential image is the first point of interest, but the same applies to the case where the first point of interest is any point where the differential value is greater than or equal to a predetermined value. All you have to do is track it. However, when using the mask shown in Figure 5, it is necessary to determine the tracking direction since the mask used differs depending on the tracking direction. The scanning direction (arrow J direction) when searching for the first point of interest A may be set as the tracking direction, and a mask in that direction may be used initially.

After determining the irradiation field as described above, reading conditions for main reading are determined based only on image information within this irradiation field among the image information obtained by pre-reading. These reading conditions can be determined in various ways based on image information within the irradiation field, but
For example, as described above, create a histogram of the amount of stimulated luminescence within the irradiation field, and from this histogram, determine the maximum amount of stimulated luminescence Smax and the minimum amount of stimulated luminescence.
Smin is determined, and 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 irradiation field as described above and determining the reading conditions for the main reading based on the image information within this irradiation field, the main reading is performed according to the determined reading conditions. As disclosed in Japanese Patent Application Laid-open No. 120346/1988, it is preferable to limit the reading area to the determined irradiation field. 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 increase reading density.

In addition, as shown in FIG. 2b mentioned above, the processed image 1
6, if 0 (zero) is assigned to the outermost pixel portion 17, even if the irradiation field is not narrowed down to the inside of the stimulable phosphor sheet, the maximum irradiation field that should be the actual outline of the irradiation field The differential value of pixels in the outer peripheral portion becomes large, and that pixel portion is detected as the contour of the irradiation field. Furthermore, if 0 (zero) is not assigned to the outermost pixel portion in the processed image as described above, a similar result can be obtained by performing differential processing on the assumption that 0 (zero) exists in the surrounding area.

Although the above embodiment deals with the case of a rectangular irradiation field, the present invention is also applicable to a case of a circular or other non-rectangular irradiation field.

Further, in the above embodiment, the case where one irradiation field 10 exists on one stimulable phosphor sheet 12 is dealt with, but for example, one sheet may be divided into two sections, and each section may be divided into two sections. The present invention is also applicable to so-called divided imaging in which imaging is performed by applying an irradiation field aperture. In other words, even in the case of divided imaging, if each section is considered as one sheet, one irradiation field will exist on that one sheet. Therefore, by obtaining information in advance that it is divided imaging, The present invention may be applied to each category.

(Effects of the Invention) As described above, the method according to the present invention recognizes an irradiation field from pre-read image information, determines main reading conditions based on the pre-read image information within this irradiation field, and In recognition, a differential image is created based on pre-read image information, an arbitrary point in this image where the differential value is the maximum or a predetermined value or more is set as the first point of interest, and surrounding positions adjacent to this first point of interest are A position whose differential value is equal to or greater than a predetermined value is found from among them, and this is set as a new second point of interest.From then on, new points of interest are searched one after another in the same manner, and the position adjacent to the first point of interest is set as a new point of interest. When a point is found, this is done by recognizing the inside of the closed curve connecting the points of interest up to that point as the irradiation field.

As described above, in the differential image, the differential value at the position where the irradiation field contour exists is larger than that at other positions. Therefore, the first point of interest, which is an arbitrary position where the differential value is the maximum or a predetermined value set appropriately, is a position on the irradiation field contour, and the surrounding positions adjacent to this first point of interest are The position where the differential value is greater than or equal to a predetermined value is set as the second point of interest,
Repeating this method to find new points of interest one after another means sequentially tracking positions on the irradiation field contour.

Therefore, according to the method according to the present invention, it is possible to accurately recognize the irradiation field, and as a result, even when the irradiation field is narrowed down, it is possible to prevent the radiation caused by scattered radiation incident on the irradiation field on the sheet. Since the reading conditions are determined based only on the effective image information within the irradiation field on the sheet while eliminating adverse effects, the optimum reading conditions can always be determined.

[Brief explanation of the drawing]

Figure 1 shows a stimulable phosphor sheet photographed with an irradiation field aperture, Figure 2a shows an original image consisting of pre-read image information for each pixel, and Figure 2b shows a median image of the original image. A diagram showing a filtered processed image. Figures 3a and 3b are diagrams showing the positions in the processed image and masks used when performing differential processing, respectively. Figures 4 and 5 a to d are new attention-grabbing images. A diagram showing a mask used when searching for a point, FIGS. 6 a to 6 e are explanatory diagrams of a method of finding a new point of interest using the mask shown in FIG. 4, and FIGS. 7 a to 5
FIG. 6 is an explanatory diagram of a method of finding a new point of interest using the masks shown in FIGS. DESCRIPTION OF SYMBOLS 10...Irradiation field, 12...Stormative phosphor sheet, 1
4...Original image, 16...Processed image, 28...Differential image,
30...Closed curve.

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, the digital image data is subjected to differential processing, and the obtained differential value is calculated. In the differential image consisting of
Search for a position whose differential value is equal to or greater than a predetermined value from among the surrounding positions adjacent to the point of interest, set this as the second point of interest, and then select the position that is the previous point of interest that is adjacent to the second point of interest. Search for a position where the differential value is greater than or equal to a predetermined value from among the positions excluding the points, set this as the third point of interest, and then repeat the process of searching for this third point of interest to find new points of interest one after another. 1
When a position adjacent to the point of interest is found as a new point of interest, the inside of the closed curve connecting the previous points of interest is recognized as the irradiation field, and the image information obtained by the pre-reading within this irradiation field is used to A method for determining reading conditions for radiation image information, the method comprising determining reading conditions for main reading. 2 When searching for a new point of interest after the second point of interest, if there are multiple points of interest whose differential values are greater than or equal to the predetermined value among the adjacent surrounding positions, the Claim 1, characterized in that a certain priority is assigned to a given point, and a position with the earliest priority among a plurality of positions whose differential value is greater than or equal to a predetermined value is set as the next new point of interest. The method for determining reading conditions for radiographic image information according to item 1. 3 When searching for a new point of interest after the second point of interest, if there is no one whose differential value is greater than or equal to the predetermined value among the adjacent surrounding positions, then the differential value is calculated among the adjacent surrounding positions. The method for determining reading conditions for radiographic image information according to claim 1, characterized in that the position where the value is maximum is determined as the next new point of interest.