JPS6215541A - Determining method for readout condition of radiation image information - Google Patents

Abstract

PURPOSE:To determine optimum readout condition at any time by deciding an optional position where a differential value is larger than a maximum or specific value as the 1st aimed point and a position where a differential value is largest or larger than a specific value among peripheral points adjoining to the 1st aimed point as the 2nd aimed point, and repeating this process and finding new aimed points one after another. CONSTITUTION:Digital image data at respective positions on a sheet are obtained and a differential image obtained by differentiation is scanned to find an optional point where the differential value is largest or larger than the specific point as the 1st aimed point. The contour of an irradiation field is traced from the 1st aimed point to recognize the irradiation field. This tracing a position where the differential value is larger than the specific value is found as the 2nd aimed point among peripheral positions adjoining to the 1st aimed point and then a point where the differential value is larger than the specific value is found as the 3rd aimed point among peripheral positions adjoining to the 2nd aimed point except said aimed point (1st aimed point). Thus, new aimed points are searched for one after another and when a position adjoining to the 1st aimed point is searched for as a new aimed point, the aimed points obtained so far are connected to draw a closed curve and the area inside of the curve is recognized as the irradiation field.

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) A certain scale's phosphor emits 1i! (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 that do not exhibit this characteristic are called stimulable phosphors.

Using this stimulable phosphor, the radiation of a subject such as a human body can be
The 11-line image information is recorded on a stimulable phosphor sheet in the form of -H sheet 1~, and then this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence light. The emitted light is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image of the subject is recorded on a recording material such as a photographic light-sensitive material,
The present applicant has already proposed a radiation image information recording and reproducing system that outputs a visible image to a display device such as a CRT (Japanese Patent Laid-Open Nos. 55-12429 and 56-113).
95 etc.).

As one aspect of the radiation image information recording and reproducing system described above, 1
, a stimulable phosphor sheet in which radiation image information of a subject is stored and recorded using radiation energy level as a medium is scanned with excitation light, and stimulated luminescence light emitted from the sheets 1 through this scanning is read by a photoelectric reading means. Prior to "book reading" to obtain electrical image signals for reading and reproducing visible images for diagnosis, the sheet is scanned in advance with excitation light of a lower level than the excitation light used for this book reading. Read an overview of stored image information
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 reading conditions, and the image signal obtained by this main reading is sent to an image processing means. The image processing means processes the image signal to obtain an output image suitable for diagnostic purposes according to the region to be photographed, the method of photographing, etc., and reproduces this image signal as a visible output image on a photosensitive material, etc. A system is known, and is disclosed in, for example, Japanese Patent Laid-Open No. 58-672404, which was previously filed by the present applicant and has already been published.

Here, the reading strip A'1 is a general term for various conditions that affect the relationship between the amount of stimulated luminescence light used for reading and the output of the reading device, such as the relationship of the number of people. It refers to the reading gain (sensitivity), scale factor (radich code), or the power of excitation light used for reading.

Furthermore, 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 received per unit area by the stimulable phosphor sheet 1 during pre-reading is It means that it is smaller than that during main reading.As a way to make the excitation light for pre-reading lower than the excitation light for 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 emitting light from the light source. Examples include a method of attenuating the excitation light in its optical path with an ND filter, ΔoM, etc., and a method of providing a light source for pre-reading and a light source for main reading separately and making the output of the former smaller than the output of the latter. Further examples include a method of increasing the beam diameter of the excitation light, a method of increasing the scanning speed of the excitation light, and a method of increasing the transport speed of the stimulable phosphor sheet.

In this way, by understanding the outline of the image information and information stored on the sheet in advance 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. The maximum stimulated luminescence light amount S max and the minimum stimulated luminescence light m S min of the range are determined, and this 3 ma
x and 3 min are respectively the maximum density of the appropriate density range in the visible output image [) WaX and the minimum Ii!
A method of determining the reading conditions for main reading so as to correspond to the maximum signal level Qm, ax and the minimum signal level Q min of the desired input signal range in the image processing means determined by Q[)sin was filed by applicant Honda. (Patent Application No. 12658/1982).

On the other hand, in order to avoid irradiating radiation to areas that are not necessary for humane diagnosis, or to avoid irradiating radiation to areas that are unnecessary for diagnosis, scattered rays 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 this scattered ray is 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 this scattered ray.

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 within the irradiation field, the obtained histogram shows that the amount of stimulated luminescence inside and outside the irradiation field is It is difficult to make a distinction. Therefore, as mentioned above, from the histogram, Smax
, 3m1n and determine the reading conditions from this, the minimum value between the stimulated luminescence lights in the irradiation field is S sin
However, there may be cases where the minimum value of the amount of stimulated luminescence due to scattered radiation outside the irradiation field is set to 31n. and,
In this way, the minimum value of the amount of stimulated luminescence outside the irradiation field is 3 min.
In the case of The value of m becomes too high, resulting in a decrease in contrast, making it difficult to make a satisfactory diagnosis.

That is, when shooting with a narrowed irradiation field, the rays generated from the subject enter the irradiation field on the sheet,
The image information obtained by pre-reading includes information based on scattered radiation of As a result, it is difficult to obtain visible images that are suitable for observation and interpretation.

(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 can eliminate the above-mentioned inconvenience caused by narrowing the irradiation field and determine optimal reading conditions.

(Structure of the Invention) In order to achieve the above-mentioned object, the reading condition determination method according to the present invention applies digital image data to 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, make this the first point of interest, and then differentiate this digital image data. Search for a position whose differential value is greater than or equal to a predetermined value from among the surrounding positions adjacent to the first point of interest, set this as the second point of interest, and then search for the position that is the second point of interest among the surrounding positions adjacent to the second point of interest. Search for a position whose differential value is greater than a predetermined value from among the positions excluding the previous point of interest, that is, the first point of interest, and set this as the third point of interest, and repeat the process of searching for this third point of interest one after another. and find new points of interest, and
When the position adjacent to the point of interest is found as a new point of interest, that is, when the points of interest are sequentially searched using the above method and the point of interest is returned to the first point of interest, the closed curve formed by sequentially connecting the points of interest up to that point is It is characterized in that the inner side is recognized as an irradiation field, and 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 include 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 for reading stimulable phosphor sheets 1 to 12 from one field 10 photographed with a rectangular irradiation field aperture, as shown in FIG. This is a method for determining reading conditions. 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
The axis indicates the sub-scanning direction.

First, the image information stored and recorded on the stimulable phosphor sheets 1 to 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 and transferring it to the sheet 1 on the sheet 12. Each scanning point (
That is, it means obtaining information consisting of an electrical signal corresponding to the amount of stimulated luminescence light for each pixel.

Next, digital image data is obtained from the image information read in the above manner at each position on the sheet. In order to obtain this digital image data, the image information read in the above-mentioned pre-reading is directly used. The image information may be obtained by performing preprocessing such as spatial filter processing on the image information.

If you want to obtain it directly, for example, you can set the positions from Sea 1 to above in pixel units, and digitize the pre-read image information of the pixels corresponding to each position as the digital image data for that position. .

When calculating by performing preprocessing such as spatial filtering,
For example, a plurality of pixels in a certain relationship are set together as one position, and based on the pre-read image information of the pixels included in this position, for example, they are averaged to calculate the digital image data of the position. Alternatively, the position on the sheet may be set in units of pixels, and the digital image data at the position may be calculated based on pre-read image information of a plurality of pixels corresponding to the position and surrounding positions. . Median filter processing can be cited as one of the latter calculation methods. This median filter processing is the median value (
This refers to processing in which the median value) is used as the image information of a predetermined pixel (position).

A specific example of this median filter processing will be explained with reference to FIG. 2. FIG. 2(a) is a diagram showing an original image 14 consisting of the pre-read image information for each pixel, and each square in the figure represents one pixel. FIG. 2(h) is a diagram showing a median filtered image 16 consisting of digital image data at each position obtained by applying the above median filtering 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, use a mask 18 of a predetermined size, for example, a 3×3 sized mask 18 that has an area of 3 pixels in the vertical and horizontal directions, and place the mask 18 in the center of the mask with a predetermined pixel (indicated by diagonal lines in the figure). The median value of the image information of the nine pixels included in the mask is digitized as the digital image data of the predetermined pixel, and this processing is performed. is applied to all pixels in the original image 14 (however, it cannot be applied to pixels located at the outermost periphery, so those pixels are excluded), the digital image data at that pixel is obtained, and the median consisting of this data is calculated. A filtered image 16 is obtained. Note that if a 3×3 size mask is used, it is not possible to perform median filter processing on the outermost pixels as described above, so the processed image 1G is smaller than the original image 14 by 17 pixels on the outermost circumference.
For example, a quantization level O (zero) can be assigned to this outermost pixel portion 17 as image data. The size of the mask is not limited to 3×3. Also, processed image 1
In order to prevent G from becoming small, for example, the original image 14
It is sufficient to perform median filter processing on the assumption that there are pixels around which have the same matrix conversion level as the outermost pixels of the original image. By performing the above median filter processing, it is possible to remove noise in cases where the quantization level is extremely high or low compared to surrounding pixels due to noise, and there is an advantage that the irradiation field contour information is not blurred.

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 in the following manner.

Figures 3(a) and <b) are diagrams showing processed images, and each square in the diagram indicates one position.

For example, as shown in FIG. 3<8), in differentiating the digital image data of a predetermined grain @20 in the processed image 16;
2 is placed in the upper left part of the mask so that the predetermined position 20 is located, and the digital image data of the four positions included in the mask 22 are arranged as shown in the figure (a, b, c).
, cl.

Perform the calculation and place the a' at the predetermined position 20.
), and the differential calculation may be performed for each position. Also, instead of the above formula,
``Differential processing by performing the following calculations'' may also be performed.

Of course, using differential expressions other than these will not solve the problem.

Furthermore, although the above example is a first-order differential process, Fig. 3(b)
As shown in the figure, a mask 24 with a pixel size of ax3 is used, the mask is arranged so that the predetermined position 2G is located at the center □ of the mask, and the digital image data of the ninth position included in the mask is transferred as shown in the figure. Nyogu a.

1) , C, d, e, f,
Various types of second-order differential processing may be used, such as performing the following calculations as g', 'h, and i, and then making e' 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. The above digital image data is Sea 1~
Corresponding to the magnitude of the energy of the radiation incident on the field, image data outside the field will generally have a low quantum level, and image data within the 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 will generally have a larger quantum level than the differential value of the image data at other positions, and as a result, the differential value in the differential image will be If the maximum position or the predetermined value is set appropriately, ε is the position where the irradiation field contour exists and is greater than or equal to the travel value and reaches the original position 1.
I can do it. '□'Urine The method according to the invention is based on the above fact, and is carried out by searching and tracking the positions where the irradiation field outline exists in the differential fraction one after another (by tracing the irradiation field outline). There are two steps: a step of detecting the first point of interest, which is the starting point of tracking, and a tracking step of tracking the right position of the contour from the first point of interest.
Consists of one.

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 1 z above the predetermined value will not be irradiated. It can be determined that this is the position where the field contour exists, and of course, the position where the differential value is maximum can also be determined to be the position where the irradiation field contour exists. Therefore, first, one of the irradiation field contour existing positions is determined by the method described above.
The first point of interest is detected and its position is set as the first point of interest.

Next, the irradiation field contour is tracked from this first point of interest,
Recognize the radiation field. This tracking first searches for a position whose differential value is greater than or equal to a predetermined Irti among the surrounding positions adjacent to the first point of interest, sets this as the second point of interest, and then
The surrounding position adjacent to the point of interest and the previous point of interest (first
The position where the differential value is greater than or equal to a predetermined value is searched among the positions excluding the point of interest), and this is set as the third point of interest.
This is done by repeating professional wrestling in search of one point, and 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 on the adjacent circumference 111 whose differential value is equal to the value of 2, then that one position can be set as the next point of interest. 2
If there are more than one position, select the position with the highest priority of -M according to a certain priority given in advance to the adjacent surrounding positions of A, or any position among the two or more positions. The position with the maximum differential value may be set as the point of interest in the method as appropriate, and if there is none, the position with the largest differential value among the adjacent surrounding positions may be set as the next point of interest.

Of course, the position for the next soup "1 point" is selected from the positions excluding the previous and specially ordered n points.

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

The mask not shown in FIG. 4 is a mask of 3×3 position size as shown in the figure, and an example of tracking performed using this mask will be explained with reference to FIG. 6.

FIGS. 6(a) to 6(e) each show a differential image 28 having a rectangular irradiation field contour and sequentially explain a method of tracking the contour.

First, as shown in Fig. 6(a), the first point of interest △ 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 arranged so that the position where the differential value is equal to or greater than a predetermined value within this mask (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 Fig. 6 (1)), move the mask so that this second point of interest B is located in the center, and similarly, within this mask, the differential value will be above the predetermined value J. (Of course, excluding the current second point of interest B and the immediately preceding first point of interest A) is the next third point of interest.If the differential values of multiple positions are greater than or equal to a predetermined value, According to the specified priority order, the earliest position in the order is set as the next third point of interest.There are various ways to assign the priority order, but in this specific example, the priority order is given as shown in FIG. Similarly, if the part that was the previous point of interest, for example, part a, is a part of the surrounding position a-h adjacent to the current point of interest, then from part a as the base point, counterclockwise, That is.

Priorities are given in the order of c, d, e, f, g, and h. Therefore, in the example of FIG. 6 (11), portions e and f of the portions that can become the new third point of interest have differential values greater than a predetermined value, and the position of portion e, which has the highest priority, is The third point of interest is C.

Next, in the same way, if there are multiple positions where the differential value is greater than or equal to the predetermined value, the position with the earlier priority is set as the new point of interest, and the sixth As shown in Figures (c) and (d), the fourth point of interest D1, the fifth
Point of interest E is selected, and new points of interest are successively selected in the same manner, and as shown in FIG. 6(e), the first point of interest A is selected.
If the position adjacent to is selected as the new point of interest,
The inside of the closed curve 30 connecting the first point of interest A to the nth point of interest F is recognized as the irradiation field 10.

Note that the arrow in Fig. 6 indicates the tracking direction of the irradiation field contour.
In this specific example, the priority order is set in a counterclockwise direction, so the tracking direction is also in a quarter-clockwise direction. but,
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 position (position), and this mask is used by changing its orientation depending on the tracking direction. Note that 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 8, then as shown in Figure 7 (a
), there are four positions (■) adjacent to the first point of interest A in the X and V axis directions.

T1. The position where the differential value is maximum is found among rff and IV, and tracking is started from the first point of interest A in the direction of the position where the differential value is maximum. In the case shown in the figure, assuming that the differential value is at the maximum at the position (■), tracking is started in the left direction toward the position (■).

In this case, the tracking direction is to the left, so Fig. 5 <
a > using a mask with a direction other than that shown, so that the first point of interest A is located in the diagonally shaded part of the mask, that is, the seventh
Arrange the mask as shown in ffi (b'), find a position (excluding the first point of interest A) where the differential value is greater than or equal to a predetermined value among the positions in the mask, and use it as the next second point of interest. shall be. 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 the corresponding portion is selected as the second point of interest B.

Next, as shown in FIG. 7(C), move this mask to position the second point of interest B in the shaded area of the mask,
In that state, the position N within the mask is greater than or equal to the predetermined value.
(The previous point of interest, 1').

(excluding the second points of interest A and B) and set it as the third point of interest. In this case, in the illustrated example, part 1) and part 0 have a differential value greater than or equal to a predetermined value, and the priority order is as shown in FIG.
a,) as shown by the long arrow T inside.

Since they are assigned in the order of b, , c, and d, the position of part b, which has the highest priority, is selected as the next third point of interest C.

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

Next, note 5: ``One point E is selected, but this time the tracking from the third point of interest C to the fourth point of interest is downward, so we use the mask in Figure 5 (H). Then, move the mask so that the '4th point of interest 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 FIG. 7(e), and then In the illustrated example, only part b has a differential value greater than a predetermined value, and the position of part ib is the fifth spout point.
It has been selected as 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 7(e) and the next point of interest is searched. be done. In this case, as shown in the figure, only the d portion of the mask has a differential value greater than or equal to a predetermined value;
The position of G is selected as the next point of interest, and when searching for the next point of interest, the tracking direction is to the right, so the fifth point is selected as the next point of interest.
Using the mask shown in FIG.
), and use the same method as above to move to the next point of interest H.
Select.

Thereafter, the mask of FIG. 5(C) is used to continue detecting points of interest in the same manner, and as shown in FIG. 7(f), the position of the lower right corner becomes a new point of interest I. Then, the next point of interest J is the position of the d part of the mask, so the tracking direction changes upward, and the next point J is the position of the d part of the mask, as shown in Fig. 7 (()).
), and as shown in Figure 7 (( )), when the position of the upper right corner becomes a new point of interest, the next point of interest becomes the d section of the mask. The tracking direction changes to the left, and the next position is (1) in Figure 7).
As shown in FIG. 5, tracking is continued using the mask shown in FIG. 5<a>.

Then, as shown in FIG. 7(h), when the position adjacent to the first point of interest 8 is selected as the new nth point of interest M, the previous first point of interest Δ to the nth point of interest M is connected. The inside of the closed curve 30 is recognized as the irradiation field 10.

In the above specific example, in the corner part of the irradiation field contour, multiple points whose differential value is equal to or greater than a predetermined value appear in the mask η-, and in the straight part of the contour, one point whose differential value is equal to or greater than the predetermined value appears. However, 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 with differential values greater than or equal to a predetermined value will appear in the mask. In that case, the item with the highest priority above is always the next point of attention. The next point to note is a.
When an object appears in parts b and c, the tracking direction is the same and the mask used is not changed, and only when it appears in part d, the mask can be changed and tracking can be continued. Regarding this point, please refer to the fourth
The same applies to the case where a mask not shown in the figure 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 example, the position of the maximum differential value in the differential image is
Although we have described the case where the point of interest is set as the first point of interest, if any point whose differential value is equal to or greater than a predetermined value is set as the first point of interest, tracking may be performed in the same manner as described above. However, when using the mask shown in Figure 5, the mask to be used differs depending on the tracking direction, so it is necessary to determine the tracking direction.
As shown in FIG. 7 (+), the scanning direction (direction of arrow J) when searching for the first point of interest 8 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, the IJ
The reading conditions for the actual reading are determined based only on the image information within this irradiation field among the image information obtained. This reading condition can be determined in various ways based on the image information within the irradiation field. 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 stimulated luminescence is determined. Determine the light amount 5IIla× and the minimum stimulated luminescence light amount 3 min, and calculate this Smax, Sm1
Reading conditions can be determined based on n.

Note that the decision to attach a reading thread is not limited to the case where it is determined based only on the pre-read image information within the irradiation field.
The determination can also be made in consideration of the part of the subject to be imaged, such as the chest or abdomen, and the imaging method, such as simple, contrast, tomographic, or magnified imaging.

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 Unexamined Patent Application Publication No. 120346/1988, it is preferable to limit the reading area to the irradiation field within the determination area.

By thus limiting the reading area for the main reading within the irradiation field, noise components due to scattered radiation recorded outside the irradiation field of the stimulable phosphor sheet are not read, and an excellent final image can be obtained.

Furthermore, by narrowing down the reading area, it is possible to shorten the reading time or increase the reading density.

Note that when O (@) is assigned to the outermost pixel portion 17 in the processed image 16 as shown in FIG. 2(b), even if the irradiation field is focused inside the stimulable phosphor sheet. Even if it is not, the differential value at the pixel in the outermost circumferential portion, which should essentially become the irradiation field contour, becomes large, and that pixel portion is detected as the irradiation field contour. Furthermore, if O (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 assuming that O (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 the case of a circle or other non-rectangular irradiation field.

Further, in the above embodiment, one stimulable phosphor sheet 12
We have dealt with the case where one irradiation field 10 exists above the
For example, the present invention is applicable to so-called divided imaging in which one sheet is divided into two sections and each section is imaged by applying a GJ to the irradiation field. That is, 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, the present invention can be implemented by obtaining information in advance that it is divided imaging. It is sufficient to apply it 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 above-mentioned first point of interest, which is an arbitrary position where the differential value is the maximum or more than a predetermined value set appropriately, is a position on the irradiation field contour, and among the surrounding positions adjacent to this first point of interest. The position where the differential value is greater than or equal to a predetermined value is set as the second point of interest, and repeating this method to find new points of interest one after another means sequentially tracking the 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, there are no adverse effects 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, the optimum reading conditions can always be determined.

[Brief explanation of drawings]

Figure 1 is a diagram showing a stimulable phosphor sheet photographed with an irradiation field aperture, Figure 2 (a) is a diagram showing an original image consisting of pre-read image information for each pixel, and Figure 2 (b) is a diagram showing a stimulable phosphor sheet photographed with an irradiation field aperture. Figures 3(a) and 5(b) are diagrams showing the positions in the processed images and masks used when performing differential processing, respectively. Figures 4 and 5 are diagrams showing processed images obtained by median filtering the original image. Figures (a') to (d) are diagrams showing masks used when searching for new points of interest, and Figure 6 (
a) to (e) are explanatory diagrams of a method for finding new points of interest using the mask shown in Fig. 4, and Fig. 7 (a) to (i)
> is an explanatory diagram of a method of finding a new point of interest using the masks shown in FIGS. 5(a) to 5(d). 10... Irradiation field 12... Stimulative phosphor sheet 14... Original image 16... Processed image 28... Differential image 30... Closed
Curved (Voluntary) Procedure Nefusho Commissioner of the Patent Office October 1986
Patent Application No. 60-155848 No. 1 dated May 1, 1989 2, Name of the invention, Method for determining reading conditions for radiographic image information 3, Relationship with the case of the person making the amendment Patent applicant Location 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name Name
Fuji Photo Film Co., Ltd. 4, Agent

Claims (3)

[Claims] (1) By irradiating the excitation light onto the stimulable phosphor sheet on which the radiation image information is stored and recorded with an irradiation field aperture, the radiation image information stored on the stimulable phosphor sheet is radiated. Prior to main reading to emit luminescent light and photoelectrically read this stimulated luminescent light to obtain an electrical image signal for outputting a visible image, excitation with energy lower than the energy of the excitation light used in the main reading is performed. Reading the radiation image information by performing pre-reading of the radiation image information stored and recorded on the stimulable phosphor sheet using light, and determining reading conditions for the main reading based on the image information obtained by this pre-reading. In the 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 a differential image consisting of the obtained differential values is obtained. , first select an arbitrary position where the differential value is the maximum or a predetermined value or more as the first point of interest, and then search for a position whose differential value is greater than or equal to the predetermined value from among the surrounding positions adjacent to this first point of interest. This is set as the second point of interest, and then a position whose differential value is greater than or equal to a predetermined value is searched among the surrounding positions adjacent to this second point of interest, excluding the previous point of interest, and this is selected as the second point of interest. The process of searching for this third point of interest is then repeated to find new points of interest one after another, and when a position adjacent to the first point of interest is found as a new point of interest, the previous point of interest is The inside of the closed curve connecting the is recognized as the irradiation field,
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 the irradiation field. (2) When searching for a new point of interest after the second point of interest, if there are multiple points whose differential value is greater than or equal to the predetermined value among the adjacent surrounding positions, the adjacent surrounding positions must be searched in advance. Give a certain priority to
The reading condition for radiographic image information according to claim 1, characterized in that the position with the earliest priority among the plurality of positions whose differential value is equal to or greater than a predetermined value is set as the next new point of interest. How to decide. (3) When searching for a new point of interest after the second point of interest, if there is no point among the adjacent surrounding positions whose differential value is greater than or equal to the predetermined value, then The method for determining reading conditions for radiographic image information according to claim 1, characterized in that the position where the differential value is maximum is determined as the next new point of interest.