JPS62104264A - Method for recognizing irradiation field - Google Patents

Abstract

PURPOSE:To detect more accurately an irradiation field by preparing lots of templates, taking the correlation between a value being the processing of a differentiation value on a differentiation picture or the value itself and a value on each template and recognizing the inside of a part of the template having the largest correlation corresponding to the irradiation field profile as the irradiation field. CONSTITUTION:Figure shows an example of lots of multi-value picture templates prepared in advance and each template 12 has an irradiation field profile corresponding part (hatched part) 14. A differentiation value on a differentiation picture and a value on each prepared template are multiplied at every same position, the total sum of the products is obtained, and when the multiplication at every same position is applied to all the templates, the products are summed. Then the summing of the products is applied to each template, the result is compared and the inside of the irradiation field profile corresponding part of the template having the maximized product sum is recognized to be the irradiation field.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention recognizes the irradiation field when radiation image information is recorded on a recording medium such as a stimulable phosphor sheet by aperture irradiation field. Regarding the method.

(Conventional technology) 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 partially 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 luminescence light, reads this stimulated luminescence light in a charged manner to obtain an image signal, performs image processing on this image signal, and creates a radiation image of the subject based on the image signal subjected to image processing. The present applicant has already proposed a radiation image information recording and reproducing system that outputs TI visual images to recording materials such as photographic light-sensitive materials and display devices such as CRTs (Japanese Patent Application Laid-open Nos. 55-12429 and 5G-11395). Such).

In the above system, the visible image I! In order to improve image interpretation aptitude, when photoelectrically reading the stimulated luminescence light or performing image processing on the image signal, the optimum reading conditions and image processing conditions determined according to each captured image are applied. It is desirable to perform reading and image processing based on the image.

As a method for optimally determining the reading conditions and image processing conditions such as gradation processing conditions as described above according to each photographed image, it is disclosed in Japanese Patent Application Laid-Open No. 58-67240, which was previously filed by the present applicant. In other words, the stimulable phosphor sheet on which radiographic image information is accumulated and recorded is scanned with excitation light, and the stimulated luminescence emitted from the sheet is read by a charging reading means, which can be used for diagnosis. Obtaining electrical image signals for reproducing visual images ``Prior to book reading, the sheet is scanned in advance with excitation light at a lower level than the excitation light used for book reading, and images are accumulated and recorded on this sheet. "Pre-reading" is performed to read the outline of the information, and the above-mentioned reading conditions (reading conditions when performing actual reading here) are performed based on the image information obtained by this pre-reading.
There are methods to determine image processing conditions.

As a specific method for determining the reading conditions for main reading based on the image information obtained by such pre-reading, for example, there is
As described in the publication, a histogram of the image information (image signal level) obtained by pre-reading is obtained, and from this histogram, the maximum image signal level 3 max and the minimum image signal level 3m1n of the desired image information range in this histogram are determined. Find this S raax
and Sm1n are the maximum density DIlla× and the minimum density [) in the appropriate a degree range in the visible output image, respectively.
A possible method is to determine the reading conditions for the main reading so as to correspond to the maximum signal level Qll1ax and the minimum signal level Q1n of the desired input signal range in the image processing means determined by min.

Further, as a specific method for determining image processing conditions, such as gradation processing conditions, based on the image information obtained by pre-reading, for example, the same method as above, that is, the image information obtained by pre-reading (image signal In addition to determining the histogram of 3 wax and 3
The maximum signal level Rmax and the minimum signal of the desired input signal range in the image reproduction means (visible image output means) are determined by the maximum density [ ) max and the minimum density Q win of the appropriate density range in the visible output image, respectively. A possible method is to determine the gradation processing conditions so as to correspond to the level Rsin.

Note that the image processing conditions such as the gradation processing conditions can be determined based not only on the image information obtained by the above-mentioned pre-reading but also based on the image information obtained by the main reading, and even in that case, For example, as in the case above, create a histogram of the image information (image signal level) obtained from the book reading, and use this histogram to calculate the 3 ma
Find x and 3m1n, and calculate this 3 wax and S1n
A method may be considered in which the gradation processing conditions are determined such that RIlaX and R1n respectively correspond to the above-mentioned RIlaX and R1n.

Note that in the above, reading conditions refer to various conditions that affect the relationship between the input and output of the reading means, for example, the relationship between the input (stimulated luminescence light amount) and the output (electrical image signal level) of the photoelectric reading means. It is a general term for conditions such as, for example, reading gain (sensitivity) and scale factor (latitude) that determine the relationship between input and output, or the power of excitation light in reading.

Furthermore, in the above, the image processing condition is a general term for various conditions that affect the relationship between input and output in the image processing means, and means, for example, gradation processing conditions, spatial frequency processing conditions, and the like.

Furthermore, in the above, 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 lower than the excitation light used for main reading. means smaller than that of .

(Problem to be solved by the invention) By the way, in order to avoid irradiating radiation to areas that are not necessary for humane diagnosis, or when radiation is applied to areas that are unnecessary for diagnosis, radiation is scattered from that area to areas necessary for diagnosis. In order to prevent lines from appearing and the contrast resolution to deteriorate, it is often preferable to narrow down the radiation 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 'rtIa phosphor sheet Since this scattered ray is also accumulated and recorded, the histogram of image information (image signal level) obtained by pre-reading also includes the image signal level based on this scattered ray. Since the image signal level outside the irradiation field on the sheet that is surrounded by these scattered rays may be higher than the image signal level inside the irradiation field, the obtained histogram is used to distinguish between the image signal levels inside and outside the irradiation field. That is difficult. Therefore, when calculating Smax and Sn+in from the histogram and determining reading conditions from the histogram as described above, the minimum value of the image signal level within the irradiation field should be Sm1n, but the image signal level due to scattered radiation outside the irradiation field is A case may occur where the minimum value is set to Sm1n. In this way, when the minimum value of the image signal level outside the irradiation field is set to 3 sin, that value is generally lower than the minimum value of the image signal level within the irradiation field, so in the main reading, unnecessary scattered radiation for diagnosis is reduced. Therefore, the density of the image in the portion necessary for diagnosis becomes too high, and as a result, the contrast decreases, making it difficult to perform a satisfactory diagnosis.

In other words, when performing dancing with a narrowed irradiation field, scattered rays generated from the subject enter the irradiation field on the sheet,
The image information obtained by pre-reading includes information based on this scattered radiation, so even if the reading conditions are determined based on such pre-read image information, it is not possible to determine the optimal reading conditions. As a result, it is difficult to obtain visible images that are suitable for observation and interpretation.

In addition, such problems occur not only when determining reading conditions based on prefetched image information, but also when determining image processing conditions such as gradation processing conditions based on the above-mentioned prefetched image information or prefetched image information. It also exists.

Therefore, when trying to determine reading conditions and image processing conditions based on pre-read or main-read image information using the method described above, it is necessary to accurately recognize the irradiation field when the irradiation field is being imaged by applying the irradiation field aperture. It is desirable to determine these conditions based only on the image information within the irradiation field in the pre-read or main-read image information to eliminate the adverse effects of the above-mentioned scattered radiation outside the irradiation field.

The above is an overview of the stimulable phosphor sheet publication and is an example of the necessity of irradiation field recognition when determining reading conditions, etc. However, this irradiation field recognition is not limited to such cases, and can be used in various other situations. This may also be necessary in the case of

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

(Means for Solving the Problems) In order to achieve the above object, the irradiation field recognition method according to the present invention uses image information read from a recording medium such as a stimulable phosphor sheet that has already been imaged to be recorded on the recording medium. The image data is obtained at each position, and this image data is subjected to differential processing to create a differential image consisting of the differential values at each position. A multivalued image template in which the position and each position in other parts have different values, and the shape and size of the part corresponding to the irradiation field outline correspond to the irradiation field outline at various irradiation field apertures that can be used for actual imaging. A large number of templates with different shapes and sizes are prepared, and the correlation between the differential 41n on the differential image or the processed value of this differential value and the value on each template is calculated, and the irradiation is performed on the template with the largest correlation. It is characterized by recognizing that the inside of the field contour corresponding portion is the irradiation field.

Note that the "recording medium" mentioned above means something that can record radiation image information, and the above-mentioned! Examples include multilayer phosphor sheets, but are not necessarily limited thereto.

Furthermore, the term "image information read from a recording medium" as used above means image information recorded on the recording medium that has been read by some method, such as pre-reading or actual reading on the stimulable phosphor sheet mentioned above. It refers to the obtained image information, but is not necessarily limited thereto.

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

(Effects of the Invention) The method according to the present invention performs differential processing on image data as described above to create a differential image consisting of differential values at each position, prepares a large number of templates as described above, and The correlation between the differential value or the value obtained by processing this differential value and the value on each template is calculated, and if the area corresponding to the irradiation field outline in the template with the highest correlation is the irradiation field, i! ! It is something to be aware of.

In the above-mentioned differential image, the differential value at each position where the irradiation field contour exists, or the value obtained by processing the differential value, is larger than the differential value at other positions, or the value obtained by processing the differential value. Therefore,
The part of the template that corresponds to the irradiation field contour (for example, each position in this part is given a value of 1 or more, and the other parts are given a value of 01)
The degree of similarity between the differential image and the template (for example, the sum of the products between the differential image and the template) in the case of a template in which the irradiation field contour is located in Therefore, it is possible to recognize that the area inside the portion corresponding to the irradiation field outline of the template where the similarity is maximum is the actual irradiation field.

Therefore, according to the method according to the present invention, it is possible to accurately recognize an irradiation field when radiation image information is recorded on a recording medium by applying an irradiation field aperture.

In addition, the method according to the present invention directly detects the irradiation field based on the differential value obtained by differential processing the image data, that is, based on the image information recorded on the recording medium, so it is more effective. The irradiation field can be detected accurately.

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

In the embodiment described below, as shown in FIG. 1, a stimulable phosphor sheet 10 having one irradiation field photographed with a rectangular irradiation field diaphragm as shown by a dashed dotted line is obtained from pre-read image information. The present invention is applied to the case of recognizing an irradiation field.

In this method, first, lr
Digital image data at each position on the stimulable phosphor sheet is obtained from the information.

The image information obtained by the above-mentioned pre-reading means each scanning point (i.e. each pixel) on the stimulable phosphor sheet obtained by reading the stimulated luminescence light emitted by the pre-reading excitation light scanning using a photoelectric conversion means. This refers to image information consisting of electrical signals corresponding to the amount of stimulated luminescence light for each image.This information, of course, corresponds to the radiation image information stored and recorded on the sheet.

FIG. 2 is an enlarged view of part A of the stimulable phosphor sheet in FIG. 1. Each square in the figure represents one pixel, and f(L 1 ), f
(1, 2), ...... is each pixel (1, 1>,
(1, 2), . . . shows the digitized version of the above image information. Further, the X direction in FIGS. 1 and 2 is the main scanning direction, and the X direction is the sub scanning direction.

In order to obtain digital image data at each position on the sheet from this image information, it is first necessary to set the position on the sheet. This position may be set at the 111th position of both A1, or by setting multiple pixels in a certain relationship, for example, four pixels adjacent to each other vertically and horizontally ((1,1>, (1,,
2), (2,1>, (2゜2) ), ((
1,3), (1,4), (2,3).

(2, 4>), . . . may be combined into one position. In the former case, the digital image data at each position means the digitized image information of the pixel corresponding to that position, and in the latter case, the digital image data at each position means the plurality of pixels included in that position. It means something determined based on the image information of a pixel, for example, digital image data obtained by averaging image information of a plurality of pixels.

In this embodiment, this position setting is performed pixel by pixel.

After obtaining digital image data at each position as described above, this image data is subjected to differential processing.

The method of differentiation may be -dimensional first-order differentiation or higher-order differentiation, or two-dimensional first-order differentiation or higher-order differentiation. Furthermore, in the case of discretely sampled images, differentiation is equivalent to finding the difference between adjacent image data. Existing nearby means not only existing adjacent to each other, but also includes, for example, existing every other location.

In this embodiment, differentiation processing using two-dimensional differentiation is performed. That is, first, the digital image data is differentiated one-dimensionally in the X direction, and the differential value δ' at each position is determined. This δ' is equivalent to the image data difference between adjacent positions in the X direction, and the following formula 0 formula % Next, one-dimensional linear differentiation is performed in the X direction in the same way to find the differential value δ'' at each position. δ〃 is the following formula 0 formula % Then, based on the differential values δ′ and δ″ of the position in the one-dimensional first-order differential in both directions, for example, the absolute values of both differential values δ′ and δ″ can be added. The two-dimensional differential value δ at J3 is determined at each position by .delta..delta. is expressed by the following formula.

δ(1,1)=lδ' (1,1) l+-1δ″(
1,1)l δ(1,2)=jδ' (L 2) l+lδ″(
1,2) + δ(2,1)=lδ'(2,1>l→1δ''(2,1)
1 δ (2,2)=l δ' (2,2) l+1
δ″(2, 2>1 By performing the above-described differentiation process, the differential value δ at each position on the stimulable phosphor sheet is obtained, and a differential image consisting of the differential value δ at each position is created. In the above embodiment, the differential value δ is always positive, but for example, when creating a differential image by -dimensional first-order differential processing, the differential calculated value may become negative depending on the position on the sheet. The absolute value of the calculated value is taken as the differential value on the differential image.Also, in the above embodiment, the differential image is created using the obtained differential value δ itself, but as the differential image in the present invention, the differential value δ is It may be created by binarizing it using a predetermined threshold value.

Once the differential image has been created, the differential image is correlated with a number of multivalued image templates prepared in advance, and the results are compared to detect the irradiation field.

FIG. 4 <a> to (Q) show examples of a large number of multivalued image templates prepared in advance, and each template 1
2 is the area corresponding to the irradiation field contour (hatched area in the figure) 1
4, and at each position in the contour corresponding portion 14, for example, 1
For example, the above values are 01I at each position in the other part 16.
II is given, and the shape and size of the irradiation field outline corresponding portion 14 of each template 12 differs depending on the shape and size of the irradiation field outline in various irradiation field apertures that can be used for actual presentation.

The size of the template 12 itself is preferably the same as the size of the stimulable phosphor sheet 10 (differential image), but b! It doesn't matter if it is. Irradiation field contour corresponding part 14
has a predetermined width t. As shown in FIG. 5.6, which will be explained below, this width t may be for two or three positions, one position, or even four or more positions. The shape of the portion corresponding to the irradiation field contour is shown in Fig. 4(a), (
The rectangle shown in b) and the circle shown in Fig. 4 (1, (d)) are referred to. Size refers to the length of one side of the rectangle, the diameter of the circle, etc. Fig. 4 (e) and (f) are diagonal apertures. In the case of imaging, Fig. 4 (l corresponds to the irradiation field contour in the case of a round aperture and divided imaging (one stimulable phosphor sheet is divided into multiple sections and imaging is performed for each section). This is a template that has an irradiation field contour corresponding portion ↑4.Each position on the template 12 corresponds to each position on the differential image, but it is not necessarily necessary to have a one-to-one correspondence; for example, 1 on the template One position may correspond to four positions adjacent to each other in the upper, lower, left, and right directions on the differential image.Each position in the irradiation field contour corresponding portion 14 is given a value of 1 or more; For example, one type of value, that is, only 1, may be assigned as shown in Figure 5, or two types of values, ie, 2 in the center and 1 on both sides, as shown in Figure 6. Of course, values of the 3PJ class or higher may be assigned, and the manner in which multiple types of values are assigned may be determined as appropriate.

Next, the correlation between the differential image and the template image is determined. Here, taking a correlation means quantifying the degree of similarity between images by, for example, a performance as described below. Then, the inside of the portion corresponding to the irradiation field contour of the template image that gives the maximum value is recognized as the irradiation field.

That is, in this embodiment, the differential value on the differential image (including both the differential value itself and the binarized case) and each of the templates prepared above and the clay of L are used in the same manner.
Multiply each position and find the sum of the products. When there is a one-to-one correspondence between a position on the differential image and a position on the template, the values at the same corresponding position are the same! 1) For example, when four positions on the differential image correspond to one position on the template as in (e), each differential value on the four positions corresponds to the value on one position on the template. Multiply. 11) If the opening of the same position fO is performed on the entire template, sum the volumes.

Then, such a summation of products is performed for each template, the results are compared, and the area inside the portion corresponding to the irradiation field contour of the template where the summation of products is maximum is recognized as the irradiation field.

That is, 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, the image data outside the irradiation field generally has a low quantum level, and the image data inside the irradiation field is generally at a high quantum level. Therefore, the difference between the image data of the part where the irradiation field contour is located is generally a larger quantum level than the difference between the image data of other parts, so the differential value of each position where the irradiation field outline exists on the differential image is larger than the differential value at other positions, and as a result, the sum of the above products in the case of a template in which the irradiation field outline is exactly located in the irradiation field outline corresponding portion 14 of the template is greater than the sum of the products in the case of a template in which the irradiation field outline is located exactly in the part 14 corresponding to the irradiation field outline of the template. Naturally, it also gets bigger. Therefore, a large number of templates having corresponding parts to the irradiation field contour are prepared according to various shapes and sizes of the expected irradiation field contour, and the above-mentioned multiplication is performed between the differential image and each of these templates. After comparing the sum of the products and finding the template that maximizes the sum,
The actual irradiation field contour exists in the irradiation field contour corresponding portion 14 of the template, and the inside of the contour corresponding portion 14 (if the portion 14 has a certain width, any The irradiation field can be recognized as the irradiation field.

In the above embodiment, the case where one irradiation field exists on one stimulable phosphor sheet 10 was dealt with (except for the case of the template shown in FIG. 4(g) above). The present invention is also applicable to the case of so-called divided imaging in which the sheet is divided into two sections and an irradiation field aperture is applied to each section to perform Oka shadowing. In other words, even in the case of divided copying, 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 All you have to do is apply it to each category.

The irradiation field recognized as described above can be used for various purposes. For example, extract only the image information within the irradiation field from the pre-reading or main reading image information as described above, and use the reading conditions and image processing conditions based on that (only the image processing conditions when recognizing the irradiation field based on the main reading image information). Of course, it can be used for other purposes, such as recognizing the irradiation field from pre-read image information, and for actual reading. As disclosed in , it can also be used to limit the reading area within the irradiation field. By limiting the reading area for the main reading to the irradiation field in this way, noise components due to scattered radiation recorded outside the stimulable phosphor sheet can be read. You can get a great final image without any problems. Furthermore, by narrowing down the reading area, it is possible to shorten the reading time or increase the reading density.

Further, the method of setting reading conditions and image processing conditions based on image information within the irradiation field is not limited to the method described above, and various methods can be used.

Note that the determination of reading conditions and image processing conditions is not limited to the case where decisions are made based only on the image information within the above-mentioned irradiation field. It can also be determined by taking into account the imitation method such as 11 pure, contrast imaging, tomography, enlarged Oka imaging, or the purpose of diagnosis.

The present invention can be modified in various ways without departing from the spirit thereof, and is not limited to the embodiments described above.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of a stimulable phosphor sheet and the contour of the irradiation field on the sheet, and Figure 2 is an enlarged view of the Δ section in Figure 1, showing digital image data at each position. figure,
Figure 3 is a partial diagram of the differential image, and Figure 3 (a>
is one-dimensionally differentiated in the
) is a differential image obtained by one-dimensional first-order differentiation in the y direction, Figure 3 (C
) is a diagram showing a differential image obtained by two-dimensionally differentiated in the x and y directions.
i Ita Template Example Diagrams, Figures 5 and 6
Each figure is a partially enlarged view of a multivalued image template. 10... Recording medium (stimulable phosphor sheet) 12...
Multivalued image template 14... Portion corresponding to the irradiation field contour 16... Other portion 4th line Figure 5 Figure 6 fc

Claims (1)

[Scope of Claims] A method for recognizing an irradiation field in a case where radiation image information is recorded on a recording medium by applying an irradiation field aperture, the method comprising: The image data is obtained at each position, and this image data is subjected to differential processing to create a differential image consisting of the differential values at each position. A multi-valued image template in which the position and each position in other parts have different values, and the shape and size of the part corresponding to the irradiation field outline is the shape of the irradiation field outline at various irradiation field apertures that can be used for actual imaging. A large number of templates with various sizes are prepared, and the correlation between the differential value on the differential image or the value obtained by processing this differential value and the value on each of the templates is calculated, and the irradiation field is determined in the template with the largest correlation. An irradiation field recognition method characterized by recognizing that the inside of a contour corresponding portion is an irradiation field.