JPH0666855B2 - Irradiation field detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention detects an irradiation field when radiation image information is recorded by narrowing the irradiation field on a recording medium such as a stimulable phosphor sheet. The present invention relates to an irradiation field detection device.

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

Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded on a sheet-shaped stimulable phosphor, and then this stimulable phosphor sheet is scanned with excitation light such as laser light. The stimulated emission light is generated, the stimulated emission light is photoelectrically read to obtain an image signal, the image signal is subjected to image processing, and a radiation image of the subject is photographed based on the image signal subjected to the image processing. A radiation image information recording / reproducing system for outputting a visible image on a recording material such as a photosensitive material or a display device such as a CRT has already been proposed by the present applicant (Japanese Patent Laid-Open Nos. 55-12429 and 56-11395, etc.). ).

In the above system, in order to improve the observation and interpretation suitability of a visible image, when photoelectrically reading the stimulated emission light or when performing image processing on the image signal, it is determined according to each captured image. It is desirable to perform the reading and the image processing based on the optimum reading condition and the image processing condition.

As a method for optimally determining the above-mentioned reading conditions and image processing conditions such as gradation processing conditions according to individual photographed images, it is disclosed in Japanese Patent Application Laid-Open No. 58-67240 previously filed by the present applicant. “Read-ahead”, that is, a stimulable phosphor sheet on which radiation image information is stored and recorded is scanned by excitation light, and the stimulated emission light emitted from the sheet by this scanning is read by a photoelectric reading means for diagnosis. Prior to "main reading" for obtaining an electrical image signal for reproducing a visual image, the sheet is scanned with the excitation light of a lower level than the excitation light used for the main reading, and the image stored and recorded on the sheet is recorded in advance. "Pre-reading" for reading an outline of information, and determining the reading conditions (the reading conditions when performing the main reading here) and the image processing conditions based on the image information obtained by the pre-reading. There is.

As a specific method of determining the reading conditions in the main reading based on the image information obtained by such pre-reading, for example, described in JP-A-60-156055 filed earlier by the present applicant. As described above, the histogram of the image information (image signal level) obtained by pre-reading is obtained, and the maximum image signal level Smax and the minimum image signal level Smin of the desired image information range in this histogram are obtained from this histogram. Are read conditions for the main reading so as to correspond to the maximum signal level Qmax and the minimum signal level Qmin of the desired input signal range in the image processing means, which are determined by the maximum density Dmax and the minimum density Dmin of the appropriate density range in the visible output image, respectively. A method of determining can be considered.

Further, as a specific method for determining the image processing condition, for example, the gradation processing condition, based on the image information obtained by the prefetch, for example, the same method as described above, that is, the image information obtained by the prefetch (image signal level) Of the desired image information range Smax and the minimum image signal level Sm in the desired image information range in this histogram.
In, Smax and Smin are the maximum density Dmax and the minimum density of the proper density range in the visible output image, respectively.
A method is conceivable in which the gradation processing condition is determined so as to correspond to the maximum signal level Rmax and the minimum signal level Rmin of the desired input signal range in the image reproducing means (visible image output means) determined by Dmin.

The image processing conditions such as the gradation processing conditions can be determined not only based on the image information obtained by the pre-reading but also based on the image information obtained by the actual reading,
Even in that case, for example, a histogram of image information (image signal level) obtained by the main reading is created as in the case described above, and the Smax and Sm are calculated from the histogram.
A method is conceivable in which in is obtained and gradation processing conditions are determined so that Smax and Smin correspond to Rmax and Rmin, respectively.

In the above description, the reading condition refers to various relationships that affect the relationship between the input and the output in the reading means, for example, the relationship between the input (stimulated luminescence amount) and the output (electrical image signal level) in the photoelectric reading means. This is a general term for the conditions, and means, for example, a read gain (sensitivity), a scale factor (latitude) that determines the input / output relationship, or the excitation light power in reading.

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

Furthermore, in the above, the excitation light used for pre-reading is at a lower level than the excitation light used for main reading, and the effective energy of the excitation light that the stimulable phosphor sheet receives per unit area during pre-reading is during the main reading. Means smaller than that of.

(Problems to be solved by the invention) By the way, in order not to irradiate a part which is not necessary for humanitarian diagnosis with radiation, or when a part which is not necessary for diagnosis is irradiated with radiation, the part is scattered to a part necessary for diagnosis. In order to prevent the line from entering and the contrast resolution being lowered, it is often preferable to narrow down the irradiation field of radiation at the time of recording the radiation image information. However, when the irradiation field of radiation is narrowed in this way, normally, scattered radiation generated from a subject in the irradiation field is incident outside the irradiation field on the stimulable phosphor sheet, and the highly sensitive stimulable phosphor sheet is Since this scattered ray is also accumulated and recorded, the image signal level based on this scattered ray is included in the histogram of the image information (image signal level) obtained by the pre-reading. Since the image signal level outside the irradiation field on the sheet based on this scattered radiation may be higher than the image signal level inside the irradiation field, the image signal levels inside and outside the irradiation field should be distinguished from the obtained histogram. It is difficult. Therefore, as described above, Smax, S
When obtaining the min and determining the reading conditions from this, the minimum value of the image signal level inside the irradiation field should originally be Smin, but the minimum value of the image signal level due to scattered radiation outside the irradiation field may be set to Smin. obtain. Then, when the minimum value of the image signal level outside the irradiation field is set to Smin in this way, since the value is generally lower than the minimum value of the image signal level inside the irradiation field, the scattered radiation unnecessary for diagnosis in the main reading is reduced in concentration. Since the image is recorded in the area, the density of the image of the portion necessary for diagnosis becomes too high, and as a result, the contrast decreases, making it difficult to perform a satisfactory diagnosis.

That is, when shooting is performed with the irradiation field narrowed down, scattered rays generated from the subject enter the outside of the irradiation field on the sheet,
Since the image information obtained by the pre-reading also includes information based on this scattered radiation, even if the reading conditions are determined based on such pre-reading image information, the optimum reading conditions cannot be determined. It is difficult, and as a result, it becomes difficult to obtain a visible image with excellent suitability for observation and interpretation.

Further, such a problem is not limited to the case where the reading condition is determined based on the prefetch image information, but is also the case where the image processing condition such as the gradation processing condition is determined based on the prefetch image information or the prefetch image information. Can also exist.

Therefore, when trying to determine the reading condition or the image processing condition based on the pre-reading or the actual reading image information by the method as described above, the irradiation field is accurately detected when the imaging is performed with the irradiation field diaphragm, It is desirable to determine those conditions based on only the image information in the irradiation field in the pre-reading or main reading image information and eliminate the above-mentioned adverse effects of scattered rays outside the irradiation field.

The above is an example of the necessity of irradiation field detection when deciding the reading conditions and the like using the stimulable phosphor sheet, but this irradiation field detection is not limited to such cases, and other various cases It can also be needed.

In view of the above circumstances, an object of the present invention is to provide an irradiation field detection device which detects an irradiation field when radiation image information is recorded by recording the irradiation field on a recording medium such as a stimulable phosphor sheet. To do.

(Means for Solving Problems) In order to achieve the above-mentioned object, the irradiation field detection apparatus according to the present invention has a function of recording on a recording medium from image information read from a recording medium such as a stimulable phosphor sheet that has been photographed. Differential image creating means for obtaining image data at each position and differentiating the image data to create a differential image composed of differential values at the above-mentioned positions; Is a multi-valued image template having different values for each position in the other field and each position in the other field, and the shape and size of the field corresponding to the field contour can be used for actual imaging. Template storage means for storing a large number of different templates according to the shape and size of the contour, a differential value on the differential image or a value obtained by processing the differential value and each template. A correlation computing means for finding a correlation between the value of the rate, characterized in that it comprises an irradiation field detection means for detecting the inside of the irradiation field contour corresponding portion of the correlation is the largest template as irradiation field.

The above-mentioned “recording medium” means a medium on which radiation image information can be recorded, and the above-mentioned stimulable phosphor sheet can be mentioned as a specific example, but it is not necessarily limited thereto. Further, the "image information read from the recording medium" in the above means that the image information recorded in the recording medium is read by some method, for example, by pre-reading or main reading in the above-mentioned stimulable phosphor sheet. It means the obtained image information,
It is not necessarily limited to them.

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

(Effect of the Invention) The apparatus according to the present invention performs differential processing on image data as described above to create a differential image composed of differential values at each position, and also stores a large number of templates as described above. The correlation between the above differential value or the value obtained by processing the differential value and the value on each template is obtained, and the inside of the irradiation field contour corresponding portion in the template having the largest correlation is detected as the irradiation field.

In the differential image, the differential value at each position where the irradiation field contour exists or the value obtained by processing the differential value becomes larger than the differential value at another position or the processed value. Therefore,
In the case of the template in which the irradiation field contour is located in the irradiation field contour corresponding portion of the template (for example, a value of 1 or more is given to each position in this portion, and 0 is given to the other portions) Since the similarity between the differential image and the template (for example, the sum of the products between the differential image and the template) is much larger than that of the other template, the irradiation field of the template having the maximum similarity is obtained. The inside of the contour corresponding portion can be detected as the actual irradiation field.

Therefore, according to the above-mentioned device of the present invention, it is possible to accurately detect the irradiation field when the radiation image information is recorded by applying the irradiation field diaphragm on the recording medium.

Further, the device according to the present invention directly detects the irradiation field based on the differential value obtained by differentiating the image data, that is, based on the image information recorded on the recording medium. The irradiation field can be detected accurately.

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

In the embodiment described below, as shown in FIG. 1, in the stimulable phosphor sheet 10 having one irradiation field photographed with a rectangular irradiation field diaphragm as shown by a chain line, the pre-reading image information is used. The present invention is applied to an apparatus for detecting an irradiation field.

As shown in FIG. 7, the apparatus of this embodiment is a differential image creating means.
20, template storage means 22, correlation calculation means 24,
And an irradiation field detecting means 26.

In the apparatus of this embodiment, first, the differential image creating means
An image to be the target of irradiation field detection is differentiated by 20 to create a differential image. In creating the differential image, first, digital image data at each position on the stimulable phosphor sheet is obtained from the image information obtained by the pre-reading as described above.

The image information obtained by the pre-reading is obtained by reading the stimulated emission light emitted by the pre-reading excitation light scanning by the photoelectric conversion means, each scanning point (that is, each pixel) on the stimulable phosphor sheet Image information consisting of an electric signal corresponding to the amount of stimulated emission light. 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 shown in FIG. 1. Each square in the figure represents one pixel, and f (1, 1), f (1, 2),
…… indicates the digitized version of the above image information in each pixel (1,1), (1,2), .... Further, the x direction in FIGS. 1 and 2 is the main scanning direction, and the y direction is the sub scanning direction.

To obtain digital image data at each position on the sheet from this image information, first set the position on the sheet as shown at S1 and S2 in the flowchart of FIG. Obtain digital image data. This position may be set on a pixel-by-pixel basis, or a plurality of pixels that have a fixed relationship, for example, four pixels vertically (left and right) [(1,1), (1,2), (2,1)] , (2,
2)], [(1,3), (1,4), (2,3), (2,4)], ...
It is also possible to put all of ... into one position. The digital image data at each position in the case of the former means that the image information of the pixel corresponding to the position is digitized,
In the latter case, the digital image data at each position means data determined based on the image information of a plurality of pixels included in that position, for example, digital image data obtained by averaging image information of a plurality of pixels. In this embodiment, this position setting is performed in pixel units.

After the digital image data at each position is obtained as described above, the image data is differentiated as shown at S3 in FIG. The method of differentiation may be one-dimensional first derivative or high-order derivative, or two-dimensional first derivative or higher-order derivative. In the case of discretely sampled images, differentiating is equivalent to obtaining the difference between image data existing in the vicinity. The presence in the vicinity means not only the case where they are adjacent to each other but also the case where they exist every other one.

In the present embodiment, the differential processing by the two-dimensional first differential is performed. That is, first, the digital image data is one-dimensionally first-order differentiated in the x direction to obtain a differential value δ ′ at each position. This δ'is equivalent to the image data difference between the positions adjacent in the x direction, and is expressed by the following equation.

δ ′ (1,1) = f (1,1) −f (1,2) δ ′ (1,2) = f (1,2) −f (1,3) :: δ ′ (2,1 ) = F (2,1) -f (2,2) δ '(2,2) = f (2,2) -f (2,3) :: Similarly, one-dimensional first derivative in the y direction. Then, the differential value δ ″ at each position is obtained. This δ ″ is expressed by the following equation.

δ ″ (1,1) = f (1,1) −f (2,1) δ ″ (1,2) = f (1,2) −f (2,2) :: δ ″ (2,1 ) = F (2,1) −f (3,1) δ ″ (2,2) = f (2,2) −f (3,2) :: and each position in the one-dimensional first derivative of both directions. Based on the differential values δ ′ and δ ″ of, the two-dimensional primary differential value δ at each position is obtained by adding the absolute values of both differential values δ ′ and δ ″. This δ is expressed by the following equation.

δ (1,1) = | δ ′ (1,1) | + | δ ″ (1,1) | δ (1,2) = | δ ′ (1,2) | + | δ ″ (1,2 ) | :: δ (2,1) = | δ ′ (2,1) | + | δ ″ (2,1) | δ (2,2) = | δ ′ (2,2) | + | δ ″ (2,2) | :: The differential value δ at each position on the stimulable phosphor sheet is obtained by performing the differential processing as described above, and a differential image composed of the differential value δ at each position is created. Although the differential value δ is always positive in the above embodiment, for example, when a differential image is created by one-dimensional primary differential processing, the differential calculated value may be negative depending on the position on the sheet. Treats the absolute value of the calculated value as the differential value on the differential image. Further, in the above embodiment, a differential image is created by using the obtained differential value δ itself, but the differential image in the present invention is created by binarizing the differential value δ with a predetermined threshold value. It may be.

After the differential image is created, the correlation calculating means 24 then stores the differential image and a large number of multivalued image templates prepared in advance, that is, the template storing means 22, as shown in S4 of FIG. Correlation with many multi-valued image templates is obtained.

FIGS. 4A to 4G show examples of a large number of multi-valued image templates stored by the template storage means 22. Each template 12 corresponds to the irradiation field contour corresponding portion (shaded lines in the figure). The portion corresponding to the contour,
For example, each position in 14 is given a value of 1 or more, each position in the other part 16 is given a value of 0, and
The shapes and sizes of the 12 irradiation field contour corresponding portions 14 are different depending on the shapes and sizes of the irradiation field contours in various irradiation field diaphragms that can be used for actual imaging.

The size of the template 12 itself depends on the stimulable phosphor sheet 10
The size of the (differential image) is preferably the same, but it may be different. The irradiation field contour corresponding portion 14 has a predetermined width t. The width t may be two positions, three positions, one position, or four positions or more, as shown in FIGS. 5 and 6 described below. The shape of the portion corresponding to the irradiation field contour refers to the rectangle in FIGS. 4 (a) and 4 (b) or the circle in FIGS. 4 (c) and 4 (d), and the size is the length of one side of the rectangle or the circle. The diameter, etc. Figure 4 (e),
FIG. 4 (g) shows a case where the aperture diaphragm is photographed at an oblique aperture, and FIG. 4 (g) is a circular diaphragm and is divided into photographs (one stimulable phosphor sheet is divided into a plurality of sections and the respective sections are photographed respectively). It is a template having an irradiation field contour corresponding portion 14 corresponding to the irradiation field contour in the case. Although each position on the template 12 corresponds to each position on the differential image, it does not necessarily have to correspond one-to-one, and for example, one position on the template is adjacent to the top, bottom, left, and right on the differential image.
It may be one corresponding to one position. A value of 1 or more is given to each position in the irradiation field contour corresponding portion 14, and as a mode thereof, for example, one kind of value, that is, only 1 may be given as shown in FIG. 2 as shown in FIG.
The type value, that is, 2 may be added to the center and 1 to both sides. Of course, three or more types of values may be given,
In addition, the manner in which a plurality of types of values are added may be appropriately determined.

Obtaining the correlation between the differential image and each template image means, for example, quantifying the degree of similarity between images by an operation as described below. That is, in the present embodiment, the differential value on the differential image (including both the case of the differential value itself and the case of binarization) and the value on the prepared template are multiplied at the same position. Find the sum of the products. When the position on the differential image and the position on the template have a one-to-one correspondence, the corresponding values on the same position are multiplied, and for example, as described above, the four positions on the differential image are on the template. When corresponding to one position, each differential value on the four positions is multiplied by the value on one position on the template. When the multiplication for each same position is performed for the entire template, the respective products are summed.

After the correlation between the differential image and each template image is obtained as described above, the irradiation field detecting means 26 then compares the correlation, that is, the sum of the products, as shown in S5 and S6 of FIG. The lowest value of the sum of products is selected, and the inside of the portion corresponding to the irradiation field contour of the template having the maximum sum of products is detected 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 has a high quantum level. Therefore, the difference between the image data comrades of the part where the irradiation field contour is located generally has a larger quantum level than the difference of the image data comrades of other parts, so the differential value of each position where the irradiation field contour exists on the differential image. Is larger than the derivative value at other positions, and as a result, the sum of the above products in the case of the template in which the irradiation field contour is located exactly in the irradiation field contour corresponding portion 14 of the template is greater than the sum of the products in the case of other templates. Will naturally grow. Therefore, a large number of templates having irradiation field contour corresponding portions according to various shapes and sizes of expected irradiation field contours are prepared, and the above-described multiplication is performed between the differential image and each of the templates. When the total sum of the products is compared and the template having the maximum total is found, it means that 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 exists. (When the portion 14 has a certain width, it may be located at any position in the portion 14, for example, from the inner edge, the outer edge or the center of the width portion) Can be detected as

In the above embodiment, the case where one irradiation field is present on one stimulable phosphor sheet 10 is dealt with (the above-mentioned fourth embodiment).
The present invention is also applicable to the case of so-called divisional imaging, in which one sheet is divided into two sections and an irradiation field stop is applied to each section, for example, except for the case of the template of FIG. It is possible. That is, even in the case of divided photographing, if each section is considered as one sheet, one irradiation field exists on that one sheet, and therefore the present invention can be realized by obtaining information that divided photographing is performed in advance. It suffices to apply it to each of the categories.

The irradiation field detected as described above can be used for various purposes. For example, only the image information in the irradiation field is extracted from the pre-reading or main reading image information as described above, and the reading conditions and the image processing conditions are based on it (only the image processing conditions when the irradiation field is recognized based on the main reading image information). Of course, it can be used for other purposes, for example, by recognizing the irradiation field from the pre-reading image information, and during the main reading, the applicant previously filed JP-A-60-120346. It is also possible to limit the reading area to the irradiation field, as disclosed in US Pat. Thus, by limiting the reading area of the main reading to the inside of the irradiation field, the noise component due to the scattered radiation recorded outside the irradiation field of the stimulable phosphor sheet can be read. And an excellent final image can be obtained. Further, by narrowing the reading area, it is possible to shorten the reading time or increase the reading density.

Further, the method of setting the reading condition and the image processing condition based on the image information in the irradiation field is not limited to the above-mentioned method, and various methods can be used.

Note that the determination of the reading condition and the image processing condition is not limited to the case of determining only based on the image information in the irradiation field, and the head, chest, abdomen, and the like of the subject to be imaged and simple, It can also be determined in consideration of imaging methods such as contrast enhancement, tomography, and magnifying imaging, or diagnostic purposes.

The present invention can be modified in various ways within the scope of the invention, and is not limited to the above-mentioned embodiments.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a stimulable phosphor sheet and an irradiation field contour on the sheet, FIG. 2 is an enlarged view of part A in FIG. 1, showing digital image data at each position, FIG. The figure is a diagram showing a part of the differential image. FIG. 3 (a) is a differential image obtained by one-dimensional primary differentiation in the x direction, and FIG. 3 (b) is a differential image obtained by one-dimensional primary differentiation in the y direction. Figure 3 (c)
The figure which shows the differential image which carried out the two-dimensional primary differential in the x and y directions, the 4th
FIGS. 5A to 5G are views showing examples of multi-valued image templates, FIGS. 5 and 6 are partially enlarged views of multi-valued image templates, and FIG. 7 is one embodiment of the apparatus according to the present invention. FIG. 8 is a block diagram showing an example, and FIG. 8 is a flowchart showing an operating procedure of the apparatus shown in FIG. 10 …… Recording medium (storable phosphor sheet) 12 …… Multi-valued image template 14 …… Field corresponding to irradiation field contour 16 …… Other part 20 …… Differential image creating means 22 …… Template storage means 24 …… Correlation Calculation means 26 ... Irradiation field detection means

Claims (1)

[Claims] 1. An irradiation field detection device for detecting the irradiation field when the radiation image information is recorded on a recording medium by narrowing the irradiation field, the recording being performed based on the image information read from the recording medium. Differential image creating means for obtaining image data at each position on the medium and differentiating the image data to create a differential image composed of the differential values at the respective positions; and an irradiation field contour corresponding portion having the irradiation field contour corresponding portion. A multi-valued image template in which each position in the corresponding part and each position in the other part have different values, and the shape and size of the corresponding part of the irradiation field contour in various irradiation field diaphragms that can be used for actual imaging. Template storage means for storing a large number of different templates according to the shape and size of the irradiation field contour, and a differential value on the differential image or a value obtained by processing the differential value. It is characterized by comprising a correlation calculation means for obtaining a correlation with a value on each template, and an irradiation field detection means for detecting as an irradiation field the inside of the irradiation field contour corresponding portion in the template having the largest correlation. Irradiation field detection device.