JP2532883B2 - Irradiation field correctness determination method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a case where one or a plurality of irradiation field candidate regions are present on a recording medium such as a stimulable phosphor sheet on which radiation image information is recorded. The present invention relates to an irradiation field correctness determination method for determining whether or not those irradiation field candidate regions are correct irradiation field candidate regions.

(Prior Art) Radiation (X rays, α rays, β rays, γ rays,
When irradiated with 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 is stimulated according to the accumulated energy. It is known to emit light, and a phosphor having such a property is called a storage phosphor.

Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded (photographed) on a sheet-shaped stimulable phosphor, and then this stimulable phosphor sheet is excited by laser light or other excitation light. Scanning produces stimulated emission light, this stimulated emission light is photoelectrically read to obtain an image signal, this image signal is subjected to image processing, and the radiation of the subject is based on the image signal subjected to this image processing. The applicant has already proposed a radiation image information recording / reproducing system for outputting an image as a visible image on a recording material such as a photographic light-sensitive material or a display device such as a CRT (Japanese Patent Laid-Open Nos. 55-12429 and 56-56). No. 11395).

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 in accordance with each captured image, 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. The "read-ahead" is performed to read the abbreviation of the information, and the reading condition (the reading condition when performing the main reading referred to here) is based on the image signal (hereinafter referred to as the "read-ahead image signal") obtained by the pre-reading. However, there is a method of determining the reading gain, scale factor, etc., and image processing conditions (gradation processing conditions, spatial frequency processing conditions, etc.).

Various methods are conceivable as a specific method for determining the reading condition based on the preread image signal, and as one example thereof, for example, Japanese Patent Application Laid-Open No. 60-156055 filed by the applicant of the present invention.
As described in Japanese Patent Publication, a histogram of the pre-read image signal is created, the maximum image signal level Smax and the minimum image signal level Smin of the desired image signal range are obtained from the histogram, and the reading is performed by using this Smax, Smin. A method for determining the conditions can be mentioned. Further, various methods are conceivable as specific methods for determining image processing conditions based on the prefetch image signal, for example, gradation processing conditions.For example, Smax and Smin are obtained in the same manner as above, and Smax and Smin are calculated as follows. It is conceivable to determine the gradation processing condition by utilizing it.

Further, a case may be considered in which image processing conditions such as gradation processing conditions are determined based on an image signal obtained by the above-mentioned main reading (hereinafter referred to as a main reading image signal). It is conceivable that the above Smax and Smin are obtained from the signal histogram and the Smax and Smin are used to make the determination.

By the way, in order not to irradiate the part that is not necessary for humanitarian diagnosis with radiation, or when irradiating the part that is not necessary for diagnosis with radiation, scattered radiation enters from that part to the part necessary for diagnosis, and the contrast resolution decreases. In order to prevent this, it is often preferable to narrow down the radiation irradiation field when recording the radiation image information. However, when the irradiation field of radiation is narrowed down in this way, normally, scattered rays generated from the subject in the irradiation field are incident outside the irradiation field on the stimulable phosphor sheet. Means that the image signal (noise) based on this scattered ray is also included. As a result, even if the reading condition and the image processing condition are determined based on the image signal containing such noise, for example, the histogram, they are appropriately determined. Is difficult.

Therefore, it is desirable to recognize the position of the irradiation field when the radiation image information is recorded by narrowing down the irradiation field and determine the reading condition and the image processing condition based on only the image signal in the irradiation field. Based on the findings, the applicant has already proposed many irradiation field recognition methods (Japanese Patent Laid-Open No. 61-39039).
Gazette, gazette 62-15536 gazette, gazette 62-15537-15541 gazette etc.).

(Problems to be Solved by the Invention) However, even if an irradiation field is detected by any of the various irradiation field recognition methods described above, it is not always possible to always uniquely detect the irradiation field. That is, a plurality of irradiation field candidate regions may be detected.

Considering the case where a plurality of such irradiation field candidate regions are detected, the following cases can be considered.
The first is a case where all of the plurality of irradiation field candidate regions are not correct, that is, does not match the true irradiation field, and the second is only one of the plurality of irradiation field candidate regions is correct, that is, matches the true irradiation field. In the third case, the number of true irradiation fields is one, and in the third case, two or more of the plural irradiation field candidate areas are correct, that is, two or more irradiation field candidate areas are all true. In the fourth case, for example, the recording area on the stimulable phosphor sheet is divided into a plurality of sections, and the irradiation field is narrowed down for each section to perform imaging. When there are two or more true irradiation fields, two or more of the plurality of irradiation field candidate areas are correct, that is, each of the two or more irradiation field candidate areas matches each true irradiation field. It is a case that is very close

Therefore, when a plurality of irradiation field candidate areas are detected as described above, it is necessary to determine whether or not each irradiation field candidate area is a correct candidate area in the above meaning.

Even if there is only one irradiation field detected by the irradiation field recognition method, it may be incorrect in some cases. Therefore, it is similarly determined whether or not it is a correct candidate area. It may be desired to do so.

Further, in addition to the case where the irradiation field candidate area is detected by the irradiation field recognition method, one or a plurality of predicted irradiation field candidate areas may be arbitrarily set on the recording medium to judge whether or not they are correct. Conceivable. If an irradiation field candidate region determined to be correct is obtained by this method, the irradiation field can be detected without using the irradiation field recognition method as described above.

In view of the above circumstances, an object of the present invention is to provide an irradiation field correctness determination method capable of determining whether or not one or a plurality of irradiation field candidate regions existing on a recording medium are correct. To provide.

(Means for Solving Problems) In order to achieve the above-mentioned object, the irradiation field correctness determination method according to the present invention is performed within the irradiation field candidate area on the recording medium for each of one or more irradiation field candidate areas. The class separation degree η used in the discriminant analysis regarding the image signal of and the image signal outside the irradiation field candidate area is calculated, and the irradiation field candidate area in which the class separation degree η is equal to or more than the predetermined threshold value is correct It is characterized in that the irradiation field candidate region having a value smaller than the threshold value is determined to be erroneous.

The above-mentioned "recording medium" means a medium capable of recording radiation image information, and specific examples thereof include the above-mentioned stimulable phosphor sheet, but the recording medium is not necessarily limited thereto.

The "image signal" means a signal obtained by reading the image information recorded on the recording medium by some method, and means, for example, the pre-reading or main-reading image signal in the above-mentioned and stimulable phosphor sheet, but not necessarily. It is not limited to them.

The above-mentioned "when one or more irradiation field candidate regions exist" means that one or more irradiation fields (irradiation field candidate regions) are detected by the irradiation field recognition method as described above, and it is arbitrarily 1 This also includes the case where one or a plurality of irradiation field candidate areas are set.

The “class separation degree η” is a discrimination criterion used in discriminant analysis, and this class separation degree η is a discrimination criterion (=
In addition to the class separation degree η) itself, a criterion equivalent to this discrimination criterion (which is mathematically equivalent and the same result can be obtained), for example, a least squares criterion or a correlation criterion may be considered (as a representative). . Regarding the discrimination criterion and the least-squares criterion, refer to "The Institute of Electronics and Communication Engineers of Japan '80 / 4 Vol.J63-D No.4
Pp. 49 to 356 ", and the correlation criterion is described in" The Institute of Electronics and Communication Engineers of Japan, '86 / 9 Vol.J69-D No.9, pp. 1355- ".
Pp. 1356 ".

Above "class separation η is greater than or equal to a predetermined threshold"
Means that if the class separation η is the class separation η in the discrimination criterion or is a correlation coefficient in the correlation criterion, they are equal to or greater than a predetermined threshold, and the square in the least squares criterion. If it is an error, it means that it is below a predetermined threshold.

(Operation) The class separation degree η is a value indicating the separability regarding the image signal levels of a plurality of regions when an image is divided into a plurality of regions, and the larger this η, the greater the separability thereof. Means

Further, the irradiation field inside area and the irradiation field outside area in the image are basically an area where the radiation is incident and an area where the radiation is not incident, and they can be extremely clearly separated with respect to the image signal level. Among the two areas, the separability is highest when the area is divided into the irradiation field inside area and the irradiation field outside area.

Therefore, the magnitude of the class separation degree η means how correct each irradiation field candidate region is (match with the true irradiation field).

Therefore, for example, the degree of class separation η for the true irradiation field, that is, the degree of class separation η when the image is divided into a true irradiation field region and a true irradiation field outside region is roughly checked in advance. In other words, based on this value, it is possible to know how much η is greater than or equal to which it is possible to determine that the irradiation field candidate region is correct (matches or is very close to the true irradiation field). it can. Therefore, in this way, the value of η that can be judged to be correct for the irradiation field candidate region is set in advance, and if it is examined whether η of each irradiation field candidate region is larger or smaller than that value, each irradiation field candidate It can be determined whether the area is correct.

(Effect of the invention) The irradiation field correctness determination method according to the present invention determines the class separation degree η in which the magnitude of the value of each irradiation field candidate region means the degree of coincidence with the true irradiation field as described above. Whether or not each irradiation field candidate region is correct is determined by whether or not the class separation degree η is equal to or greater than a predetermined threshold value. Therefore, as described above, by appropriately setting this predetermined threshold value, The correctness of the irradiation field candidate area can be correctly determined.

(Examples) Examples of the present invention will be described below with reference to the drawings.

In the examples described below, the pre-reading image signal carrying the captured image by pre-reading the stimulable phosphor sheet on which the radiation image information is recorded is obtained, that is, the sheet is scanned with the excitation light for pre-reading, The stimulated emission light emitted from the sheet is read by the photoelectric conversion means to obtain a preread image signal composed of an electric signal corresponding to the amount of stimulated emission light at each scanning point (each pixel) on the sheet, and this preread image signal is obtained. In the case where a plurality of irradiation fields (irradiation field candidate regions) are detected as a result of irradiation field detection based on an appropriate irradiation field recognition method based on various irradiation field recognition methods proposed by the applicant of the present application, The present invention is applied to the case of determining the correctness of a plurality of irradiation field candidate regions.

The figure shows a stimulable phosphor sheet with radiation image information recorded.
10 shows the area where the dashed-dotted line on the sheet 10 indicates three irradiation field candidate regions detected by the irradiation field recognition method.
12a, 12b and 12c are shown.

First, for each irradiation field candidate area 12a, 12b, 12c, the class separation degree η used in the discriminant analysis regarding the pre-reading image signal in the irradiation field candidate area on the sheet 10 and the pre-reading image signal outside the irradiation field candidate area. calculate. This class separation degree η is expressed by the following equation.

η = δ _B ² / δ _T ² δ _B ² = ωi · ωo (μi−μo) ^{2 where} ωi and ωo are the ratio of the number of pixels in the irradiation field candidate area and outside the irradiation field candidate area (all pixels The ratio of the number of pixels in the candidate area and the number of pixels in the candidate area to the number, ωi + ωo = 1), and μi, μo are the average values (average image signal level) of the image signal levels of all the pixels in the candidate area and It is the average value of the image signal levels of all pixels outside the candidate area (average image signal level), and δ _T ² means the variance in the recording area (all areas on the sheet) that combines the inside and outside of the irradiation field candidate area. To do.

In the irradiation field candidate area and outside the irradiation field candidate area, for example, in the case of the irradiation field candidate area 12a, in the one-dot chain line showing the area 12a, that is, the range surrounded by the one-dot chain line is the irradiation field candidate. The area is within the area, and the area outside the one-dot chain line is outside the irradiation field candidate area.

When the class separability ηa, ηb, ηc for each of the candidate regions 12a, 12b, 12c is obtained based on the above equation, then the class separability η is equal to or greater than a preset threshold value Th. It is determined that the irradiation field candidate area is correct and the irradiation field candidate area smaller than Th is incorrect.

As described above, the magnitude of the class separation degree η in each irradiation field candidate area means the degree of matching with the true irradiation field of each irradiation field candidate area. Whether the region can be judged to be correct can be roughly known based on the magnitude of the class separation degree η with respect to the true irradiation field which is experimentally and empirically obtained in advance. Therefore, the value of η that can be judged to be correct is appropriately determined based on the value of the class separation degree η for the true irradiation field, etc., and the class of each irradiation field candidate region is set as a predetermined threshold value. By determining whether or not the degree of separation η is greater than or equal to the predetermined threshold value, it is possible to correctly determine the correctness of each irradiation field candidate region.

As a mode of the determination result, for example, all cases may be incorrect, one is correct, and two or more are correct. If there are two or more, the irradiation field is 1
However, if two or more candidate areas are extremely close to each other, or if there are two or more irradiation fields, and there are two correct candidate areas,
There may be more than one.

The method of using the irradiation field candidate area (irradiation field) determined to be correct according to the present invention is not limited at all,
It can be used for various purposes.
Specifically, for example, when determining the reading condition or the image processing condition based only on the pre-reading image signal in the irradiation field as described above, when determining the image processing condition based on only the main reading image signal in the irradiation field, Can be used, for example, when the reading area for the main reading is limited to the irradiation field, as disclosed in JP-A-60-120346 previously filed by the present applicant.

In the above embodiment, when an irradiation field is recognized by various irradiation field recognition methods, a plurality of irradiation fields (irradiation field candidate areas)
However, even if only one irradiation field appears, the present invention can determine the correctness. Furthermore, the present invention is not limited to such a candidate area, but can be applied to, for example, one or more candidate areas arbitrarily set as described above. In this case, the present invention substantially detects the irradiation field. It will be close to the method.

Although the image signal in the above-described embodiment is the pre-read image signal, the present invention can be applied to the main read image signal as a matter of course, and the image signal read from a recording medium other than the stimulable phosphor sheet may be used. The present invention is applicable.

Although the class separation degree (discrimination criterion) η is used in the above embodiment, a least squares criterion or a correlation criterion equivalent thereto may be used. Further, in the above-described embodiment, the class separation degree η = δ _B ² / δ _T ² , but in one captured image, δ _T
² is the same for all irradiation field candidate regions, so δ _B ²
Needless to say, may be treated as the class separation degree η.

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]

The figure is a plan view showing a stimulable phosphor sheet having a plurality of irradiation field candidate regions. 10: Recording medium (storable phosphor sheet) 12a, 12b, 12c ... Irradiation field candidate area

Claims (1)

(57) [Claims] 1. When one or a plurality of irradiation field candidate regions are present on a recording medium on which radiation image information is recorded,
An irradiation field correctness determination method for determining whether or not those irradiation field candidate areas are correct, wherein an image signal in the irradiation field candidate area on the recording medium and an area outside the irradiation field candidate area are provided for each of the irradiation field candidate areas. Class separation η used in discriminant analysis with respect to the image signal of
It is characterized in that an irradiation field candidate area having the class separation η equal to or greater than a predetermined threshold value is correct, and an irradiation field candidate area having a class separation degree η smaller than the predetermined threshold value is determined to be incorrect. Irradiation field correctness determination method.