JPH0279177A - Method and detecting contour of breast in radiation picture - Google Patents

Abstract

PURPOSE:To accurately recognize the contour of a breast by finding plural candidate points which are considered to be on the contour and approximating the contour of the breast to a circle or polygon extended along the candidate points. CONSTITUTION:In a radiation picture photographing section 20, a cassette 104 housing an accumulating phosphor sheet 103 is placed on a photographing table 105 and a breast 101 which is an object is put on the cassette 104 in a state where the breast 101 is pressed against the cassette 104 from the top by means of a press plate 106 of an acrylic plate, etc., and becomes flat. The breast 101 which is pressed in such state is recorded in the form of a half circle (proper circle or ellipse). Therefore, plural candidate points which are considered to be on the contour of the breast 101 are detected and a circle extended along the candidate points is found by approximation as the contour of the breast 101. Thus the contour of the breast can be detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for detecting the outline of a breast in a radiographic image of the breast.

(Prior art) When a certain type of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated in the phosphor, and this It is known that when a phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy. It is called an exhaustible phosphor).

Using this stimulable phosphor, radiation image information of the human body, etc. is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence light. The resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image is output as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT. An image information recording and reproducing system has already been proposed by the applicant. (Unexamined Japanese Patent Publication No. 55-124
No. 92, No. 5B-11395, etc. ) In this system, in order to eliminate the influence of fluctuations in imaging conditions or to obtain radiographic images with excellent observation and interpretation suitability, it is necessary to Recording patterns (hereinafter collectively referred to as "accumulated recorded information") determined by the part of the subject such as the abdomen, the imaging method such as plain radiography or contrast radiography, etc. are visualized for observation and interpretation. It is determined before the image is output, and the reading gain is adjusted to an appropriate value based on the acquired recorded information, and the recording scale factor is determined so that the resolution is optimized according to the contrast of the recorded pattern. It is desirable to do so.

As a method for grasping the accumulated record information of radiographic images before outputting visible images, Japanese Patent Laid-Open No. 58-67240
The method disclosed in No. This method uses excitation light of a lower level than the excitation light that should be irradiated during the reading operation (hereinafter referred to as "main reading") to obtain a visible image for observation and interpretation. Perform a reading operation (hereinafter referred to as "pre-reading") to understand the accumulated record information of the radiation image stored and recorded on the stimulable phosphor sheet, grasp the outline of the accumulated record of the radiation image, and perform the main reading. At this time, the reading gain is appropriately adjusted, the recording scale factor is determined, or the signal processing conditions are determined based on this pre-read information.

Various methods have been considered for grasping the accumulated record information of a stimulable phosphor sheet from the pre-read image signal obtained by the above-mentioned pre-reading, and one such method is to create a histogram of the pre-read image signal. method is known. In other words, since it is possible to grasp the accumulated recording information from this histogram, for example, the signal maximum value, minimum value, signal value at the maximum frequency point, etc., the reading conditions such as the reading gain and recording scale factor can be determined based on this histogram. By determining the image processing conditions, it becomes possible to reproduce radiation images with excellent diagnostic suitability.

Furthermore, as shown in, for example, Japanese Patent Application Laid-Open No. 63-31840, a method has been proposed in which a radiation image with excellent diagnostic suitability can be obtained without performing the above-mentioned pre-reading. In this method, radiation image information is read by widening the photostimulated light detection range, the above-mentioned accumulated record information is grasped from the read image signal obtained thereby, and this image signal is grasped based on that. The conversion process is performed so that the accumulated recorded information becomes equivalent to a read image signal obtained when reading is performed with optimally set reading conditions.

By the way, when taking a radiograph of the human breast, the breast is pressed and held between two holding members (usually one of which is a cassette containing a radiation image recording medium), and the image is taken in a nearly flat state. be. At this time, in order to prevent radiation from being irradiated to areas that are not necessary for diagnosis, it is recommended to focus the radiation irradiation field into an approximately semicircular shape for the entire recording area of the recording medium such as the stimulable phosphor sheet. Common. An example of a radiation image of a breast taken in this manner is shown in FIG. 103 in the figure is a stimulable phosphor sheet as an example of a radiation image recording medium. In addition, B in the figure shows the outline of the radiation irradiation field, the upper side is the outside irradiation area, the lower side is the irradiation field area, and the shaded area is the direct radiation irradiation area (so-called bare area). .

(Problems to be Solved by the Invention) However, as described above, the radiation irradiation field is narrowed down to the image recording area of the stimulable phosphor sheet 103,
Then, when performing the above-mentioned pre-reading and the above-mentioned conversion processing, the reading is performed in an area that is considerably larger than the irradiation field (for example, the sheet 10
3), a problem arises in that the stored recorded information regarding the breast actually recorded within the irradiation field is erroneously grasped. In other words, in the above case, the histogram is formed including the read image signals for the area outside the radiation irradiation field, so this histogram does not accurately reflect the actual accumulated recorded information within the radiation field. It is.

The above problem is caused by the subject area (breast area) within the radiation irradiation field.
This problem can be solved by recognizing the area and grasping the accumulated record information only for this recognition area. In order to recognize the breast region in this way, it is first necessary to detect the outline of the breast in a radiographic image. This breast contour can be detected, for example, by a method such as that disclosed in Japanese Patent Application Laid-open No. 170178/1983, but such conventional methods sometimes result in erroneous detection of the breast contour.

Therefore, the present invention provides, as described above, in a radiographic image taken of a breast pressed and held between two holding members,
It is an object of the present invention to provide a method that can accurately detect breast contours.

(Means and effects for solving the problem) In the breast contour detection method in a radiographic image of the present invention, the breast that is pressed and held as described above has a round shape (a perfect circle or an ellipse) as shown in FIG. It was obtained by focusing on the fact that the image is recorded in a shape that divides the breast into two, and it detects multiple candidate points that are thought to exist on the contour of the breast and approximates a circle that extends along these candidate points. This circle is then detected as the outline of the breast.

Of course, the breast held as described above does not have a shape that is exactly a part of a perfect circle or an ellipse. Therefore, some parts of the breast contour detected by the above method may protrude outward 17 from the actual breast contour, while some parts may retract inward. However, as mentioned earlier, in order to understand the accumulated record information of the breast area, even if the inside of the contour where there is such a coming and going in and out of the real object is regarded as the subject area (breast area), the image within that area The general accumulated record information indicated by the set of signals is almost the same as the actual accumulated record information in the subject area, and poses no practical problem.

Furthermore, based on the above findings, the present invention provides another breast contour detection method, which includes:
This method is characterized in that a polygon extending along the aforementioned candidate points is approximately found and this polygon is detected as a breast contour.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a radiation image information recording and reproducing system that detects breast contours using the method of the present invention. This radiation image information recording and reproducing system basically consists of:
It is composed of a radiation image capturing section 20, a pre-reading reading section 30, a main reading reading section 40, and an image reproduction section 50. In the radiographic imaging unit 20, a cassette 104 containing a stimulable phosphor sheet 103 as described above is placed on an imaging table 105, and a breast 101 as a subject placed on this cassette 104 is , is pressed from above by a pressing plate 106 made of an acrylic plate or the like, and held in a nearly flat state. Radiation 102 is emitted from a radiation source 100, such as an X-ray tube, placed above the imaging table 105 toward the breast 101 through a cone cylinder 108 having a semicircular cross section. The radiation 102 that has passed through the breast is irradiated onto the stimulable phosphor sheet 103, whereby transmitted radiation image information of the breast 101 is stored and recorded on the sheet 103.

The image recording state on the stimulable phosphor sheet 103 on which the radiation image has been taken in this manner is as shown in FIG. 2 above. In other words, there is a semicircular irradiation field, within which there is a background area J (radiation direct irradiation area: the shaded area in the figure) and a subject area K. Outside the irradiation field, there is light scattered by the subject. There is a portion that has been irradiated with radiation (the portion marked with fine dots in the figure).

The stimulable phosphor sheet 103 on which the radiation image information of the subject 101 has been recorded in this manner is sent to the pre-reading reading section 30 by sheet transport means 110 such as a transport roller. In the pre-reading reading section 30, the pre-reading laser light source 2
The laser beam 202 emitted from the laser beam 2
A filter 2 that cuts the wavelength range of stimulated luminescence light emitted from the stimulable phosphor sheet 103 by excitation of 02
03, the light is linearly deflected by a light deflector 204 such as a galvanometer mirror, and is incident on the stimulable phosphor sheet 103 via a flat reflecting mirror 205. Here, the laser light source 201 is selected so that the wavelength range of the laser light 202 as excitation light does not overlap with the wavelength range of the stimulated luminescence light emitted by the stimulable phosphor sheet 103. On the other hand, the phosphor sheet 103 is moved by a sheet transport means 21 such as a transport roller.
0, the phosphor sheet 103 is moved in the direction of the arrow 20B for sub-scanning, and as a result, the entire surface of the phosphor sheet 103 is irradiated with the laser light 202. Here, the emission intensity of the laser light source 201, the beam diameter of the laser light 202, the laser light 202
The scanning speed of the stimulable phosphor sheet 103 and the transport speed of the stimulable phosphor sheet 103 are as follows.
The energy of the excitation light (laser light 202) for pre-reading is selected to be smaller than that for main reading performed in the main reading reading unit 40, which will be described later.

When irradiated with the laser beam 202 as described above, the stimulable phosphor sheet 103 emits stimulated luminescent light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light is transmitted to the pre-reading light guide 207. incident on . The stimulated luminescence light is guided through the light guide 207, exits from the exit surface, and is received by a photodetector 208 such as a photomultiplier. A filter is attached to the light receiving surface of the photodetector 208, which transmits only light in the wavelength range of stimulated luminescence light and cuts light in the wavelength range of excitation light, and detects only stimulated luminescence light. It is now possible to do so. The detected stimulated luminescence light is converted into an electrical signal carrying accumulated recording information, and is sent to an amplifier 2.
09. The signal output from the amplifier 209 is digitized by the A/D converter 211 and inputted to the main reading control circuit 814 of the main reading reading section 40 as a pre-read image signal sp. This book reading control circuit 314 is
Based on the accumulated recording information indicated by the pre-read image signal Sp, the reading gain setting value a1 recording scale factor setting value b1
Determine reproduction image processing condition setting value C. The pre-read image signal Sp is also input to a subject recognition circuit 220, which will be described in detail later.

The stimulable phosphor sheet 103 whose pre-reading has been completed as described above is transferred to the reading section 40 for main reading.

In the main reading reading section 40, the main reading laser light source 301
The laser beam 302 emitted from this laser beam 302
A filter 303 that cuts the wavelength range of stimulated luminescent light emitted from the stimulable phosphor sheet 103 by excitation of the stimulable phosphor sheet 103.
After passing through the stimulable phosphor sheet 103, the beam diameter is strictly adjusted by a beam expander 304, linearly deflected by an optical deflector 305 such as a galvanometer mirror, and passed through a flat reflecting mirror 306 to the stimulable phosphor sheet 103. incident on the top. There is f between the optical deflector 305 and the plane reflecting mirror 30B.
A θ lens 307 is arranged so that the beam diameter of the laser beam 302 scanning the stimulable phosphor sheet 103 is made uniform. On the other hand, the stimulable phosphor sheet 103 is transported in the direction of the arrow 308 by a sheet transport means 320 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the stimulable phosphor sheet 103 is irradiated with laser light. When irradiated with the laser beam 302 in this manner, the stimulable phosphor sheet 103 emits stimulated luminescence light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light enters the main reading light guide 309. do. Stimulated luminescent light guided through the main reading light guide 309 while undergoing repeated total reflection is emitted from its exit surface and is received by a photodetector 310 such as a photomultiplier. Photodetector 3
A filter that selectively transmits only the wavelength range of the stimulated luminescent light is attached to the light receiving surface of the photodetector 310 so that the photodetector 310 detects only the stimulated luminescent light.

The output of the photodetector 310 that photoelectrically detects the stimulated luminescent light representing the radiation image recorded on the stimulable phosphor sheet 103 has a read gain based on the read gain setting value a determined by the control circuit 314. The electric signal is amplified to an appropriate level by the amplifier 311 set to . The amplified electrical signal is input to the A/D converter 312, and based on the recording scale factor setting value, it is converted into a digital signal with a recording scale factor suitable for the signal fluctuation range, and is input to the signal processing circuit 313. . The above digital signal is
In this signal processing circuit 313, signal processing (image processing) is performed based on the reproduction image processing condition setting value C so that a radiographic image with excellent observation and interpretation suitability is obtained, and is output.

The read image signal (actual read image signal) So output from the signal processing circuit 313 is transmitted to the optical modulator 401 of the image reproducing unit 50.
is input. In this image reproducing unit 50, a laser beam 403 from a recording laser light source 402 is transmitted to an optical modulator 40.
1, it is modulated based on the actual reading image signal So input from the signal processing circuit 813, and is transmitted to the scanning mirror 404.
The light beam is deflected by the light beam and scans over a photosensitive material 405 such as photographic film. The photosensitive material 405 is then transported in a direction perpendicular to the scanning direction (arrow 406 direction) in synchronization with the scanning, and a radiation image based on the actual reading image signal So is output onto the photosensitive material 405. [Method for reproducing radiographic images] 7. In addition to this method, the above-mentioned CRT
Various methods can be adopted, such as display by.

Next, a mechanism for appropriately determining the reading gain setting value a, the recording scale factor setting value b, and the image processing condition setting value C will be explained with reference to FIG. This third
As shown in the figure, the control circuit 314 includes a signal extraction section 350, a histogram analysis section 351, a reading section 352, and a storage section 353.

The pre-read image signal Sp is input to the signal extracting section 350, and the signal extracting section 350 extracts the pre-read image signal Sp' for only the specified area as will be described later. The pre-read image signal Sp' outputted from the signal extraction section 350 is input to the histogram analysis section 351. The histogram analysis unit 351 uses the pre-read image signal S
Create a histogram of p', find its maximum value, minimum value, maximum frequency value, etc., and obtain information Sr indicating these values.
is sent to the reading unit 352. The storage unit 358 stores the optimum reading gain setting value a, recording scale factor setting value and image processing condition setting value C corresponding to these maximum values, minimum values, etc., and the reading unit 352 reads the above information Sr. The corresponding setting values a, b, and c are read from the storage unit 353 and are applied to the amplifier 311 and the A/D converter 3, respectively, as described above.
12 and signal processing circuit 313.

Next, signal extraction in the signal extraction section 350 will be explained. The object recognition circuit 220 includes a binarization processing section 221, a contour candidate point detection section 222, and an area determination section 228. The pre-read image signal Sp is input to the binarization processing section 221 in the subject recognition circuit 220. The binarization processing unit 221 compares the digitized pre-read image signal Sp for each pixel with a predetermined threshold value, and
The image information is binarized by giving a "0 (zero)" value to a pixel whose value is less than the threshold value, and giving a "1" value to a pixel whose value is equal to or more than the threshold value. In the stimulable phosphor sheet 103 on which a radiation image is accumulated and recorded in the state shown in FIG. Since the amount of stimulated luminescence from the irradiated outdoor area is clearly higher than that of the irradiated field, by setting the above threshold appropriately,
This background part J has a value of "1", and the other parts have a value of "0".
” value will be given. The thus obtained binary data sb regarding the stimulable phosphor sheet 103 is sent to the contour candidate point detection section 222. This contour candidate detection unit 222 is a four -way DI, D2, D 3, as an example of the predetermined one side 103a, as shown in Fig. 4, the two -directional D2, D2, D 3, as shown in Fig. 4.
DA Search in the direction of A. When such a search is performed, in any direction Dl-D, the data value at point Q is rOJ, and a "0" value is subsequently detected, but when the object part K enters the background part J. By the way, the "]" value will be detected. Contour candidate point detection unit 2
22 detects the points El, EZ, E3, and EA where the search value changes from "0" to "1" as candidate points on the contour of the subject, and calculates the pixel position of each of these points. The information Sg shown is sent to the area determination unit 223. The area determination unit 223 approximately determines a semicircle (half of a perfect circle or an ellipse) extending along the four points E1 to E4 located at the pixel position indicated by the information Sg.

The approximate circle R obtained in this manner substantially matches the contour of the subject, as described above. Then, the area determination unit 223 transfers the information St indicating the area surrounded by the approximate circle R and one side 103A of the sheet to the signal extraction unit 35 of the control circuit 314.
Send to 0. The signal extraction unit 350 extracts only the signal for the area indicated by the information St from the pre-read image signal Sp and sends it to the histogram analysis unit 351. Therefore, the histogram analysis in the histogram analysis section 351 is performed almost only on the subject J on the stimulable phosphor sheet 103, so the above-mentioned setting values a, b, and C are different from the actual accumulated recording information. It can be the most suitable one.

In the embodiment described above, the outline of the subject is approximated to a part of a circle, but this outline is approximated to, for example, half of a regular polygon (for example, a regular hexagon, a regular dodecagon, etc.). You may also do so. Although the shape of such a polygon itself is quite different from that of the subject, which is a breast, the area surrounded by this polygon and one side 103A of the sheet is not much larger than the actual subject area. The above-mentioned approximation to a polygon is also effective in grasping the accumulated recorded information in the subject area, as described above, since there is no shortage of information. Note that the accuracy of the approximation increases as a polygon with a larger number of sides is used as the approximated polygon.

Furthermore, in the embodiment described above, the orientation of the stimulable phosphor sheet 103 when subjected to radiography and the orientation of the stimulable phosphor sheet 103 when subjected to reading processing are determined to be respectively predetermined orientations. Therefore, the starting point of the search for the binarized data is set to a predetermined side 10 of the sheet.
3A, but if this is not known in advance, choose which of the four sides of the stimulable phosphor sheet 103 is included in the radiation field. (that is, the edge on which the starting point of the above search should be set). As a method for determining such sides, for example, Japanese Patent Application Laid-Open No. 61-17017
The method shown in No. 8 can be used.

Furthermore, in the above embodiment, the binarized data is used to identify contour candidate points that are considered to be on the contour of the subject from I'OJ.
I am looking for it by looking at the points that change to 1.
This candidate point can also be detected by other methods. That is, since the amount of stimulated luminescence light differs greatly between the subject area and the background area J, when the pre-read image signal Sp is differentiated in the directions D1 to D4 shown in FIG. It takes a uniquely large or small value at the boundary with part J. Therefore, the contour candidate points can be found by finding points where the absolute value of the differential value exceeds a predetermined threshold. Regarding the above-mentioned differential processing, for example, Japanese Patent Application Laid-Open No. 82-115969
A detailed explanation is given in the issue.

In addition, "pre-reading" as explained above is usually called "book-reading".
This is done on a coarser pixel basis than in . The above-mentioned binarization processing and differentiation processing may be performed on the image data itself obtained by such relatively coarse reading operations, or these image data may be interpolated to obtain more fine image data. It may also be performed on those image data after that. Furthermore, the binarization process and differentiation process may be performed on image data obtained by averaging image signals of a plurality of pixels.

Furthermore, the present invention is applicable not only to the case where reading conditions etc. are determined based on the above-mentioned pre-reading, but also when the reading gain and recording scale factor are optimized by the conversion process described above without performing this pre-reading. It can be used to grasp the accumulated record information related to only the above information. Furthermore, the present invention can also be used to detect breast contours for purposes other than those described above.

Furthermore, in the embodiments described above, a stimulable phosphor sheet is used as a recording medium for radiographic image information, but the method of the present invention is capable of producing radiation from conventionally known silver halide photographic film for X-ray photography. The same method can be applied when reading an image to obtain an image signal.

(Effects of the Invention) As explained in detail above, in the breast contour detection method in radiographic images of the present invention, a plurality of candidate points that are considered to be on the breast contour are obtained, and circles and polygons extending along these candidate points are determined. Since the breast contour is approximated to a rectangular shape, it is possible to accurately determine the breast contour. Therefore, according to this method, it is possible to accurately recognize the breast contour, correctly grasp the accumulated recorded information 12 regarding the subject, and optimally set the reading conditions and image processing conditions for radiographic image information. Therefore, according to the method of the present invention, it is possible to always reproduce radiographic images with excellent suitability for observation and interpretation.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an apparatus for detecting breast contours and reading radiation image information using the method of the present invention. FIG. 2 is an explanation showing the state of recording radiation image information on a stimulable phosphor sheet according to the present invention. 3 is a block diagram showing in detail a part of the apparatus shown in FIG. 1, and FIG. 4 is an explanatory diagram for explaining the search for binarized image data according to the present invention. 20...Radiation image capturing unit 30...Reading unit for pre-reading 40...Reading unit for main reading 100...
Radiation source 101... Breast 102...
- Radiation 103...Stormable phosphor sheet 104...Cassette 106...Press plate 201...Laser light source for pre-reading 202...Laser light for pre-reading 204...Light deflector for pre-reading 208... - Pre-reading photodetector 210... Pre-reading sheet transport means 220... Subject recognition circuit 221... Binarization processing section 222... Contour candidate point detection section 223...
Area determining unit 301...Laser light source for main reading 302...Laser light for main reading 305...Light deflector for main reading 310...Photodetector for main reading 311...Amplifier 312...A/D conversion 313...Signal processing circuit 314...Control circuit 320...Main reading sheet transport means a...Reading gain setting value b...Recording scale factor setting value C...Reproduction image processing condition setting value D1 to D4... Binarized data search direction E1. E,・
...Contour candidate point J...Background part K...Subject part So...
・Actual reading image signal Sp ・・・Pre-reading image signal R・
・Approximate circle

Claims (2)

[Claims] (1) A method for detecting the outline of a breast in a radiographic image taken of a breast held under pressure between two holding members, which detects multiple candidate points that are considered to exist on the outline of the breast, and detects these points. 1. A breast contour detection method in a radiographic image, comprising: approximately determining a circle extending along candidate points, and detecting this circle as the contour of the breast. (2) A method for detecting the contour of a breast in a radiographic image taken of a breast held under pressure between two holding members, which detects a plurality of candidate points that are considered to exist on the contour of the breast, and detects these points. 1. A breast contour detection method in a radiographic image, characterized in that a polygon extending along candidate points is approximately determined, and this polygon is detected as the contour of the breast.