JPH01238649A - Method for recognizing object of radiograph - Google Patents

Abstract

PURPOSE:To recognize small area groups in response to the areas of an object in a radiograph by obtaining characteristic value at every area in many small areas divided from the radiograph and putting together approximate characteristic value into the plural small area groups. CONSTITUTION:The radiograph 21 is reproduced based on image data obtained by radiograph information on a part of which the object is recorded. The image 21 is made up of an object part 22 which is the radiant ray transmitting image of, for example, the breast of a human body, a direct radiant ray part 23 and a scattering line part 24. The image 21 is divided into small areas enclosed with grid shape dashed lines. The mean value and the variance of the image data are obtained at every small area and plotted so as to put together the approximate value into small area groups. Round marks in areas 22, 23 and 24 enclosed with the dashed lines show each small area in the object part 22, a direct part 23 and a scattering part 24, respectively and an area 25 shows a small area bridging two parts.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to reading a radiation image in which a subject is partially recorded and obtaining a large amount of image data carrying radiation image information. The present invention relates to a radiation image subject recognition method for recognizing an area occupied by a subject in a radiation image.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain image data, perform appropriate image processing on this image data, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the recorded film and converted into an electrical signal. Contrast sharpness is achieved by converting this electrical signal (image data) to image processing and then reproducing it as a visible image in a photocopy, etc.

Efforts have been made to obtain reproduced images with good image quality performance such as graininess (see Japanese Patent Publication No. 61-5193).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a portion of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. Radiographic image information of a subject such as a human body is partially recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is read photoelectrically to obtain image data, and based on this image data, a radiation image of the subject can be recorded on a recording material such as a photographic light-sensitive material, a CRT, etc. A radiation image recording and reproducing system that outputs visual images has already been proposed (Japanese Unexamined Patent Publication No. 5
No. 5-12429, No. 5B-11395.

No. 55-163472, No. 5G-1041345,
No. 55-116340 etc. ).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in stimulable phosphors, it is recognized that the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electrical signal (image data) and using this image data to output the radiation image as a visible image to a recording material such as a photosensitive material or a display device such as a CRT, it is not affected by fluctuations in radiation exposure. Radiographic images can be obtained.

In the above system, the stimulable phosphor sheet is scanned in advance with a low-level light beam before obtaining image data by reading it under optimal reading conditions depending on the dose of radiation irradiated on the stimulable phosphor sheet. Pre-reading is performed to read the outline of the radiation image recorded on this sheet, the pre-read image data obtained by this pre-reading is analyzed, and then the sheet is irradiated with a strong light beam and scanned, and this radiation image 3- There is a system that is configured to perform main reading in which image data is obtained by reading images under optimal reading conditions.

Here, the reading conditions are a general term for various conditions that affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading, such as the reading gain, scale factor, or , the power of excitation light during reading, etc. , - In addition, regardless of whether the system performs this pre-reading or the system does not perform pre-reading, the obtained image data (including the pre-read image data) is analyzed and the optimal image processing is performed when performing image processing on the image data. Some systems are designed to determine conditions. The method for determining the optimal image processing conditions based on this image data is not limited to systems using stimulable phosphor sheets, but for example, image data is obtained from a radiation image recorded on a recording sheet such as a conventional X-ray film. It is also applied to the system.

By analyzing the image data (including pre-read image data) and determining optimal reading conditions and image processing conditions, it becomes possible to reproduce and output a radiation image that is highly suitable for observation.

(Problem to be solved by the invention) By the way, in one radiographic image corresponding to read image data (including pre-read image data), a subject that needs to be read and image processed in the actual reading is photographed. area around the subject (direct radiation area), where the radiation emitted during imaging was directly irradiated onto the sheet (direct radiation area); There are areas (scattered radiation areas) on the sheet that are shielded from radiation and are irradiated with only a slight amount of scattered radiation.

Among these areas, the only area that needs to be read by reading in a system that performs pre-reading, or the area that requires image processing to improve image quality, regardless of whether the system performs pre-reading or not, is the subject area. .

The other areas may be made, for example, solid black in the reproduced image so as not to be overlooked when observing the subject. When determining reading conditions and image processing conditions, it may be impossible to obtain a reproduced image with the best image quality unless the object part is recognized. For example, when calculating the average value of image data of a subject, if image data of other areas are also averaged, the values may be completely different.

However, until now, there was no known effective means for automatically recognizing the subject area, so the next best method was to recognize the area of the irradiation field, which is the combination of the subject area and the direct radiation area. Reading conditions were determined to obtain image data within the irradiation field, or image processing conditions were determined to perform image processing on the image data within the irradiation field. This is because the boundary between the irradiation field and the scattered radiation area changes quite rapidly on the image, so we were able to automatically recognize this change and determine the irradiation field area (for example, 155968 (1986). By recognizing the irradiation field, it is possible to obtain reproduced images of fairly high quality for most images, and if it is possible to recognize the subject area, it is possible to further improve the image quality.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a method for recognizing a subject in a radiographic image, which recognizes a region occupied by a subject in a radiographic image from image data.

(Means for Solving the Problems) The object recognition method of the present invention reads a radiation image in which the object is partially recorded to obtain a large number of image data carrying radiation image information, and then divides the radiation image. One or more types of characteristic values are determined for each of the large number of small regions, the large number of small regions are divided into a plurality of small region groups in which the obtained characteristic values are similar, and the object in the radiographic image is determined based on the characteristic values. This method is characterized by recognizing a group of small regions corresponding to the region.

Here, the image data includes pre-read image data obtained by pre-reading.

(Function) The subject part is composed of a complex image of bones, blood vessels, etc. of a human body, and the image data of the subject part has a complicated pattern corresponding to the complexity of the image. However, when the subject is divided into small regions and multiple image data corresponding to these small regions are collected, the characteristic values such as the mean value and 1 variance of the multiple image data usually do not show similar values. This was discovered through experiments conducted by the present inventors. It has also been found that this characteristic value usually has a large difference from the characteristic value obtained from a plurality of image data corresponding to small areas of the direct radiation part and the scattered radiation part other than the subject part.

The object recognition method of the present invention is based on the above-mentioned background, and divides an entire radiographic image into a large number of small areas, and extracts one type of image data for each of the large number of small areas from the image data in the large number of small areas. Alternatively, multiple types of characteristic values are obtained, each small region with similar characteristic values is divided into multiple small region groups, and from the above characteristic values it is recognized which small region group corresponds to the subject part. It is something.

One or more types of characteristic values that are statistically most suitable for recognizing the object part are used by examining similar types of radiation images in advance. Characteristic values that can be used include mean, 1 variance, and median value.

There are mode values, maximum values, minimum values, etc.

By recognizing the subject portion in this manner, reading conditions and image processing conditions can be determined so as to obtain the best reproduced image.

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

First, referring to FIG. 3, the entire apparatus using the present invention will be described.

FIG. 3 is a perspective view showing an example of a radiation image information reading device using the subject recognition method of the present invention.

This device uses a stimulable phosphor (as described above) which accumulates a portion of this radiation energy when it is irradiated with radiation, and then exhibits stimulated luminescence in response to the accumulated energy when it is irradiated with excitation light such as visible light. This device uses a stimulable phosphor.

In a photographing device (not shown), a subject such as a human body is irradiated with radiation and photographed, and a radiation image of the subject is stored and recorded on a stimulable phosphor sheet.

The photographed stimulable phosphor sheet 1 is set at a predetermined position in the radiation image reading apparatus shown in FIG.

The stimulable phosphor sheet 1 set in this manner is conveyed (sub-scanning) in the direction of arrow Y by a sheet conveying means 3 such as an endless belt driven by a motor 2.

On the other hand, the excitation light 5 emitted from the laser light source 4 is transmitted to the motor 1.
A rotating polygon mirror 6 that is driven by 3 and rotates at high speed in the direction of the arrow.
After passing through a focusing lens 7 such as an fθ lens, the optical path is changed by a mirror 8 and the sheet 1
, and main scanning is performed in the direction of arrow X, which is substantially perpendicular to the sub-scanning direction (direction of arrow Y). From the part of the sheet 1 irradiated with this excitation light 5, stimulated luminescence light 9 is emitted in an amount corresponding to the radiation image information stored and recorded, and this stimulated luminescence light 9 is collected by a light condenser lO. The light is emitted and is photoelectrically detected by a photomultiplier (photomultiplier tube) 11 as a photodetector. The light condenser IO is made by molding a light guide material such as an acrylic plate, and has a linear incident end surface 10a extending along the main scanning line on the stimulable phosphor sheet 1. The light receiving surface of the photomultiplier 11 is coupled to the output end surface 10b formed in an annular shape. The stimulated luminescence light 9 entering the light condenser 10 from the incident end face 10a travels through the light condenser 10 through repeated total reflection, exits from the output end face 10b, and is received by the photomultiplier 11, A photomultiplier 11 detects the amount of stimulated luminescence light 9 carrying the radiation image information.

The analog data S outputted from the photomultiplier 11 is amplified by the amplifier 16 and then sent to the A/D converter 1.
7, it is digitized with a predetermined recording scale factor. The digital image data S2 obtained in this manner is manually input to the memory 18 and stored. memory 18
The image data S2 stored in is then read out by the calculation unit 19, and as described later, from the image data S2,
The subject part of the radiation image corresponding to this image data S2 is recognized, and image processing is performed on the image data corresponding to this subject part. The image data S3 that has been subjected to image processing is
The radiation image is sent to the image display device 20, and the radiation image is reproduced and displayed based on the image data S3.

FIG. 1 is a diagram showing an example of a radiation image.

The area within the surrounding rectangular frame forms one radiation image 21. This radiographic image 21 includes a subject part 22 which is a radiographic image of the subject (human breast), a direct radiation part 23 which is a radiation irradiated directly onto the stimulable phosphor sheet without going through the subject, and a radiographic part 23 which is a radiographic image of the subject (human breast), and a radiation part 23 which is a radiation transmitted directly to the stimulable phosphor sheet without going through the subject. 5. By dividing the irradiated scattered radiation into parts 24. Wear. In the figure, each portion surrounded by broken lines drawn in a grid pattern vertically and horizontally indicates a small region that is a unit for determining characteristic values. Each small area does not represent a pixel, and a large number of pixels (image data) exist within each small area. Characteristic values are determined for each of the above-mentioned small regions.

Figure 2 shows each small region of the radiographic image shown in Figure 1.
It is a diagram in which the average value and variance value of image data are calculated and plotted on a plane. The horizontal axis shows the average value, and the vertical axis shows the variance value. The circles in the areas 22, 23, and 24 surrounded by broken lines in this figure are the object part 22 and the direct radiation part 2 in FIG. 1, respectively.
3, and each small region within the scattered radiation section 24.

In this way, the characteristic values of the small areas within each part show approximately approximate values.

A circle in the area 25 outside the broken line indicates a small area that spans two parts, for example, a small area that spans both the subject area 22 and the direct radiation area 23. Dispersion tends to increase when spanning two parts.

In this way, radiological images of similar subjects under similar imaging conditions are systematically investigated, and the characteristic values that can best separate the subject area from other areas are determined, and the range within which this characteristic value lies. By determining in advance whether a region is to be a subject part, it becomes possible to subsequently recognize the subject part from the read image data.

The above embodiment describes a radiation image information reading device that does not perform pre-reading, but it performs pre-reading to obtain pre-read image data, recognizes a subject part based on this pre-read image data, and It goes without saying that the radiation image object recognition method of the present invention can also be used in a system for determining reading conditions for main reading based on read image data.

Furthermore, this object recognition method is not limited to devices using a stimulable phosphor sheet as shown in FIG.
The present invention can be applied to various devices, such as a device that reads an X-ray image from a film on which the line image is recorded to obtain image data, and reproduces and displays the X-ray image on a display device based on this image data.

(Effects of the Invention) The radiation image subject recognition method of the present invention obtains one or more types of characteristic values for each of a large number of small regions into which a radiation image is divided, and each small region in which these characteristic values are similar. The system is divided into multiple small region groups, and it is possible to recognize which small region group corresponds to the object part from the above characteristic values, so it is possible to recognize the region in the radiographic image where the object is present, and select this region as the best one. This means that reading conditions and image processing conditions can be determined so that the image is reproduced as an image.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a radiation image, and FIG. 2 is a diagram in which the average value and variance value of image data are calculated for each small region of the radiation image shown in FIG. 1 and plotted on a plane. FIG. 3 is a perspective view showing an example of a radiation image information reading device using the subject recognition method of the present invention. 1. Stimulative phosphor sheet 2. 13. Motor 3. Sheet transport means 4. - The - 6. Rotating polygon mirror 9. Stimulated luminescent light 10. Concentrator 11 Photo multiplier 16. Width device 17/A/D converter 18
・Memory 19・Calculation part 2
0.Image display device 21.Radiation image 22..Subject section 23.Direct radiation section 24..Scattered radiation section -17--I Engraving of drawing (no change in content) Figure 1 April 21, 1988 Day

Claims (1)

[Claims] (1) After reading a radiation image in which the subject is partially recorded and obtaining a large number of image data carrying radiation image information, one or more types of image data are obtained for each of the many small areas into which the radiation image is divided. determining a characteristic value, dividing the large number of small regions into a plurality of small region groups having similar characteristic values, and recognizing a small region group corresponding to the region of the subject in the radiation image based on the characteristic value. Characteristic method for recognizing objects in radiographic images.