JPH01238650A - Object recognition method for radiographic image - Google Patents

Abstract

PURPOSE:To suitably set object region reading conditions and image processing conditions by dividing a radiographic image into many small regions, grouping them into plural small region groups by histogram similarity and obtaining characteristic values for the each small region group. CONSTITUTION:The radiographic image 21 composed of the object part 22, a direct radiation part 23 and a scattered line part 24 is regenerated based on image data (S) composed of the radiographic image accumulatively recorded on a fluorescent sheet. Then, the histogram based on the data S is made for the each small adjacent region surrounded by a short dashed line as a grating, the similarity of the histogram is evaluated for the each small adjacent region using a specified evaluation function, and the small regions are grouped into the plural small region groups (e.g. groups 22-24) by the similarity. Then, more than one characteristic values (e.g. average value, dispersion value) of the data S are obtained by the small region. Thus, the characteristic value that allows the object part 22 to be mostly separated from others is obtained.

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 film on which it is recorded and converted into an electrical signal. After converting and performing image processing on this electrical signal (image data), contrast and sharpness can be improved by reproducing it as a visible image in photocopies, etc.

Efforts have been made to obtain reproduced images with good image quality such as graininess (see Japanese Patent Publication No. 81-5193).

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. 513-11395.

No. 55-163472, No. 5B-104645, No. 55-116340. ).

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, for stimulable phosphors, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over a very wide range. Even if the amount of radiation exposure varies considerably, the amount of stimulated luminescence light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means with the reading gain set to an appropriate value and an electrical signal (image data) is generated. It is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure by converting this image data into a recording material such as a photographic material or outputting the radiation image as a visible image to a display device such as a CRT. can.

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, 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 reading gain, scale factor, or , the power of excitation light during reading, etc.

In addition, regardless of whether the system performs this prefetching or the system that does not, the obtained image data (including prefetched image data) is analyzed to determine the optimal image processing conditions when performing image processing on the image data. Some systems let you decide. 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 blurred radiation image 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 (subject area), and area around the subject where the radiation emitted during imaging was directly irradiated onto the sheet (
The direct radiation area (this direct radiation area and the subject area are collectively called the irradiation field), and the area that is shielded from radiation on the sheet and is irradiated with only a slight amount of scattered radiation ( Scattered rays) etc. are present.

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

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 not be possible to obtain a reproduced image of the best quality unless the subject 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 this change was automatically recognized and the irradiation field area could be determined (for example, Kaisho 62-1559 [i8]. By recognizing the irradiation field, it is possible to obtain fairly high-quality reproduced images for most images, but it is possible to further improve the image quality if the subject area can be recognized.

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 method for recognizing a subject in a radiographic image of the present invention reads a radiographic image in which a subject is partially recorded to obtain a large amount of image data carrying radiographic image information, and then A histogram of image data is obtained for each of the many small regions into which the image is divided, and the similarity is evaluated for each of two adjacent small regions using an evaluation function that evaluates the similarity between two histograms. Divide the small region into multiple small region groups with similar histograms, obtain one or more types of characteristic values of image data for each of these multiple small region groups, and use these characteristic values to determine the area of the subject in the radiographic image. This method is characterized by recognizing a group of small regions corresponding to .

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, the inventors' experiments have shown that when a subject is divided into small regions and histograms of multiple image data corresponding to these small regions are obtained, the histograms usually show roughly similar patterns. . It has also been found that this histogram usually has a large difference in pattern from a histogram obtained from a plurality of image data corresponding to small areas of direct radiation areas and scattered radiation areas other than the subject area.

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 image data for each of the large number of small areas from the image data within the large number of small areas. Obtain histograms, and use an evaluation function to evaluate the similarity between two histograms.
By evaluating the similarity for each small region, the above-mentioned large number of small regions are divided into a plurality of small region groups whose histograms are similar. A characteristic value is obtained, and from this characteristic value it is recognized which small area group corresponds to the subject part.

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. 4, the entire apparatus using the present invention will be described.

FIG. 4 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 (stimulable phosphor) that, as mentioned above, 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 is a device that uses a fluorescent 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 stimulable phosphor sheet 1 that has been photographed 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 is focused by a light condenser 10. and is photoelectrically detected by a photomultiplier (photomultiplier tube) 11 as a photodetector. The light collector 10 is made by molding a light guide material such as an acrylic plate, and extends along the linear incident end surface 10a or 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 fob formed in an annular shape. The stimulated luminescence light that enters the light collector 10 from the incident end face 10a travels through the light collector 10 through repeated total reflection, exits from the output end face 10b, is received by the photomultiplier 11, and is then received by the photomultiplier 11. The light intensity of the stimulated luminescent light 9 carrying radiation image information or the photomultiplier 1
Detected by 1.

Analog data S1 output 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 thus obtained is 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 in which the stimulable phosphor sheet is directly irradiated with radiation without going through the subject, and a part that contains only scattered radiation. It can be divided into irradiated scattered radiation parts 24. In the figure, each part surrounded by broken lines drawn in a grid pattern vertically and horizontally indicates a small area that is a unit for calculating a histogram. Each small area does not represent a pixel; each small area also contains many pixels (
image data) exists. In the calculation unit 19 shown in FIG. 4, a histogram is first obtained for each of the above-mentioned small areas based on the input image data S2.

FIG. 2 is a graph showing an example of a histogram obtained from a large amount of image data corresponding to each of two adjacent small areas A and B. The horizontal axis of the figure shows a large number of divisions al, a2, . ..., a. , , and the vertical axis represents each segment a1+ a2+ .

It shows the appearance frequency of image data, which shows how many pieces of image data exist within each range of ao and . Among the object part 22, direct radiation part 23, and scattered radiation part 24 in FIG. are quite different.

After obtaining a histogram for each small region, the similarity of two adjacent small regions is evaluated using an evaluation function that evaluates the similarity of two histograms. The above-mentioned evaluation function is, for example, the absolute value of the difference in appearance frequency for each of the mutually corresponding sections a1+a2+., a, . . . between two histograms, for example, Δ1. Δ2゜..., Δ. −1,Δ. ,Δo+1
．． Find the absolute value of this difference and divide it into multiple categories al, a
2. ... ,a,.

The value of the evaluation function obtained in this way is compared with a predetermined value to determine whether or not the two histograms being evaluated are similar. Furthermore, the above-mentioned evaluation function has mutually corresponding sections al, a2, . ... ,
Find the difference in appearance frequency for each of an,..., and calculate the maximum absolute value of the difference thus found (for example, the second
Δ in the figure. -2).

In this way, the similarity of the histograms of adjacent small regions over the entire surface of the radiographic image 21 (see FIG. 1) is evaluated, and a large number of small regions within the radiographic image 21 are divided into a plurality of small regions with similar histograms. Divided into area groups.

Thereafter, one or more types of characteristic values are determined for each of the plurality of small region groups based on the image data corresponding to each small region group.

Figure 3 shows that each small area of the radiographic image shown in Figure 1 is divided into multiple groups of similar histograms as described above, and for each group of small areas, the average value and variance of the image tape are calculated. , plotted on a plane. The horizontal axis shows the average value, and the vertical axis shows the variance value. The positions of the ○ marks in this diagram are the numbers 22, 23, 24 written inside the 200 mark.
These correspond to the subject section 22, direct radiation section 23, and scattered radiation section 24 shown in FIG. 1, respectively.

In this way, radiographic images of similar subjects under similar imaging conditions are statistically investigated in advance, and characteristic values that can best separate the subject area from other areas are determined, and small values within the range of these characteristic values are determined. By determining in advance whether a region group 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 subject recognition method of the present invention can also be used in a system that determines reading conditions for main reading based on read image data.

This object recognition method is not limited to the apparatus using the stimulable phosphor sheet shown in FIG. The present invention can be applied to various devices such as a device that reproduces and displays an X-ray image on a display device.

(Effects of the Invention) The radiation image subject recognition method of the present invention obtains a histogram of image data for each of a large number of small regions obtained by dividing a radiation image, and uses an evaluation function to evaluate the similarity of two histograms to determine whether the two histograms are adjacent to each other. By evaluating the similarity of each two small regions, the large number of small regions is divided into histograms or groups of similar small regions, and one type or multiple types of image data are generated for each of these groups of small regions. We determined the characteristic value of , and used this characteristic value to recognize a group of small areas corresponding to the subject area in the radiographic image.We recognized the area where the subject is present in the radiographic image, and selected this area as the best image. This means that reading conditions and image processing conditions can be determined so that the image is reproduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a radiographic image, Fig. 2 is a graph showing an example of a histogram, and Fig. 3 is a graph showing an example of a histogram. seek,
FIG. 4, which is a diagram plotted on a plane, 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 conveyance means 4... - The - 6... Rotating polygon mirror 9 - Stimulated luminescence light 10 - Concentrator 11... Photo multiplier 16... Amplifier 17... A/D converter 18・Memory 19... Arithmetic unit 20 ・Image display device 21... Radiographic image 2
2. Subject section 23... Direct radiation section 24
・Scattered line part suspension=, Showa 6:3 April 21, 1939

Claims (1)

[Claims] (1) After obtaining a large number of image data carrying radiographic image information by reading a radiographic image in which the subject is partially recorded, a histogram of the image data is obtained for each of a large number of small regions into which the radiographic image is divided. , by evaluating the similarity for each two adjacent small areas using an evaluation function that evaluates the similarity of two histograms, the large number of small areas are divided into multiple small areas whose histograms are similar. dividing the image data into region groups, determining one or more types of characteristic values of the image data for each of the plurality of small region groups, and recognizing the small region group corresponding to the region of the subject in the radiation image based on the characteristic values; A method for recognizing objects in radiographic images, characterized by: