JPH1063812A - Method for reproducing picture information and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically extract an abnormal shadow candidate at the time of reproducing a radiation picture, and to observe the abnormal shadow candidate. SOLUTION: Whole picture data S are processed by a first gradation processing and a first frequency processing by a whole picture processing means 10, and a whole picture is displayed on a first displaying means 20. Also, picture data in a local area extracted by an abnormal shadow extracting means 30 are processed by a second gradation processing and a second frequency processing by a local picture processing means 40 so that contrast lower than that of the whole picture can be obtained, and frequency components lower than those of the whole picture can be emphasized, and this processed picture in the local area is displayed on a second displaying means 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for reproducing image information. More specifically, the present invention relates to image processing for an entire radiation image of a subject, and automatically detects an abnormal shadow candidate such as a tumor shadow from the image. The present invention relates to a method and apparatus for reproducing image information that is extracted and subjected to image processing for this abnormal shadow candidate and reproduced.

[0002]

2. Description of the Related Art A radiation image of a subject recorded on a stimulable phosphor sheet or a film is read to obtain image information, and after appropriate image processing is performed on the image information, an image is reproduced on a display means. Has been performed in various fields. In particular, in recent years, digital radiography technology called computed radiography in combination with a computer has been developed, and various types of digital radiography have been put to practical use.

[0003] This digital radiography has a fundamentally different feature from conventional analog radiography in that it can quantitatively analyze image data. Especially for medical diagnosis of the human body, computer-aided image diagnosis or CADM (Computer Aided Diagnosis of Medical) aiming to more positively utilize the features of digital radiography.
Image) has been proposed.

[0004] The computer-assisted image diagnosis or the like assists diagnosis by image interpretation at a medical site.
That is, conventionally, a recording medium such as a film or a CR
A specialist views and interprets the radiological image reproduced by the display device such as T, etc. visually, and displays an abnormal tumor shadow or a high-density microcalcification shadow as a sign of cancer (hereinafter, collectively referred to as abnormal shadow). Was trying to find it early. However, there is a possibility that such abnormal shadows may be overlooked or a misjudgment may occur due to a subjective judgment due to a difference in image reading ability between the readers who observe and read the radiation image.

Therefore, in computer-aided image diagnosis, abnormal shadow candidates considered as abnormal shadows are automatically detected on the basis of image information, and markings are displayed on the detected abnormal shadow candidates to pay attention to a reader of a radiological image. By provoking the or by quantitatively presenting the characteristic features of the abnormal shadow candidate detected as a material useful for the interpreter's objective judgment, it is possible to prevent the above-mentioned oversight and misunderstanding beforehand The aim is to improve diagnostic performance.

For example, a radiographic image (mammogram) of the breast
, A tumor shadow and a microcalcification shadow, which are characteristic features of a cancerous site, are known, and the computer-aided image diagnosis detects the tumor shadow as an abnormal shadow (“DR
Detection of tumor shadows in images (iris filter) ”Transactions of the Institute of Electronics, Information and Communication Engineers, D-II Vol.J75-D-II No.3 P663-670
Detecting microcalcification shadows as abnormal shadows (March 1992) ("Extraction of microcalcification images using morphological filters using multiple structural elements", D-II Vol.J75-D-
II No.7, P1170-1176, July 1992).

[0007] By the way, in these proposals for computer-aided image diagnosis, as described above, markings are displayed on abnormal shadow candidates (tumor shadows or microcalcification shadows) of the entire reconstructed image, or the abnormal shadow candidates are quantitatively determined. It only stops displaying a typical rating scale.

[0008] However, displaying only such markings or rating scales is effective for alerting the reader or preventing the reader's subjective misunderstanding,
In order for the radiogram interpreter to actually diagnose the abnormal shadow candidate portion, it is necessary to provide an image having high diagnostic performance suitable for radiogram interpretation.

Therefore, the applicant of the present application has proposed in Japanese Patent Application No. 7-42277 (Japanese Patent Application No. 7-316679) that the automatically extracted abnormal shadow candidate has a higher contrast than the whole image. It has been proposed to perform image processing on image information representing this abnormal shadow so that the degree of enhancement of the high-frequency component is increased. Further, the applicant of the present application has filed
No. 94693, No. 7-73433, No. 7-73497, etc. propose a method for determining the degree of emphasis in performing the above emphasis.

[0010]

By the way, in the image processing for abnormal shadows in the above-mentioned Japanese Patent Application Nos. 7-316679 and 7-94693, the gradation of the extracted abnormal shadow candidate is higher than that of the whole image. So that the high frequency component of the abnormal shadow candidate is emphasized more than the whole image,
Although the processing is performed, the opposite processing may be desired depending on the image reader such as a doctor.

SUMMARY OF THE INVENTION The present invention has been made in order to respond to various demands of a user when reproducing a radiographic image. The present invention observes the presence / absence of an abnormal shadow candidate in a whole image, and checks the state of the abnormal shadow candidate in a local image. It is an object of the present invention to provide a method and an apparatus for reproducing image information capable of judging the image information.

[0012]

According to the method and apparatus for reproducing image information of the present invention, an abnormal shadow candidate is automatically extracted from the whole image, and the gradation of the abnormal shadow candidate is changed to the whole image. Lower contrast and / or
Alternatively, image processing is performed so that the sharpness of the low-frequency component is higher than that of the entire image, and the image is displayed on the display means.

That is, the method of reproducing image information according to the present invention comprises:
First image processing is performed on image information carrying a radiation image of a subject such as a mammogram, and the image-processed image information is displayed on a predetermined display unit as a visible image, and based on the image information. An abnormal shadow candidate such as a tumor shadow is extracted from the radiation image by an iris filter process or the like, a second image process is performed on image information representing the abnormal shadow candidate, and the image-processed abnormal shadow candidate is extracted. The image information to be displayed as the visible image together with the visible image subjected to the first image processing on the predetermined display means or another display means separate from the predetermined display means. In the reproducing method, the second image processing may include a gradation processing for lowering contrast than the first image processing and / or a frequency enhancement for lower frequency components than the first image processing. It is characterized in that a number processing.

Further, according to the present invention, there is provided an apparatus for reproducing image information, comprising: an entire image processing means for performing first image processing on image information carrying a radiation image of a subject, such as a mammogram; First display means for displaying as a visible image, and abnormal shadow extracting means for extracting an abnormal shadow candidate such as a tumor shadow from the radiation image based on the image information, for example, using an iris filter processing means or the like Local image processing means for performing second image processing on the image information representing the abnormal shadow candidate, and second display means for displaying the image information representing the image-processed abnormal shadow candidate as a visible image Wherein the second image processing is performed at a lower frequency than the first image processing, and / or the gradation processing for lowering the contrast than the first image processing. Is characterized in that minute is emphasizing frequency processing.

[0015] The first display means may also serve as the second display means.

The iris filter processing is proposed by the present applicant in Japanese Patent Application No. 7-316679.
Abnormal shadow detection processing that automatically detects tumor shadows,
Specifically, a gradient vector of the density value of the radiation image is calculated, and a threshold value processing is performed on an evaluation value corresponding to the degree of concentration of the gradient vector to determine whether the image is a tumor shadow or a non-tumor shadow such as a blood vessel or a mammary gland. Is determined, and the tumor shadow is accurately separated and detected from the non-tumor shadow, which will be described in detail below.

In a radiographic image, for example, in a radiographic image on X-ray film (an image that outputs a high-density high-signal level image signal), it is known that the density of a tumor shadow is slightly lower than that of its surroundings. Therefore, the gradient vector at an arbitrary pixel in the tumor shadow points near the center of the tumor shadow. On the other hand, in an elongated shadow such as a blood vessel shadow, the gradient vector does not concentrate on a specific point. Therefore, locally evaluate the distribution of the direction of the gradient vector,
If a region concentrated at a specific point is extracted, it becomes a candidate for a tumor shadow. This is the basic concept of iris filter processing. The specific algorithm steps are shown below.

(Step 1) Calculation of Gradient Vector For all the pixels constituting the target image, the direction θ of the gradient vector of the image data is calculated for each pixel j based on the calculation formula shown in the following equation (1). Ask.

[0019]

(Equation 1)

Here, f _{1 to} f ₁₆ are, as shown in FIG.
It is a pixel value (image data) corresponding to a pixel on the outer periphery of the mask of 5 pixels × 5 pixels centered on the pixel j.

(Step 2) Calculation of Concentration of Gradient Vector Next, for all the pixels constituting the target image,
For each pixel, the degree of concentration C of the gradient vector having that pixel as the pixel of interest is calculated according to the following equation (2).

[0022]

(Equation 2)

Here, N is the number of pixels existing in a circle having a radius R around the pixel of interest, and θj is a straight line connecting the pixel of interest and each pixel j in the circle, and the above equation for each pixel j. This is the angle formed by the gradient vector calculated in (1) (see FIG. 5). Therefore, the concentration C expressed by the above equation (2)
Has a large value when the direction of the gradient vector of each pixel j is concentrated on the target pixel.

By the way, the gradient vector of each pixel j in the vicinity of the tumor shadow is determined regardless of the contrast of the tumor shadow.
Since the pixel of interest is directed substantially toward the center of the tumor shadow, the pixel of interest having a large value of the degree of concentration C can be said to be the pixel at the center of the tumor shadow. On the other hand, in the shadow of a linear pattern such as a blood vessel, the value of the degree of concentration C is small because the direction of the gradient vector is biased in a certain direction. Therefore, the value of the degree of concentration C with respect to the pixel of interest is calculated for each of all the pixels constituting the image, and whether or not the value of the degree of concentration C exceeds a predetermined threshold value is evaluated. Can be detected. In other words, this filter is less susceptible to blood vessels and mammary glands than a normal differential filter,
It has the feature that tumor shadows can be detected efficiently.

Further, in actual processing, in order to achieve a detection power independent of the size and shape of the tumor, a device for adaptively changing the size and shape of the filter is used. FIG. 6 shows the filter. This filter is different from the filter shown in FIG.
/ M kinds of directions for each / M (in FIG. 6, 32 directions for every 11.25 degrees)
The evaluation of the degree of concentration is performed only with the pixels on the radial line (example of direction).

Here, the coordinates ([x], [y]) of the n-th pixel on the i-th line and from the pixel of interest are as follows if the coordinates of the pixel of interest are (k, l): Equation (3),
Given by (4).

[0027]

(Equation 3)

Here, [x] and [y] are the maximum integers not exceeding x and y.

Further, the output value up to the pixel at which the maximum concentration is obtained for each line on the radial line is defined as the concentration in that direction, and the concentration is averaged in all directions (32 directions in the example). Then, the concentration degree C of the gradient vector group for the target pixel is set. Specifically, the concentration Ci (n) obtained from the pixel of interest to the n-th pixel on the i-th radial line is obtained by the following equation (5).

[0030]

(Equation 4)

(Rmin represents the minimum value of the radius of the tumor shadow to be extracted, and Rmax represents the maximum value of the radius of the tumor shadow to be extracted.) That is, for each of the plurality of lines, The average value of the index values cos θj of all the pixels from the target pixel to the pixels at the distances corresponding to the minimum to maximum sizes of the tumor shadow to be detected is calculated.

Next, the degree of concentration C of the gradient vector group is calculated by the following equations (6) and (7).

[0033]

(Equation 5)

Equation (6) is the maximum value of the degree of concentration Ci (n) for each radial line obtained by equation (5).
The region from the pixel of interest to the pixel at which the degree of concentration Ci (n) is the maximum value is a candidate region for a tumor shadow in the direction of the line. By obtaining the area of all the radial lines by the equation (6), the shape of the outer peripheral edge of the area that can be a candidate for the tumor shadow can be specified.

In equation (7), a value obtained by averaging the maximum value of the degree of concentration given by equation (6) in this area in all directions of the radial line is obtained. By comparing the obtained value with a preset threshold value T, it is determined whether or not an area around the target pixel is likely to be an abnormal shadow candidate.

The area for evaluating the degree of concentration C of the gradient vector group in the equation (7) is similar to the manner in which the iris (iris) of the human eye expands and contracts according to the brightness of the outside world. Since the size and the shape are adaptively changed according to the distribution of the vector, it is referred to as an iris filter.

The above calculation of the degree of concentration Ci (n) may use the following equation (5 ') instead of equation (5).

[0038]

(Equation 6)

That is, for all of the plurality of lines, for each of the lines, a pixel corresponding to the maximum size from the pixel located at a distance corresponding to the minimum size of the tumor shadow to be detected from the pixel of interest on the line. It is sufficient to calculate the average value of the index values cos θj of all the pixels up to the pixel at the distance.

(Step 3) Evaluation of shape of tumor shadow candidate In general, the shadow of a malignant tumor is 1) the edge is irregular 2) the shape is almost circular 3) The inside has an uneven density distribution Morphological features.

Therefore, normal tissues are removed from the detected abnormal shadow candidates, and a more definite “abnormal shadow candidate”
That is, in order to extract only shadow candidates having a very high probability of being a tumor, shape determination is performed in consideration of these features. The feature amount used here is a spread degree (Spread
ness), Elongation, Roughnes
s), circularity (Circularity) and internal roughness (En
tropy).

According to the above steps, the iris filter can effectively detect a tumor shadow from a radiographic image.

[0043]

The method and apparatus for reproducing image information according to the present invention can automatically extract an abnormal shadow from a radiation image, and can recognize the abnormal shadow in the entire image displayed on the display means. The abnormal shadow can be reproduced as an image whose gradation is lower in contrast than the entire image and / or an image in which the low-frequency component is emphasized.

Therefore, the image reader who desires an image processed so that the extracted gradation of the abnormal shadow candidate has a lower contrast than the entire image and / or the low frequency component of the abnormal shadow candidate is emphasized more than the entire image. Can also meet the demands.

[0045]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the image information reproducing apparatus according to the present invention.

FIG. 1 is a block diagram showing an embodiment of an image information reproducing apparatus according to the present invention, and FIG. 2 shows a radiation image (mammogram) P to be reproduced by the image information reproducing apparatus 100 of the present embodiment. FIG. The illustrated image information reproducing apparatus 100 is configured to perform first gradation processing and first frequency processing on digital image data (whole image data) S representing a whole radiation image (whole image) P of a subject. A processing means 10; and a first display means 20 for reproducing and displaying the whole image data S 'after the image processing has been performed (hereinafter, the processed whole image data is referred to as processed whole image data) as a visible image. And abnormality extracting a candidate P1 of a tumor shadow and a rectangular area near the candidate P1 which is a characteristic form of a cancerous part from the entire image P based on the entire image data S (these areas are collectively referred to as a local area P2). Shadow extraction means 30
And a local image processing means 40 for performing a second gradation process and a second frequency process on the image data (local region image data) S2 corresponding to the extracted local region P2, and the image processing is performed. Local area image data (hereinafter, referred to as
The processed local area image data is referred to as processed local image data.) S2 'is reproduced and displayed as a visible image.
And a display means 50.

Here, the first gradation processing by the whole image processing means 10 is a processing performed based on a gradation processing table set according to the type and density distribution of the image. The whole image is processed so as to have the optimum gradation for observation and interpretation. Also, in the first frequency processing, high-frequency components of the entire image are emphasized so as to have an optimal spatial frequency for observing and reading the entire image.

On the other hand, the local image processing means 40 performs the second gradation processing for performing gradation processing so as to have a lower contrast than the first gradation processing by the whole image processing means 10 and the first frequency processing. Also performs a second frequency process that emphasizes low frequency components.

In this embodiment, the abnormal shadow extracting means
A description will be given of a case where an iris filter is applied as 30. However, the image information reproducing device of the present invention is not limited to this embodiment, and various abnormal shadow extracting means are provided according to the type of abnormal shadow to be extracted. Can be applied.

Here, the iris filter calculates the gradient of the image signal (density value) for detecting a tumor shadow in a radiographic image as a gradient vector, and outputs the degree of concentration of the gradient vector. The iris filter processing refers to an algorithm for detecting a candidate for a tumor shadow based on the degree of concentration of the gradient vector (Equation (7)).
It does not refer to the algorithm itself, but means means for performing a process of detecting a tumor shadow candidate by the algorithm.

Hereinafter, the image information reproducing apparatus 10 according to the present embodiment will be described.
The operation of 0 will be described.

First, the entire image data S is stored in the image information reproducing apparatus.
The whole image data S is input to the whole image processing means 10 and the abnormal shadow extracting means 30 inside the image information reproducing apparatus 100.

The whole image processing means 10 to which the whole image data S has been input performs the first gradation processing and the first gradation processing on the whole image data S based on a preset gradation processing table.
Is performed. As described above, this first gradation processing processes the whole image so as to have the optimum gradation for observing and interpreting the whole image according to the type and density distribution of the input image. Similarly, by the first frequency processing,
High-frequency components of the entire image are emphasized so as to have an optimal spatial frequency for observing and interpreting the entire image.

The processed whole image data S 'which has been subjected to the first gradation processing and the first frequency processing is inputted to the first display means 20, and the first display means 20 outputs the processed whole image data S'. The visible image (entire image) P 'represented by S' is displayed on its display surface as shown in FIG.

On the other hand, the abnormal shadow extracting means 30 extracts the tumor shadow image data S1 representing the tumor shadow candidate P1 by applying an iris filter process to the input whole image data S, and further, the tumor shadow candidate A nearby rectangular area including P1 is extracted as local area image data S2 representing the local area P2. The extracted local area image data S2 is input to the local image processing means 40, and the local image processing means 40 performs second gradation processing on the local area image data S2 based on a preset gradation processing table. And a second frequency process is performed.

By the second gradation processing, the local area image data S2 is converted into processed image data having a lower contrast than that of the processed whole image data S '. It is processed image data (processed local image data S2 ') in which the low-frequency components are emphasized compared to the data S'.

The processed local image data S2 'thus obtained is input to the second display means 50, and the second display means 50 displays the visible image (local image data) represented by the processed local image data S2'. The area image P2 'is displayed on its display surface as shown in FIG.

Accordingly, the second display means 50 has a lower gradation than that of the whole image P 'displayed on the first display means 20, and its sharpness is lower than that of the whole image P'. The local area image P2 'in which the frequency component is emphasized is displayed.

As described above, according to the image information reproducing apparatus of the present embodiment, the presence or absence of a tumor shadow is determined by the first display means.
It is possible to meet the needs of the user who wants to grasp in the whole image P ′ displayed on 20 and observe the tumor shadow itself with the smoother image displayed on the second display means 50. it can.

In the present embodiment, the first display means and the second display means are separate, but the local area image P2 'to be displayed on the second display means is displayed on the first display means. As a part of the whole image P 'displayed on the display means, the first
In such a configuration, the second display unit becomes unnecessary, and the configuration can be simplified.

The local image processing means 40 does not necessarily need to perform both the gradation processing and the frequency processing, but may perform only one of the processing.

Further, the local image processing means 40 performs an interpolation process on the processed local image data S2 ', etc.
Other image processing such as enlarging the display size of the image may be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image information reproducing apparatus according to the present invention.

FIG. 2 is a view showing a radiation image processed by the image information reproducing apparatus shown in FIG. 1;

3A is a diagram showing an entire image P ′ displayed on a first display unit, and FIG. 3B is a diagram showing a local region image P2 ′ displayed on a second display unit.

FIG. 4 is a view showing a mask of 5 × 5 pixels for calculating the direction of a gradient vector in an iris filter.

FIG. 5 is a diagram showing the concept of the degree of concentration of a gradient vector.

FIG. 6 is a diagram for evaluating a degree of concentration, centering on a pixel of interest
Diagram showing pixels on radial lines in 32 directions

[Explanation of symbols]

 10 Overall image processing means 20 First display means 30 Abnormal shadow extraction means 40 Local image processing means 50 Second display means 100 Image information reproducing device

Claims (7)

[Claims] An image information carrying a radiation image of a subject is subjected to a first image processing, and the image information subjected to the image processing is displayed as a visible image on a predetermined display means. An abnormal shadow candidate is extracted from the radiation image based on the image information, a second image process is performed on the image information representing the abnormal shadow candidate, and the image information representing the image-processed abnormal shadow candidate is converted into a visible image. In a method of reproducing image information, the image information is displayed on the predetermined display means or another display means separate from the predetermined display means, together with the visible image on which the first image processing has been performed. Wherein the image processing is a gradation processing for lowering the contrast than the first image processing and / or a frequency processing for emphasizing a low-frequency component more than the first image processing. Law. 2. The method according to claim 1, wherein the radiation image is a mammogram. 3. The image information reproducing method according to claim 1, wherein the extraction of the abnormal shadow candidate from the radiation image is performed by an iris filter process. 4. An overall image processing unit for performing a first image processing on image information carrying a radiation image of a subject, and a first display unit for displaying the image processed image information as a visible image. An abnormal shadow extraction unit that extracts an abnormal shadow candidate from the radiation image based on the image information; a local image processing unit that performs a second image process on the image information representing the abnormal shadow candidate; A second display unit for displaying the image information representing the image-processed abnormal shadow candidate as a visible image, wherein the second image processing is performed more than the first image processing. An image information reproducing apparatus, which is a gradation processing for lowering a contrast and / or a frequency processing for emphasizing a lower frequency component than the first image processing. 5. The apparatus according to claim 4, wherein said first display means also serves as said second display means. 6. The apparatus according to claim 4, wherein the radiation image is a mammogram. 7. The image information reproducing apparatus according to claim 4, wherein the extraction of the abnormal shadow candidate by the abnormal shadow extracting means is performed by an iris filter process.