JP7526503B2 - Image processing device and image processing method - Google Patents

Description

The present invention relates to a technology for extracting specific substances that appear in X-ray images.

Image processing devices that process X-ray images are required to accurately extract metals that appear in X-ray images in order to reduce metal artifacts, etc.

JP 2013-240584 A

The image processing device proposed in Patent Document 1 uses projection data as a basis to calculate and obtain pseudo projection data when a virtual metal object with a specified X-ray absorption coefficient is placed in the X-ray CT imaging area, and uses the pseudo projection data to extract the metal that appears in the X-ray image.

However, the image processing device proposed in Patent Document 1 requires a long calculation time because it performs a process of reconstructing pseudo-projection data.

In addition, there may be cases where it is necessary to extract non-metallic substances that appear in X-ray images.

In view of the above, the present invention aims to provide an image processing device and an image processing method that can improve extraction accuracy and reduce processing time when extracting a specific substance that appears in an X-ray image.

In order to achieve the above object, the image processing device according to the present invention is configured (first configuration) to include a setting unit that sets a predetermined region surrounding a pixel of interest in an X-ray image, a calculation unit that calculates a representative luminance value of the entire unit region that is provisionally set as a first region in which a first substance is captured, based on the average luminance value of each of a plurality of unit regions that make up the predetermined region, and a determination unit that determines whether the pixel of interest captures the first substance or a substance other than the first substance, based on the magnitude relationship between the ratio of the luminance value of the pixel of interest to the representative luminance value and a threshold value.

In the image processing device of the first configuration, the threshold value may be variable depending on the representative luminance value (second configuration).

In the image processing device of the first or second configuration described above, the threshold value may be configured to vary depending on the irradiation angle of X-rays with respect to the subject when the X-ray image is captured (third configuration).

In order to achieve the above object, the image processing method according to the present invention is configured (fourth configuration) to include a setting step of setting a predetermined region surrounding a pixel of interest in an X-ray image, a calculation step of calculating a representative luminance value of the entire unit region provisionally set as a first region in which a first material is captured, based on the average luminance value of each of a plurality of unit regions constituting the predetermined region, and a determination step of determining whether the pixel of interest captures the first material or a material other than the first material, based on the magnitude relationship between the ratio of the luminance value of the pixel of interest to the representative luminance value and a threshold value.

The present invention is expected to improve extraction accuracy and reduce processing time when extracting specific substances seen in X-ray images.

FIG. 1 is a diagram showing a configuration of an information processing device according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing an example of a function of the information processing device shown in FIG. 1 . FIG. 1 is a diagram showing an example of a pixel of interest and a predetermined region; FIG. 13 is a diagram showing another example of a pixel of interest and a predetermined region; FIG. 1 is a diagram showing the average luminance distribution of unit areas in a given area. FIG. 13 is a diagram showing an example of the relationship between the average luminance value of an entire unit region, which is provisionally set as a first region in which a non-metallic object is captured, and the luminance value of a pixel of interest; A binarized image in which pixels representing metals and pixels representing non-metals have different brightness values. Axial image diagram A diagram showing a binarized axial image. Diagram showing forward projection image

Embodiments of the present invention are described below with reference to the drawings.

Figure 1 is a diagram showing the configuration of an information processing device according to one embodiment of the present invention. An information processing device 1 according to one embodiment of the present invention (hereinafter referred to as information processing device 1) includes a control unit 2, a storage unit 3, a communication unit 4, a display unit 5, and an operation unit 6.

The control unit 2 is, for example, a microcomputer. The control unit 2 performs overall control of the information processing device 1. The control unit 2 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), all of which are not shown.

The storage unit 3 is, for example, a flash memory, a hard disk drive, etc. The storage unit 3 stores various programs such as an image reconstruction processing program for generating a reconstructed image, an image processing program for extracting a specific substance shown in an X-ray image, and various data such as setting values of various parameters and image data used when executing the various programs.

The communication unit 4 is a communication interface for communicating with an external device. The communication method between the communication unit 4 and the external device may be wired communication, wireless communication, or a combination of wired and wireless communication. Examples of the external device include an X-ray imaging device that captures X-ray images, a storage device that stores X-ray images, etc.

The display unit 5 is, for example, a liquid crystal display device, an organic EL (Electro Luminescence) display device, etc. The display unit 5 displays various images based on the control of the control unit 2.

The operation unit 6 is, for example, a keyboard, a pointing device, etc. The operation unit 6 outputs a signal according to the user's operation to the control unit 2.

FIG. 2 is a functional block diagram showing an example of the functions of the information processing device 1. The information processing device 1 functions as an image processing device 10 by executing an image processing program. The image processing device 10 includes a setting unit 11, a calculation unit 12, and a determination unit 13.

The setting unit 11 sets a predetermined region surrounding a pixel of interest in an X-ray image. For example, as shown in FIG. 3, the setting unit 11 sets a predetermined region 22 of m pixels in the horizontal direction by n pixels in the vertical direction surrounding a pixel of interest 21 in a transmitted X-ray image 20, which is an example of an X-ray image. m and n are each a plurality of natural numbers. m and n may be the same value or different values. Here, the predetermined region 22 is a region that includes the pixel of interest 21, but the predetermined region 22 may be a region of (m×n-1) pixels that does not include the pixel of interest 21. The setting unit 11 also sets a unit region into which the X-ray image is divided. The unit region is a pixels in the horizontal direction and b pixels in the vertical direction. a and b are each natural numbers. a and b may be the same value or different values. a is smaller than m, and b is smaller than n. m is a multiple of a, and n is a multiple of b. For example, m, n, a, and b can be set to m = 240, n = 420, a = 12, and b = 12. Note that when a = 1 and b = 1, the unit region is the pixel of interest 21 itself.

As shown in FIG. 3, it is desirable for the setting unit 11 to set the specified region 22 so that the pixel of interest 21 is located approximately at the horizontal center of the specified region 22 and at the vertical center of the specified region 22. However, when the pixel of interest 21 is located near the outer edge of the transmitted X-ray image 20, the setting unit 11 may set the specified region 22 so that the deviation of the position of the pixel of interest 21 from the horizontal center of the specified region 22 and the deviation from the vertical center of the specified region 22 are as small as possible, for example, as shown in FIG. 4.

The calculation unit 12 calculates the average luminance of each of a plurality of unit areas obtained by dividing the X-ray image. The calculation unit 12 calculates an average luminance value L1 (see FIG. 5) of m pixels in the horizontal direction by n pixels in the vertical direction of a predetermined area 22. Specifically, the calculation unit 12 calculates an average luminance value L1 (see FIG. 5) of m pixels in the horizontal direction by n pixels in the vertical direction of a predetermined area 22 including the unit area to which the target pixel 21 belongs, with the unit area to which the target pixel 21 belongs being the center. In the calculation to calculate the average luminance value L1 and the following calculations, the average luminance value of the unit area is used instead of the luminance value of the pixel.

Next, the calculation unit 12 provisionally determines the unit area having an average brightness value higher than the average brightness value L1 as the first area in which a non-metallic object is depicted.

Then, the calculation unit 12 calculates the average brightness value L2 (see FIG. 5) of the entire unit area, which is provisionally determined to be the first area in which non-metallic material is captured.

The determination unit 13 determines whether the pixel of interest 21 contains a non-metal or a material other than a non-metal based on the magnitude relationship between the ratio of the luminance value of the pixel of interest 21 to the representative luminance value of the entire unit area, which is provisionally determined to be the first area containing a non-metal, and a threshold value.

Figure 6 is a diagram showing an example of the relationship between the average brightness value L2 of the entire unit region provisionally designated as the first region in which a non-metal is depicted and the brightness value of the pixel of interest 21. As shown in Figure 6, when the average brightness value L2 of the entire unit region provisionally designated as the first region in which a non-metal is depicted is plotted on the horizontal axis and the brightness value of the pixel of interest 21 is plotted on the vertical axis, the pixels in which a metal is depicted (pixels indicated by circles in Figure 6) and the pixels in which a non-metal is depicted (pixels indicated by diamonds in Figure 6) can be separated by the characteristic line T1.

Therefore, for example, the determination unit 13 determines that metal is included in the pixel of interest 21 when the ratio of the luminance value of the pixel of interest 21 to the average luminance value L2 of the entire unit area, which is provisionally determined to be a first area in which a non-metal is included, is smaller than a threshold value. The threshold value is set to a value corresponding to the characteristic line T1. When the characteristic line T1 is an approximately straight line, the threshold value can be set to a fixed value. On the other hand, when the characteristic line T1 is a curve, it is desirable for the determination unit 13 to vary the threshold value according to the average luminance value L2. By varying the threshold value according to the average luminance value L2, the determination accuracy is improved.

The image processing device 10 repeats the above-mentioned process by sequentially treating all pixels in the X-ray image as "pixels of interest" one by one. The image processing device 10 generates an image that reflects the judgment result, for example, the binary image shown in FIG. 7 in which pixels depicting metals and pixels depicting non-metals have different brightness values. In the binary image shown in FIG. 7, the brightness value of pixels depicting metals (black parts in FIG. 7) is smaller than the brightness value of pixels depicting non-metals (white parts in FIG. 7).

For example, in CT imaging using a dental X-ray imaging device, multiple X-ray images are taken while changing the X-ray irradiation angle of the subject. When the X-ray irradiation angle of the subject changes, the relationship between the average luminance value L2 of the entire unit area, which is provisionally set as the first area in which non-metal is captured, and the luminance value of the pixel of interest 21 also changes. Therefore, it is desirable for the determination unit 13 to vary the threshold value depending on the X-ray irradiation angle of the subject when the X-ray image is taken. By varying the threshold value depending on the X-ray irradiation angle of the subject when the X-ray image is taken, the determination accuracy is improved.

The image processing device 10 generates a 3D image by performing reconstruction processing on the above-mentioned multiple binary images with different X-ray irradiation angles to the subject, and generates the axial image shown in FIG. 8 from the 3D image. Next, the image processing device 10 performs threshold processing on the axial image shown in FIG. 8 to generate the binary axial image shown in FIG. 9. After that, the image processing device 10 performs forward projection processing on the binary axial image shown in FIG. 9 to generate the forward projection image shown in FIG. 10. In the forward projection image shown in FIG. 10, pixels that show metal are white, and the metal has been extracted.

Compared to the image processing device proposed in Patent Document 1, the image processing device 10 is expected to improve extraction accuracy and reduce processing time when extracting a specific substance (e.g., metal) that appears in an X-ray image.

In addition to the above-described embodiment, the configuration of the invention can be modified in various ways without departing from the spirit of the invention. The above-described embodiment should be considered to be illustrative in all respects and not restrictive, and the technical scope of the present invention is indicated by the claims, not by the description of the above-described embodiment, and should be understood to include all modifications that are equivalent in meaning and scope to the claims.

For example, in the embodiment described above, metal is extracted in the forward projection image shown in FIG. 10, but metal may be extracted from the binarized image shown in FIG. 7.

For example, in the above-described embodiment, a material with high X-ray attenuation is extracted, but conversely, a material with low X-ray attenuation may be extracted. Note that in the above-described embodiment, metal is extracted as an example of a material with high X-ray attenuation, but the material with high X-ray attenuation may be a material other than metal.

For example, in the above-mentioned embodiment, a transmitted X-ray image (measurement image) is processed, but a projected image in which black and white are inverted with respect to the transmitted X-ray image (measurement image) may be processed. If the luminance value of a pixel in a transmitted X-ray image (measurement image) captured with a subject installed is Bv, and the luminance value of a pixel in a transmitted X-ray image captured without a subject installed is W, the value x obtained by logarithmic transformation of the following formula (1) is the luminance value of a pixel in the projected image. This logarithmic transformation is defined here as black and white inversion.

For example, in the above-described embodiment, the average brightness value L2 of the entire unit area provisionally designated as the first area in which a non-metal is temporarily depicted is used as the representative brightness value of the entire unit area provisionally designated as the first area in which a non-metal is temporarily depicted, but this is merely one example. For example, a value obtained by multiplying the average brightness value L2 of the entire unit area provisionally designated as the first area in which a non-metal is temporarily depicted by a predetermined constant may be used as the representative brightness value of the entire unit area provisionally designated as the first area in which a non-metal is temporarily depicted.

Multiple thresholds may be provided, and image processing using each of the multiple thresholds may be performed in parallel. For example, a first threshold may be provided for determining whether an AuAgPa alloy or a material other than an AuAgPa alloy is shown, and a second threshold may be provided for determining whether an AuAgPa alloy or Ti is shown, or a material other than an AuAgPa alloy and Ti is shown.

For example, in the above-described embodiment, X-ray images taken by a dental X-ray device are used, but this is merely one example. For example, the present invention may also be applied to X-ray images taken by a non-destructive testing device.

REFERENCE SIGNS LIST 1 Information processing device according to one embodiment of the present invention 2 Control unit 3 Storage unit 4 Communication unit 5 Display unit 6 Operation unit 10 Image processing device 11 Setting unit 12 Calculation unit 13 Determination unit 20 Transmission X-ray image 21 Pixel of interest 22 Predetermined area

Claims (4)

A setting unit that sets a predetermined region surrounding a pixel of interest in an X-ray image;
a calculation unit that calculates a representative luminance value of an entire unit region that is provisionally determined as a first region in which a first material is captured, based on an average luminance value of each of a plurality of unit regions that constitute the predetermined region;
a determination unit that determines whether the first material or a material other than the first material is included in the pixel of interest based on a magnitude relationship between a ratio of the luminance value of the pixel of interest to the representative luminance value and a threshold value;
An image processing device comprising: The image processing device according to claim 1, wherein the threshold value varies depending on the representative luminance value. The image processing device according to claim 1 or 2, wherein the threshold value varies depending on the angle of X-ray irradiation with respect to the subject when the X-ray image is captured. A setting step of setting a predetermined region surrounding a pixel of interest in the X-ray image;
a calculation step of calculating a representative luminance value of the entire unit region provisionally determined as a first region in which a first material is captured, based on an average luminance value of each of a plurality of unit regions constituting the predetermined region;
a determining step of determining whether the first material or a material other than the first material is depicted in the pixel of interest based on a magnitude relationship between a ratio of the luminance value of the pixel of interest to the representative luminance value and a threshold value;
An image processing method comprising:

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