KR101018051B1 - Method for reducing metal artifact from X-ray image - Google Patents

Abstract

The present invention provides a method for reducing metal artifacts in X-ray imaging images taken with an X-ray imaging apparatus, in particular, X-ray imaging images taken with a dental X-ray imaging apparatus. It is about a method.

X-Ray Imaging Device, Metal Artifact, Projection, FBP

Description

Method for reducing metal artifacts from X-ray images

The present invention relates to a method for reducing metal artifacts in an X-ray imaging image, and more particularly, to reduce metal artifacts in an X-ray imaging image providing a method for reducing metal artifacts generated in an X-ray imaging image captured by an X-ray imaging apparatus. It is about a method.

In the medical field, an X-ray imaging apparatus is an apparatus that acquires an X-ray photographed image by detecting X-rays on a portion to be photographed.

On the other hand, in dental practice, when tooth damage occurs, such as tooth decay in the patient's teeth, the damaged tooth is filled with dental fillings (dental fillings) or replaced by prosthetic devices (prosthetic devices).

When X-ray imaging of a patient having the dental filler or the tooth mounted with the prosthetic device, the metal object such as the dental filler or the prosthetic device almost do not penetrate the X-rays so that the surrounding soft tissue ( Metal artifacts such as shade artifacts, artifact streak artifacts, and star-burst artifacts are created by soft tissue or skeletal structures.

The metal artifact affects an image of not only itself but also other objects around it, causing a problem of obscuring the X-ray photographed image.

The metal artifact may make the X-ray image unclear and the doctor may read the unclear X-ray image to misdiagnose the dental state of the patient.

Accordingly, the present invention is to solve the above-mentioned disadvantages and problems of the prior art, it is generated from the X-ray imaging image obtained by photographing a portion in which the material or the low transmittance of X-rays, such as metal is mounted or inserted with the X-ray imaging apparatus It is an object of the present invention to provide a method for reducing metal artifacts in an X-ray image showing a method for reducing metal artifacts.

The object of the present invention is to obtain an initial reconstruction image from the X-ray projection data obtained from the X-ray imaging apparatus; Separating a metal image corresponding to a metal region from the initial reconstructed image, and finding a metal-trace each of the metal regions corresponding to the X-ray projection data; Processing the metal region as a first missing region, and processing the first missing region by interpolation using values around the first missing region to obtain a first modified reconstructed image; Acquiring a second modified reconstructed image having reduced streak artifacts through a smoothing method of the first modified reconstructed image; Reprojecting the second modified reconstructed image to obtain first reprojection data; The region in which the metal-traces of the first reprojection data overlap is treated as a second missing region, and the second missing region is processed by interpolation using data values around the second missing region of the first reprojection data. Create virtual data, and compare pixels of the virtual data and the first reprojection data to compare the virtual pixels with respect to pixels having a value smaller than corresponding pixels of the virtual data among the pixels of the first reprojection data; Obtaining second reprojection data by substituting pixels of data; The data of the region corresponding to the metal traces of the second reprojection data is extracted, and the data of the region corresponding to the metal traces from the X-ray projection data is extracted from the second reprojection data. Obtaining final projection data by substituting data of an area corresponding to the data; And reconstructing the final projection data to obtain a final reconstruction image and pasting a metal image separated from the initial reconstruction image to the final reconstruction image to complete a final reconstruction image. Is achieved by a method of reducing metal artifacts.

In addition, the object of the present invention is also achieved by a method for reducing metal artifacts in an X-ray imaging image, characterized in that at least two metal artifacts are present in the initial reconstructed image.

In addition, the object of the present invention is also achieved by a method for reducing metal artifacts in an X-ray imaging image, characterized in that the X-ray imaging apparatus is a dental computerized tomography (CT) imaging device.

In addition, the object of the present invention is also achieved by a method for reducing the metal artifacts in the X-ray imaging, characterized in that the initial reconstructed image is a reconstructed image by the FBP (filtered back-projection) method.

In addition, the object of the present invention is also achieved by a method for reducing metal artifacts in X-ray imaging, characterized in that the smoothing method is a TV-based smoothing (Total Variation-based smoothing) method.

The method of reducing metal artifacts in an X-ray photographing image of the present invention has an effect of providing a method of reducing metal artifacts in an X-ray photographing image photographed by an X-ray photographing apparatus.

In addition, the method for reducing metal artifacts in the X-ray image of the present invention, in particular, by presenting a method for reducing the metal artifacts in the tooth X-ray image of the patient taken by the dental X-ray imaging device in the teeth X-ray image of the patient The present invention has an effect of providing a method of reducing metal artifacts in an X-ray photographing image to remove metal artifacts generated by a filler or an artificial prosthetic device inserted into or mounted on the X-ray photographing apparatus to provide a clear and high read rate X-ray photographing image.

Details of the above objects and technical configurations and the effects thereof according to the present invention will be more clearly understood by the following detailed description with reference to the drawings showing preferred embodiments of the present invention. Like numbers refer to like elements throughout the specification.

First, a method of acquiring a reconstructed image from X-ray projection data obtained by using an X-ray imaging apparatus will be briefly described.

First, the object is positioned between the X-ray light source unit and the X-ray sensor unit included in the X-ray photographing apparatus, the X-ray generated by the X-ray light source unit is irradiated with the object, the X-ray sensor unit detects the data, and acquires two-dimensional projection data. .

The X-ray light source unit and the X-ray sensor unit acquire a plurality of projection data while scanning rotating the circular trajectory by 360 degrees while moving at the same angle.

Finally, the reconstructed image of the object is obtained by reconstructing the plurality of projection data.

At this time, there are several techniques for obtaining the reconstructed image, but in the present invention, the FBP (filtered back-projection algorithm) technique proposed by Feldkamp, Davis, and Kress (FDK) was used.

The FBP technique is treated according to the following method.

First, preprocessing and filtering are performed. The projection data acquired by the X-ray imaging apparatus are loaded one by one.

Then, the Jacobian weighting process is performed on the projection data.

In this case, the Jacobian weighting process is a process for correcting a change in a value between polar coordinates and rectangular coordinates during a mathematical process.

The projection data is filtered using a filter.

At this time, the filtering becomes the core of the FBP technique. When the filtering is not performed, the shape of the object part derived as a result of the reconstruction appears blurred and unclear. In order to solve this problem, each projection data is filtered so that the shape of the original object can be approximated. The filtering process is performed between the Jacobian weighting process and the back-projection process to be described later.

Then back-projection is performed. The weighting factor of the target point data of the projection data according to the distance is calculated.

Then, interpolation is performed using the projection data to determine the value of each target point of the three-dimensional volume. And the value of the target point is stored.

The reconstructed slice is then stored.

Each of the projection data is sequentially processed through the preprocessing, filtering, back-projection processing, and reconstruction section storage, and the reconstruction result is stored in the cross section to obtain a reconstruction image.

1 is a flowchart illustrating a method of reducing metal artifacts according to an embodiment of the present invention, and FIGS. 2 to 12 are images showing results of the method of reducing metal artifacts according to an embodiment of the present invention. The figures are shown.

Referring to FIG. 1, first, an X-ray projection data of a patient as shown in FIG. 2 is obtained from an X-ray imaging apparatus having an X-ray light source unit generating X-rays and an X-ray sensor unit corresponding to the X-ray light source unit and detecting the X-rays. Acquire it.

In this case, the method for reducing metal artifacts according to an embodiment of the present invention may be used as a method for reducing metal artifacts in X-ray projection data obtained from X-ray imaging apparatuses used in various medical fields. computerized tomography) may be applied to the X-ray projection data obtained from the imaging device.

An initial reconstructed image is obtained from the X-ray projection data obtained from the X-ray imaging apparatus by the above-described FBP technique (S100).

At this time, the initial reconstructed image is filled or replaced with a filler or an artificial prosthetic device at three tooth positions 10 to cause metal artifacts, as shown in FIG. 3.

Meanwhile, the method for reducing metal artifacts according to an embodiment of the present invention may be generated by filling or replacing three tooth positions 10 with filler or prosthetic device in the initial reconstruction image shown in FIG. 3. In addition to reducing metal artifacts, it may also be applied to reducing metal artifacts caused by filling or replacing at least two or more tooth locations 10 with a filler or prosthetic device or the like.

That is, the method for reducing metal artifacts according to an embodiment of the present invention reduces metal artifacts in X-ray projection data of an X-ray image of a patient's teeth stuffed or replaced with filler or prosthetic device at least two or more tooth positions. Here's a useful way to help.

The metal artifacts are not only direct metal artifacts by the filler or prosthetic device located at the tooth position 10, but also shade artifacts 20 and streak artifacts generated by the filler or prosthetic device as shown in FIG. 60 is also included.

Subsequently, the metal image 40 corresponding to the metal region by the filler or the prosthetic device located at the tooth position 10 is separated from the initial reconstructed image, and the position corresponding to the X-ray projection data of each of the metal regions is determined. The metal trace 30 is found (S200).

4A and 4B show the metal regions 40 and the metal-trace 30 separated from the initial reconstructed image.

Meanwhile, in order to separate the metal image from the initial reconstructed image, a method of distinguishing a metal region from other regions is performed using a hounsfield unit.

That is, when X-rays pass through a specific material, the amount of X-rays is attenuated by the physical characteristics of the specific material. The attenuation of the specific material is expressed numerically. Is the Hounsfield unit.

On the other hand, the higher the hounsfield unit, the higher the value means that the attenuation of X-rays, that is, the degree of blocking the X-rays is larger.

If X-rays of the human head are taken, the soft tissue of the head will show the lowest Hounsfield unit value, and the bone will have a higher unit value than the soft tissue, such as a filler or prosthetic device. Metallic objects that block X-rays will exhibit much higher Hounsfield unit values than the soft tissue and bone.

In this case, Table 1 below shows representative Hounsfield unit values as a table.

Material Hounsfield unit (HU) Air -1000 Soft tissue -100 to 60 Bone 1000 Temporary fillings 6000-8500 Composite fillings 4500-17000 Gold ＞ 30710

Therefore, in the method of separating the metal region from the initial reconstructed image, the X-ray projection data corresponding to the initial reconstructed image are converted into hounsfield units, and then the houns are higher than the hounsfield units of bone in the hounsfield units. The metal region may be separated from the initial reconstructed image by setting the region having the spfield units as the metal region and separating the region.

Accordingly, the first missing area refers to an area after the metal image is separated from the initial reconstructed image, that is, the data corresponding to the metal image is extracted, and the first missing area is a 'null' value or a '0' value. Process.

Subsequently, the first missing area, that is, the area treated as the 'null' value or the '0' value, is processed by interpolation using data values around the first missing area to obtain the first missing area as shown in FIG. 5. The first missing area 45 obtains a first modified reconstructed image processed by interpolation (S300).

In this case, the interpolation method is performed by inferring and filling a 'null' value or '0' value of the first sewing area from data around the first sewing area. In this case, the interpolation may be performed by various methods such as linear interpolation.

Subsequently, the first modified reconstructed image is obtained by reducing the streak artifact 60 through a smoothing method as illustrated in FIG. 6 (S400).

At this time, the twenty singbeop is Gaussian smoothing filter method (Gaussian smoothing filter), median filter method (median filter), and TV- based twenty singbeop (Total Variation smoothing-based) but the like, the derivative of the image L ₁ It is desirable to use a TV-based smoothing method that minimizes -norm (sum or integration of absolute values) and preserves the edges of the image.

Subsequently, the second reconstruction image is reprojected to obtain first reprojection data as illustrated in FIG. 7 (S500).

Subsequently, an area 50 in which the metal-traces 30 overlap with each other in the first reprojection data is processed.

As illustrated in FIG. 7, the second sewing area refers to an area 50 in which the metal traces overlap, and the second sewing area is 'null' in the same manner as the first sewing area. Treat as a value or '0' value.

Subsequently, the second missing region, that is, the region 50 in which the metal traces overlap, is processed by interpolation using data values around the second missing region of the first reprojection data to generate a virtual image as shown in FIG. 8. Create data, compare each pixel of the virtual data with the first reprojection data, and compare the virtual data with respect to pixels having a value smaller than corresponding pixels of the virtual data among pixels of the first reprojection data; The second reprojection data as shown in FIG. 9 is obtained by substituting the pixels of S (S600).

In this case, the method of obtaining the second reprojection data from the first reprojection data will be described in detail with reference to FIG. 13. The first reprojection data (shown with a solid line) is processed by interpolation and the virtual data (shown with a dotted line) After obtaining, the first reprojection data and the virtual data are compared, that is, the pixels of the first reprojection data and the pixels of the virtual data corresponding to the pixels of the first reprojection data are compared with each other. The second reprojection data is obtained by replacing the pixels of the virtual data having a value larger than the pixels of the first reprojection data with the pixels of the first reprojection data.

The interpolation method for acquiring the second reprojection data may be the same as the interpolation method of filling the data of the metal region.

Next, data of an area corresponding to the metal traces 30 of the second reprojection data is extracted and replaced with data of an area corresponding to the metal traces 30 in the X-ray projection data. The final projection data including the data corresponding to the metal-traces 30 of the second reprojection data as shown in the drawing are obtained (S700).

Subsequently, the final projection data is reconstructed to obtain a final reconstructed image as shown in FIG. 11.

Subsequently, since the metal image does not exist in the final reconstructed image shown in FIG. 11, as shown in FIG. 12, the metal region 40 separated from the initial reconstructed image, that is, the metal image (in FIG. 4A). Paste) to complete the final reconstruction image (S800).

In this case, the final reconstruction images shown in FIGS. 11 and 12 show that the metal artifacts are considerably reduced in comparison with the initial reconstruction images shown in FIG. 3. In particular, the streak artifact 60 Significantly reduced, the metal artifacts present in the initial reconstructed image have been significantly reduced, such that the final reconstructed image is clearly reconstructed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

1 is a flowchart illustrating a method of reducing metal artifacts according to an embodiment of the present invention.

2 to 12 are images showing results of performing a method of reducing metal artifacts according to an embodiment of the present invention.

13 is a conceptual diagram illustrating a method of obtaining second reprojection data from first reprojection data.

<Description of the symbols for the main parts of the drawings>

10: tooth position 20: shade artifact

30: metal-trace 40: metal area

50: region where metal-traces overlap

60: Strike Artifact

Claims (5)

Obtaining an initial reconstructed image from the X-ray projection data obtained from the X-ray imaging apparatus; Separating a metal image corresponding to the metal region from the initial reconstructed image, and finding a metal-trace each of the metal regions corresponding to the X-ray projection data; Processing the metal region as a first missing region, and processing the first missing region by interpolation using values around the first missing region to obtain a first modified reconstructed image; Acquiring a second modified reconstructed image having reduced streak artifacts through a smoothing method of the first modified reconstructed image; Reprojecting the second modified reconstructed image to obtain first reprojection data; The region in which the metal-traces of the first reprojection data overlap is treated as a second missing region, and the second missing region is processed by interpolation using data values around the second missing region of the first reprojection data. Create virtual data, and compare pixels of the virtual data and the first reprojection data to compare the virtual pixels with respect to pixels having a value smaller than corresponding pixels of the virtual data among the pixels of the first reprojection data; Obtaining second reprojection data by substituting pixels of data; The data of the region corresponding to the metal traces of the second reprojection data is extracted, and the data of the region corresponding to the metal traces from the X-ray projection data is extracted from the second reprojection data. Obtaining final projection data by substituting data of an area corresponding to the data; And Reconstructing the final projection data to obtain a final reconstructed image, and pasting a metal image separated from the initial reconstructed image to the final reconstructed image to complete a final reconstructed image. How to reduce metal artifacts. The method of claim 1, And at least two metal artifacts are present in the initial reconstructed image. The method of claim 1, The X-ray imaging apparatus is a dental computerized tomography (CT) imaging device, characterized in that for reducing metal artifacts in the X-ray imaging. The method of claim 1, And the initial reconstructed image is an image reconstructed by a filtered back-projection (FBP) method. The method of claim 1, The smoothing method is a TV-based smoothing method. The method for reducing metal artifacts in an X-ray photographed image.

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