KR101751750B1 - Method for Correcting Defects in a Medical X-ray Image - Google Patents

Abstract

A method of correcting the defects in an X-ray detection image representing a subject to be photographed and including a grid pattern and a defect is disclosed. The method includes the steps of: obtaining a first image from which the defect is excluded from the X-ray detected image; obtaining a second image in which the defect is corrected from the detected image using the first image; Obtaining a third image in which the grid pattern is corrected in the image, and obtaining the defected corrected image in which the defect is corrected in the third image.

Description

[0001] The present invention relates to a method of correcting a defect in an X-ray medical image,

The present invention relates to image processing techniques and, more particularly, to a method for processing defects in a detected image acquired by a DR retrofit system.

In a conventional analog X-ray medical imaging apparatus, a CR (Computed Radiography) apparatus is known in which an imaging plate made of a phosphorescent material is attached to a cassette instead of a film. With such a CR apparatus, it is possible to acquire a digital image only by reading the imaging plate by a specially-manufactured laser scanner or CR reader without developing the exposure film in a dark room as in the conventional X-ray apparatus. It is also known that DR (Direct Radiography) equipment is a little advanced equipment in CR equipment. DR devices and CR devices are structurally different from each other. Among them, the main features of DR devices compared to CR devices are that, instead of mounting the imaging plate on a cassette as in the case of a CR device, a TFT (Thin Film Transistor ) Flat panel detector to detect an X-ray beam that has passed through a subject and does not employ a grid system. The grid system employed in the CR equipment is composed of a component that is erroneous from the time when the X-ray beam is radiated and a component that is reflected / diffused from the object to be photographed-a noise appears in the detected image when these components are detected by the detector. It is known to act as a filtering through the walls.

On the other hand, DR Retrofit System (DR Radiography Retrofit System), which uses the configuration of CR equipments while changing the detector to a TFT-based flat panel detector used in DR and adds DR / computing platform / However, since this Retrofit system uses the Grid system used in the CR equipment, grid patterns necessarily appear in the detected image. For this reason, the image processing that removes the grid pattern from the detected image is performed using a technique called GPR (Grid Pattern Remover). Another problem associated with the retrofit system is that since the system uses a TFT-based detector like a DR device, if a defect occurs at a specific location of the TFT, a defect corresponding to the detected image is generated due to the defect . Therefore, it is necessary to remove or correct the defects like the grid pattern.

However, even more serious problem is that if the defect is processed by using the pixel value around the defect, the result of using the pixel value of the grid pattern is not corrected and the artifact such as ringing ). Furthermore, even if you try to remove the grid pattern first without leaving the defect, you can not even compensate for the grid pattern because of the defect around the grid pattern. In summary, in the DR retrofit system, defects in the detector's TFTs cause defects and grid patterns to appear at the same time in the detected image. Even if one of them is removed / corrected, Is difficult.

SUMMARY OF THE INVENTION The present invention provides a method of correcting a defect in a detected image acquired by a DR retrofit system so as not to leave an artifact as much as possible without being influenced by a grid pattern.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

According to embodiments of the present invention, there is provided a method of correcting the defect in an X-ray detection image that represents an object to be imaged and includes a grid pattern and a defect. The method includes the steps of: obtaining a first image from which the defect is excluded from the X-ray detected image; obtaining a second image in which the defect is corrected from the detected image using the first image; Obtaining a third image in which the grid pattern is corrected in the image, and obtaining the defected corrected image in which the defect is corrected in the third image.

In one embodiment, the obtaining of the first image may include obtaining a first frequency domain image by converting the detected image into a frequency domain, obtaining at least one Extracting a frequency component of the second frequency domain image to obtain a second frequency domain image, and inversely transforming the second frequency domain image into a spatial domain.

In one embodiment, the method may further include a step of temporarily adjusting at least one pixel value representing the defect in the detected image, prior to the step of obtaining the first image.

In one embodiment, the obtaining of the second image may include replacing a pixel value of at least one pixel representing the defect in the detected image with a pixel value of a corresponding pixel in the first image, For example,

In one embodiment, the obtaining of the third image may include changing pixel values of pixels representing the grid pattern using pixel values of at least one pixel around the pixels representing the grid pattern in the second image Step < / RTI >

In one embodiment, the step of obtaining the third image may include generating a third frequency domain image by converting the second image into a frequency domain, generating at least one frequency domain image corresponding to the grid pattern in the third frequency domain image, Generating a fourth frequency domain image by removing a frequency component, and generating the third image by inversely transforming the fourth frequency domain image into a spatial domain.

According to embodiments of the present invention, an apparatus for correcting the defect from an X-ray detected image including a grid pattern and a defect is also provided. The apparatus includes an input unit to which the detected image is input, a second image obtained by correcting the defect from the detected image using the first image from which the defect is excluded from the detected image, An image processing and control unit for obtaining a third image having the grid pattern corrected and obtaining the defected corrected image corrected in the third image, and a storage unit for storing the detected image and the defected corrected image .

According to the embodiment of the present invention, it is possible to correct the defect so that the artifact is not left as much as possible without being affected by the grid pattern in the detection image acquired by the DR retrofit system, There is a technical effect that the image can be improved and thus a more suitable image for medical diagnosis can be provided.

Figure 1 shows an embodiment of a block diagram of an apparatus for correcting defects in a detected image acquired by a DR retrofit system in accordance with the present invention.
FIG. 2 shows an embodiment of a flowchart for explaining a method of correcting a defect in a detected image acquired by a DR retrofit system according to the present invention.
3 is a photograph showing a detection image acquired by the DR retrofit system.
4 is a photograph of a first frequency domain image generated by converting a provisionally corrected detection image into a frequency domain according to an embodiment of the present invention.
5 is a diagram illustrating a photograph of a second image generated by correcting at least one pixel representing a defect in a detected image based on a virtual grid image according to an embodiment of the present invention.
6 is a diagram illustrating a photograph of a third image generated by correcting a grid pattern in a second image according to an embodiment of the present invention.
FIG. 7 is a flowchart illustrating a procedure for generating a defect-corrected image by correcting a defect in a third image in which a grid pattern is corrected according to an exemplary embodiment of the present invention. Referring to FIG.
8 is a diagram illustrating one embodiment of a directional map showing edge directionality of edge pixels generated in accordance with the present invention.
9 is a view showing a photograph of a defect-corrected image generated by correcting a defect in a third image according to an embodiment of the present invention.
10 (a) and 10 (b) are photographs of images obtained by an existing image processing method and images of defocus-corrected images according to an embodiment of the present invention, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of attaining them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. To fully disclose the scope of the invention to a person skilled in the art, and the invention is only defined by the scope of the claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. For example, an element expressed in singular < Desc / Clms Page number 5 > terms should be understood to include a plurality of elements unless the context clearly dictates a singular value. In addition, in the specification of the present invention, it is to be understood that terms such as "include" or "have" are intended to specify the presence of stated features, integers, steps, operations, components, The use of the term does not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, parts or combinations thereof. Further, in the embodiments described herein, 'module' or 'sub-unit' may mean at least one function or a functional part performing an operation.

In addition, all terms used herein, including technical or scientific terms, unless otherwise defined, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be construed as meaning consistent with meaning in the context of the related art and may be interpreted in an ideal or overly formal sense unless explicitly defined in the specification of the present invention It does not.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

Figure 1 shows an embodiment of a block diagram of an apparatus for correcting defects in a detected image acquired by a DR retrofit system in accordance with the present invention.

As shown in FIG. 1, the apparatus 100 may include an input unit 110, an image processing and control unit 120, and a storage unit 130. The input unit 110 may be configured to be operable to receive a detection image acquired by the DR retrofit system (not shown) under the control of the image processing and control unit 120 and to store the detection image in the storage unit 130 have. In one embodiment, the input 110 may be implemented as an input interface configured to receive a detected image provided from a DR retrofit system. In one embodiment, input 110 may be implemented by a recording medium input terminal, such as a USB terminal of a computer.

The storage unit 130 may store a detection image provided from the input unit 110. [ The storage unit 130 may further store software / firmware necessary for implementing the image processing and control unit 120. The storage unit 130 stores various data processed or used by the image processing and control unit 120, intermediate image data generated according to the embodiment of the present invention, final processed data generated according to the embodiment of the present invention The image data can be further stored. The storage unit 130 may further store a direction map indicating an edge direction of edge pixels generated according to an embodiment of the present invention. The storage unit 130 may be a flash memory type, a hard disk type, a MultiMedia Card (MMC), a card type memory (for example, SD (Secure Digital) card or XD (Random Access Memory), SRAM (Static Random Access Memory), ROM (Read Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), PROM (Programmable Read-Only Memory) A magnetic disk, a magnetic disk, and an optical disk. However, those skilled in the art will appreciate that the embodiment of the storage unit 130 is not limited thereto.

The image processing and control unit 120 may be configured to perform image processing for reading a part or all of the detected image from the storage unit 130 and correcting the defect according to an embodiment of the present invention. Here, correcting the defect means that the visual effect of the defect is alleviated by changing the pixel value of at least one pixel corresponding to the defect, which does not necessarily mean completely eliminating the defect itself . For the defect correction, the image processing and control unit 120 generates a virtual grid image from the detected image including the grid pattern and the defects, and generates at least one pixel representing the defect in the detected image, based on the virtual grid image A series of processes for generating a temporary corrected image by correcting the grid pattern, correcting the grid pattern in the provisionally corrected image to generate a corrected grid pattern image, and correcting the defect in the grid pattern corrected image to generate a defect corrected image And can be configured to perform arithmetic processing.

In one embodiment, the image processing and control unit 120 may be configured to perform image processing on a pixel-by-pixel basis or block-based image processing on other images generated by processing a detected image or a detected image. In one embodiment, the image processing and control unit 120 generates a frequency domain image or a signal by applying a 2-D fast Fourier transform (FFT) to other images generated by processing the detected image or the detected image Lt; / RTI > In one embodiment, the image processing and control unit 120 may be further configured to generate a spatial domain image by applying a 2-D IFFT (2-Dimensional Inverse Fast Fourier Transform) to the frequency domain image or signal. In one embodiment, the image processing and control unit 120 may be further configured to filter the image signal in the spatial domain and / or the frequency domain. Here, the filtering may include low pass filtering, high pass filtering, band pass filtering, and band rejection filtering, but the image processing and control unit It should be noted that the types of filtering that can be performed in the buffer 120 are not limited thereto.

In one embodiment, the image processing and control unit 120 may further be configured to correct pixel values of pixels of interest in the image signal using pixel values of at least one pixel in the vicinity of the pixel. Here, correcting the pixel value of the pixel of interest by using the pixel value of at least one pixel in the periphery of the pixel means that the pixel value of the pixel of interest is the pixel of at least one pixel around the pixel Value, or a representative value, a weighted average value, or an average value of pixel values of these pixels, but the meaning is not limited thereto. In one embodiment, the image processing and control unit 120 may be further configured to generate an edge image by performing edge detection on other images generated by processing the detected image or the detected image. In an example, the image processing and control unit 120 may be further configured to generate a binarized image by applying a thresholding technique to the edge image. In one embodiment, the image processing and control unit 120 may be further configured to generate a recorded direction map by calculating the edge direction of each edge pixel in the binarized image. In one embodiment, the edge orientation of each edge pixel may be represented by an angle formed by the edge pixel in the clockwise direction with respect to the X axis of the image and the other edge pixels neighboring the edge pixel.

The image processing and control unit 120 may be implemented in hardware by application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs) Programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, micro-controllers, and microprocessors. Or the like. The image processing and control unit 120 may also be implemented as a firmware / software module executable on the aforementioned hardware platform. In this case, the firmware / software module may be implemented by one or more software applications written in an appropriate program language.

FIG. 2 shows an embodiment of a flowchart for explaining a method of correcting a defect in a detected image acquired by a DR retrofit system according to the present invention. 3 is a photograph showing a detection image acquired by the DR retrofit system. As shown in Fig. 3, the detected image I includes a grid pattern G of vertical stripes and a defect D in addition to the object to be imaged.

One embodiment of the present method starts with temporarily correcting the detected image I (S201). In this step, the pixel values of the pixels representing the defective (D) portion in the detected image (I) can be changed using the pixel values of at least one pixel around the defect D. In one embodiment, it is possible to identify the positions of the pixels of the defective portion with reference to a defect map that records at least one pixel location where the defect D exists in the detected image I. It should be appreciated that the reason for performing this step is to increase the fidelity of the Virtual Grid Image to be created in the following steps, so this step is not essential to the implementation of the method.

In step S202, a first frequency domain image is generated by converting the detected image I or the temporally corrected detected image into a frequency domain. In this case, the conversion into the frequency domain can be performed by performing 2-D fast Fourier transform (2-D FFT) on the detected image I as is well known. A photograph of the first frequency domain image obtained by the execution of this step is shown in Fig. In step S203, at least one frequency component fs corresponding to the object to be imaged and at least one frequency component fg corresponding to the grid pattern are extracted from the first frequency domain image, And generates an image. In one embodiment, the second frequency domain image includes at least one frequency component corresponding to an object to be imaged in the first frequency domain image, and the remaining frequency components excluding at least one frequency component corresponding to the grid pattern, Masking < / RTI > In this case, the frequency (i.e., position in the frequency domain) of the at least one frequency component corresponding to the grid pattern is experimentally determined based on the specifications of the detector of the DR retrofit system and the grid included in the detector Can be determined. In one embodiment, the second frequency domain image may include a second frequency domain image that selectively passes the at least one frequency component corresponding to the object to be imaged and the at least one frequency component corresponding to the grid pattern, A 2-dimensional Gaussian filter may be used.

In step S204, a first image is generated by inversely transforming the second frequency domain image into a spatial domain. Since the first image is synthesized using only the frequency components corresponding to the object to be photographed and the grid pattern, the frequency components corresponding to the defects D are substantially excluded, Virtual Grid Image). This step may be performed by performing 2-D IFFT (2-Dimensional Inverse Fast Fourier Transform) on the second frequency domain image as is well known. In step 205, at least one pixel representing the defect D in the detected image I is corrected based on the first image to generate a second image. In one embodiment, the pixel value of at least one pixel representing the defect D in the detected image I is replaced with the pixel value of the corresponding pixel in the first image (virtual grid image) to generate a second image can do. In one embodiment, a portion representing the defect D in the detected image I may be replaced with a corresponding portion in the first image (virtual grid image) to generate a second image. The second image can be regarded as a grid pattern-based image in which the video effect of the defect D is suppressed. The technical reason for carrying out this step is that if the grid pattern correcting process is performed immediately after replacing the defective portion with the corresponding portion of the first image (virtual grid image), a defect such as ringing This is because artifacts are generated. A photograph of the second image generated by this step is shown in FIG.

In step 206, a third image is generated by correcting the grid pattern in the second image. In one embodiment, the grid pattern correction may be performed in the spatial domain. For example, a grid pattern correction can be made by changing the pixel values of the pixels representing the grid pattern using the pixel values of at least one pixel around the pixels representing the grid pattern in the second image. In one embodiment, grid pattern correction may be performed in the frequency domain. A fourth frequency domain image is generated by removing at least one frequency component corresponding to the grid pattern from the third frequency domain image by generating the third frequency domain image by converting the second image by FFT to the frequency domain, It is possible to generate a third image in which the grid pattern is corrected / removed by performing inverse transform (IFFT) on the frequency domain image again to the spatial domain. A photograph of the third image generated by this step is shown in Fig. In step S207, the defect-corrected image is generated by correcting / removing the defect D from the third image whose grid pattern has been corrected / removed.

FIG. 7 is a flowchart illustrating an example of a detailed procedure of step S207 of FIG. 2. Referring to FIG.

In step S701, low pass filtering is performed on the third image generated in step S206 of FIG. 2 in the spatial domain. In one embodiment, the low pass filtering for the third image may be performed using a Gaussian filter. In one embodiment, a procedure may be performed to correct the defect D in the third image using pixel data around the defect D prior to performing the low-pass filtering. In step S702, edge detection is performed on the low-pass filtered third image to generate an edge image. In one embodiment, instead of performing an edge detection on the entire third image, it may comprise at least one pixel representing the defect D and surrounding pixels around the at least one pixel representing the defect D It is possible to reduce the processing time by performing edge detection only on the local area of the third image. In one embodiment, the local area may be a block of a predetermined size comprising at least one pixel representing a defect D and surrounding pixels around at least one pixel representing a defect D. In one embodiment, the edge detection may be performed by high pass filtering.

In step S703, pixels having a luminance value or more selected from the edge image are classified into edge pixels. In one embodiment, edge pixels may be identified by binarizing an edge image by applying a thresholding technique to the edge image. In step S704, at least one pixel representing the defect D in the third image among the edge pixels and corresponding edge pixels are classified as first edge pixels, and the edge direction of each of the first edge pixels edge direction. In one embodiment, the edge direction of the first edge pixel may be represented by an angle formed by the first edge pixel in the clockwise direction with respect to the other first edge pixel neighboring the first edge pixel and the X axis of the image. In step S705, edge pixels corresponding to neighboring pixels in the periphery of at least one pixel representing the defect D in the third image among the edge pixels are classified as second edge pixels, And calculates the edge directionality of each of the pixels. Likewise, the edge directionality of the second edge pixel may be represented by an angle formed by the second edge pixel in the clockwise direction with respect to the second edge pixel neighboring the second edge pixel and the X axis of the image. In the above-described embodiment, the edge direction of the first edge pixels and the edge direction of the second edge pixels are separately calculated in steps S704 and S705. However, the directional map of all the edge pixels it is possible to generate a direction map in advance and refer to the directional map when it is necessary to consider the edge direction of each edge pixel in the subsequent procedure. Referring to FIG. 8, there is shown a directional map generated in accordance with an embodiment of the present invention.

The pixels in the third image corresponding to the first edge pixels classified in step S704 are pixels whose edge components are strong among the pixels representing the defect in the third image, . ≪ / RTI > Thus, in step S706, the following processing is performed for each of the first edge pixels. First, at least one second edge pixel whose edge direction matches the corresponding first edge pixel of the second edge pixels is found and identified as at least one third edge pixel. Next, the pixel value of the pixel in the third image corresponding to the first edge pixel is corrected using the pixel value of the pixel in the third image corresponding to the identified at least one third edge pixel. Here, the pixel in the third image corresponding to the first edge pixel is a pixel whose edge component is strong among the pixels representing the defect D, and is corrected by this step. In one embodiment, a directional map may be referenced in performing step S706. A photograph of the image in which the defect D is corrected through the step S706 is shown in Fig. In step S707, a random noise is generated for a local area including at least one pixel representing the defect in the third image and a pixel around the at least one pixel representing the defect, . This step is an optional step, and the reason for performing this step is to alleviate the visual effects of strong pixels or artifacts that can only remain.

10 (a) and 10 (b) are photographs of images obtained by an existing image processing method and images of defocus-corrected images according to an embodiment of the present invention, respectively. Referring to FIGS. 10A and 10B, in the case of an image corrected for a defect according to an embodiment of the present invention, the image quality of the defective portion is remarkably improved as compared with an image processed in the conventional manner Can be confirmed.

In the embodiments disclosed herein, the order of arrangements or steps of the components shown may vary depending on the environment or requirements in which the invention is implemented. For example, some components or some steps may be omitted or some components or some steps may be integrated into one. In addition, the arrangement order and connection of some components may be changed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Accordingly, the technical scope of the present invention should be determined only by the appended claims.

100: Defect correction device
110: input unit
120: Image processing and control unit
130:
I: Detection video
G: grid pattern
D: Defect
fs: frequency component corresponding to the object to be photographed
fg: frequency component corresponding to the grid pattern

Claims (8)

A defect correction method by a defect correction apparatus including an input unit, an image processing unit, and a control unit,
Obtaining a first image from which the defect is excluded from an X-ray detection image including an input unit grid pattern and a defect,
The image processing and control unit obtaining the defective second image from the detected image using the first image,
The image processing and control unit obtaining a third image in which the grid pattern is corrected in the second image, and
And the image processing and control unit obtains the defect-corrected image in which the defect is corrected in the third image
A defect correction method. The method according to claim 1,
The obtaining of the first image may include:
The image processing and control unit converting the detected image into a frequency domain to obtain a first frequency domain image,
Extracting at least one frequency component corresponding to an object to be photographed and the grid pattern from the first frequency domain image to obtain a second frequency domain image;
And the image processing and control unit inversely transforming the second frequency domain image into a spatial domain. The method according to claim 1,
Before the step of obtaining the first image,
Further comprising the step of the image processing and control section adjusting the at least one pixel value indicating the defect in the detected image to temporarily correct the pixel value. The method according to claim 1,
The obtaining of the second image may include:
And the image processing and control unit generating the second image by replacing the pixel value of the at least one pixel representing the defect in the detected image with the pixel value of the corresponding pixel in the first image. Defect correction method. The method according to claim 1,
The obtaining of the third image may include:
And the image processing and control unit modifying pixel values of pixels representing the grid pattern using pixel values of at least one pixel around pixels representing the grid pattern in the second image, Way. The method according to claim 1,
The obtaining of the third image may include:
The image processing and control unit converting the second image into the frequency domain to generate a third frequency domain image,
Wherein the image processing and control unit removes at least one frequency component corresponding to the grid pattern from the third frequency domain image to generate a fourth frequency domain image,
And the image processing and control unit generating the third image by inversely transforming the fourth frequency domain image into a spatial domain. 7. A computer readable recording medium having stored thereon a program for executing a method according to any one of claims 1 to 6 when executed by a computer, Possible recording medium. An apparatus for correcting a defect from an X-ray detection image including a grid pattern and a defect,
An input unit for inputting the detection image,
Obtaining a second image in which the defect is corrected from the detected image using the first image from which the defect is excluded from the detected image, obtaining a third image in which the grid pattern is corrected in the second image, An image processing and control unit for obtaining a defect corrected image in which the defect is corrected in three images, and
And a storage unit for storing the detection image and the defect correction image.

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