CT local imaging

Abstract

The present invention relates to a CT local imaging method, wherein a CT scanning section is arranged through a rotating shaft of a turntable, and the turntable is used to place a scanned object, and the method comprises the following steps: performing a CT scan of the scanned object once in an initial state, and setting the CT scanning section in the initial state as an anchor surface; stepping and rotating the turntable, performing a CT scan once in each step, and recording the angle θ between the CT scanning section and the anchor surface; performing differential back-projection Hilbert inverse transform reconstruction to realize local imaging reconstruction. The method can realize the elimination of artifacts of CT local imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of CT three-dimensional imaging, and in particular to a CT local imaging method. Background Art

[0002] CT (Computed Tomography) is a new non-destructive testing method formed by the intersection of computer science and high-energy physics. This technology realizes the scanning and reconstruction of tomographic images of the object being tested. It is widely used in fields such as medicine and industry.

[0003] Among CT image reconstruction algorithms, the most mature scanning reconstruction algorithm is filtered back projection reconstruction (FBP). This method is an analytical algorithm for image reconstruction and supports parallel computing, so it can reconstruct clearer CT images in a shorter time.

[0004] However, with the expansion of the application field of industrial CT, the rotation radius of the workpiece increases. The field of view defined by the detector size cannot completely cover the workpiece. However, most areas of the workpiece are usually not the detection area, and only part of the area of ​​interest to be detected, and this local area can be included in the field of view. However, only scanning this local area and then using filtered back projection reconstruction (FBP) will lead to serious truncation effects and produce artifacts. Therefore, it is particularly necessary to study a new industrial CT local scanning and reconstruction method to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a CT local imaging method to eliminate the artifacts of CT local imaging.

[0006] The technical solution of the present invention is:

[0007] A CT local imaging method, wherein the CT scanning section is arranged through a rotating axis of a turntable, and the turntable is used to place the scanned object, comprising the following steps:

[0008] The scanned object is scanned once by CT in the initial state, and the CT scanning section in the initial state is set as the anchor surface;

[0009] The turntable is rotated step by step, and a CT scan is performed at each step, and the angle θ between the CT scan section and the anchor surface is recorded;

[0010] Perform differential back-projection Hilbert inverse transform reconstruction to achieve local imaging reconstruction.

[0011] Preferably, the differential back-projection Hilbert inverse transform reconstruction method comprises the following steps:

[0012] Weighted calculation to process the index data

[0013] (1)

[0014] Where D is the distance from the ray source to the center of the detector, ξ is the rotation angle of the turntable, and u is the distance between the detector unit and the center. is the graduation data;

[0015] Differentiation weighted data

[0016] (2)

[0017] Weighted data after back-projection differential operation

[0018] (3)

[0019] in, , , R represents the distance from the ray source to the rotation center;

[0020] Inverse Hilbert transform backprojection data

[0021] (4)

[0022] Get the reconstructed image f(x).

[0023] Preferably, the method for recording the angle between the CT scanning section and the anchor surface is to calculate the rotation angle of the turntable.

[0024] Preferably, it also includes a camera for photographing the scanned object and the turntable, and the method for recording the angle between the CT scanning section and the anchor surface is: photographing the scanned object and the turntable; using an image segmentation algorithm based on RGB color information to obtain the air area in the field of view; using a fitting algorithm to calculate the angular deviation between the CT ray direction and the initial scanning position.

[0025] Further preferably, the image segmentation algorithm based on RGB color information includes the following steps: setting the turntable RGB color standard value Color (r, g, b), setting the color threshold; segmenting the color value in the image , , The pixels within the range are air areas.

[0026] Further preferably, the method for calculating the angular deviation between the CT ray direction and the initial scanning position is: perform Canny edge extraction on the segmented air area image to obtain an edge image; perform least squares fitting on the edge image to obtain the circular arc areas on both sides; calculate the rotation angles corresponding to the circular arc areas on both sides, and take the average to obtain the deviation angle θ between the initial scan and the specific ray direction.

[0027] The beneficial effects of the present invention are:

[0028] 1. The method of the present invention can eliminate the artifacts of CT local imaging and realize CT local imaging. DETAILED DESCRIPTION

[0029] The present invention is described below in the form of embodiments to assist those skilled in the art in understanding and implementing the present invention. Unless otherwise specified, the following embodiments and the technical terms therein should not be understood without departing from the technical knowledge background of the technical field.

[0030] Embodiment 1: A CT local imaging method, wherein the CT scanning section is arranged through a rotating axis of a turntable, and the turntable is used to place the scanned object, comprising the following steps:

[0031] The scanned object is scanned once by CT in the initial state, and the CT scanning section in the initial state is set as the anchor surface;

[0032] The turntable is rotated step by step, and a CT scan is performed at each step, and the angle θ between the CT scan section and the anchor surface is recorded;

[0033] Perform differential back-projection Hilbert inverse transform reconstruction to achieve local imaging reconstruction.

[0034] Preferably, the differential back-projection Hilbert inverse transform reconstruction method comprises the following steps:

[0035] Weighted calculation to process the index data

[0036] (1)

[0037] Where D is the distance from the ray source to the center of the detector, ξ is the rotation angle of the turntable, and u is the distance between the detector unit and the center. is the graduation data;

[0038] Differentiation weighted data

[0039] (2)

[0040] Weighted data after back-projection differential operation

[0041] (3)

[0042] in, , , R represents the distance from the ray source to the rotation center;

[0043] Inverse Hilbert transform backprojection data

[0044] (4)

[0045] Get the reconstructed image f(x).

[0046] Preferably, the method for recording the angle between the CT scanning section and the anchor surface is to calculate the rotation angle of the turntable.

[0047] Preferably, it also includes a camera for photographing the scanned object and the turntable, and the method for recording the angle between the CT scanning section and the anchor surface is: photographing the scanned object and the turntable; using an image segmentation algorithm based on RGB color information to obtain the air area in the field of view; using a fitting algorithm to calculate the angular deviation between the CT ray direction and the initial scanning position.

[0048] Further preferably, the image segmentation algorithm based on RGB color information includes the following steps: setting the turntable RGB color standard value Color (r, g, b), setting the color threshold; segmenting the color value in the image , , The pixels within the range are air areas.

[0049] Further preferably, the method for calculating the angular deviation between the CT ray direction and the initial scanning position is: perform Canny edge extraction on the segmented air area image to obtain an edge image; perform least squares fitting on the edge image to obtain the circular arc areas on both sides; calculate the rotation angles corresponding to the circular arc areas on both sides, and take the average to obtain the deviation angle θ between the initial scan and the specific ray direction.

[0050] The present invention has been described in detail above with reference to the embodiments. It should be understood that it is impossible to describe all possible implementation methods in practice, and the inventive concept of the present invention is described as much as possible by way of example. Without departing from the inventive concept of the present invention and without creative work, the technical personnel in this technical field make selections and combinations of the technical features in the above embodiments, make experimental changes to the specific parameters, or use the prior art in this technical field to conventionally replace the technical means disclosed in the present invention to form specific embodiments, which should all belong to the implicit disclosure of the present invention.

Claims

1. A CT local imaging method, characterized in that: The CT scanning section is set through the rotating axis of the turntable, and the turntable is used to place the scanned object, including the following steps: The scanned object is scanned once by CT in the initial state, and the CT scanning section in the initial state is set as the anchor surface; The turntable is rotated step by step, and a CT scan is performed at each step, and the angle θ between the CT scan section and the anchor surface is recorded; Perform differential back-projection Hilbert inverse transform reconstruction to achieve local imaging reconstruction; The differential back-projection Hilbert inverse transform reconstruction method includes the following steps: Weighted calculation to process the graduation data: （1） Where D is the distance from the ray source to the center of the detector, ξ is the rotation angle of the turntable, and u is the distance between the detector unit and the center. , is the graduation data; Differentiation weighted data: （2） Back-project the weighted data after the differential operation: （3） in, , R represents the distance from the ray source to the rotation center, x1 and x2 represent the spatial coordinates of the target point x; Inverse Hilbert transform backprojected data: （4） Get the reconstructed image f(x).

2. The CT local imaging method according to claim 1, characterized in that: The method for recording the angle between the CT scanning section and the anchor surface is to calculate the rotation angle of the turntable.

3. The CT local imaging method according to claim 1, characterized in that: The system also includes a camera for photographing the scanned object and the turntable. The method for recording the angle between the CT scanning section and the anchor surface is: photographing the scanned object and the turntable; using an image segmentation algorithm based on RGB color information to obtain an air area in the field of view; The fitting algorithm is used to calculate the angular deviation between the CT ray direction and the initial scanning position.

4. The CT local imaging method according to claim 3, characterized in that: The image segmentation algorithm based on RGB color information includes the following steps: setting the turntable RGB color standard value Color (r, g, b), setting the color threshold; segmenting the color value in the image , , The pixels within the range are air areas, where δ represents the color threshold.

5. The CT local imaging method according to claim 3, characterized in that: The method for calculating the angle deviation between the CT ray direction and the initial scanning position is: performing Canny edge extraction on the segmented air area image to obtain the edge image; performing least squares fitting on the edge image to obtain the arc areas on both sides; The rotation angles corresponding to the arc areas on both sides are calculated and the average is taken to obtain the deviation angle θ between the initial scan and the CT ray direction.

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