Asymmetric Filter for CT Short-Scan Shading Correction

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Solution Overview

Problem

Short-scan computed tomography (CT) image reconstruction often results in low-frequency cone-beam artifacts, manifesting as shading in reconstructed images due to non-uniform data redundancy, which complicates the imaging of moving objects like a beating heart.

Innovation Solution

The method involves reconstructing a full-scan image and a short-scan image, calculating their difference, and then filtering this difference using asymmetric or view-dependent filters to correct for shading artifacts, thereby improving the quality of short-scan images by combining the filtered difference with the short-scan image.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If short-scan CT reconstruction is used to improve time resolution, then time resolution is improved, but shading artifacts are introduced due to non-uniform data redundancy

Engineering Contradiction:

Improvetime resolutionVSAvoidshading artifacts

Core Design Contradiction:

Loss of timeVSObject-affected harmful factors

Solution Approach 1:

A full-scan image is introduced as an intermediary reference to correct the short-scan image. The full-scan image, which lacks motion blur and has uniform data redundancy, serves as a mediator to identify and correct shading artifacts in the short-scan reconstruction without sacrificing time resolution.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The method uses feedback from the full-scan image to correct the short-scan image. By comparing the short-scan reconstruction with the full-scan reference image and applying asymmetric filtering based on the difference, the system iteratively improves the short-scan image quality while preserving its temporal advantages.

Inventive Principle:

Principle #23Feedback

2Object-affected harmful factors

If asymmetric filtering is applied to correct shading artifacts, then artifact correction is improved, but computational complexity increases

Engineering Contradiction:

Improveshading artifact correctionVSAvoidcomputational complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Asymmetric filtering is applied locally and anisotropically based on the specific characteristics of shading artifacts. The filter parameters are adapted to the local image structure and artifact distribution, applying stronger correction where needed and preserving fine details where the artifact presence is low, thus optimizing correction effectiveness while managing computational load.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9805448B2Method and apparatus for computed tomography using asymetric filter for volume half reconstruction

Publication Date: 2017.10.31 TOSHIBA MEDICAL SYST CORP

AI summary

An apparatus and method of processing cone-beam X-ray projection data using a short-scan method (e.g., filtered back projection and weighting the projection data using the Parker weights for projection angles spanning 180° plus the fan angle) to reconstruct an image. Imaging artifacts in the short-scan image are corrected by combining the short scan image with a correction image. The correction image is obtained by applying an asymmetric filter to the difference between the short-scan image and a full-scan image, the full scan image being obtained using image reconstruction of the full-scan projection data. In one implementation, the asymmetric filter is a low-pass filter that, in the spatial domain, is foreshortened along a center-view axis corresponding to the short scan.