X-Ray Image Noise Adjustment With Dose-Dependent Local Filtering
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Solution Overview
Problem
Existing noise adjustment methods in x-ray imaging fail to account for the differences between detector noise and quantum noise, leading to varying noise impressions across an x-ray image, particularly at low doses, which affects image quality and subsequent processing algorithms.
Innovation Solution
A computer-implemented method using a local, dose-dependent filter that adjusts the correlation between image points, transforming initial statistics to a common target statistics through a linear transformation of the covariance matrix, stabilizing variance and covariance to achieve a uniform noise impression across the image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If variance stabilization is applied to x-ray images, then the standard deviation of noise is stabilized, but the noise color and correlation structure between image points are not addressed
Solution Approach 1:
The patent segments the noise stabilization process into two independent stages: first applying a variance stabilization transformation to stabilize the standard deviation, then applying a correlation stabilization transformation to address the covariance structure. This segmentation allows each stage to focus on a specific aspect of noise characterization without interfering with the other, resolving the contradiction between achieving comprehensive noise stabilization and maintaining processing complexity.
Solution Approach 2:
The patent introduces an intermediary correlation matrix R that represents the desired target correlation structure between image points. This intermediary correlation matrix serves as a mediator between the actual correlation structure and the final noise-adjusted image, allowing the system to transform the covariance matrix into a form that achieves both variance stabilization and correlation structure correction without directly solving the complex joint optimization problem.
2Ease of operation
If detector noise and quantum noise are not differentiated, then processing is simplified, but image quality deteriorates due to different noise characteristics in different areas
Solution Approach 1:
The patent applies local quality by differentiating between detector noise-dominated regions and quantum noise-dominated regions through the use of a dose-dependent filter. The filter automatically adapts its characteristics based on the local dose level, applying different noise correction strategies to different areas of the image. This allows the system to maintain processing simplicity while achieving high image quality by handling different noise types appropriately in their respective regions.
Solution Approach 2:
The patent utilizes parameter changes by making the filter characteristics dose-dependent. The filter's response varies as a function of the local x-ray dose, allowing the system to change processing parameters dynamically based on the dominant noise type in each region. This parameter adaptation enables the system to simplify processing in uniform regions while maintaining precision in regions with different noise characteristics.
3Device complexity
If a single filter is used for the entire image, then processing is simplified, but noise statistics cannot be stabilized uniformly across different dose regions
Solution Approach 1:
The patent applies dynamics by making the filter characteristics variable rather than fixed. The dose-dependent filter automatically adjusts its response based on the local dose level, transforming from a static single-filter approach to a dynamic multi-regime approach. This allows the system to maintain simplicity in the filter design while achieving uniform noise statistics stabilization across different dose regions through automatic adaptation.
Solution Approach 2:
The patent employs preliminary action by pre-calculating and storing the correlation matrix R and its inverse in lookup tables before actual image processing. This preliminary preparation allows the system to quickly retrieve and apply the appropriate correlation information during image processing without performing complex calculations in real-time, thus reducing processing complexity while maintaining precise noise statistics stabilization.
Data Source
AI summary
A computer-implemented method for noise adjustment of an x-ray image recorded with an x-ray facility by an x-ray detector with image points is disclosed. In the method, image values are assigned, measured according to an incident x-ray dose, wherein the image values of the x-ray image include a first detector noise component arising from detector-internal noise and a second dose-dependent signal component arising from the imaging including quantum noise. A local, dose-dependent filter, adjusting the correlation between image points, evaluating a subarea of the x-ray image around an image point currently being processed, is applied to the image values of all image points of the x-ray image, which brings about a change of at least a part of the initial statistics of image values of the subareas to common target statistics of all subareas.