Direction-Dependent Lowpass Filter for X-Ray Noise Reduction
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Solution Overview
Problem
Existing noise reduction filters in X-ray imaging, particularly in CT examinations, face limitations in achieving maximum noise reduction while preserving edges, as they often emphasize statistical outliers and can adversely affect small structures due to their spatial coverage and reliance on statistical analysis.
Innovation Solution
A method that combines diffusion and morphological filters by applying a direction-dependent lowpass filter with a smaller spatial coverage than the predetermined distance, taking into account morphological information for direction-dependent weighting, to improve noise and dose reduction in X-ray imaging examinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffusion filters are used to reduce noise, then noise reduction is improved, but edge preservation deteriorates due to statistical outliers and fraying
Solution Approach 1:
The patent combines diffusion filtering with morphological filtering into a unified edge-preserving filter. The diffusion filter component reduces noise by considering statistical uncertainty, while the morphological component analyzes structural characteristics and edge orientation. By merging these approaches, the filter achieves both noise reduction and edge preservation, overcoming the limitation where diffusion filters alone emphasize statistical outliers and cause edge fraying.
Solution Approach 2:
The filter adapts its behavior locally by determining edge orientation and statistical properties for each pixel neighborhood. The filter strength and direction are adjusted based on local image characteristics, allowing aggressive noise reduction in homogeneous regions while preserving edges where structural variations are detected. This local adaptation prevents the global application of diffusion filtering from causing uniform edge degradation.
2Reliability
If morphological filters with large spatial coverage are used to preserve edges, then edge detection reliability is improved, but small structures are adversely affected
Solution Approach 1:
The patent segments the filtering operation into multiple scales by applying the filter at different neighborhood radii. A larger radius is used for reliable edge orientation determination in prominent structures, while a smaller radius preserves fine details and small structures. The filter results are combined to achieve both reliable edge detection and small structure preservation, overcoming the limitation of single-scale morphological filtering.
Solution Approach 2:
The filter applies morphological operations partially by using a radius that is sufficient for reliable edge detection in most regions but not excessively large to damage small structures. The filter strength is modulated based on local confidence in orientation determination, applying stronger filtering only where reliable edge detection is achieved, thereby preserving small structures that would otherwise be adversely affected by aggressive large-radius filtering.
3Object-affected harmful factors
If radiation dose is reduced in X-ray imaging, then patient safety is improved, but image quality deteriorates due to increased noise
Solution Approach 1:
The patent converts the harmful effect of noise (which increases with reduced radiation dose) into a beneficial feature by using noise statistics to guide the filtering process. The filter analyzes the statistical properties of pixel values and adapts its strength accordingly, allowing aggressive noise reduction in low-dose regions while preserving genuine image features. This approach enables significant radiation dose reduction while maintaining image quality by making the noise itself the basis for intelligent filtering.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances image quality by effectively reducing noise and radiation dose while preserving edge sharpness, allowing for simultaneous application of short-range and pixel value difference-dependent filters with orientation analyses on greater length scales.
Implementation Method 1
scanning or fluoroscopy of the patient by X-raying
Implementation Method 2
a direction-dependent lowpass filter is applied to the examined pixel, which filter has a smaller spatial coverage than the predetermined distance and takes into account the morphological information of a structure that may be present with a direction-dependent weighting of the lowpass filter
Data Source
AI summary
A method and an X-ray system are disclosed for reduction of the radiation dose used within the framework of an imaging X-ray examination. In at least one embodiment, for each pixel of a recorded image, structure information of a structure which may be present at a distance around the examined pixel is determined and a direction-dependent lowpass filter is applied to the pixel examined in each case, which filter's spatial coverage is less than the distance and which takes into account the morphological information of a structure which may be present with a direction-dependent weighting of the lowpass filter.