Subtraction Histogram for X-ray Image Contrast Normalization
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Solution Overview
Problem
Subtraction angiography in X-ray imaging is challenged by variations in image contrast due to external factors and motion artifacts, which can lead to incorrect diagnoses or navigational errors during interventions.
Innovation Solution
A method is implemented using a calculation unit to determine a subtraction histogram, mapping the difference in relative frequencies of intensities to normalize image pixels, thereby reducing contrast variations and accounting for motion artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If subtraction angiography is used to enhance vessel visibility, then image contrast is improved, but variations in image contrast occur due to external effects and motion artifacts
Solution Approach 1:
The patent applies preliminary action by calculating a normalization histogram from a reference subtraction image before processing the current subtraction image. This pre-computed histogram serves as a baseline to guide the normalization process, allowing the system to correct contrast variations in advance rather than reacting to them after they occur. The reference histogram captures the expected intensity distribution under ideal conditions, enabling proactive correction of motion artifacts and external effect variations.
Solution Approach 2:
The patent implements parameter changes by transforming the intensity values of the subtraction image based on the normalization histogram. Specifically, it maps the intensity values from the current subtraction image to new intensity values that align with the reference histogram distribution. This parameter transformation corrects contrast variations caused by motion artifacts and external effects, ensuring consistent image quality across different acquisition conditions.
2Reliability
If statistical analysis is used to reduce contrast variation, then image consistency is improved, but motion artifacts cannot be adequately handled
Solution Approach 1:
The patent introduces a normalization histogram as an intermediary element that mediates between the current subtraction image and the reference image. This histogram acts as a bridge, capturing the intensity distribution characteristics and using them to transform the current image intensities. The intermediary histogram enables the system to handle motion artifacts effectively by providing a flexible mapping mechanism that adapts to different motion conditions while maintaining image consistency.
3Reliability
If normalization based on reference image is applied, then contrast variation is reduced, but processing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the normalization process into distinct stages: first computing the reference subtraction histogram from a reference image, then using this pre-computed histogram to normalize current subtraction images. This segmentation allows the complex normalization task to be broken down into manageable steps, with the reference histogram serving as a pre-computed lookup table that simplifies real-time processing of subsequent images.
Data Source
AI summary
A method is for providing a normalized image. The method includes receiving a non-normalized image including first pixels and non-normalized intensities, each of the first pixels being characterized by one of the non-normalized intensities. Furthermore, the method includes determining a subtraction histogram, the subtraction histogram being configured to map a first intensity to the difference between the relative frequency of the first intensity and the relative frequency of a second intensity, the first intensity being one of the non-normalized intensities and the second intensity being one of the non-normalized intensities. Furthermore, the method includes providing a normalized image including second pixels and normalized intensities based on the non-normalized image and based on the subtraction histogram, each of the second pixels being characterized by one of the normalized intensities.