Lock-in Amplifier Filtering for Dynamic X-ray Angiography
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Solution Overview
Problem
Current methods for visualizing blood flow in vessels, such as those using dynamic X-ray angiography, face challenges in accurately assessing blood velocity and flow patterns, especially in noisy or cluttered environments, due to blurring of contrast agent bolus and measurement uncertainties.
Innovation Solution
A method involving dynamic X-ray angiography that modulates image contrast with a steady contrast agent injection, synchronized with heartbeat frequency, using lock-in amplifier principles to extract harmonic frequency components and phase information, enhancing visualization through windowed harmonic filtering and spatial low-pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If dynamic X-ray angiography is used to visualize blood flow, then blood flow patterns can be observed, but image quality deteriorates due to blurring of contrast agent bolus and noise in cluttered environments
Solution Approach 1:
The patent applies periodic action by synchronizing the filtering process with the heartbeat frequency. The lock-in amplifier filters image sequences at the reference frequency corresponding to the heartbeat, allowing periodic extraction of blood flow information while suppressing non-periodic noise and blurring artifacts. This enables reliable measurement of blood velocity and flow patterns despite the challenging dynamic imaging conditions.
2Illumination intensity
If contrast agent is injected to enhance blood flow visibility, then blood vessels become visible, but measurement precision deteriorates due to blurring of the contrast agent bolus
Solution Approach 1:
The patent introduces an intermediary filtering process using a lock-in amplifier that acts as a mediator between the contrast agent signal and the final measurement. The filter selectively passes frequency components matching the heartbeat reference frequency while attenuating blurring artifacts and noise. This intermediary processing step preserves the visibility enhancement provided by the contrast agent while eliminating the measurement precision degradation caused by bolus blurring.
3Shape
If temporal frequency filtering is applied to extract blood vessels, then vessel extraction is achieved, but visualization of flow patterns deteriorates due to loss of temporal dynamics
Solution Approach 1:
The patent implements feedback by using the known heartbeat frequency as a reference signal to guide the filtering process. The lock-in amplifier continuously compares the incoming image sequence with the reference frequency and adjusts the filtering to maximize the extraction of periodic blood flow signals. This feedback mechanism ensures that both vessel structure and temporal flow dynamics are preserved, as the filtering is adapted to the actual physiological rhythm rather than applying fixed temporal constraints.
Data Source
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AI summary
Method of image processing, the method comprises providing a sequence (2) of images (F) which have contrast modulation (100) along said sequence (2); providing a reference frequency (fm, 10) related to said contrast modulations (100) along said sequence (2); and filtering said sequence of images depending on said reference frequency (fm, 10). According to an embodiment, a windowed harmonic filtering is applied to the sequence of input images to extract fundamental in-phase (122) and quadrature (124) components at a heart beat frequency (fm). The resultant time- signal phase is displayed (34) as image sequence.