Modified Hilbert Transform for Bidirectional Blood Flow Imaging
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Solution Overview
Problem
Current Doppler spectral domain optical coherence tomography (SDOCT) techniques are oversampled, leading to reduced imaging speed and increased susceptibility to motion artifacts, and are unable to detect bidirectional flow in a single B-scan pass, while lacking velocity-resolved blood flow information.
Innovation Solution
The method employs a modified Hilbert transform algorithm to separate moving and non-moving scatterer data in interferometric signals, enabling single-pass volumetric bidirectional blood flow imaging (SPFI-SDOCT) without spatial frequency modulation, applicable to both spectrometer-based and swept-source OCT systems, allowing for bidirectional flow detection in a single B-scan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Doppler SDOCT techniques are used with phase differences between sequential A-scans, then velocity calculation is achieved, but imaging speed is reduced and motion artifacts increase
Solution Approach 1:
The patent segments the interferometric signal into moving scatterer components and non-moving scatterer components by applying the modified Hilbert transform algorithm. This separation allows independent processing of flow information (from moving scatterers) and structural information (from non-moving scatterers), enabling faster imaging without sacrificing velocity measurement accuracy.
Solution Approach 2:
The patent extracts the moving scatterer data from the interferometric signals using the modified Hilbert transform algorithm. By taking out only the relevant flow information and separating it from the non-moving components, the system achieves faster processing speed while maintaining velocity measurement precision.
2Measurement precision
If joint spectral and time domain acquisition scheme (STdOCT) is used, then near phase-noise limited velocity resolution is achieved, but imaging speed is reduced and motion artifacts increase
Solution Approach 1:
The patent replaces the mechanical/time-domain oversampling approach of STdOCT with a frequency-domain approach using the modified Hilbert transform. Instead of acquiring multiple sequential A-scans at the same lateral position (time-domain oversampling), the system uses spectral analysis of the interferometric signal to extract velocity information, achieving similar or better velocity resolution with reduced temporal sampling requirements and thus higher imaging speed.
3Measurement precision
If spatial frequency modulation technique is used for full range complex conjugate resolved imaging, then real and complex conjugate reflectivities are separated, but device complexity increases and bidirectional flow detection in single B-scan is not achieved
Solution Approach 1:
The patent extracts the complex conjugate components and separates them from the real components by applying the modified Hilbert transform algorithm to the interferometric signal. This mathematical operation naturally separates the moving scatterer signals (containing complex conjugate information) from non-moving scatterers, achieving full range complex conjugate resolution without requiring additional spatial frequency modulation hardware.
Solution Approach 2:
The modified Hilbert transform algorithm acts as an intermediary mathematical tool that processes the interferometric signal to separate real and complex conjugate reflectivities. Instead of using physical spatial frequency modulation devices, the patent uses this computational intermediary to achieve the same separation effect, simplifying the overall system while enabling bidirectional flow detection in a single B-scan.
4Measurement precision
If power Doppler ultrasonography analog technique is used, then sensitivity for moving scatterers is improved, but velocity information is eliminated
Solution Approach 1:
The patent segments the power spectrum into different frequency components, allowing the system to detect moving scatterers (which produce Doppler frequency shifts) while preserving velocity information through spectral analysis. The modified Hilbert transform algorithm processes the spectral data to maintain both sensitivity for moving scatterers and velocity measurement capability, unlike conventional power Doppler which integrates all frequencies and loses directional information.
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 improves data acquisition speed and sensitivity for imaging small spatial volumes with moderately high flow velocities, providing velocity-resolved blood flow information and reducing motion artifacts, while maintaining resolution and sensitivity for small vessels.
Implementation Method 1
separating the moving scatterer data from the non-moving scatterer data in the interferometric signals using a modified Hilbert transform algorithm
Implementation Method 2
determining the velocity of moving scatterers using their temporal frequency shifts rather than the phase differences between sequential A-scans at a single lateral scan position
Implementation Method 3
combining the first reflected light and the second reflected light to produce interferometric signals
Data Source
AI summary
The present subject matter relates to in vivo volumetric bidirectional blood flow imaging using single-pass flow imaging spectral domain optical coherence tomography. This technique uses a modified Hilbert transform algorithm to separate moving and non-moving scatterers within a depth. The resulting reconstructed image maps the components of moving scatterers flowing into and out of the imaging axis onto opposite image halfplanes, enabling volumetric bidirectional flow mapping without manual segmentation.