OCT Blood Flow Quantification Using Dynamic Forward Scattering
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Solution Overview
Problem
Existing optical coherence tomography (OCT) methods struggle to provide robust measurement of blood flow due to challenges in signal modulation and reliance on back-scattering, especially for vessels oriented approximately orthogonal to the imaging beam, leading to unreliable flow calculations.
Innovation Solution
The approach focuses on dynamic forward scattering (DFS) signals from red blood cells, utilizing both inside and outside the vessel lumen to measure blood flow parameters, such as flow speed, velocity, and flux, by analyzing forward-scattered light from tissues adjacent to the vessel, particularly in the sclera and retinal pigment epithelium, to overcome anisotropic phase responses and improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional OCT methods focus on single back-scattering within blood vessels to measure flow, then the measurement process is simplified, but the reliability and accuracy of flow quantification deteriorates, especially for vessels oriented orthogonally to the imaging beam
Solution Approach 1:
The patent transitions from analyzing only intravascular back-scattered signals to incorporating extravascular forward-scattered signals from the sclera. This dimensional expansion from intra-vessel to extra-vessel space enables measurement of vessels at any orientation, particularly improving detection of orthogonally oriented vessels that are invisible to conventional back-scattering methods
Solution Approach 2:
The patent uses the sclera as an intermediary medium to detect choroidal blood flow. Instead of directly measuring weak signals from choroidal vessels, the method measures forward-scattered light signals from the sclera that are modulated by passing red blood cells, providing a reliable indirect measurement of flow that is insensitive to vessel orientation
2Loss of information
If OCT systems analyze signals directly from inside blood vessels, then the measurement target is direct, but the signal-to-noise ratio deteriorates and artifacts increase, particularly in the choroid
Solution Approach 1:
The sclera serves as an intermediary that provides a brighter, artifact-free signal compared to direct choroidal vessel signals. The scleral tissue acts as a scattering medium that modulates light in response to blood flow, producing signals with superior signal-to-noise ratio and no motion artifacts
Solution Approach 2:
The patent converts the typically problematic forward-scattered light, which creates artifacts in conventional OCT angiography, into a useful signal source. By analyzing the scleral tissue that is illuminated by forward-scattered light from choroidal vessels, the method transforms what was considered noise or artifact into the primary measurement signal
3Ease of operation
If conventional methods use axial motion bias and anisotropic phase response for flow measurement, then the measurement approach is straightforward, but the accuracy deteriorates for vessels with Doppler angles near 90 degrees
Solution Approach 1:
The patent changes the measurement parameter from phase shift (which is anisotropic and orientation-dependent) to signal modulation rate of forward-scattered light (which is isotropic and orientation-independent). This parameter transformation enables accurate flow measurement at any Doppler angle, including 90 degrees where conventional phase-based methods fail
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
DFS-based methods provide a robust and reliable estimation of blood flow parameters, especially for vessels with Doppler angles near 90°, offering higher signal-to-noise ratio and more voxels for analysis, and can be implemented on conventional OCT systems for clinical use.
Implementation Method 1
the optical signals we focus on are modulated by the photons that are forward scattered from red blood cells in a blood vessel
Implementation Method 2
obtain interferometric data from a tissue adjacent to and outside of a distal side of the blood vessel opposite the proximal side
Data Source
AI summary
An apparatus for measuring a blood flow parameter in a blood vessel, including: an interferometric data collection apparatus including a light source and a sensor coupled to a controller, the controller being configured to: direct the light source toward a proximal side of a blood vessel; obtain interferometric data from a tissue adjacent to and outside of a distal side of the blood vessel opposite the proximal side; determine a signal modulation rate based on the interferometric data; and estimate a blood flow parameter in the blood vessel based on the signal modulation rate.