Low-Coherence CW DCS for Pathlength-Resolved Deep Tissue Flow
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Solution Overview
Problem
Conventional DCS methodologies face limitations such as reduced sensitivity to deep tissue due to partial volume effects, increased cost and complexity from hybrid probes, and errors from differing tissue sampling volumes, necessitating high-coherence pulsed or modulated light sources that introduce noise and require separate instruments for optical property measurements.
Innovation Solution
Employing a low-coherence continuous-wave (CW) light source with pathlength resolution achieved by adjusting time-delay in a Mach-Zehnder interferometer configuration, allowing pathlength-resolved DCS measurements without pulsed or modulated light, thus improving signal-to-noise ratio and enabling deeper tissue penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-coherence pulsed or modulated light sources are used in conventional DCS, then pathlength resolution is achieved, but signal-to-noise ratio deteriorates and tissue penetration depth is limited
Solution Approach 1:
The patent changes the coherence parameter of the light source from high-coherence (pulsed/modulated) to low-coherence (continuous-wave), which fundamentally alters the interference mechanism. This parameter change enables pathlength resolution through temporal gating of low-coherence interference, achieving both deep tissue penetration and acceptable signal-to-noise ratio by operating in the continuous-wave regime with optimized detection
2Measurement precision
If hybrid probes are used to achieve depth sensitivity, then measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes a single low-coherence CW interferometric probe capable of performing both DCS (blood flow measurement) and DOS (optical property measurement) functions. The unified probe design eliminates the need for separate hybrid probes, reducing device complexity and cost while maintaining depth sensitivity through pathlength-resolved measurements achieved by temporal delay adjustment
3Reliability
If conventional DCS systems are used, then blood flow measurement is achieved, but depth sensitivity is reduced due to partial volume effects
Solution Approach 1:
The patent segments the total light path into distinct pathlength components using low-coherence temporal gating. By adjusting the temporal delay in the reference arm, the system selectively gates interference from specific photon pathlengths, effectively segmenting the measurement depth and eliminating partial volume effects that convolve signals from multiple depths in conventional DCS
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
Enables accurate, cost-effective, and portable depth-sensitive blood flow measurements up to 4 cm below the tissue surface with improved signal-to-noise ratio, independent of tissue optical properties, using off-the-shelf CW laser diodes and standard detectors.
Implementation Method 1
producing (at the optical detection system) signals that represent interference between the second portion of light and the sample light
Implementation Method 2
employing a low-coherence continuous-wave (CW) light source with pathlength resolution achieved by adjusting time-delay in a Mach-Zehnder interferometer configuration
Data Source
AI summary
A system configured to perform the DCS-type measurements with the use of low-coherence continuous-wave (CW) light source at levels of light intensities that are substantially lower and with pathlengths through the tissue that are substantially longer than those afforded by the use of conventional methods. The method includes utilizing the optical detection system to producing signals representing interference between the portion of CW light arriving through reference arm of interferometer and the sample CW light potion that has traversed the sample arm including different paths through the target tissue while switching between first and second of said different paths only by adjusting a delay in the delay line. The spatial resolution of different pathlengths of sample light through tissue is defined by coherence length of CW light.