Speckle Contrast System Photon Path Discrimination
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Solution Overview
Problem
Speckle contrast optical spectroscopy (SCOS) faces limitations in sensitivity to deep tissues due to optical sensor saturation at short source-detector pairs and the partial volume effect, which results in poor accuracy and practicality issues for biomedical applications.
Innovation Solution
The method involves categorizing photons based on their time-of-flight to enhance depth specificity and reduce partial volume effects, allowing for improved measurement of scatterer dynamics in deep layers without compromising lateral resolution or requiring high dynamic range detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If source-detector separation is increased to enhance depth penetration, then sensitivity to deep tissues is improved, but signal-to-noise ratio decreases and detector saturation occurs
Solution Approach 1:
The patent segments the detected photons into different groups based on their time-of-flight values. Photons are divided into early-arriving photons (shorter path lengths, more superficial layers) and late-arriving photons (longer path lengths, deeper layers). By analyzing speckle contrast separately for each photon group, the system can selectively measure deep tissue blood flow using late photons while avoiding saturation from early photons, thus resolving the contradiction between depth sensitivity and signal quality
Solution Approach 2:
The system dynamically adjusts the measurement approach by using time-resolved photon detection. Instead of a static measurement that integrates all photons, the system adapts by selectively weighting or filtering photons based on their arrival time. This dynamic separation allows optimization of measurement conditions for deep tissue detection without being constrained by the limitations of fixed source-detector separations
2Measurement precision
If source-detector separation is increased to reduce partial volume effect, then depth specificity is improved, but lateral resolution is compromised and probe size increases
Solution Approach 1:
The patent introduces a new dimension - the time dimension - to differentiate photons based on their path lengths. Instead of relying solely on spatial separation (source-detector distance) to achieve depth specificity, the system uses temporal information (time-of-flight) to separate superficial and deep tissue signals. This allows maintaining short source-detector separations for good lateral resolution while achieving depth specificity through time-resolved measurement
3Illumination intensity
If injected light intensity is increased to compensate for light loss, then signal strength is improved, but detector saturation and safety risks increase
Solution Approach 1:
The patent extracts and removes the problematic early-arriving photons that cause detector saturation from the measurement. By using time-gating to identify and exclude these photons (which travel shorter paths and arrive first), the system can use lower overall light intensities without sacrificing the ability to detect deep tissue signals. The late-arriving photons from deep tissues are analyzed separately, avoiding the saturation issue while maintaining adequate signal strength
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 enhances the diagnostic capability for deep tissue imaging by minimizing superficial layer influences, improving the detection of deep lesions and reducing variability in blood flow measurements, particularly beneficial for cancer detection and monitoring in tissues like the breast and thyroid.
Implementation Method 1
estimating each photon time-of-flight by the difference between its time tag and the laser pulse emission
Implementation Method 2
measuring the speckle contrast for each categorized set of recorded photons intensity at the detector
Data Source
Figure 1~2
Figure 3~4
AI summary
Speckle contrast method and system that discriminates photons based on their path length in tissue, the method comprising the steps of: - directing light from a pulsed light into a sample by optical elements; - synchronizing the time between the pulse injection to sample and the detection unit; - collecting the photons that have travelled through the sample by optics, and conveying the photons of a single or a limited number of speckles from the sample to one or more detection elements; - time-tagging photons thanks to the synchronization of the detector element and/or the time-tagging electronics with the laser pulse emission; - estimating each photon time-of-flight by the difference between its time tag and the laser pulse emission; - categorizing the detected photons based on the value of the time-of-flight in a certain number of time gates; - measuring the speckle contrast