Time-of-flight optical measurement for fast-optical signal decoding
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Solution Overview
Problem
Current optical measurement techniques for detecting fast-optical signals in the brain suffer from limited sensitivity and poor temporal resolution due to the diffusive nature of light propagation through tissues like the skull, leading to challenges in accurately measuring fast changes in optical scattering.
Innovation Solution
An optical measurement system utilizing a single pulse of light with a photodiode detector and a processor that acquires a time-of-flight profile, applies weighting functions to enhance contrast-to-noise ratio, and identifies physiological states based on processed profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional diffusive optical measurement techniques are used to detect fast-optical signals, then the measurement can be performed non-invasively through skull tissue, but the sensitivity is limited due to light scattering and diffusive propagation
Solution Approach 1:
The patent segments the detected optical signal into multiple time bins based on time-of-flight, separating early-arriving photons (which have traveled shorter paths) from late-arriving photons (which have traveled longer paths through the brain). This segmentation allows selective analysis of photon populations that have penetrated deeper into the brain tissue, improving sensitivity to fast-optical signals while mitigating the effects of superficial light scattering.
Solution Approach 2:
The patent introduces the time dimension to the optical measurement by resolving photons according to their time-of-flight. This temporal dimensionality transformation converts a spatially diffusive problem into a temporally-resolved measurement, enabling discrimination between photons based on their propagation paths and depths, thereby improving sensitivity despite scattering.
2Speed
If conventional diffusive optical measurement techniques are used, then hemodynamic changes can be detected, but the temporal resolution is poor (100 ms-1 sec per sample)
Solution Approach 1:
The patent employs periodic pulsed laser illumination at high repetition rates (e.g., 80 MHz) to generate a continuous stream of photon packets. By accumulating photon arrival times across many pulses and analyzing the time-of-flight distribution, the system achieves both high temporal resolution (picosecond to nanosecond scale) and reliable detection through statistical accumulation of signals.
Solution Approach 2:
The patent performs preliminary temporal gating of photons based on their time-of-flight before analyzing fast-optical signals. By pre-segregating photons into time bins and selecting specific temporal windows for analysis, the system prepares the data in advance to enhance temporal resolution and isolate fast-optical signal changes from slower hemodynamic background.
3Speed
If frequency domain near infrared spectroscopy (FD-NIRS) is used to measure fast-optical signals, then the light source can be intensity modulated at specific frequencies, but the modulation frequency is slower than the timescale of fast-optical signal changes
Solution Approach 1:
The patent changes the fundamental parameter of light delivery from continuous wave or low-frequency modulation to ultrashort pulsed illumination at high repetition rates. This parameter change enables the system to probe fast-optical signals on their native timescale (picoseconds to nanoseconds) while using time-of-flight analysis rather than frequency modulation to extract signal information, thereby achieving both high speed and high sensitivity.
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
The system achieves improved sensitivity and temporal resolution in detecting fast-optical signals, outperforming conventional methods by orders of magnitude in sensitivity and approaching a mathematical optimum in distinguishing between physiological states.
Implementation Method 1
an optical detector configured for detecting the physiological-encoded signal light
Implementation Method 2
because optical measurement techniques rely on light, which scatters many times inside brain, skull, dura, pia, and skin tissues
Implementation Method 3
Time-of-flight optical measurement and decoding of fast-optical signals
Data Source
AI summary
An optical measurement system comprising an optical source configured for delivering sample light in an anatomical structure, such that the sample light is scattered by the anatomical structure, resulting in physiological-encoded signal light that exits the anatomical structure, an optical detector configured for detecting the physiological-encoded signal light, and a processor configured for acquiring a TOF profile derived from the physiological-encoded signal light, the initial TOF profile having an initial contrast-to-noise ratio (CNR) between a plurality of states of a physiological activity in the anatomical structure. The processor is further configured for applying one or more weighting functions to the initial TOF profile to generate a weighted TOF profile having a subsequent CNR greater than the initial CNR between the plurality of states of the physiological activity. The processor is further configured for processing the weighted TOF profile, and identifying one of the plurality of states of the physiological activity.