Non-invasive Optical Detection System for Brain Imaging
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Solution Overview
Problem
Conventional optical coherence tomography (OCT) systems face challenges in effectively separating signal photons from those that wander in the scalp and skull, leading to a low signal-to-noise ratio and reduced imaging resolution due to the highly scattering properties of these tissues, which are not adequately addressed by existing methods like Ultrasound Modulated Optical Tomography (UOT).
Innovation Solution
A non-invasive optical detection system using an interferometer that delivers sample light into a scattering medium with distinct volumes of interest and non-interest, employing ultrasound to decorrelate background light from the interference pattern, allowing for the separation of signal and background photons without the need for focused ultrasound, using a single-element ultrasound transducer and varying frequencies, amplitudes, and phases to enhance signal detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OCT systems are used to measure neural activity in the brain, then the method is non-invasive and uses safe light radiation, but the signal from neural activity is masked by a much larger background signal from light wandering in the scalp and skull
Solution Approach 1:
The patent applies ultrasound vibration to the scalp and skull tissues to induce mechanical oscillation. This vibration causes the background light photons traveling through these tissues to undergo frequency shifts and phase randomization, effectively decorrelating them from the neural activity signal. The ultrasound frequency (typically 1-10 MHz) creates a dynamic modulation that allows separation of the static or slowly varying neural signal from the vibrated background signal through frequency filtering or coherence detection methods.
Solution Approach 2:
The patent employs periodic ultrasound pulses or continuous wave ultrasound at specific frequencies to modulate the background light. By applying periodic mechanical action at a known frequency, the system can use lock-in detection or frequency-domain analysis to distinguish the periodic background modulation from the neural activity signal, thereby improving signal-to-noise ratio through synchronous detection techniques.
2Measurement precision
If path-length selection is used in OCT to eliminate photons that have not propagated through the target tissue voxel, then some background photons are removed, but photons that wander in the scalp and skull may still travel along paths matching the optical path length within the coherence length
Solution Approach 1:
The patent combines path-length selection with ultrasound-induced mechanical vibration. The ultrasound applied to the scalp and skull creates time-varying optical path length fluctuations for background photons, causing their interference patterns to become temporally unstable. This dynamic path length modulation allows the system to distinguish between photons with stable path lengths (from the target tissue voxel) and those with fluctuating path lengths (from wandering photons), enhancing the reliability of background rejection.
Solution Approach 2:
The patent introduces ultrasound as an intermediary mechanism between the light source and the detector. The ultrasound waves act as a mediator that selectively affects background photons passing through the scalp and skull, imposing a distinctive temporal signature on these photons. This intermediary action enables the detection system to identify and reject background-contaminated photons even when their optical path lengths coincidentally match the target voxel paths, thereby improving reliability of signal separation.
3Measurement precision
If Ultrasound Modulated Optical Tomography (UOT) is used to address background light, then some separation is achieved, but the system still faces challenges with highly scattering properties of scalp and skull tissues
Solution Approach 1:
The patent applies local quality by targeting ultrasound application specifically to the scalp and skull regions rather than requiring uniform or focused coverage. By confining the ultrasound field to the overlying tissues, the system creates a localized modulation zone that affects only the background photons passing through these specific regions. This localized approach reduces the complexity requirements compared to full-brain focused ultrasound systems while maintaining effective background light separation in the highly scattering scalp and skull tissues.
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 significantly improves the signal-to-noise ratio and spatial resolution by effectively masking background photons, allowing for accurate detection of physiologically-dependent optical parameters in the brain, such as neural activity, without the complexity and cost of focused ultrasound systems.
Implementation Method 1
An interference light pattern is formed by any sample light that has an optical path length that matches, within the coherence length of the optical source, the optical path length traveled by the reference light
Implementation Method 2
employing ultrasound to decorrelate background light from the interference pattern
Data Source
AI summary
In a non-invasive optical detection system and method, sample light is delivered into a scattering medium. A first portion of the sample light passing through a volume of interest exits the scattering medium as signal light, and a second portion of the sample light passing through a volume of non-interest exits the scattering medium as background light that is combined with the signal light to create a sample light pattern. Reference light is combined with the sample light pattern to create an interference light pattern having a holographic beat component. Ultrasound is emitted into the volume of non-interest in a manner that decorrelates the background light of the sample light pattern from the holographic beat component. The holographic beat component is detected during the measurement period. An optical parameter of the volume of interest is determined based on the detected holographic beat component.