Lock-in Camera Quasi-Ballistic Photon OCT Imaging
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Solution Overview
Problem
Traditional optical coherence tomography (OCT) methods have limited penetration depth and spatial resolution, making it difficult to image brain activity effectively, especially through the human skull and into the brain tissue, as they primarily detect ballistic photons and disregard quasi-ballistic photons that have encountered multiple scattering events.
Innovation Solution
The system employs a low-coherence interferometry method using a lock-in camera to selectively detect and image quasi-ballistic photons by adjusting the phase of the reference light beam across pre-selected phase shifts over a time interval less than the speckle decorrelation time, allowing for the detection of photons with straight travel paths within a user-determined path-length range, thereby enhancing imaging depth and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If traditional OCT methods are used to image deep tissue structures, then spatial resolution can be maintained at 1-10 μm, but penetration depth is limited to only 1-2 mm
Solution Approach 1:
The patent changes the detection parameter from exclusively ballistic photons to include quasi-ballistic photons that have undergone limited scattering. This is achieved by using a lock-in camera to detect photons within a specific path-length range (e.g., 5-15 mm), thereby extending penetration depth while maintaining acceptable spatial resolution through selective detection of photons that have not undergone excessive scattering.
Solution Approach 2:
The system dynamically adjusts the path-length selection window to optimize detection for different imaging depths. By varying the acceptance range of photon path lengths based on the specific imaging target and depth requirements, the system adapts to maintain optimal resolution while maximizing penetration capability for different tissue structures.
2Length of stationary object
If conventional OCT detects only ballistic photons, then spatial resolution is maintained, but imaging depth cannot exceed 1-2 mm due to light scattering
Solution Approach 1:
The patent introduces a lock-in camera as an intermediary detection device that enables depth extension. This specialized detector acts as a mediator between the scattered light field and the imaging system, selectively recovering quasi-ballistic photons that conventional detectors would reject, thereby extending imaging depth without proportionally increasing overall system complexity.
Solution Approach 2:
The system employs periodic modulation of the reference beam phase to enable lock-in detection of quasi-ballistic photons. By modulating at a specific frequency and using synchronous detection, the system can selectively extract signals from photons within the desired path-length range, enabling deeper imaging while managing detection complexity through frequency-domain separation.
3Measurement precision
If the reference beam phase is cycled through multiple shifts, then quasi-ballistic photons can be selectively detected, but the measurement time increases
Solution Approach 1:
The patent uses periodic phase modulation of the reference beam at a specific frequency, combined with lock-in detection, to achieve precise path-length selection. By measuring at multiple phase points (e.g., 0°, 90°, 180°, 270°) and using synchronous detection, the system can precisely differentiate photons by their optical path length while maintaining efficient measurement through frequency-domain multiplexing rather than sequential scanning.
Solution Approach 2:
The system performs preliminary phase cycling and lock-in detection to pre-select and characterize quasi-ballistic photons before final image reconstruction. By conducting the phase-modulated measurements and path-length filtering in advance, the system prepares the data in a form that enables efficient subsequent processing and imaging, reducing overall measurement time.
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 enables the generation of high-resolution images of deep tissue structures and functional activities by selectively measuring the optical properties of the human skull and brain, improving upon the limitations of traditional OCT by including photons that have experienced some degree of scattering, thus achieving greater imaging depth and spatial resolution.
Implementation Method 1
The returning light from both arms recombine or merge at a coupler to generate an interference pattern
Implementation Method 2
light from a low-coherence source is split into two paths along two different arms of an interferometer
Implementation Method 3
a lock-in camera to generate images of deep structures in diffusive, high-scatter media. The system may comprise a light source and a processor configured to phase-shift the reference light beam across a pre-selected set of phase shifts or offsets
Implementation Method 4
The returning light from both arms recombine or merge at a coupler to generate an interference pattern. By tuning the position of the mirror in the reference arm, the optical distance for the light propagating through the reference arm can be adjusted and the interference pattern is formed only with light that traveled, to within approximately the coherence length of the light source, the same optical distance in the sample
Implementation Method 5
light from a low-coherence source is split into two paths along two different arms of an interferometer
Implementation Method 6
the interference pattern is formed only with light that traveled, to within approximately the coherence length of the light source, the same optical distance in the sample
Data Source
AI summary
Described herein are systems and methods for noninvasive functional brain imaging using low-coherence interferometry (e.g., for the purpose of creating a brain computer interface with higher spatiotemporal resolution). One variation of a system and method comprises optical interference components and techniques using a lock-in camera. The system comprises a light source and a processor configured to rapidly phase-shift the reference light beam across a pre-selected set of phase shifts or offsets, to store a set of interference patterns associated with each of these pre-selected phase shifts, and to process these stored interference patterns to compute an estimate of the number of photons traveling between a light source and the lock-in camera detector for which the path length falls within a user-defined path length range.