Photothermal OCT Retinal Tissue Contrast via Modulated Laser Heating
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Solution Overview
Problem
Conventional optical coherence tomography (OCT) imaging of the eye struggles to effectively highlight specific tissue layers due to the lack of contrast materials that alter the index of refraction, leading to ineffective emphasis of particular tissues, and reducing laser power or pigment concentration to clinical levels results in the photothermal signal being obscured by background noise.
Innovation Solution
The application of photothermal heating using a modulated thermal laser with reduced power levels, centered on the absorption peaks of indocyanine green or melanin, to selectively heat and expand retinal tissue layers, allowing for their detection amidst background noise through analysis of apparent depth changes in OCT images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If laser power and pigment concentration are reduced to clinical levels, then safety for human eye is improved, but photothermal signal becomes obscured by background noise
Solution Approach 1:
The patent applies periodic modulation of the thermal laser at a specific frequency (e.g., 500 Hz) to create time-varying thermal expansion signals. By modulating the laser power periodically and detecting the corresponding periodic changes in tissue layer position, the system can distinguish the photothermal signal from static or non-periodic background noise, enabling safe clinical-level power operation while maintaining detectable signal quality
Solution Approach 2:
The system uses feedback processing to detect and analyze the modulated photothermal signal. The computer processes the OCT signals to identify the characteristic frequency response caused by thermal expansion, comparing heated versus unheated states to extract the photothermal signal from background noise through signal processing and pattern recognition
2Loss of information
If conventional contrast materials are used, then tissue layer differentiation is improved, but index of refraction alteration is insufficient for effective OCT highlighting
Solution Approach 1:
The patent changes the physical parameter being measured from optical reflection (index of refraction) to thermal expansion (dimensional change). By using photothermal heating to induce localized thermal expansion in pigmented layers, the system detects position shifts of tissue layers rather than relying on index of refraction differences, providing effective contrast for OCT imaging without requiring contrast materials that alter refraction
Solution Approach 2:
The invention directly exploits thermal expansion of pigmented retinal layers when heated by the modulated thermal laser. The pigment selectively absorbs thermal laser energy, causing localized heating and thermal expansion of the tissue layer, which produces detectable shifts in layer position that can be visualized in OCT images, providing inherent contrast without additional materials
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 clinically acceptable photothermal OCT imaging by reducing background noise, allowing for accurate depth measurements and quantitative volumetric analysis of retinal tissue, facilitating the detection and monitoring of degenerative diseases while avoiding harmful light exposure.
Implementation Method 1
the pigment, while not directly visible in OCT, selectively absorbs light from a 'thermal' laser that heats the tissue
Implementation Method 2
This heating produces localized thermal expansion causing slight shifts in the dimension of the layers that can be detected in OCT
Implementation Method 3
The high speeds of light propagation (compared, for example, to propagation speed of ultrasound) is accommodated by deducing light transit time indirectly by looking at interference between the outgoing light and returning light using an interferometer
Implementation Method 4
light is projected into retinal tissue where it reflects off of boundaries between tissue layers in the retina having different indices of refraction
Data Source
AI summary
An optical coherence tomography system for ophthalmic use identifies tissue by selected laser heating of that tissue at reduced power levels decreasing background noise to boost signal-to-noise ratio allowing detection of minute changes in thermal expansion caused by that heating at clinically acceptable levels.