Optical Sensor Multiwavelength Calibration for Tissue Measurement Accuracy
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Solution Overview
Problem
Optical sensors for measuring physiological parameters in tissue, such as oxygenation levels, are sensitive to variations in placement due to superficial absorbers like liver spots, leading to inaccurate and unreliable measurements.
Innovation Solution
A multiwavelength method that applies wavelength-specific correction factors to measured intensities, using auxiliary wavelengths for calibration to account for wavelength-dependent absorption and scattering effects, enhancing accuracy and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-wavelength or non-corrected optical measurement is performed, then the measurement process is simple and fast, but the measurement precision deteriorates due to sensitivity to superficial absorbers like liver spots
Solution Approach 1:
The patent applies wavelength-specific correction factors that are determined based on auxiliary wavelengths. These correction factors compensate for wavelength-dependent absorption and scattering effects caused by superficial absorbers. By changing the parameter of wavelength and applying specific correction factors for each wavelength, the measurement accuracy is improved while accounting for variations in tissue optical properties at different wavelengths
Solution Approach 2:
The patent performs preliminary calibration measurements using auxiliary wavelengths before conducting the actual measurement at the measurement wavelength. These preliminary measurements determine wavelength-specific correction factors that are then applied to compensate for superficial absorbers. This preliminary action prepares the system to accurately measure physiological parameters despite the presence of superficial absorbers like liver spots
2Reliability
If wavelength-specific correction factors are applied using auxiliary wavelengths, then the reliability of measurement is improved, but the device complexity and measurement time increase
Solution Approach 1:
The patent uses the same detector to measure both auxiliary wavelengths (for calibration) and measurement wavelengths (for actual measurement). This multi-functionality allows the system to perform both calibration and measurement tasks with a single detector, reducing the need for additional components and minimizing device complexity while maintaining measurement reliability
Solution Approach 2:
The patent combines the calibration function and measurement function into a unified process. The wavelength-specific correction factors determined from auxiliary wavelengths are integrated with the actual measurement process, allowing the system to simultaneously account for superficial absorber effects and determine physiological parameters. This merging reduces the need for separate calibration and measurement systems
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 method provides accurate and robust optical measurements by correcting for wavelength-dependent variations, improving the reliability of physiological parameter estimation in tissue.
Implementation Method 1
The infrared light penetrates the cranial bones and is scattered by the tissue and also partially absorbed by chromophores such as oxy- and deoxyhemoglobin
Implementation Method 2
partially absorbed by chromophores such as oxy- and deoxyhemoglobin
Implementation Method 3
measuring primary intensities (Im1, Im2) of the primary radiation for each of said at least two measurement wavelengths (λm1, λm2) after said primary radiation has propagated through said medium
Implementation Method 4
irradiating the medium with a secondary radiation comprising at least two distinct auxiliary wavelengths (λa1≠λa2) which are emitted by at least one auxiliary light source; measuring secondary intensities (Is1, Is2) of the secondary radiation for each of said at least two auxiliary wavelengths (λa1, λa2), after said secondary radiation has propagated through said medium along a respective secondary optical path
Implementation Method 5
determining for each of the at least two measurement wavelengths (λm1, λm2) a wavelength specific correction factor (c1(λm1), c2(λm2)) based on said secondary intensities (Is1, Is2)
Data Source
AI summary
Technical improvements for performing optical NIRS measurements using an optical sensor are provided, including A) a specific measurement method, B) a specific cable design for such a sensor, C) a light shielding cover to be used with such a sensor, and D) a specific internal light shielding to be used inside the sensor. All of these aspects can be used for improving the accuracy and robustness of the optical measurements to be performed with the sensor.