NIRS Spectrometer Wavelength Path Length Correction
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Solution Overview
Problem
Near infrared spectroscopy (NIRS) devices face challenges in accurately measuring tissue oxygenation due to light attenuation from absorption and scattering in body tissue, which complicates the estimation of chromophore concentrations and oxygen saturation levels, leading to potential inaccuracies in clinical assessments.
Innovation Solution
A NIRS spectrometer system that includes broadband light sources, photodetectors, and a light attenuation model to estimate tissue chromophore concentrations by comparing measured light attenuations with modeled attenuations, using temperature sensors to account for temperature-dependent spectral changes and eliminating the need for light source conditioning optics to simplify the device and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light sources emit broadband near-infrared measurement light into body tissue, then tissue oxygenation can be measured non-invasively, but light attenuation from absorption and scattering reduces measurement accuracy
Solution Approach 1:
The system uses feedback by comparing measured light attenuations with modeled light attenuations to iteratively estimate chromophore concentrations. The light attenuation model predicts expected attenuation based on known tissue properties, and this prediction is fed back to refine the concentration estimates, improving measurement accuracy despite light attenuation losses.
Solution Approach 2:
The system changes parameters by using multiple wavelengths of near-infrared light and varying the spectral characteristics of the light sources. By measuring attenuation across different wavelengths and adjusting the spectral parameters in the light attenuation model, the system can compensate for absorption and scattering effects to accurately determine tissue oxygenation.
2Measurement precision
If complex mathematical algorithms are used to relate light attenuation to chromophore concentrations, then tissue oxygenation can be calculated, but measurement accuracy is reduced due to scattering effects
Solution Approach 1:
The system performs preliminary action by pre-calculating and storing light attenuation models that account for scattering effects. Instead of solving complex scattering equations in real-time, the model predictions are prepared in advance based on known tissue optical properties, simplifying the real-time calculation while maintaining accuracy.
Solution Approach 2:
The light attenuation model acts as an intermediary between the raw light attenuation measurements and the chromophore concentration estimates. The model translates measured attenuations into concentration information by accounting for scattering effects, serving as a mediator that simplifies the relationship between measurement and result.
3Measurement precision
If light source conditioning optics are used to control spectral output, then wavelength accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system extracts only the essential spectral information needed for measurement by using broadband light sources without complex conditioning optics. Instead of filtering and shaping the light spectrum with multiple optical components, the system uses the broad spectral output directly and compensates for wavelength variations through computational methods in the light attenuation model.
Solution Approach 2:
The system replaces mechanical/optical wavelength control mechanisms with computational control. Instead of using filters, monochromators, or other optical components to precisely define wavelengths, the system uses software-based spectral characterization and modeling to achieve wavelength accuracy, substituting optical mechanics with computational methods.
4Measurement precision
If temperature variations are not compensated, then device operation is simpler, but spectral changes due to temperature reduce measurement accuracy
Solution Approach 1:
The system uses feedback by incorporating temperature sensors that continuously monitor light source temperature and feeding this information back to the light attenuation model. The model adjusts its predictions based on the measured temperature, compensating for spectral drift and maintaining measurement accuracy without requiring complex active temperature control.
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 provides improved accuracy in tissue oxygenation measurements by compensating for wavelength and path length variations, reducing errors and enhancing clinical decision-making by providing reliable StO2 levels and chromophore concentration data.
Implementation Method 1
light attenuation occurs from absorption and scattering events. Light absorbing molecules, called chromophores, convert light to heat energy thus reducing the amount of detected light
Implementation Method 2
Light scattering molecules, such as tissue cells and organelles, refract light thereby changing the direction and hence path length that the light travels
Implementation Method 3
using temperature sensors to account for temperature-dependent spectral changes
Data Source
AI summary
A near infrared spectrometer and method for wavelength and path length correction are disclosed. The spectrometer includes a number of photodiodes that transmit broadband near infrared measurement light into the tissue and at least one broadband detector which measures the light signal transmitted through the tissue. A processor estimates chromophore concentrations through a comparison of measured light attenuation and modeled light attenuation. The light attenuation model utilizes a light path length distribution derived from a Monte Carlo model and accounts for the spectral shape of the light source as a function of temperature.