Non-Invasive Medical Sensor Self-Calibration
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Solution Overview
Problem
Current non-invasive medical sensors face challenges in accurately measuring light wavelength without prior knowledge, leading to production costs and defect rates, and are prone to errors due to wavelength shifts, patient movement, and skin pigmentation variations, which can result in false readings and safety issues.
Innovation Solution
A self-calibrating sensor system with multiple light sources and detectors that emit and measure light periodically, using a ratio of signals from detectors with differing spectral responses to determine spectral absorption and generate oxygen saturation data, while also detecting motion events and wavelength shifts, and alerting for disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If monochromatic light sources with strict wavelength tolerance are selected through binning process, then measurement accuracy is improved, but production costs increase and defect rates rise due to rejection of 40-60% of emitter components
Solution Approach 1:
The sensor system performs self-calibration by automatically measuring the actual wavelength of its light source using a diffraction grating and photodetector array, eliminating the need for manual wavelength selection and binning during production. The system self-determines its operational parameters, allowing all emitted LEDs to be used without rejection.
Solution Approach 2:
The system dynamically adjusts operational parameters based on measured wavelength. By measuring the actual wavelength and using this information to calibrate the measurement algorithm, the system adapts to each light source's specific characteristics rather than requiring uniform manufacturing tolerances.
2Measurement precision
If complex wavelength measurement systems with multiple photodetectors and filters are implemented, then wavelength detection accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The photodetector array serves multiple functions: it acts as both the wavelength measurement device during calibration and as the primary sensor for oxygen saturation measurement during operation. The diffraction grating serves dual purposes of wavelength separation and signal generation.
Solution Approach 2:
The patent extracts the wavelength measurement function from a separate complex calibration system and integrates it into the primary sensing mechanism. The wavelength measurement is performed using the same photodetector array that performs oxygen saturation measurement, eliminating the need for separate calibration hardware.
3Device complexity
If traditional oximetry systems are used without self-calibration, then device simplicity is maintained, but measurement reliability deteriorates due to wavelength shifts from temperature, aging, and drive current variations
Solution Approach 1:
The system implements continuous feedback by periodically measuring the light source wavelength and using this information to adjust the measurement algorithm. The measured wavelength feeds back into the calculation process, allowing real-time compensation for drift without adding complex hardware.
Solution Approach 2:
The system performs preliminary wavelength measurement and calibration before conducting oxygen saturation measurements. By determining the actual wavelength in advance, the system prepares the measurement parameters to account for expected drift, improving subsequent measurement reliability.
4Measurement precision
If monochromatic light sources are used, then oxygen saturation measurement capability is achieved, but the system becomes vulnerable to motion artifacts and cannot detect sensor disengagement
Solution Approach 1:
The photodetector array performs multiple measurement functions simultaneously: oxygen saturation measurement, motion artifact detection, and sensor disengagement detection. By analyzing the spectral content across multiple wavelengths, the system can distinguish between physiological signals and motion artifacts.
Solution Approach 2:
The system performs periodic wavelength measurements and analyzes the temporal characteristics of the optical signals. By examining how the spectral composition changes over time during motion events versus normal conditions, the system can identify and correct motion artifacts.
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 accurate and reliable oxygen saturation data during patient movement and detects sensor disengagement, reducing production costs and error rates by self-calibrating and compensating for wavelength variations, ensuring accurate and safe monitoring.
Implementation Method 1
a diffraction grating positioned to disperse the light from the light source into a spectrum
Implementation Method 2
a photodetector positioned to receive the dispersed light and produce an output signal proportional to the wavelength of the light source
Implementation Method 3
The photodetector receives and measures a portion of transmitted coherent light that is neither absorbed nor reflected from the blood in the biological tissue in order to determine the oxygen saturation (SPO2) within the blood
Data Source
AI summary
A method and system for measuring oxygen levels and various blood constituents utilizing a sensor having one or more light sources, and one or more light detectors is disclosed. The system is capable of using data collected by the one or more detectors from a non-monochromatic light source to provide accurate information during motion events occurring with an extremity the sensor. The system is also capable of detecting and providing an alert if the sensor is not properly placed on a patient or becomes disengaged therefrom.