Optical Sensor Calibration Using Standard Spectral Response
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Solution Overview
Problem
Current methods for calibrating optical sensors to measure absolute oxygen saturation (StO2) require stringent manufacturing specifications and complex components, leading to increased costs and device rejection, as well as the need for individual calibration using a blood flow loop, which is time-consuming and costly.
Innovation Solution
A method and apparatus for calibrating optical sensors using a standard spectral response and reference material to derive device-specific calibration coefficients, allowing for absolute StO2 measurement without requiring calibration of each individual device using a blood loop, by establishing a standard spectral response for blood and a reference material to create standardized remittance curves applicable to multiple devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stringent manufacturing specifications with narrow tolerances are used to enable single calibration applicability, then measurement precision is improved, but manufacturing cost increases and device rejection frequency increases
Solution Approach 1:
The calibration process is segmented into two parts: (1) a universal spectral response characterization that applies to all devices of the same type, and (2) device-specific calibration coefficients that are determined individually but require less stringent tolerances. This segmentation allows the majority of calibration to be done universally while only requiring minimal device-specific adjustments.
Solution Approach 2:
The patent changes the calibration approach from requiring precise physical component tolerances to using spectral response parameters and mathematical transformations. By measuring the spectral response at multiple wavelengths and using ratio-based calculations, the system achieves absolute StO2 measurement without requiring narrow manufacturing tolerances on individual components.
2Measurement precision
If individual device calibration using blood flow loop is performed, then measurement precision is improved, but productivity decreases due to time burden and cost
Solution Approach 1:
Instead of requiring actual blood flow loop calibration for each device, the patent uses a standardized spectral response model that serves as a template. Each device is calibrated by comparing its measured spectral response to this standard model and applying appropriate correction factors, eliminating the need for complex blood loop apparatus while maintaining accuracy.
Solution Approach 2:
The patent introduces a standardized spectral response model as an intermediary between the theoretical calibration requirements and actual device calibration. This model acts as a reference that mediates the calibration process, allowing devices to be calibrated against it without requiring direct blood loop calibration for each unit.
3Measurement precision
If complex components and highly restrictive tolerances are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical/physical calibration systems (blood flow loops, precise mechanical alignment fixtures) with optical measurement and computational methods. By using spectral analysis and mathematical transformations of light absorption at multiple wavelengths, the system achieves precise calibration without complex mechanical calibration apparatus.
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 reduces manufacturing costs and time burdens by enabling calibration without highly restrictive tolerances or complex components, allowing for accurate absolute StO2 measurement across multiple devices using standardized calibration curves.
Implementation Method 1
Four wavelength optical sensors have been implemented in external monitoring devices, which allow absolute StO2 to be measured
Implementation Method 2
optical sensors have been proposed or implemented in medical devices for monitoring changes in blood or tissue oxygen concentration
Data Source
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AI summary
A method for using a medical device comprising an optical sensor to measure calibrated oxygen saturation in a body tissue uses a standard spectral response of blood established for multiple of oxygen saturations and a standard spectral response of a reference material. The standard responses are established using a spectrometer. The spectral power output of the optical sensor is measured using a spectrometer. The optical sensor output signal response to the reference material is obtained. A processor computes a device-specific calibration curve for the medical device using the measured spectral power output and the standard spectral response of blood and computes an optical gain using the standard spectral response of the reference material and the measured spectral power output of the optical sensor. The device-specific calibration curve and optical gain of the optical sensor are stored in a memory of the medical device.