Pulse Oximetry Sensor Calibration Using LED Power Ratios
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Solution Overview
Problem
Variations in components of pulse oximetry sensors, such as skin pigmentation, thickness, and abnormalities, affect light absorption and scattering, leading to errors in oxygen saturation readings.
Innovation Solution
A calibration system determines a power ratio of LEDs in sensors by using an integrating sphere or calibration block to normalize detected signals, accounting for variations in optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional pulse oximetry sensors are used without calibration, then the device complexity is low and manufacturing is simple, but measurement precision deteriorates due to variations in skin pigmentation, thickness, and abnormalities affecting light absorption and scattering
Solution Approach 1:
The patent applies preliminary action by performing calibration of the pulse oximetry sensor before actual use. A calibration structure with known optical properties is used to determine attenuation factors and power ratios of LED wavelengths in advance. This pre-calibration process creates correction factors that are stored and applied during subsequent measurements, eliminating the need for complex real-time adjustments while improving measurement precision across different skin types.
2Measurement precision
If calibration structures are introduced to improve measurement precision, then oxygen saturation reading accuracy improves, but the manufacturing process becomes more complex
Solution Approach 1:
The patent introduces an intermediary calibration structure that mediates between the sensor and the patient's skin. This calibration structure has known optical properties and serves as a reference standard. By measuring how the sensor responds to this intermediary with known characteristics, the system can calculate correction factors that compensate for variations in actual patient skin properties, thereby improving SpO2 accuracy without requiring direct modification of the sensor manufacturing process.
3Measurement precision
If multiple wavelengths and attenuation factors are measured to improve measurement precision, then reading accuracy improves, but loss of time increases due to additional measurement steps
Solution Approach 1:
The patent performs wavelength power ratio measurements and attenuation factor determinations as preliminary actions during an initial calibration phase. These time-consuming measurements are conducted once using a calibration structure with known properties, and the results are stored as correction factors. During subsequent actual patient measurements, these pre-determined factors are applied directly, eliminating the need to repeat the lengthy calibration measurements and thus reducing time loss while maintaining improved measurement precision.
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
Improves the accuracy of oxygen saturation measurements by correcting for variations in sensor components, ensuring precise physiological parameter calculations.
Implementation Method 1
determining a first photocurrent generated by the detector due to a respective portion of the light emitted by the first LED and a second photocurrent generated by the detector due to a respective portion of the light emitted by the second LED
Implementation Method 2
an attenuation factor of the calibration structure
Implementation Method 3
physiological factors, such as skin (e.g., tissue) pigmentation of a patient, skin thickness of the patient, and/or skin abnormalities (e.g., scarring) of the patient, may affect light absorption and scattering
Data Source
AI summary
A calibration system includes a sensor including a light emitter to emit a first light and a second light, and a detector to detect the first light and the second light. The calibration system also includes a calibration structure, processing circuitry, and a memory including instructions that, when executed by the processing circuitry, cause the processing circuitry to instruct a first light-emitting diode (LED) of the light emitter to emit the first light at a first wavelength and a second LED of the light emitter to emit the second light at a second wavelength, receive a signal indicative of the first light at the first wavelength and the second light at the second wavelength, determine a first power at the first wavelength and a second power at the second wavelength based on the signal, and determine a power ratio as a ratio of the first power and the second power.