Quantifying Blood Flow via Fluorescence Mediated Photoplethysmography
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Solution Overview
Problem
Current photoplethysmography (PPG) technology cannot provide quantitative measurements of blood flow in tissue in standardized units, limiting its application in clinical settings where direct comparisons are necessary.
Innovation Solution
The method involves exciting a fluorescence agent like indocyanine green (ICG) in the blood, acquiring a time-varying light intensity signal during pulsatile flow, and processing it using a modified Beer-Lambert law to measure time-varying changes in blood volume, enabling the determination of blood flow in standardized units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PPG technology is used to assess blood flow, then the technology can be deployed in commercially available medical devices for assessing pulse rate, oxygen saturation, blood pressure, and cardiac output, but it cannot provide measurements in standardized units
Solution Approach 1:
The patent introduces a fluorescence agent (indocyanine green) that changes the optical parameters of blood, enabling quantitative measurement of blood flow in standardized units. The fluorescence agent alters the light absorption and emission characteristics, allowing the device to transition from qualitative PPG waveforms to quantitative blood flow measurements in mL/min/cm²
Solution Approach 2:
The fluorescence agent acts as an intermediary substance that mediates between the light source and the blood flow measurement. By introducing this intermediate element, the system can convert light intensity variations into standardized blood flow measurements, resolving the limitation of conventional PPG technology
2Measurement precision
If quantitative assessment of tissue perfusion is desired for direct inter-site and inter-subject comparisons, then standardized units of volume/unit time/tissue area are needed, but such measurements have remained elusive to date
Solution Approach 1:
The patent modifies the optical parameters by introducing a fluorescence agent that emits light at a different wavelength than the excitation light. This parameter change enables the detection system to distinguish between excitation light and fluorescence emission, allowing for quantitative measurement of blood flow in standardized units through the modified Beer-Lambert law
Solution Approach 2:
The patent replaces the conventional PPG detection mechanism with a fluorescence-based detection system. Instead of relying on subtle light absorption changes in conventional PPG, the system uses fluorescence emission intensity variations, which provide a stronger signal and enable more precise quantitative measurements in standardized units
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 allows for the measurement of blood flow, including microvascular blood flow, in standardized units, facilitating direct inter-site and inter-subject comparisons, and providing accurate volumetric measurements.
Implementation Method 1
exciting a fluorescence agent such as for example indocyanine green (ICG) in the blood, acquiring a time-varying light intensity signal
Implementation Method 2
a modified Beer Lambert law is applied at the diastolic and systolic phases such that ΔL=ln[(IeΦ−Im)/(IeΦ−Ip)](εC)−1
Data Source
AI summary
A method and an apparatus for measuring a time-varying change in an amount of blood in a tissue include exciting a fluorescence agent in the blood, acquiring a time-varying light intensity signal during a pulsatile flow of the blood through the tissue volume, the pulsatile flow having a systolic and a diastolic phase resembling a conventional photoplethysmogram, and processing the acquired signal by applying a modified Beer-Lambert law to obtain the measurement of the time-varying change in the amount of blood in the tissue volume. The instantaneous molar concentration of the fluorescence agent is determined by utilizing a concentration-mediated change in a fluorescence emission spectrum of the fluorescence agent.