Fiber Optic Flow Sensor Using Etalon Interferograms in Blood Vessels
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Solution Overview
Problem
Existing methods for measuring fluid flow in physiological environments, such as blood vessels, suffer from inaccuracies due to angle dependence, complexity, cost, susceptibility to interference, and reliance on precise vessel dimensions or assumptions, making them unsuitable for standard clinical practice.
Innovation Solution
A fibre optic sensor with multiple reflective surfaces and etalons is used to measure fluid flow by encoding interferograms, allowing decoupling of pressure and temperature changes, and using Doppler FD-OCT for sub-nanometer resolution, with integrated excitation light for heating and temperature measurement, enabling compact, accurate flow and pressure measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If acoustic Doppler flow measurements are used in invasive medical devices, then time-resolved flow speed measurements are provided, but measurement accuracy deteriorates due to angle dependence and alignment requirements
Solution Approach 1:
The patent replaces acoustic Doppler measurement with optical coherence tomography (OCT) based flow measurement. The OCT system uses light instead of sound waves to measure flow velocity, eliminating the angle dependence issue that plagues acoustic Doppler methods. The optical system provides direct velocity measurement without requiring precise alignment with flow direction.
2Speed
If ultrasound travel time methods with two acoustic transducers are used, then flow measurement is achieved, but measurement accuracy deteriorates due to requirement for precise knowledge of acoustic distance
Solution Approach 1:
The patent substitutes acoustic travel time measurement with optical phase detection. The OCT system measures flow velocity by detecting phase shifts in reflected light rather than measuring acoustic travel time. This eliminates the need for precise knowledge of transducer spacing and acoustic distance, as the optical system directly provides velocity information through phase analysis.
3Measurement precision
If optical methods based on laser Doppler anemometer are used, then blood flow rate information is obtained, but device complexity and cost increase
Solution Approach 1:
The patent integrates multiple functions into a single OCT-based system. The same OCT apparatus that provides structural imaging also measures flow velocity through Doppler frequency shift analysis. This multi-functionality eliminates the need for separate laser Doppler anemometer equipment, reducing overall system complexity and cost while maintaining measurement precision.
4Speed
If micro-hair sensors are used for blood flow measurement, then flow measurement is achieved, but reliability deteriorates due to clot formation and sensor degradation
Solution Approach 1:
The patent replaces mechanical micro-hair sensors with a non-contact optical measurement system. The OCT system measures flow velocity by detecting phase shifts in light reflected from moving blood cells, eliminating the need for physical sensors that protrude into the blood flow. This eliminates the problems of clot formation, sensor encapsulation, and mechanical degradation.
5Quantity of substance
If photoplethysmogram sensors are used, then surrogate parameters for blood pressure and flow are determined, but measurement accuracy deteriorates due to reliance on assumed models and parameters
Solution Approach 1:
The patent replaces indirect PPG-based surrogate parameter measurement with direct optical velocity measurement. The OCT system directly measures red blood cell velocity through Doppler frequency analysis, providing accurate flow rate data without relying on assumed blood flow models or intermediate calculations. This direct measurement approach eliminates the inaccuracies inherent in model-based surrogate parameter determination.
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 sensor provides highly accurate, stable, and robust flow and pressure measurements without interference, suitable for clinical use, with minimal manufacturing costs and no need for additional components or electrical power, suitable for integration into medical devices like guidewires.
Implementation Method 1
an optical source for providing excitation light for heating the medium in which the sensor is located
Implementation Method 2
reflection from the deformable structure creates an interference pattern that varies with wavelength and according to the sizing of the deformable structure
Implementation Method 3
Doppler FD-OCT for sub-nanometer resolution
Data Source
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AI summary
A sensor is provided for measuring a flow of a fluid in a physiological environment, such as within a vessel of a human or animal subject. The sensor comprises an interrogation light guide extending from a proximal end to a distal end of the sensor. The interrogation light guide is configured to transmit interrogation light to, and receive reflected interrogation light from, the distal end of the sensor. The sensor further comprises an excitation light guide configured to transmit excitation light to the distal end of the sensor. The excitation light is provided for heating the fluid (directly or indirectly). The sensor further comprises a sensing element located at the distal end of the sensor. The sensing element comprises at least two etalons for reflecting interrogation light back along the interrogation light guide towards the proximal end of the sensor. Each etalon has a respective optical path length and further has at least one reflective surface external to the interrogation light guide. The sensing element is configured to be in thermal contact with the fluid such that the optical path length of at least one etalon is dependent on a temperature of the fluid. The reflected interrogation light forms an interferogram which is dependent on the optical path lengths of the respective etalons.