Interferometric CMOS Blood Flow Sensing for Deep Tissue Monitoring
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Solution Overview
Problem
Current non-invasive techniques for measuring cerebral blood flow, such as diffuse correlation spectroscopy (DCS), are limited by high costs, susceptibility to ambient light noise, and low photon count rates, making continuous monitoring in natural environments impractical.
Innovation Solution
A non-invasive interferometric technique using a multi-mode fiber collector and a CMOS sensor array to detect interference patterns, which enhances photon count rates and reduces noise, enabling high-speed, low-cost cerebral blood flow monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photon-counting technology is used for DCS measurements, then measurement precision is improved, but device cost increases significantly and susceptibility to ambient light noise worsens
Solution Approach 1:
The patent replaces expensive, fragile photon-counting detectors with inexpensive CMOS camera sensors that can be mass-produced. The CMOS sensors achieve sufficient measurement precision through high photon count rates and parallel detection, eliminating the need for costly single-photon-counting technology while maintaining blood flow measurement accuracy.
Solution Approach 2:
The patent substitutes the mechanical/electronic photon-counting detection system with an optical interferometric system using CMOS cameras. By using heterodyne interferometry with frequency-shifted reference light, the system converts weak blood flow-induced phase modulations into detectable intensity variations, enabling precise measurements with conventional CMOS sensors.
2Measurement precision
If DCS measures light fluctuations to determine blood flow, then non-invasive measurement is achieved, but photon count rates are limited and source-detector separation must be kept short
Solution Approach 1:
The patent transitions from measuring only intensity fluctuations (one dimension) to measuring phase information through interferometry (adding a temporal dimension via frequency modulation). The heterodyne technique introduces a reference frequency that shifts the blood flow signal into a higher frequency band, enabling deep tissue penetration with extended source-detector separations while maintaining measurement precision.
3Productivity
If multiple avalanche photodiodes are used for parallel detection, then photon count rates increase, but device cost becomes prohibitively expensive
Solution Approach 1:
The patent replaces expensive avalanche photodiodes with inexpensive CMOS camera pixels that can be manufactured in large arrays. The CMOS sensors provide sufficient detection speed and sensitivity through their high pixel count and parallel readout capability, achieving high photon count rates at a fraction of the cost of avalanche photodiode arrays.
Solution Approach 2:
The patent makes CMOS camera sensors perform the specialized function of blood flow detection through interferometric processing. By using heterodyne detection with frequency-modulated light, the system enables conventional CMOS sensors to measure dynamic blood flow parameters, eliminating the need for specialized expensive detectors while maintaining measurement capability.
4Illumination intensity
If DCS detectors are placed less than 3 cm from the source to increase photon counts, then signal strength is improved, but sensitivity to deep tissues decreases
Solution Approach 1:
The patent uses periodic frequency modulation of the reference light to shift the blood flow signal into a higher frequency range. This heterodyne technique allows the system to distinguish deep tissue signals from superficial noise, enabling extended source-detector separations while maintaining deep tissue sensitivity through frequency-domain signal separation.
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 technique achieves high signal-to-noise ratios and deep tissue sensitivity, allowing continuous cerebral blood flow monitoring in natural conditions without the need for single-photon-counting detectors.
Implementation Method 1
obtains light from a temporally coherent source
Implementation Method 2
uses a sensor array to detect an interference pattern resulting from the recombination
Implementation Method 3
multiply scatters light from the sample path by passing the light through the sample
Data Source
AI summary
The disclosed embodiments provide a system that non-invasively analyzes blood flow in a sample of living tissue. During operation, the system obtains light from a temporally coherent source, and splits the obtained light between a reference path and a sample path. Next, the system multiply scatters light from the sample path by passing the light through the sample. The system then recombines light from the reference path and the multiply scattered light from the sample path. Next, the system uses a sensor array to detect an interference pattern resulting from the recombination. Finally, the system analyzes signals from the sensor array to determine a blood flow in the sample.