SYSTEMS AND METHODS FOR MEASURING BIOLOGICAL METRICS AND BLOOD VESSEL GEOMETRY USING A MULTIPLE OPTICAL PATH PHOTOPLETHYSMOGRAPHY DEVICE

Systems and methods for monitoring blood flow metrics using a patch of a flexible substrate configured to attach to an area of skin over a blood vessel. The patch includes a plurality of light sources arranged on the substrate to form a matrix and a row of photodetectors disposed on the substrate substantially in parallel with the rows of LEDs. The patch includes an optical signal interface configured to drive each light source and to input an intensity signal at one of the photodetectors. The intensity signals are used to determine AC and DC components corresponding to each optical path. AC to DC component ratios are calculated for each optical path and used to determine ratio-of-ratio values. At least a subset of the ratio-of-ratio values are used to determine a biological metric or a cross-sectional area of the blood vessel.