AU2019250179A1 — Quantification of absolute blood flow in tissue using flourescence-mediated photoplethysmography

USPTO Abstract

The application describes a method, an apparatus and a kit for measuring a time-varying change in an amount of blood in a tissue volume by use of an excitation of a fluorescence agent in the blood, followed by acquiring a time-varying light intensity signal during a pulsatile flow's diastolic and a systolic phase resembling a conventional photo-plethysmogram of the blood through the tissue volume and processing the said light intensity signal for determining the time-varying change in the amount of blood in the tissue volume during the systolic and diastolic phases. These changes are the changes in the aggregate blood layer thickness within a given tissue volume calculating by using a modified Beer-Lambert for the time varying changes in the diastolic and systolic phases, where the calculation is logarithmically proportional to the intensity of the excitation light that excites the fluorescence agent, multiplied by the quantum efficiency of the fluorescent agent and when taken into account the time varying light intensity signal during the diastolic phase minimum scaled by the said intensity and quantum efficiency and when also is subtracted the intensity of time-varying light intensity during the systolic phase maximum of the pulsatile flow, all of that scaled by the multiplication of a molar coefficient of the fluorescent agent and the instantaneous molar concentration of the fluorescence agent in the blood. 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. WO 2016/055837 PCT/IB2014/065189 Figure 6