A clinical method for quantification of tissue microvascular blood perfusion in absolute terms [blood-volume/(time·tissue-area)]

Fluorescence-mediated photoplethysmography (FM-PPG) was developed to facilitate determination of tissue microvascular (capillary) blood perfusion, requiring intra-venous injection of a small bolus (~0.33mL) of dye (25mg/mL ICG) and acquisition of high-speed angiogram images (>15images/s). The methodology is applicable to microvascular capillary beds of tissues that can be optically imaged, directly or laparoscopically. Proof of concept of the methodology and feasibility of its implementation are demonstrated in human forearm skin and in the choroid of a monkey eye, determined to have blood perfusion rates on the order of 1e−5mL/(s·mm2) and 10e−5mL/(s·mm2), respectively. Ability to obtain absolute quantified tissue perfusion data ultimately can provide the means by which to characterize blood flow information at the nutritive capillary-vessel level in an objective and universally understood manner, in much the same sense that body temperature or blood pressure are. •FM-PPG is the first clinical method by which absolute tissue blood perfusion is determined in standard international units.•FM-PPG requires only IV-injection of a small volume of ICG dye and subsequent acquisition of ICG fluorescence angiograms.•Lesions can be examined using FM-PPG without having to make any physical contact with tissue.•FM-PPG measurements are absolute, as opposed to relative, so measurements from different subjects can be directly compared.•FM-PPG measurements can be unequivocally understood and compared in the same sense as body temperature or blood pressure are.