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.

Observation and characterization of microvascular vasomotion using erythrocyte mediated ICG angiography (EM-ICG-A).

A clinical method for characterizing the state of micro-vasculature vasomotion is demonstrated, based on observing in capillaries the dynamics of autologously re-injected erythrocytes containing ICG dye. Since a manifestation of vasomotion is transient erythrocyte pausing, vasomotion state within a field of capillaries is characterized by an histogram plot of the number of paused erythrocytes as a function of pause duration during a fixed period of observation, then the ratio of long-pausing to short-pausing erythrocytes was calculated. The method was first applied to the posterior pole retinal vasculatures of anesthetized-monkey eyes, and normal vasomotion state during air-breathing was compared to the state induced by O2-breathing, known to cause mild arteriolar vasoconstriction in the mature eye. Subsequently, the effects of other antagonists to normal arteriolarvasotonia state (long-standing experimentally-induced ocular hypertension and branch-vein occlusion, as well as tissue edema) were similarly characterized and the results compared to those obtained during baseline air-breathing. The feasibility of applying the histogram characterization of vasomotion state to human eyes and skin was also preliminarily explored.