2.3. Microvascular Indocyanine Green Angiography (mICG-A)

In this clinical study, Indocyanine Green (ICG) was administered as an intravenous bolus (3 mL VERDYE 5 mg/mL) after arterial and venous anastomosis and flap reperfusion. The anastomosed flap pedicle was placed below the microscope (KINEVO 900, Carl Zeiss, Oberkochen, Germany). Recordings of the supplying artery and draining vein started immediately after intravenous ICG application and were continued until the intensity of the ICG markedly decreased in the artery and vein. Intraoperative fluorescence analysis requires the selection of certain regions of interest (ROI). Two ROIs were placed at the flap pedicle, one at the supplying artery, and the other at the draining vein close to the anastomosis, uncovered from any surrounding tissue (Figure 2). FLOW800 measures the intensity of ICG in the regions of interest for a time period and enables the instant visualization of blood flow variations within small vessels. The time between the maximum ICG intensity of arterial inflow and venous outflow is defined as Intrinsic Transit Time (ITT), which is considered as a parameter of blood flow velocity within the flap (Figure 2) [27].

(A) Microvascular Indocyanine Green Angiography (mICG-A) flow curves in two selected regions of interest (ROI) (green curve: arterial flow, blue curve: venous flow). The spikes are artefacts caused by respiratory movements. (B) Delay Map obtained with FLOW800 illustrating both ROIs (green ROI placed at the artery, blue ROI placed at the vein) and picturing the two flow curves. (C) Gray-scale map of fluorescence intensity (Intensity Map) illustrating both artery and vein after anastomosis.