Quantitative Blood Flow Assessment by Multiparameter Analysis of Indocyanine Green Video Angiography

Measurements of quantitative blood flow are crucial during brain vascular surgery. Indocyanine green video angiography (ICG-VAG) is an accepted method of blood flow visualization; however, quantitative techniques have not yet been established. Thus, the aim of this study was to further develop ICG analysis for visualizing intraoperative flow changes.

We conducted basic experiments and clinical investigations to establish a relationship between ICG-VAG and measured blood flow. We evaluated several parameters and identified optimal indicators that precisely reflect blood (or fluid) flow. Both in vitro and in vivo studies were performed to calculate the interval between baseline and the intensity peak (Grad) and to measure actual flow rate.

Grad and actual flow rate showed good exponential correlation, with R² values of 0.90 in vitro and 0.82 in vivo. In a representative patient (case 3), we performed intraoperative flow analysis using FlowInsight, which identified a marked elevation in Grad on the brain surface. Because this observation is predictive of brain hyperperfusion, we used these data to carefully manage blood pressure postoperatively.

Grad is the optimum parameter for estimating flow conditions. Although ICG-VAG provides only visual profiles of blood circulation in the brain, this procedure has the potential to be widely used in clinical situations. ICG-based flow measurement can be used to identify normal and abnormal blood flow conditions, such as graft flow and vascular pathology. The novelty of this technique is that the fluorescence intensity of Grad enables surgeons to quantitatively measure real blood flow.