Quantitative assessment of the flow distribution in the branches of the external carotid by non-injected flow MRI.

Owing to the lack of databases of blood flow distributions in the external carotid branches, surgeons currently rely on per-operative imaging and on their experience to choose the recipient vessels for microsurgical facial reconstructions. But, thanks to three-dimensional phase contrast angiography (PCA) and kinematic CINE phase contrast (PC) sequences, MRI technologies have the potential to provide quantitative anatomical and hemodynamic information without injection of contrast agent. Having developed and optimized PC-MRI sequences for the small facial vessels, our objective was to investigate the haemodynamic and blood flow distribution in the external carotid branches. We included 31 healthy volunteers in an MRI prospective study. Two-dimensional CINE PC-MRI sequences (average duration time of 2 min 40 s ± 24 s) were performed in the external carotid collaterals (n = 290). A statistical analysis of the flow measurements showed that, despite large interpersonal variabilities, a general flow distribution pattern was obtained by dividing the vessel flow rates by the external carotid artery one (providing local percentages of the incoming flow). The vessels could then be classified in three haemodynamic groups (p < 0.05 Student's test): "low flow" group (lingual artery-12.5 ± 5% of incoming flow), "intermediate flow" group (superior thyroid artery-16.5 ± 10%, internal maxillary artery-20.5 ± 11%, superficial temporal artery-18.4 ± 6%), "high flow" group (facial artery -26.6 ± 10%). Thanks to this general flow distribution mapping, it is now possible to estimate the flow rates in the distal branches of any individual from a single blood flow measurement in the external carotid artery.