  Capillaries are the smallest vessels in the body responsible for the delivery
of oxygen and nutrients to the surrounding cells. Various diseases have been
shown to alter the density of nutritive capillaries and the flow velocity of
erythrocytes. In previous studies, capillary density and flow velocity have
been assessed manually by trained specialists. Manual analysis of a 20-second
long microvascular video takes on average 20 minutes and requires extensive
training. Several studies have reported that manual analysis hinders the
application of microvascular microscopy in a clinical setting. In this paper,
we present a fully automated system, called CapillaryNet, that can automate
microvascular microscopy analysis and thus enable the method to be used not
just as a research tool, but also for clinical applications. Our method has
been developed by acquiring microcirculation videos from 50 different subjects
annotated by trained biomedical researchers. CapillaryNet detects capillaries
with an accuracy comparable to trained researchers in less than 0.1% of the
time taken by humans and measures several microvascular parameters that
researchers were previously unable to quantify, i.e. capillary hematocrit and
intra-capillary flow velocity heterogeneity.
