Robust quantification of microvascular transit times via linear dynamical systems using two-photon fluorescence microscopy data.

Vascular transit time is an important indicator of microcirculatory health. We present a second-order-plus-dead-time (SOPDT) model for robust estimation of kinetic parameters characterizing microvascular bolus passage using two-photon fluorescence microscopy (2PFM) in anesthetized rats receiving somatosensory stimulation. This methodology enables quantification of transit time, time-to-peak, overshoot, and rate of bolus passage through the microvascular network. The overall transit time during stimulation, of 2.2 ± 0.1 seconds, was shorter (P ~ 0.0008) than that at rest (2.7 ± 0.2 seconds). When compared with conventional γ-variate modeling, the SOPDT modeling yielded better quality of fit both at rest (P<0.0001) and on activation (P<0.001).