Capillaries susceptible to frequent stall dynamics revealed by comparing OCT and bessel-2PM measurements

Transient stoppages of red blood cell (RBC) flow through capillaries-termed capillary stalls-occur persistently in neurological disorders such as Alzheimer's disease and ischemic stroke and can interrupt oxygen delivery and exacerbate neurological damage. Effective imaging tools and analyses are necessary to understand the nature, role, and prevention of stalls. In this study, we dissect differences in stalls measured by two-photon Bessel beam microscopy (Bessel-2PM) and optical coherence tomography (OCT) to gain insight into the temporal dynamics of stalls. Twenty-minute series of volumetric angiograms were obtained separately with Bessel-2PM and OCT on the same day in awake, head-fixed mice. The temporal dynamics of stalling in both methods revealed a minority population of susceptible capillaries that exhibited frequent stalls and a large majority of capillaries with infrequent stalls. Differences between OCT and Bessel-2PM in the repeatability and dynamics of stalls are explained by differences in their sensitivity to short or infrequent stalls based on scanning speed and detection off-time. Finally, stroke caused a shift toward the frequently stalling capillary subpopulation, lasting 1 week post-stroke. Dynamic stall analysis therefore enables examination of physiological and methodological contributions to the stalls measured in disease models and across studies.