In vivo, label-free, three-dimensional quantitative imaging of kidney microcirculation using Doppler optical coherence tomography.

Doppler optical coherence tomography (DOCT) is a functional extension of optical coherence tomography (OCT) and is currently being employed in several clinical arenas to quantify blood flow in vivo. In this study, the objective was to investigate the feasibility of DOCT to image kidney microcirculation, specifically, glomerular blood flow. DOCT is able to capture three-dimensional (3D) data sets consisting of a series of cross-sectional images in real time, which enables label-free and non-destructive quantification of glomerular blood flow. The kidneys of adult, male Munich-Wistar rats were exposed through laparotomy procedure after being anesthetized. Following exposure of the kidney beneath the DOCT microscope, glomerular blood flow was observed. The effects of acute mannitol and angiotensin II infusion were also observed. Glomerular blood flow was quantified for the induced physiological states and compared with baseline measurements. Glomerular volume, cumulative Doppler volume, and Doppler flow range parameters were computed from 3D OCT/DOCT data sets. Glomerular size was determined from OCT, and DOCT readily revealed glomerular blood flow. After infusion of mannitol, a significant increase in blood flow was observed and quantified, and following infusion of angiontensin II, a significant decrease in blood flow was observed and quantified. Also, blood flow histograms were produced to illustrate differences in blood flow rate and blood volume among the induced physiological states. We demonstrated 3D DOCT imaging of rat kidney microcirculation in the glomerulus in vivo. Dynamic changes in blood flow were detected under altered physiological conditions demonstrating the real-time imaging capability of DOCT. This method holds promise to allow non-invasive imaging of kidney blood flow for transplant graft evaluation or monitoring of altered-renal hemodynamics related to disease progression.