Spatial refractive index measurement of porcine artery using differential phase OCT

We describe a methodology to record spatial variation of refractive index of porcine renal artery using differential phase optical coherence tomography (DP-OCT). DP-OCT provides a quantitative measure of thin specimen phase retardation and refractive index with phase resolution of 5 nm and lateral resolution of 3 μm. DP-OCT instrumentation is an all-fiber, dual channel Mchelson interferometer constructed using polarization maintaining fiber. Two orthogonal polarization modes of light are spatially separated using a Wollaston prism and directed into separate photoreceivers. Because phase noise in the environment is equally present in both channels, computation of phase difference between the two signal channels is attributed exclusively to variation in the specimen's composite refractive index. Porcine renal artery is freshly harvested from a local slaughter house. The lumen is cut open and sliced at 5 μm thickness. Microscopic slide for the tissue section is processed by standard histology method with mounting media. Two dimensional en face dual-channel phase images are taken over 150 μm ×200 μm region on the microscopic slide and the images are reconstructed by plotting relative phase variation as the OCT beam is moved across the artery cross section.