 Optical coherence tomography ( OCT ) is a medical imaging technique using low @-@ coherence interferometry to provide tomographic visualization of internal tissue microstructures . As seen in Fig . 22 , the core of a typical OCT system is a Michelson interferometer . One interferometer arm is focused onto the tissue sample and scans the sample in an X @-@ Y longitudinal raster pattern . The other interferometer arm is bounced off a reference mirror . Reflected light from the tissue sample is combined with reflected light from the reference . Because of the low coherence of the light source , interferometric signal is observed only over a limited depth of sample . X @-@ Y scanning therefore records one thin optical slice of the sample at a time . By performing multiple scans , moving the reference mirror between each scan , an entire three @-@ dimensional image of the tissue can be reconstructed . Recent advances have striven to combine the nanometer phase retrieval of coherent interferometry with the ranging capability of low @-@ coherence interferometry . 
