The principle OCT is white light or low coherence interferometry. The optical setup typically consists of an interferometer with a low coherence, broad bandwidth light source. Light is split into and recombined from reference and sample arm, respectively.
Typical optical setup of single point OCT. Scanning the light beam on the sample enables non-invasive cross-sectional imaging up to 3 mm in depth with micrometer resolution.
The optical carrier is due to the Doppler effect resulting from scanning one arm of the interferometer, and the frequency of this modulation is controlled by the speed of scanning.
-One beam travels through the sample and the other through a controllable delay before reflection through the interferometer. -The rate of coincidence of photons at the output ports of the beam splitter is measured as a function of by use of two photon-counting detectors and a coincidence counter. -Because of quantum destructive interference, when the optical path lengths are equal, the coincidence rate exhibits a sharp dip. -An image of the backscattered light is obtained by scanning in the transverse direction.
Optical coherence tomography (OCT) of the human brain (tom) uses serial A-scan images to build a cross-sectional image of the retina (bottom) and measure retinal nerve fiber layer thickness.
Imaging of Deep Brain in a Mouse Head Acquired with Non-invasive Photoacoustic Tomography (PAT). (A1) and (A2) are non-invasive PAT images of the cross-sections in a mouse brain, which was acquired with the skin and skull intact. The imaging depth for (A1) and (A2) are 5 mm and 8 mm, respectively. (B1) and (B2) are the anatomic photographs of the mouse brain corresponding to (A1) and (A2), respectively. CB: cerebellum; CT: cortex cerebri; FL: fissura longitudinal cerebri; FT: fissura transversa cerebri; HC: hippocampus; OL: olfactory lobes; and VL: ventriculi lateralis.