Optical Coherence Tomography with Applications in Cancer Imaging

Optical coherence tomography (OCT) is a rapidly emerging optical imaging technique for a wide range of biological, medical, and material investigations [1, 2]. OCT was initially developed in the early 1990s, and has provided researchers with a novel means by which biological specimens and nonbiological samples can be visualized. A primary advantage of OCT is the ability to image tissue microstructure in situ at micron-scale image resolution, without the need for excision of a specimen for tissue processing. The optical ranging in OCT is analogous to ultrasound B-mode imaging, except that OCT uses low-coherence light rather than high-frequency sound. Cross-sectional OCT images can be generated, as is commonly done in ultrasound, or en face OCT sections can be acquired, as in confocal and multiphoton microscopy. The OCT imaging principle involves optical ranging, where the optical reflection of light from a low-coherence optical source is spatially localized using interferometry. The OCT image that is assembled is a gray-scale or false-color multidimensional spatial representation of backscattered light intensity. The signal intensity represented within an OCT image represents the differential backscattering contrast between different tissue types on a micron scale. OCT performs imaging using light; therefore, it has a one to two order-of-magnitude higher spatial resolution than ultrasound. Because the optical imaging beam can be transmitted readily through air, OCT beam-delivery systems do not require contact with the specimen or sample, as do ultrasound probes. Spectroscopic characterization of tissue and cellular structures is also possible within the optical spectrum of the light source.