Optical coherence tomography (OCT) is an emerging technology for performing high-resolution cross-sectional imaging. OCT is analogous to ultrasound imaging, except that it uses light instead of sound. OCT can provide cross-sectional images of tissue structure on the micron scale in situ and in real time. Using OCT in combination with catheters and endoscopes enables high- resolution intraluminal imaging of organ systems.

OCT can function as a type of optical biopsy and is a powerful imaging technology for medical diagnostics because unlike conventional histopathology which requires removal of a tissue specimen and processing for microscopic examination, OCT can provide images of tissue in situ and in real time. OCT can be used where standard excisional biopsy is hazardous or impossible, to reduce sampling errors associated with excisional biopsy, and to guide interventional procedures. In this paper, we review OCT technology and describe its potential biomedical and clinical applications.

Optical coherence tomography (OCT) is a fundamentally new type of optical imaging modality. OCT performs high-resolution, cross-sectional tomographic imaging of the internal microstructure in materials and biologic systems by measuring backscattered or backreflected light. OCT images are two-dimensional data sets which represent the optical backscattering in a cross-sectional plane through the tissue. Image resolutions of 1 to 15 µm can be achieved one to two orders of magnitude higher than conventional ultrasound. Imaging can be performed in situ and in real time. The unique features of this technology enable a broad range of research and clinical applications. This review article provides an overview of OCT technology, its background, and its potential biomedical and clinical applications.

OCT, imaging the internal cross-sectional microstructure of tissues using measurements of optical backscattering or backreflection, was first demonstrated in 1991 . OCT imaging was performed in vitro in the human retina and in atherosclerotic plaque as examples of imaging in transparent, weakly scattering media and nontransparent, highly scattering media. OCT was initially applied for imaging in the eye and, to date, OCT has had the largest clinical impact in ophthalmology. The first in vivo tomograms of the human optic disc and macula were demonstrated in 1993 .

OCT enables the noncontact, noninvasive imaging of the anterior eye as well as imaging of morphologic features of the human retina including the fovea and optic disc. Working in collaboration with the New England Eye Center, our group has examined over 10,000 patients to date. The technology was transferred to industry and introduced commercially for ophthalmic diagnostics in 1996 (Humphrey Systems, Dublin, CA). Numerous clinical studies have been performed by many groups in the last several years.

Optical Coherence Tomography Compared to Ultra-sound

OCT imaging is somewhat analogous to ultrasound B mode imaging except that it uses light instead of sound. Because of the analogy between OCT and ultrasound, it is helpful to begin by considering the factors which govern OCT imaging compared to ultrasound imaging. To perform cross-sectional or tomographic imaging, it is first necessary to measure the internal structure of materials or tissues along a single axial or longitudinal dimension. In OCT, the first step in constructing a tomographic image is the measurement of axial distance or range information within the material or tissue. There are several different embodiments of OCT, but in essence OCT performs imaging by measuring the echo time delay and intensity of backscattered or backreflected light from internal microstructure in materials or tissues. OCT images are a two- dimensional or three-dimensional data set which represent differences in optical backscattering or backreflection in a cross-sectional plane or volume.