OpticalCoherenceTomography

Optical coherence tomography (OCT) is a non-invasive imaging modality that provides high-resolution, cross-sectional images of biological tissue by exploiting low-coherence interferometry. In a typical OCT system, light from a broadband source is split into a sample arm that scans the tissue and a reference arm. Reflected light from tissue microstructures interferes with light from the reference arm; the interference is detected only when optical path lengths are matched within the light source's short coherence length, yielding depth-resolved information.

Two main families exist: time-domain OCT, where depth information is obtained by moving the reference mirror; and Fourier-domain variants, including spectral-domain OCT and swept-source OCT, which acquire depth profiles by detecting the interference spectrum or sweeping the light frequency. Fourier-domain OCT is faster and has become the dominant form in many applications.

OCT is widely used in ophthalmology to image retinal layers and the anterior segment, enabling diagnosis and monitoring of diseases such as age-related macular degeneration, glaucoma, and diabetic retinopathy. It is also employed in dermatology, cardiology, and oncology, as well as in industrial nondestructive testing and materials science. Functional extensions, such as Doppler OCT and optical coherence tomography angiography, allow assessment of blood flow and microvasculature.

Advantages of OCT include micrometer-scale resolution, real-time imaging, and deep enough penetration in transparent or scattering tissues. Limitations include shallow imaging depth in highly scattering tissues and sensitivity to motion. Since its development in the early 1990s, OCT has evolved with higher speeds, broader spectral bandwidths, and improved image processing, expanding its clinical and research utility.