Optical coherence tomography

Imaging technique / From Wikipedia, the free encyclopedia

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Optical coherence tomography (OCT) is an imaging technique that uses interferometry with short-coherence-length light to obtain micrometer-level depth resolution and uses transverse scanning of the light beam to form two- and three-dimensional images from light reflected from within biological tissue or other scattering media. Short-coherence-length light can be obtained using a superluminescent diode (SLD) with a broad spectral bandwidth or a broadly tunable laser with narrow linewidth. The first demonstration of OCT imaging (in vitro) was published by a team from MIT and Harvard Medical School in a 1991 article in the journal Science.[1] The article introduced the term “OCT” to credit its derivation from optical coherence-domain reflectometry, in which the axial resolution is based on temporal coherence. [2] The first demonstrations of in vivo OCT imaging quickly followed. [3][4][5]

A high-resolution spectral-domain OCT scan (3x3-mm) of a dry age-related macular degeneration eye showing geographic atrophy and drusen in macula on both cross-sectional and en face fly-through.

The first US patents on OCT by the MIT/Harvard group described both a time-domain OCT (TD-OCT) system [6][7] and a Fourier-domain OCT (FD-OCT) system of the swept-source variety.[6] These patents were licensed by Zeiss and formed the basis of the first generations of OCT products until 2006. Tanno et al. obtained a patent on optical heterodyne tomography (similar to TD-OCT) in Japan in the same year. [8]

In the decade preceding the invention of OCT, interferometry with short-coherence-length light had been investigated for a variety of applications.[9][10][11][12][13][14][15][16][17][18][19][20]  The potential to use interferometry for imaging was described, [20] and measurement of retinal elevation profile and thickness had been demonstrated.[19]

The initial commercial clinical OCT systems were based on point-scanning TD-OCT technology, which primarily produced cross-sectional images due to the speed limitation (tens to thousands of axial scans per second). Fourier-domain OCT became available clinically 2006, enabling much greater image acquisition rate (tens of thousands to hundreds of thousands axial scans per second) without sacrificing signal strength. The higher speed allowed for 3-dimensional imaging, which can be visualized in both en face and cross-sectional views. Novel contrasts such as angiography, elastography, and optoretinography also became possible by detecting signal change over time. Over the past 3 decades, the speed of commercial clinical OCT systems has increased more than 1000-folds, doubling every 3 years and rivaling the Moore’s law of computer chip performance. Development of parallel image acquisition approaches such as line-field and full-field technology may allow the performance improvement trend to continue.

OCT is most widely used in ophthalmology, in which it has transformed the diagnosis and monitoring of retinal diseases, optic nerve diseases, and corneal diseases. It has greatly improved the management of the top 3 causes of blindness – macular degeneration, diabetic retinopathy, and glaucoma – thereby preventing vision loss in many patients. By 2016 OCT was estimated to be used in more than 30 million imaging procedures per year worldwide. [21]

OCT angioscopy is used in the intravascular evaluation of coronary artery plaques and to guide stent placement. Beyond ophthalmology and cardiology, applications are also developing in other medical specialties such as dermatology, gastroenterology (endoscopy), neurology, oncology, and dentistry. [22][23]