PIONEERING EXPERIMENT Optical Coherence Tomography
Clinical Applications of OCT
OCT was initially developed using sources in the optical or first near-infrared( NIR-I) window(~ 650 – 900 nm) to primarily image the eye, owing to the almost transparent nature of eye tissues within that wavelength range, and making ophthalmology the primary field of application of OCT. OCT has become the standard of care in treating a multitude of eye disease conditions such as diabetic retinopathy, age-related macular degeneration( AMD), and glaucoma. OCT is also used for detecting and monitoring glaucoma progression by evaluating retinal nerve fiber layer thinning and optic nerve damage. In AMD in particular, OCT has played a major role in monitoring the progression and treatment response to intravitreal anti-VEGF therapy. However, highly scattering tissues such as skin were challenging to image owing to the limited penetration of light beyond a couple hundred of micrometers. The later development of broadband sources in the second near-infrared( NIR-II) window(~ 1000 – 1700 nm), enabling lower tissue scattering and deeper light penetration in highly scattering tissues, together with advanced technologic development in fiber optic telecommunication and photonics, has facilitated the adoption of OCT in other biomedical fields such as dermatology, dentistry, and beyond. Additionally, the integration of OCT into endoscopes and catheter probes has also opened new era of opportunities in endoscopy, cardiology, gastroenterology, urology, and neurology.
Current trends and outlook
Despite the rapid development and adoption of OCT in the past few decades, the technology still holds great potentials with further improvements not only in hardware and software, but also in clinical utilities through multidisciplinary collaborations of engineers, scientists, clinicians, and entrepreneurs. Hardware ' s improvements will be driven by new integrated technologies and photonics including broader and faster SS-OCT sources, faster and more sensitive detectors, to cite a few. The ongoing integration and adoption of machine learning and artificial intelligence( AI) into the OCT imaging pipeline, especially for processing and analysing data, will dominate the software sector, which will significantly enhance the clinical utility of OCT, allowing to detect diseases in the early stage, improving the diagnosis accuracy, and assisting with automated and real-time diagnostic and decision-making. Other ongoing efforts in OCT development are the integration of more functional imaging capabilities into OCT systems, including OCT elastography for biomechanical evaluation of tissues, polarization-sensitive OCT for evaluating the birefringence of tissues in normal and diseased conditions, OCT optoretinography for assessing lightevoked change in scattering properties and response of photoreceptors, dynamic OCT to enable label-free evaluation of cellular motility, to cite a few. Finally, the development of cost-effective miniaturized and portable OCT systems, including ona-chip and smartphone-based OCT
REFERENCES
[ 1 ] D. Huang, E. A. Swanson, C. P. Lin et al., Science 254, 1178( 1991) [ 2 ] A. F. Fercher and E. Roth, Proc SPIE. 658, 48( 1986) [ 3 ] A. F. Fercher, C. K. Hitzenberger, G. Kamp et al., Opt. Commun. 117, 43( 1995) [ 4 ] G. Hausler, M. W. Lindner, J. Biomed. Opt. 3, 21( 1998) [ 5 ] S. R. Chinn, E. A. Swanson, and J. G. Fujimoto, Opt. Lett. 22, 340( 1997) [ 6 ] R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, Opt. Express 11, 889( 2003) [ 7 ] S. Makita, Y. Hong, M. Yamanari et al., Optics express 14, 7821( 2006)
systems could boost the adoption of home- or community-based OCT systems, facilitating clinical care access to underserved rural areas and reducing patients’ burden from frequent follow-up visits to the clinic.
Conclusion
This review provides a short summary of key milestones in the development of OCT that have contributed to its broader adoption in the medical field. The author would like to emphasize that while this review highlighted a few of the pioneering experiments in OCT, these innovations often built upon other scientific contributions, often at the boundaries of fields, which have significantly impacted the development of OCT. It is also important to highlight that the impact of OCT wouldn’ t be possible without the synergy of multidisciplinary collaborations of scientists, engineers, clinicians, and entrepreneurs, as well as the support of industry and governments. Looking forward, several areas of research and development, including optoretinography, parallel OCT, dynamic OCT, enface OCT, and others are underway and have the potential to expand the capabilities and application fields of OCT. Also, the strategic integration of IA into the OCT imaging pipeline is transforming the workflow in clinical practices.
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