11/9/2023 0 Comments Loss of phase coherenceSo Fujimoto assigned MD-PhD student Huang a mission: Replicate the results obtained from the femtosecond lasers using instead interferometry with short coherence-length light. ![]() Even electronic clocks are not fast enough to measure the miniscule time delays, but interferometry does the trick. Interferometry can amplify the feeble signals that ricochet from anatomical substructures, and this attribute facilitates extraction of the desired spatial information. This property enables resolution of interactions between light waves that have been reflected from the sample of interest and the reference mirror, a key operational element. Unlike most lasers, short coherence-length light spans a wide optical spectrum. In the 1980s, Fujimoto wanted to investigate whether that avenue could be opened further by combining recent technical advances with short coherence-length interferometry. This approach offered powerful advantages relative to ultrafast lasers in terms of sensitivity, speed, and cost.Īlthough interferometric principles had been known for hundreds of years, their methodology was not implemented in biological tissues until the 20 th century. By exploiting this behavior, scientists can measure weak reflections and distances from unknown objects. This phenomenon results from waves whose amplitudes combine when they are in phase and cancel when they are out of phase. When certain types of light beams meet, they interact to create patterns. Furthermore, measurement times were slow and the lasers were prohibitively expensive.įujimoto began considering a different tactic, based on a phenomenon called interference that had originally been described in the 1600s. Although this scheme achieved the time resolution necessary to inspect some tissues, it lacked the sensitivity required to detect surfaces that reflect poorly, such as the retina. In 1986, Fujimoto, an expert in ultrashort lasers, reported that he could use them to distinguish layers within skin and to determine the corneal thickness of anesthetized rabbits. The development of femtosecond optics moved Duguay’s vision forward. Unlike ultrasound, however, there would be no contact with the instrumentation. In this way, analogous to ultrasound, light could pinpoint object depth within the body. ![]() The farther the target, the longer the time for the echoes to return. He proposed that related methods might eventually facilitate “seeing through the human skin.” In this scenario, light shot into the body would bounce back from structures that it encountered. Duguay (then at Bell Laboratories, now at Laval University in Québec). Constructive interferenceĪ major inspiration for surmounting these limitations came from a 1971 study of ultrahigh-speed photography by Michael A. Eye pressure, which forms a mainstay of glaucoma detection, fluctuates, so diagnoses could be missed, and visual field testing, another conventional tool for glaucoma assessment, can be unreliable. The intravenous dye injections that were typically used to spot the pernicious blood vessels that leak fluid into the retina in severe AMD and diabetic retinopathy can trigger nausea and vomiting-and, on rare occasions, they even spur a dangerous allergic reaction. Furthermore, aspects of eye examinations were often subjective, especially for early-stage disease. Until the early 1990s, ophthalmologists used clinical ophthalmoscopic examination to diagnose eye disorders, including leading causes of blindness such as age-related macular degeneration (AMD), diabetic retinopathy, and glaucoma, but the instrumentation lacked the fine depth resolution needed to provide valuable structural information. In ophthalmology, for instance, surveying details of the retina can help uncover and decipher conditions that threaten sight. ![]() To diagnose and monitor health problems, clinicians often peer inside the body with procedures that expose the underlying pathological processes.
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