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2009-03-08 06:05 |
光學(xué)相干斷層成像術(shù)Optical coherence tomography (OCT)
光學(xué)相干斷層成像術(shù)(OpticalCoherenceTomography,OCT)是一種新的光學(xué)診斷技術(shù),可進(jìn)行活體眼組織顯微鏡結(jié)構(gòu)的非接觸式、非侵入性斷層成像.OCT是超聲的光學(xué)模似品,但其軸向分辨力取決于光源的相干特性,可達(dá)10um,且穿透深度幾乎不受眼透明屈光介質(zhì)的限制,可觀察眼前節(jié),又能顯示眼后節(jié)的形態(tài)結(jié)構(gòu),在眼內(nèi)疾病尤其是視網(wǎng)膜疾病的診斷,隨訪觀察及治療效果評價(jià)等方面具有良好的應(yīng)用前景. +kTAOf M
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Optical coherence tomography (OCT) is an optical signal acquisition and processing method allowing extremely high-quality, micrometre-resolution, three-dimensional images from within optical scattering media (e.g., biological tissue) to be obtained. In distinction with other optical methods, OCT, an interferometric technique, is able to penetrate significantly deeper into the scattering medium, for example ~3× deeper than its nearest competitor, Confocal microscopy. Depending on the use of high-brightness and wide-spectrum light sources such as superluminescent diodes or ultrashort pulse lasers, OCT has achieved sub-micrometre resolution (with very wide-spectrum sources emitting over a ~100 nm wavelength range). It is one of a class of optical tomographic techniques. A relatively recent implementation of OCT, frequency-domain OCT, provides advantages in signal-to-noise ratio and therefore faster signal acquisition. OCT systems, now commercially available following years of testing, are finding diverse application areas such as art conservation and diagnostic medicine (notably in ophthalmology where it permits remarkable noninvasive images to be obtained from within the retina). '"QC^J oz
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Starting from white-light interferometry for in vivo ocular eye measurements [1] [2] imaging of biological tissue, especially of the human eye, was investigated by multiple groups worldwide. A first two-dimensional in vivo depiction of a human eye fundus along a horizontal meridian based on white light interferometric depth scans has been presented at the ICO-15 SAT conference in 1990[3]. Further developed 1990 by Naohiro Tanno [4][5], then a professor at Yamagata University, and in particular since 1991 by Huang et al.[6], optical coherence tomography (OCT) with micrometer resolution and cross-sectional imaging capabilities has become a prominent biomedical tissue-imaging technique; it is particularly suited to ophthalmic applications and other tissue imaging requiring micrometer resolution and millimeter penetration depth[7]. First in vivo OCT images – displaying retinal structures – were published in 1993. [8] [9] OCT has also been used for various art conservation projects, where it is used to analyze different layers in a painting. OCT has critical advantages over other medical imaging systems. Medical ultrasonography, magnetic resonance imaging (MRI) and confocal microscopy are not suited to morphological tissue imaging: the first two have poor resolution; the last lacks millimeter penetration depth.[10][11] e3YZ-w^W~h
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OCT is based on low coherence interferometry.[12][13][14] In conventional interferometry with long coherence length (laser interferometry), interference of light occurs over a distance of meters. In OCT, this interference is shortened to a distance of micrometres, thanks to the use of broadband light sources (sources that can emit light over a broad range of frequencies). Light with broad bandwidths can be generated by using superluminescent diodes (superbright LEDs) or lasers with extremely short pulses (femtosecond lasers). White light is also a broadband source with lower powers. =BY)>0?z
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Light in an OCT system is broken into two arms -- a sample arm (containing the item of interest) and a reference arm (usually a mirror). The combination of reflected light from the sample arm and reference light from the reference arm gives rise to an interference pattern, but only if light from both arms have travelled the "same" optical distance ("same" meaning a difference of less than a coherence length). By scanning the mirror in the reference arm, a reflectivity profile of the sample can be obtained (this is time domain OCT). Areas of the sample that reflect back a lot of light will create greater interference than areas that don't. Any light that is outside the short coherence length will not interfere. This reflectivity profile, called an A-scan, contains information about the spatial dimensions and location of structures within the item of interest. A cross-sectional tomograph (B-scan) may be achieved by laterally combining a series of these axial depth scans (A-scan). En face imaging (C-scan) at an acquired depth is possible depending on the imaging engine used. M x
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