Optical Frequency Domain Imaging
In most OCT systems, one-dimensional (depth) ranging is provided by lowcoherence interferometry [2, 3] in which the optical path length difference between the interferometer reference and sample arms is scanned linearly in time. This embodiment of OCT, referred to as “time-domain OCT,” has demonstrated promising results for minimally invasive, early detection of disease. The relatively slow imaging speed (approximately 2 kHz A-line rate) of time-domain OCT systems, however, has precluded its use for screening large tissue volumes, which is required for a wide variety of medical applications. Imaging speed has a fundamental significance because of its relationship to detection sensitivity (minimum detectable reflectivity). As the A-line rate increases, the detection bandwidth should be increased proportionally, and therefore the sensitivity drops. The sensitivity of state-of-the-art time-domain OCT systems that operate at 2-kHz, ranges between −105 and −110 dB. Most biomedical applications require this level of sensitivity for sufficient depth of penetration and cannot tolerate a reduction in sensitivity to achieve a higher frame rate. Although increasing the optical power would, in principle, improve the sensitivity, available sources and maximum permissible exposure levels of tissue represent significant practical limitations.
KeywordsDiscrete Fourier Transform Sample Signal Axial Resolution Spectral Envelope Relative Intensity Noise
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