OCT+Zhang - Jun Zhang, Ph. D. Email: junzhang@uci.edu...

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Unformatted text preview: Jun Zhang, Ph. D. Email: junzhang@uci.edu Beckman Laser Institute University of California, Irvine Optical coherence tomography Optical coherence tomography (OCT) (OCT) Ultrasound image of a growing fetus (approximately 12 weeks old) inside a mother's uterus. This is a side view of the baby, showing (right to left) the head, neck, torso and legs. How ultrasound imaging works Ultrasound pulses Skin surface Probe Reflection boundaries Working principle Z = V * t Optical Coherence Tomography (OCT) OCT is analogous to ultrasound imaging which relies on measuring the time-of-flight of reflected echoes. However, because the speed to light is orders of magnitude faster than sound, OCT uses low coherence interferometry rather than reflection time measurement to measure the light reflection positions in the sample. Tomos in Greek means section. A tomogram is a sectional image of the internal structure of a three-dimensional object. Anterior chamber of human eye Optical coherence tomography Cross sectioning of a tree Ultrasound tomography 10 mm V sound ~ 300 m/s V light ~ 300,000 km/s Optical tomographic imaging Why optical technology? Why optical technology? Noncontact (unlike ultrasound) Noninvasive, non-ionizing (unlike X-rays) High contrast with molecular signature High spatial resolution Inexpensive, portable Light as an Electromagnetic Wave The Electromagnetic Wave Spectrum 760 nm 400 nm Wave function: U 2 ) , ( t z Z -- = ) ( 2 cos ) , ( t z U t z The field in a wave: U = the amplitude = the wavelength v = the frequency (the oscillation rate) is the round frequency k = the wavenumber / 2 [ ] -- = t kz U t z cos ) , ( is the phase constant -- = vt kz 2 is the phase 2 = Complex notation & complex amplitude ] r n cos[ ) , , , ( -- = t k U t z y x } Re{ ) , , , ( ] ) r ( [ t i Ue t z y x - = Where is the spatial dependent phase - = r n ) r ( k t i i t i e Ue Ue t z y x -- = = ) ( ) , , , ( ) r ( ) r ( ~ i Ue u = Complex amplitude can be written as Complex wave function: t i t i i e u e Ue t z y x -- = = ~ ) , , , ( x y n r cos r n r = Intensity Most common detectors are only sensitive to light intensity which is proportional to absolute square of the field amplitude Media for direct recording of field does not exist 2 * ~ ~ ~ u u u I = = t i e r u t z y x - = ) ( ~ ) , , , ( Youngs interferometer y Interferometer Wavefront division )) 2 cos( 1 ( 2 ) ( x z D I x I + = D z x Youngs interferometer Slit Slit Screen D z L = Monochromatic and chromatic light Sun Light bulb LED Laser Diode Wavelength (nm) I 400 700 400 700 Wavelength (nm) I Wavelength (nm) I 400 700 Wavelength (nm) I 400 700 = ) ( d s I Interference of monochromatic light General description of two waves with same frequency...
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OCT+Zhang - Jun Zhang, Ph. D. Email: junzhang@uci.edu...

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