Homodyne mixing of scattered light as a novel technique for the measurement of ciliary beat frequency

Michael J. Wilson; Adrian Drake-Lee; Ruikang K. Wang

doi:10.1117/12.384153

28 April 2000 Homodyne mixing of scattered light as a novel technique for the measurement of ciliary beat frequency

Michael J. Wilson, Adrian Drake-Lee, Ruikang K. Wang

Proceedings Volume 3915, Coherence Domain Optical Methods in Biomedical Science and Clinical Applications IV; (2000) https://doi.org/10.1117/12.384153
Event: BiOS 2000 The International Symposium on Biomedical Optics, 2000, San Jose, CA, United States

Abstract

Cilia are finger like organelles present throughout the epithelium of the human respiratory tract. Typically 5-6 micrometers long, with a density of around 8/micrometers ², they 'beat' at frequencies of 10-20Hz and propel an overlying mucus layer. The mucus traps airborne particulars providing an essential respiratory cleaning/infection control mechanism. A novel method for measurement of ciliary beat frequency in-vivo is presented. Homodyne mixing of scattered coherent light promises a relatively large signal with minimal sensitivity to vibrational when compared with existing methods: Vibrational susceptibility is minimized since all scattered pathlengths are similarly affected, while phase discrepancies introduced by the muco-ciliary surface produce high contrast speckle giving good signal quality. The need to illuminate a relatively small area of epithelium to give large speckle has been addressed using a 'shortened' gradient index rod as a combined delivery/focusing device. Results are good when the ciliary surface reflectivity is increased. However the relatively low reflection co-efficient of the unprepared surface allows homodyne mixing from deeply scattered light giving a speckle structure too small to resolve and consequent signal loss. Evidence is presented that demonstrates how a source with limited temporal coherence might be used to suppress the interference from these 'longer pathlength' photons.

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Michael J. Wilson, Adrian Drake-Lee, and Ruikang K. Wang "Homodyne mixing of scattered light as a novel technique for the measurement of ciliary beat frequency", Proc. SPIE 3915, Coherence Domain Optical Methods in Biomedical Science and Clinical Applications IV, (28 April 2000); https://doi.org/10.1117/12.384153

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KEYWORDS

Light scattering

Homodyne detection

Speckle

Relays

Signal detection

Photons

Speckle pattern

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