Signal competition in optical coherence tomography and its relevance for cochlear vibrometry.
The usual technique for measuring vibration within the cochlear partition is heterodyne interferometry. Recently, spectral domain phase microscopy (SDPM) was introduced and offers improvements over standard heterodyne interferometry. In particular, it has a penetration depth of several mm due to working in the infrared range, has narrow and steep optical sectioning due to using a wideband light source, and is able to measure from several cochlear layers simultaneously. However, SDPM is susceptible to systematic error due to "phase leakage," in which the signal from one layer competes with the signal from other layers. Here, phase leakage is explored in vibration measurements in the cochlea and a model structure. The similarity between phase leakage and signal competition in heterodyne interferometry is demonstrated both experimentally and theoretically. Due to phase leakage, erroneous vibration amplitudes can be reported in regions of low reflectivity that are near structures of high reflectivity. When vibration amplitudes are greater than ∼0.1 of the light source wavelength, phase leakage can cause reported vibration waveforms to be distorted. To aid in the screening of phase leakage in experimental results, the error is plotted and discussed as a function of the important parameters of signal strength and vibration amplitude.
Department of Electrical Engineering, Columbia University, 500 West 120th Street, New York, New York 10025, USA.
Nathan C
NC
Lin
Department of Electrical Engineering, Columbia University, 500 West 120th Street, New York, New York 10025, USA.
Christine P
CP
Hendon
Department of Otolaryngology, Head and Neck Surgery, and Department of Biomedical Engineering, Columbia University, 630 West 168th Street, New York, New York 10032, USA.
Elizabeth S
ES
Olson
D016477:Artifacts; D003051:Cochlea / Q000000981:diagnostic imaging* / Q000502:physiology; D006801:Humans; D008857:Microscopy, Interference / Q000379:methods*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D041623:Tomography, Optical Coherence / Q000379:methods*; D014732:Vibration