Feature Of The Week 3/17/13: Using Optical Coherence Tomography to Study Mechanisms of Hearing
The Oregon Hearing Research Centre (OHRC) at the Oregon Health and Science University (OHSU), Portland, Oregon is one of the strongest hearing research groups in the world, and one of the early adopters of optical coherence tomography technology in the field of hearing research. Researchers at OHRC have developed a couple of novel OCT based imaging technologies for functional imaging of middle and inner ear. This includes high-speed OCT system for in vivo imaging of microstructural morphology and micvascular perfusion within the cochlea [1,2], phase-sensitive time-domain and Fourier domain OCT for studying cochlear micromechanics [3,4] and middle ear vibration imaging .
In the hearing research community, Laser Doppler Vibrometry (LDV) is firmly established as the gold standard method for non-contact vibration measurement analysis. However, there are a couple of issues with using LDV techniques to measure inner-ear tissue vibration. First, the LDV does not provide high-resolution depth-resolved cross-sectional map of structural and vibrational information, because the long coherence length of the laser attributes interference over a long range and yield a complex signal that is not assigned to various microstructures within inner-ear. The second issue is that LDV requires reflected light from the surface of interest and traditional LDV system use visible light, which degrades the depth of penetration. Additionally, the microstructures of organ of Corti (OC) has relatively low level of reflectivity due to its close refractive index with the inner-ear fluids. To enhance the signal to noise ratio, LDV measurements require reflective microbeads that adhere to the OC surface, which face to the scala tympani. Since it is not practical to place reflective objects for the measurement of vibration at different cellular compartments in two and three dimensions, there is a pressing need for an optical sectioning method to perform structural and vibrational imaging of various microstructures of organ of Corti.
Recently, there has been a growing interest in the field of hearing research community to adopt OCT as a tool for the studies of cochlear mechanics. We demonstrated OCT homodyne interferometry and have used this method to obtain a first “glimpse” at the in vivo action of cellular mechanics in the sensitive and high frequency region of the cochlea. We are the first to develop phase sensitive Fourier Domain OCT (PSFDOCT) for vibration of tissue at sub-nanometer scale. However, the proposed PSFDOCT was based on traditional single beam interferometric technique and is capable of measuring vibration vector components only parallel to the optical axis of the imaging beam and they do not offer the motion scenario along the transverse direction, which is required to address the hypothesis of the cochlear amplification. In this study, in order to overcome this limitation, we implemented a dual angle delay-encoded sample beam (dual beam) approach into our PSFDOCT system, which is capable of measuring the radial and transverse motion without angular ambiguity in a single 2D plane.
For more information see recent Article. Courtesy Hrebesh Subhash from Oregon Health & Science University.
1. Hrebesh M. Subhash, Viviana Davila, Hai Sun, Anh T. Nguyen-Huynh, Alfred L. Nuttall, Ruikang K. Wang, “Volumetric in vivo imaging of intracochlear microstructures in mice by high- speed spectral domain optical coherence tomography", J. Biomed. Opt., Vol. 15, 036024 (2010). http://dx.doi.or /10.1117/1.3456554
2. Hrebesh M. Subhash, Viviana Davila, Hai Sun, Anh T. Nguyen-Huynh, Alfred L. Nuttall, Ruikang K. Wang, “Volumetric in vivo imaging of microvascular perfusion within the intact cochlea in mice using ultra-high sensitive optical microangiography”, IEEE Trans Med Imaging.,30(2), 224 - 230 (2011). DOI: 10.1109/TMI.2010.2072934 3. Chen F, Zha D, Fridberger A, Zheng J, Choudhury N, Jacques SL, Wang RK, Shi X, Nuttall AL., “A differentially amplified motion in the ear for near-threshold sound detection”, Nat Neurosci.,14:770–774, (2011)
4. Wang. R. K, and A. L. Nuttall, “Phase-sensitive optical coherence tomography imaging of the tissue motion within the organ of Corti at a subnanometer scale: a preliminary study”, J. Biomed. Opt. 15, 056005 (2010).
5. Hrebesh M. Subhash, Anh Nguyen-Huynh, Ruikang K. Wang, Steven L. Jacques and Alfred L. Nuttall, "Feasibility of spectral-domain phase-sensitive optical coherence tomography for middle ear vibrometry”, J. Biomed. Opt. 17(6), 060505 (2012). DOI: 10.1117/1.JBO.17.6.060505.