Implementation and evaluation of single frame recording techniques for holographic measurements of the tympanic membrane in-vivo

Abstract

We are developing an advanced computer-controlled digital holographic system (DHS) with the ability to measure both shape and acoustically induced deformations of the tympanic membrane of several species, including humans. The DHS has been deployed in the clinic and is currently being optimized for in-vivo measurements. The clinical environment presents numerous challenges such as disturbances due to patient's heartbeat, breathing, patient's tremor as well as environmentally induced mechanical vibrations of several orders of magnitude larger (1-10 Hz, 0.1-100 μm) than the nanometer measuring resolution of the system. Biological samples and the tympanic membrane in particular represent numerous challenges for optical systems including non-uniform light scattering, random internal and external reflections as well as low reflectivity (<10%) and high transparency (>50%). Design and optimization of the system for clinical use includes the development and implementation of various acquisition strategies and algorithms for minimization of measurement disturbances in clinical conditions as well as in-vivo measurements. In this work we show implementation of several single frame acquisition algorithms based on both lens and lensless optical holographic configurations. We also evaluate their performance in terms of acquisition speed, external mechanical disturbance tolerance, appropriate depth of field, as well as tolerance to non-uniform light scattering typical in biological samples. © The Society for Experimental Mechanics, Inc. 2014.