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A method to measure sound transmission via the malleuseincuscomplex *Ivo Dobreva , * , Sebastian Ihrle b , Christof R €o € oslia , Rahel Gerig a , Albrecht Eiber b ,Alexander M. Hubera , Jae Hoon Sim aa University Hospital Zurich, University of Zurich, Zurich, Switzerlandb University of Stuttgart, Stuttgart, Germanya r t i c l e i n f oArticle history:Received 31 July 2015Received in revised form22 October 2015Accepted 29 October 2015Available online xxxKeywords:Malleuseincus complex3D laser Doppler vibrometerRigid-body motionHuman middle-ear3D transfer functionIncudo-malleolar jointMicro-CTa b s t r a c tBackground: The malleuseincus complex (MIC) plays a crucial role in the hearing process as it trans-forms and transmits acoustically-induced motion of the tympanic membrane, through the stapes, intothe inner-ear. However, the transfer function of the MIC under physiologically-relevant acoustic stim-ulation is still under debate, especially due to insufficient quantitative data of the vibrational behavior ofthe MIC. This study focuses on the investigation of the sound transformation through the MIC, based onmeasurements of three-dimensional motions of the malleus and incus with a full six degrees of freedom(6 DOF).Methods: The motion of the MIC was measured in two cadaveric human temporal bones with intactmiddle-ear structures excited via a loudspeaker embedded in an artificial ear canal, in the frequencyrange of 0.5e5 kHz. Three-dimensional (3D) shapes of the middle-ear ossicles were obtained by sequentmicro-CT imaging, and an intrinsic frame based on the middle-ear anatomy was defined. All data wereregistered into the intrinsic frame, and rigid body motions of the malleus and incus were calculated withfull six degrees of freedom. Then, the transfer function of the MIC, defined as velocity of the incuslenticular process relative to velocity of the malleus umbo, was obtained and analyzed.Results: Based on the transfer function of the MIC, the motion of the lenticularis relative to the umboreduces with frequency, particularly in the 2e5 kHz range. Analysis of the individual motion componentsof the transfer function indicates a predominant medial-lateral component at frequencies below 1 kHz,with low but considerable anterior-posterior and superior-inferior components that become prominentin the 2e5 kHz range.Conclusion: The transfer function of the human MIC, based on motion of the umbo and lenticularis, hasbeen visualized and analyzed. While the magnitude of the transfer function decreases with frequency, itsspatio-temporal complexity increases significantly.© 2015 Elsevier B.V. All rights reserved.1. IntroductionAcoustically-induced motions of the tympanic membrane causethree-dimensional vibrations of the middle-ear ossicles. Sophisti-cated techniques are needed to measure the vibrational motions ofthe middle-ear ossicles because the amplitude of the ossicular vi-bration is on a nanometer scale. Previous investigations(Decraemer et al., 1999; Puria, 2003) have revealed that the LaserDoppler Vibrometer (LDV) provides sufficiently sensitive, reliableand accurate measurements for determining vibration modes ofthe middle-ear bones.Considering motion of each of the middle-ear ossicles (i.e., themalleus, incus, and stapes) as a rigid body motion underAbbreviations: ASTM, American Society for Testing and Materials; DOF, de-gree(s) of freedom; IMJ, incudo-malleolar joint; ISJ, incudo-stapedial joint; LDV,laser Doppler vibrometry; LPI, lenticular process of the incus; MIC, malleuseincuscomplex; RBM, rigid body motion; SNR, signal-to-noise ratio; TB, temporal bone;3D, three dimensional*For submission to Hearing Research as part of the proceedings of the MEMRO2015 meeting, Aalborg, Denmark, July 1e5, 2015.* Corresponding author. Otolaryngology, Head and Neck Surgery, UniversityHospital Zurich, University of Zurich, Frauenklinikstrasse 24, 8091 Zurich,Switzerland.E-mail address: ivo.dobrev@uzh.ch (I. Dobrev).Contents lists available at ScienceDirectHearing Researchjournal homepage: www.elsevier.com/locate/heareshttp://dx.doi.org/10.1016/j.heares.2015.10.0160378-5955/© 2015 Elsevier B.V. All rights reserved.Hearing Research xxx (2015) 1e10Please cite this article in press as: Dobrev, I., et al., A method to measure sound transmission via the malleuseincus complex, Hearing Research(2015), http://dx.doi.org/10.1016/j.heares.2015.10.016