Original Article HFUS Imaging of the Cochlea: A Feasibility Study for Anatomical Identification by Registration with MicroCT LUCAS LAVENIR, 1 NABIL ZEMITI , 1 MOHAMED AKKARI, 2 GE ´ RARD SUBSOL, 1 FRE ´ DE ´ RIC VENAIL, 2,3 and PHILIPPE POIGNET 1 1 LIRMM, University of Montpellier, CNRS, Montpellier, France; 2 Department of ENT and Head and Neck Surgery, University Hospital Gui de Chauliac, University of Montpellier, Montpellier, France; and 3 Institute for Neurosciences of Montpellier, INSERM U105, Montpellier, France (Received 20 April 2020; accepted 21 October 2020; published online 30 October 2020) Associate Editor Ka-Wai Kwok oversaw the review of this article. Abstract—Cochlear implantation consists in electrically stimulating the auditory nerve by inserting an electrode array inside the cochlea, a bony structure of the inner ear. In the absence of any visual feedback, the insertion results in many cases of damages of the internal structures. This paper presents a feasibility study on intraoperative imaging and identification of cochlear structures with high-frequency ultrasound (HFUS). 6 ex-vivo guinea pig cochleae were subjected to both US and microcomputed tomography (lCT) we respectively referred as intraoperative and preop- erative modalities. For each sample, registration based on simulating US from the scanner was performed to allow a precise matching between the visible structures. According to two otologists, the procedure led to a target registration error of 0.32 mm ± 0.05. Thanks to referring to a better preop- erative anatomical representation, we were able to intraop- eratively identify the modiolus, both scalae vestibuli and tympani and deduce the location of the basilar membrane, all of which is of great interest for cochlear implantation. Our main objective is to extend this procedure to the human case and thus provide a new tool for inner ear surgery. Keywords—Cochlea, High-frequency ultrasound, Microcom- puted tomography, US/CT registration, Computer-assisted surgery. INTRODUCTION Hearing loss is a major public health problem as 466 million people in the world suffer from hearing disor- ders. By 2050, the World Health Organization an- nounced that this number could rise to 900 million, i.e., 10% of the world population. Among the main causes of hearing disabilities, the most common is sen- sorineural hearing loss. The latter occurs in the inner ear and directly affects the internal structures of the cochlea. For instance, hair cell degeneration is caused by presbycusis and ototoxic agents. Whereas both the Reissner’s and basilar membranes, which respectively separate the scalae tympani, media and vestibuli, are affected by Me´ nie` re’s disease and noise exposure. Nevertheless, since the cochlea cannot regenerate itself, cochlear implantation (CI) is the standard hearing restoration care strategy. This surgical procedure consists of inserting an electrode array into the scala tympani through the round window to electrically stimulate the cochlear nerve by bypassing the impaired hair cells. CI has resulted in significant benefits for implanted patients thanks to improvements in the technique in recent decades. The indication, which was restricted to profound deafness cases, has been ex- tended to individuals with residual low-frequency hearing. Yet hearing preservation (HP) is quite chal- lenging since electrode array insertion may cause irre- versible anatomical damage. 7,17 Even with the most modern surgical techniques, CI resulted in HP declin- ing over time. 23 Presently, verification of the preser- vation of the internal structures of the cochlea is performed postoperatively thanks to cone beam com- puted tomography (CBCT). Imaging the Cochlea Therefore CI would benefit from computer-assisted surgery (CAS) by providing real-time visual feedback Address correspondence to Nabil Zemiti, LIRMM, University of Montpellier, CNRS, Montpellier, France. Electronic mail: nabil. zemiti@lirmm.fr Annals of Biomedical Engineering, Vol. 49, No. 5, May 2021 (Ó 2020) pp. 1308–1317 https://doi.org/10.1007/s10439-020-02671-1 BIOMEDICAL ENGINEERING SOCIETY 0090-6964/21/0500-1308/0 Ó 2020 Biomedical Engineering Society 1308