PET Imaging of Tissue Reactions in the Implanted Cochlea: Results of a Pilot Study

Philipp Deutsch^1,2*Jens Peter Bankstahl¹Martin Mamach³Michael Willmann¹Frank Michael Bengel¹Thomas Lenarz^2,4,5Georg Berding^1,2Verena Scheper^2,4,5Jana Schwieger^4,5

• ¹Department of Nuclear Medicine, Hannover Medical School, Hanover, Germany
• ²Cluster of Excellence Hearing4all, Hannover Medical School, University of Oldenburg, Oldenburg, Germany
• ³Department of Radiation Protection and Medical Physics, Hannover Medical School, Hanover, Germany
• ⁴Department of Otolaryngology, Hannover Medical School, Hanover, Germany
• ⁵Lower Saxony Centre for Biomedical Engineering, Implant Research and Development (NIFE), Hannover, Germany

After cochlear implantation, molecular processes at the electrode-nerve interface significantly influence the variability in clinical outcomes. The present study investigates molecular processes in a guinea pig model of cochlear implant (CI) using positron emission tomography/ computed tomography (PET/CT) and correlates the imaging findings with histological analyses. Animals were examined with PET in the 3 weeks post-implantation and 9-12 months post-implantation using the inflammation marker [ 18 F]FDG and, at the later time points, [ 68 Ga]FAPI-46 as a marker for fibrosis. Tracer accumulation in the cochlea was determined from PET imaging based on the co-registered CT. 9 animals (7 with unilateral CI) were included. Uptake in non-implanted cochleae served as reference. Tissue growth around the implant was evaluated histologically. Post-implantation, [ 18 F]FDG uptake was significantly increased when pooling early and late in investigation time points while after one year, [ 68 Ga]FAPI-46 uptake was increased inside the cochlear. Cochlear volumes measured by CT did not show significant differences between compared groups. Tissue growth around the implant was observed in all animals, with a trend toward increased growth associated with insertion depth. However, no clear correlation was observed between the extent of tissue growth and the uptake intensities of FDG and FAPI. The data indicate that increased accumulation of PET biomarkers in the cochlea after implantation can be detected in guinea pigs using a dedicated PET/CT. Given the high resolution of current clinical PET/CT devices, this method is expected to be suitable for use in patients, particularly for assessing the effect of anti-inflammatory or anti-fibrotic therapies.