High-resolution 7-Tesla magnetic resonance imaging and post-processing for 3-dimensional reconstruction of the membranous labyrinth in healthy adults.

The membranous labyrinth of the inner ear is a complex network of endolymph-filled structures critical for auditory and vestibular function. Pathological distension of these spaces, termed endolymphatic hydrops (EH), is associated with disorders such as Ménière's disease (MD). However, diagnosing inner ear pathologies remains challenging due to limitations in traditional imaging techniques, which lack the spatial resolution required to assess these intricate structures. Advances in 7-Tesla (7T) magnetic resonance imaging (MRI) now allow for high-resolution visualization of the inner ear. In this study, we used 7T T2-weighted and delayed post-contrast 3D-FLAIR sequences to improve visualization of the membranous labyrinth. As the inner ear region is particularly challenging for MRI due to severe transmit (B) field inhomogeneity, dielectric pads and radiofrequency (RF) shimming were used to optimize the sequences. Subtracted images were processed using 3D segmentation techniques to isolate endolymphatic compartments, enabling the first in vivo 3D reconstructions using 7T MRI and volumetric analyses of the utricle, semicircular canal ducts, saccule, and cochlear duct. The total mean endolymphatic volume in five healthy adult participants was 192.62 mm ± 36.83 mm. These imaging techniques provide a quantitative framework for assessing EH and comparing normal versus diseased inner ear anatomy. Our findings demonstrate the potential of 7T MRI to enhance the diagnosis and understanding of inner ear disorders, particularly MD.