Ex vivo and in vivo imaging of the inner ear at 7 Tesla MRI

Abstract

Hypothesis: The implementation of 7.0 Tesla magnetic resonance imaging (MRI) for human use has the potential to further advance spatial resolution beyond that of 1.5T and 3T. This could result in potential advantages in the depiction of the membranous structures of the inner ear.

Background: The inner ear is particularly challenging to visualize at 7T. Where the signal-to-noise ratio will scale linear with the field strength, the proximity of the inner ear to the cerebrospinal fluid, nerves, and bone can lead to susceptibility banding artifacts and signal loss at the interface between the inner ear and its surroundings.

Methods: A human head specimen as well as 2 healthy volunteers underwent MRI at a 7 Tesla scanner. First aim was to scan with ultrahigh resolution, independent of scan duration. Second aim was to reduce scan duration. The final step was to develop a scanning protocol suitable for clinical practice, based on previous information from ex vivo imaging.

Results: Both in and ex vivo, large objects like the cochlear basal turn, vestibule, and semicircular canals were visualized clearly. The nerves were depicted in more detail in vivo. The interscalar septum was visible in all images. A prolonged acquisition time ex vivo showed more detail of the scala tympani and vestibuli. However, the scala media was never visible, even with maximal resolution.

Conclusion: Although inhomogeneities remain present, maximum resolution scanning ex vivo as well as scanning in vivo at 7T MRI resulted in clear depiction of the major membranous structures of the inner ear.