Visualization of human inner ear anatomy with high-resolution MR imaging at 7T: initial clinical assessment

Abstract

Background and purpose: In many centers, MR imaging of the inner ear and auditory pathway performed on 1.5T or 3T systems is part of the preoperative work-up of cochlear implants. We investigated the applicability of clinical inner ear MR imaging at 7T and compared the visibility of inner ear structures and nerves within the internal auditory canal with images acquired at 3T.

Materials and methods: Thirteen patients with sensorineural hearing loss eligible for cochlear implantation underwent examinations on 3T and 7T scanners. Two experienced head and neck radiologists evaluated the 52 inner ear datasets. Twenty-four anatomic structures of the inner ear and 1 overall score for image quality were assessed by using a 4-point grading scale for the degree of visibility.

Results: The visibility of 11 of the 24 anatomic structures was rated higher on the 7T images. There was no significant difference in the visibility of 13 anatomic structures and the overall quality rating. A higher incidence of artifacts was observed in the 7T images.

Conclusions: The gain in SNR at 7T yielded a more detailed visualization of many anatomic structures, especially delicate ones, despite the challenges accompanying MR imaging at a high magnetic field.

© 2015 by American Journal of Neuroradiology.

Figures

Fig 1.

Mean differences in scoring of anatomic structures depicted at 3T and 7T. The bars on the right side of the zero line indicate differences in favor of the 7T images. The bars on the left side indicate differences in favor of the 3T images. The structures showing significant differences are marked with an asterisk on the left, and P values are mentioned if significant.

Fig 2.

Axial cross-section of a right inner ear, rendered at 3T (A) and 7T (B); improved discrimination of the intracochlear structures and compartments is shown. In addition, sharper delineation of the nerves in the internal auditory canal is demonstrated. The single arrow indicates the scala media at the first turn. The double arrows indicate the superior ampullary nerve.

Fig 3.

Axial cross-section along the course of the facial nerve of a left inner ear, rendered at 3T (A) and 7T (B). A sharp delineation of the neural structures and clear depiction of the intermediate nerve between cranial nerves VII and VIII are demonstrated on the 7T image.

Fig 4.

In 2 different patients, 7T images showing stripelike-artifacts at the level of the first turn of right (A) and left (B) cochleas, disturbing the quality of the representation and impeding the distinction of the scala vestibuli and tympani.