Development of 7T MRI Techniques for Comprehensive Inner Ear Imaging

About This Grant

PROJECT SUMMARY/ABSTRACT There is a need to improve the ability to see the inner ear in living patients. Inner ear hearing and balance disorders are clinical syndromes that lack biological correlates visible on imaging studies, such as MRI. Current 3T MRI scans can detect structures that are about 0.7 mm, but the inner ear contains much smaller structures, such as membranes and sensory patches, that are 0.4 mm or tinier. The present project takes aim at using higher field MRI (such as 7 Tesla (T)) to overcome spatial resolution limitations of lower field strengths (1.5T and 3T) when visualizing inner ear anatomy and disease processes. The overall goal of this project is to develop clinical 7T MRI of the inner ear and use improved signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) to better visualize inner ear disease processes. The present project aims to apply techniques for 7T MRI developed elsewhere to the inner ear to develop higher resolution pre-contrast scans to see inner ear membranes and cristae (Aim 1), improve the resolution of post-contrast membranous labyrinth anatomy (Aim 2), and functionally image the inner ear by measuring permeability of the blood-labyrinth barrier (BLB, Aim 3). By applying barium dielectric pads and B1+ shimming protocols, we can now image the inner ear with approximately five times the spatial resolution of 3T. This provides an opportunity to visualize membranous labyrinth structures, such as the semicircular canal crista, utricular macula, and semicircular canal ducts, which were previously obscured at lower magnetic field strengths. The proposed research will reference the obtained images to micro-CT and histopathology to differentiate artifacts from true anatomy and provide context when searching for structures that had previously been invisible. This research builds on 3T characterization of otologic conditions like vestibular schwannoma and Meniere's disease to improve the spatial resolution and identify previously unknown disease processes. To facilitate the dissemination of the protocols, we will develop machine learning techniques that can segment the membranous labyrinth and vestibular schwannoma tumors and can be applied at other centers with 7T MRI. A total of 150 individuals (50 healthy adults, 50 vestibular schwannoma, and 50 Meniere’s disease) will undergo pre-contrast and post-contrast scans with pulse sequences that will image membranes and sensory structures (T2-weighted), 3D volumes of the membranous labyrinth (3D-FLAIR), and permeability of the BLB (cDSC). With improved spatial resolution, we can map where gadolinium enters the inner ear in healthy and diseased ears and understand how diseases affect the rate of entry. In summary, 7T MRI will be optimized to improve the spatial resolution of imaging the inner ear and see key structures that are not possible to see with current MRI techniques. This project fits into a larger body of work that aims to leverage the strong signal of high field MRI to reveal disease processes that have previously been invisible and improve the value of MRI in diagnosing inner ear hearing and balance disorders.