High-Resolution 3T MRI of the Membranous Labyrinth Using Deep Learning Reconstruction

The labyrinth is a complex anatomic structure in the temporal bone. However, high-resolution imaging of its membranous portion is challenging because of its small size and the limitations of current MRI techniques. Deep learning reconstruction (DLR) represents a promising approach to advancing MR image quality, enabling higher spatial resolution and reduced noise. This study aims to evaluate DLR high-resolution 3D heavy T2-weighted TSE (3D-T2) MRI sequences for visualizing the labyrinthine structures, comparing them with conventional 3D-T2 sequences. The goal is to improve spatial resolution without prolonging acquisition times, allowing a more detailed view of the labyrinthine microanatomy.

High-resolution heavy T2-weighted TSE SPACE images were acquired in patients by using 3D-T2 and improved T2 weighted turbo spin-echo sequence incorporating deep learning reconstruction (DLR-3D-T2). Two radiologists rated structure visibility on a 4-point qualitative scale for the spiral lamina, scala tympani, scala vestibuli, scala media, utricle, saccule, utricular and saccular maculae, membranous semicircular ducts, and ampullary nerves. Ex vivo 9.4T MRI served as an anatomic reference.

DLR-3D-T2 significantly improved the visibility of several inner ear structures. The utricle and utricular macula were systematically visualized, achieving grades ≥3 in 95% of cases (P < .001), while the saccule remained challenging to assess, with grades ≥3 in only 10% of cases. The cochlear spiral lamina and scala tympani were better delineated in the first 2 turns but remained poorly visible in the apical turn. Semicircular ducts were only partially visualized, with grades ≥3 in 12.5% to 20% of cases, likely due to resolution limitations relative to their diameter. Ampullary nerves were moderately improved, with grades ≥3 in 52.5% to 55% of cases, depending on the nerve.

While DLR does not yet provide a complete anatomic assessment, it represents a important step forward in the noninvasive evaluation of inner ear structures. Pending further technical refinements, this approach may help reduce reliance on delayed gadolinium-enhanced techniques for imaging membranous structures.