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

Background And Purpose: The labyrinth is a complex anatomical structure in the temporal bone. However, high-resolution imaging of its membranous portion is challenging due to its small size and the limitations of current MRI techniques. Deep Learning Reconstruction (DLR) represents a promising approach to advancing MRI image quality, enabling higher spatial resolution and reduced noise. This study aims to evaluate DLR-High-Resolution 3D-T2 MRI sequences for visualizing the labyrinthine structures, comparing them to conventional 3D-T2 sequences. The goal is to improve spatial resolution without prolonging acquisition times, allowing a more detailed view of the labyrinthine microanatomy.

Materials And Methods: High-resolution heavy T2-weighted TSE SPACE images were acquired in patients using 3D-T2 and DLR-3D-T2. Two radiologists rated structure visibility on a four-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 anatomical reference.

Results: 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 < 0.001), 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 two turns but remained poorly visible in the apical turn. Semicircular ducts were only partially visualized, with grades ≥3 in 12.5-20% of cases, likely due to resolution limitations relative to their diameter. Ampullary nerves were moderately improved, with grades ≥3 in 52.5-55% of cases, depending on the nerve.

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

Abbreviations: 3D-T2 = Three-dimensional T2-weighted turbo spin-echo; DLR-3D-T2 = improved T2 weighted turbo spinecho sequence incorporating Deep Learning Reconstruction; DLR = Deep Learning Reconstruction.