Temporal Bone Anatomy at 0.55 T: Comparison to 1.5/3T MR and High-Resolution CT

The purpose of this study is to evaluate whether the whole-body 0.55 T MRI may be a clinically acceptable or non-inferior alternative to 1.5T/3T for internal auditory canal (IAC) imaging due to greater field homogeneity and resultant reduced susceptibility artifacts near air-bone interfaces. We compare image quality, visibility of IAC anatomy, and cochlear measurements at 0.55 T vs. 1.5T/3T. In this IRB-approved retrospective study, 25 patients who underwent 0.55 T MRI using IAC protocol with prior/ subsequent comparative scans at 1.5T/3T scans were selected. A subset (n=13) also had high-resolution CT (HRCT). 3 board-certified neuroradiologists independently scored the visibility of anatomical structures and overall image quality on a 4-point Likert scale in one non-pathological ear. Readers also measured cochlear length, cochlear width, and IAC width on double oblique coronal images. All three readers rated the visualization of anatomic structures as clinically acceptable (scores ≥ 2) at 0.55 T. Two of the three readers reported no significant difference in visualization of these structures between 0.55 T and higher field strengths. Quantitative measurements (cochlear length, width, and IAC width) at 0.55 T were comparable to 1.5T/3T. One reader (R2) rated overall image quality significantly lower at 0.55 T (mean score: 3.1 at 0.55 T vs. 2.6 at HF; p = 0.005). Clinical evaluation of IAC and inner ear structures using a 3D T2w SPACE sequence at 0.55 T is an acceptable alternative to imaging at conventional field strengths of 1.5/3T.