Evaluation of 5T high-field MRI for identification of mandibular third molar and inferior alveolar nerve structures: a study compared with 3T MRI and CBCT

This pilot study is the first to investigate the effect of 5T magnetic resonance 3D imaging on the identification of mandibular third molar (MTM) and inferior alveolar nerve (IAN) and to compare it with 3T MRI and CBCT. Sixteen healthy volunteers participated in the study (The clinical trial registration number is “ChiCTR2300074886”. Trial Registration date is 2023.08.18). Four 3D imaging sequences, T1-weighted 3D fast spoiled gradient echo (T1 QUICK3D), T1 QUICK3D with fat suppression (T1 QUICK3D FS), T1-weighted 3D modulated flip angle technique in refocused imaging with extended echo train (T1 MX3D) and T2-weighted MX3D with fat suppression (T2 MX3D FS) were used for comparison. Two blinded independent observers performed qualitative comparisons between 5T MRI, 3T MRI and CBCT using a 5-point Likert scale, and quantitative comparisons between 5T MRI and 3T MRI using signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). The scan times of 5T MRI and 3T MRI were also compared. The inter-observer and intra-observer agreements of the assessments were moderate to excellent (Kappa = 0.590-1.000, ICCs = 0.645-1.000, p < 0.05). All qualitative assessment metrics showed that 5T MRI was significantly better than 3T MRI (p < 0.05). Both SNR and CNR were significantly higher with 5T compared to 3T (p < 0.001). The T1 MX3D sequence on 5T was comparable to CBCT for MTM and IAN imaging. The T1 MX3D had the best contrast for MTM imaging, and the T1 QUICK3D FS sequence was best suited for imaging the IAN. This study preliminarily demonstrates that 5T MRI can provide high-resolution 3D imaging of the MTM and IAN in vivo, and can be a powerful complement to existing detection techniques in the imaging evaluation of extracting third molars.