Mid-field MRI with cochlear implants: A healthy volunteer study of magnet displacement, pressure perception, and temporal bone imaging

<title>Abstract</title> <p>Purpose We hypothesised that 0.55T MRI would reduce magnet displacement risk and pressure perception compared to 1.5T MRI in healthy volunteers with bandaged cochlear implants (CIs) containing axial or rotating diametric magnets, while maintaining temporal bone image interpretability. Methods Ten healthy volunteers were bandaged with CIs (5 axial magnet; 5 rotating diametric magnet) and underwent consecutive 0.55T and 1.5T MRI sessions. Pressure perception was assessed using a visual analogue scale and magnet displacement was evaluated. Optimised 2D T2-weighted fast spin echo (2D T2-FSE) and constructive interference in steady state (CISS) temporal bone sequences were acquired at both field strengths in seven participants. Diagnostic confidence, artefactual degradation, and distances from CI-related artefact to anatomical structures were assessed. CI magnet translational and torque force were measured. Paired ordinal data were analysed using Wilcoxon signed-rank and Bland–Altman analysed agreement of distances. Results Axial CI magnets were displaced after 1.5T MRI in 4/5 participants but not 0.55T (p = 0.04) with corresponding torque measured as 0.133 v 0.062 Nm. Rotating diametric magnets showed no displacement at either 1.5T or 0.55T with similar torque measurements at both field strengths (0.046 v 0.044 Nm). Pressure perception did not differ between MRI systems. Both CISS and 2D T2-FSE sequences provided adequate diagnostic confidence at both field strengths. The 0.55T 2D T2-FSE sequence reduced CI-related artefact and allowed similar diagnostic confidence to 1.5T. Distances between artefact and anatomical structures did not differ between scanners. Conclusion Mid-field 0.55T MRI reduced axial CI magnet displacement while maintaining clinically acceptable temporal bone imaging. It may provide a useful addition to CI imaging in patients with axial magnet CIs who have experienced magnet complications or pain when undergoing high field MRI.</p>