Characterizing Cochlear Implant Magnet-Related MRI Artifact

Objective: To evaluate cochlear implant (CI) magnet-related MRI artifact shape and size, as well as imaging indications and clinical adequacy of scans. Methods: A retrospective chart review was performed for patients undergoing CI and subsequent MRI head imaging from 2014 to 2020 at a single institution. Indications and adequacy of each scan was recorded, and interpretability compared by indication. Magnet-related artifact size was determined by performing ellipsoid modeling at axial slice of greatest signal loss. Artifact radius in centimeters was calculated for 5 sequence categories, and size compared between sequences, manufacturers, and by time from implantation. Results: Twenty patients underwent 58 head MRI scans. Approximately 76% of MRIs (n = 44) for 70% of patients (n = 14) were performed for indications known of prior to implantation; the remainder were performed during workup of new issues. Desired structures were interpretable in 23 (52%) of known-indication MRIs and 8 (57%) of new-indication MRIs, without significant difference (P =.751). Magnet-related artifact magnitude, compared to the reference T1-weighted fast spin echo (FSE) (4.47 cm), was similar in T2 FSE (4.57 cm, P =.068) and T1 gradient echo (GRE) sequences (4.79 cm, P =.28), but significantly greater in T2 GRE (6.86, P <.0001) and DWI (7.56 cm, P <.0001) sequences. Conclusions: DWI and T2 GRE sequences are less useful in MRI evaluation of CI patients. With a more favorable artifact profile, T1 FSE, T2 FSE, and T1 GRE sequences more likely yield clinically useful information. The large proportion of scans performed for known pathology represents an opportunity to optimize for magnet location preoperatively.