Resident Physician NYU Langone Health new york, New York
Objective: To determine if metal reduction MRI sequences and changes in implant placement minimize artifact from cochlear implants (CI) and improve visualization of intracranial structures.
Study Design: /b>Cadaveric study.
Setting: Tertiary referral center.
Patients: Five cadaveric heads.
Interventions: Specimens were implanted with Advanced Bionics HiRes Ultra3D devices at nasion-external ear canal (EAC) angles of 90, 120, 160 degrees; and distances from the EAC of 9 or 12cm. Standard brain/internal auditory canal (IAC) sequences with metal artifact reducing technique were acquired in a 1.5-T scanner.
Main Outcome Measures: The primary outcome was visibility of 14 intracranial structures graded on a 4-point scale (1:structures <50% visible, 2: >50% visible with some areas nonvisible from artifact, 3: artifact present but adequate for diagnosis, and 4 high-quality). Scores were determined by an experienced head and neck radiologist and compared with one-way ANOVA.
Results: Imaging sequences included axial 5mm whole-brain turbo spin echo (TSE) T2 and fluid-attenuation inversion recovery high bandwidth, axial 5mm whole-brain slice-encoding metal artifact correction (SEMAC), axial IAC constructive interference in steady state (CISS), and axial 3mm T1 IAC with and without fat saturation. In all cases, SEMAC (mean:3.7,SD:0.7) was superior to TSE (mean:3.5,SD:0.8) for ipsilateral cortex and brainstem/cerebellum, and equivalent for the inner ear and cerebellopontine angle. CISS and T1 with fat saturation were poor for ipsilateral structures (p=0.03, p < 0.01). The 120°/9cm position afforded visualization of ipsilateral structures except the brainstem/cerebellum, where 120°/12cm was best (p < 0.01).
Conclusions: SEMAC sequence provides artifact suppression while retaining excellent image quality. Different placement angles didn’t confer improvement in visualization, although placement distances provided slight advantages for some structures.
*Professional Practice Gap & Educational Need: Many patients with CIs require advanced imaging after implantation, whether related to their hearing loss or another indication. With the prevalence of MRI-compatible devices, improving the quality of neuro imaging obtained with the device in place in these patients is important.
*Learning Objective: Review recent technological advances in MRI metal artifact suppression for CIs. Determine an improved proposed MRI protocol for artifact reduction and discuss the role of implant positioning for a contemporary MRI compatible CI.
*Desired Result: Discuss how to adapt implantation techniques to suit potential future imaging needs and develop a CIspecific MRI protocol.