CI Atlas · Preoperative Imaging · Module 16

16MRI compatibility of the implanted device

A cochlear implant is a piece of metal with a magnet in the skull, so for years it was an absolute bar to MRI — a serious problem for a patient who later needs to image the brain, the spine or the other ear. That has changed: conditional scanning is now routine at 1.5 T, and increasingly at 3 T, provided the rules are followed. The chief hazards are the magnet twisting or demagnetising and local heating, and the chief inconvenience is a large signal void that blacks out the nearby skull base. Device design has answered with removable, magnetless and self-aligning magnets, and a simple compression dressing tames the demagnetisation risk. Crucially, because the artefact is local, the opposite side can still be followed — the counselling point that matters most for surveillance. This module covers scanning the recipient.

Imaging note

Representative CT and MRI images for this chapter are being added soon. The interactive figures here are original schematic teaching diagrams; to respect copyright we do not reproduce third-party radiographs.

TFrom contraindication to conditional

Cochlear implants contain metallic/ferromagnetic components and an internal magnet, historically a contraindication to MRI. Conditional authorisation began in 1995 (first 0.2 T, progressively higher under strict conditions), with FDA 1.5 T MRI-compatible approval in 2013 for the major manufacturers. Recipients must remove all external parts before entering the scanner.[2022]

CRisks & demagnetisation

The risks are device torque/repositioning, localised heating, unusual sounds or pain, magnet demagnetisation, device dysfunction, and image distortion. Demagnetisation depends on the angle between the implant and the scanner field — low (~6.6%) near 90° but much higher beyond it — and a compression head dressing can prevent magnet displacement at 1.5 T.

A cochlear implant contains an internal magnet, historically a contraindication to MRI; conditional scanning began in 1995 and 1.5 T compatibility was approved in 2013. The chief risk besides heating and torque is magnet demagnetisation, which depends on the angle between the implant and the scanner field — low (~6.6%) near 90° but much higher beyond it. A compression head dressing can prevent magnet displacement at 1.5 T; alternatives are removable magnets, magnetless devices, or modern self-aligning magnets. Illustrative figures; schematic.

CMagnet strategies

Three questions guide scanning: is there a magnet, is it removable, and are the internal components ferromagnetic. The engineering answers: removable magnets (extractable through a small incision under local anaesthesia, replaced by a silicone plug), magnetless devices, titanium-silastic housings, and modern rotating/self-aligning magnets.

CThe artefact zone

A large signal-void / susceptibility artefact of ~2–4 cm surrounds the device, blacking out the adjacent skull base and brain — relevant when following ipsilateral pathology. But because the artefact is local, contralateral pathology (e.g. a contralateral vestibular schwannoma) can still be followed on serial MRI — a key counselling and surveillance point, and a reason device choice matters for patients who will need lifelong imaging (Devices chapter).

Even when scanning is permitted, the implant creates a signal-void / susceptibility artefact of roughly 2–4 cm that blacks out the adjacent skull base and brain — a problem when following ipsilateral pathology. The artefact is local, though, so contralateral pathology (e.g. a contralateral vestibular schwannoma) can still be followed on serial MRI — an important counselling and surveillance point, and a reason device choice (removable/magnetless magnet) matters for patients who will need lifelong imaging. Schematic.

Case 12.16 · The recipient needs an MRI

An implant recipient develops a contralateral vestibular schwannoma needing serial MRI surveillance.

What is true about scanning them?

Self-assessment — Module 152 questions

Question 1 · Trainee

Are cochlear implants compatible with MRI?

Question 2 · Clinician

Why can a recipient still have surveillance MRI for contralateral pathology?

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