Neuro Zti implant – designed for MRI

By: Oticon Medical
Date: 8 July 2019

Magnetic Resonance Imaging (MRI) is a well-established technique used in clinical settings around the world to provide professionals with valuable diagnostic and prognostic information about a patient’s health. Users of the Oticon Medical Neuro Zti can be reassured that their implant will not stop them undergoing this type of scan. 

MRI and CI patients

MRI scans are an established diagnostic tool used for body, as well as brain scans, ranging in strength from 0.2 Tesla to 7 Tesla. Recent estimates show that around 79% of MRI scanners in use around the world are 1.5 Tesla, making this the most common type by far¹.

The Neuro Zti implant is fully compatible with 1.5 Tesla scans with the magnet in place for both body and head scans. The implant has been designed to ensure this type of scan is safe and painless and does not produce ‘magnet flip’ as the magnet is held firmly in place by the rigid implant structure². This means it can’t dislodge and remains locked in even after multiple MRI exams, while the implant itself remains stable throughout the MRI scan thanks to a unique screw fixation system that securely attaches it to the bone. This has been confirmed by an independent study from Berlin³. Furthermore, if needed, the implant structure of the Neuro Zti is designed for easy magnet removal.

Why radiologists often want the magnet removed regardless of Tesla strength

Brain scans account for 20-25% of MRI scans among people worldwide^1,4,5. For CI patients, this figure increases to 49%⁶, making brain scans the most common MRI exams they are likely to undergo. For this reason, it’s important to understand how an MRI scan affects a cochlear implant – and also how the images are affected by the magnet.

Leaving the implant magnets in place during head scans of either 1.5 Tesla or 3 Tesla can usually influence the image quality. The magnet may create artefacts that distort the result and prevent reliable diagnosis. This is even more common in scans of 3 Tesla because of the additional magnetic strength. See figure 1.

In fact, when asked radiologists stated that they could not make an accurate diagnosis from images scanned with 3 Tesla with the magnets in place because of the interference created by the magnets⁷ (see table below). This can be clearly seen on figure 1 of the MRI head scan, where the magnet creates artefacts. When this happens, the magnet has to be removed. For this reason, its ease of removal is an important factor when considering an implant.

Summary of the visibility of the rated anatomical structures at the side of the cochlea implant; with and without magnet at 1.5T and 3T.

Ref: Wagner, F., Wimmer, W., Leidolt, L., Vischer, M., Weder, S., Wiest, R., Mantokoudis, G. and Caversaccio, M.D., 2015. Significant artifact reduction at 1.5 T and 3T MRI by the use of a cochlear implant with removable magnet: an experimental human cadaver study. PloS one, 10(7), p.e0132483.

Neuro Zti – direct, easy and quick magnet removal

The Neuro Zti is 3 Tesla compatible without magnet and is designed for easy magnet removal under local anesthesia with only a small skin incision.  The implant is attached using screws and not drilled into the skull. With the dedicated Oticon Medical surgical tool, the magnet is removed in a few steps and can then be replaced again after the scan. 

The dedicated surgical tool simplifies magnet removal 

Furthermore, the Neuro Zti implant magnet can be removed multiple times without damaging the body of the implant. This can be an issue for CI magnets cased in silicone that can loosen over time causing the magnet to flip and migrate⁸. For younger cochlear implant patients who are likely to undergo several MRI scans during their lifetime, ease of removal should be part of the decision making process when choosing an implant system.