Magnetic resonance imaging with the Digisonic SP Neurelec cochlear implant.

The goal of this study was to evaluate the MR compatibility of the Neurelec Digisonic SP cochlear implant by performing in vitro and in vivo tests. All tests were performed on 1.5 T machine. Torque and force were measured to observe a potential displacement of the internal receiver. Demagnetisation of the internal magnet was monitored inside the MRI scanner and outside the MRI scanner (in the MRI room). Potential-induced voltage on electrodes was measured in vitro, performing the usual MR sequences. Heating around the internal receiver was measured after the same MR sequences. Following in vitro tests, in vivo MR imaging (brain and posterior fossa MRI) was performed to evaluate the induced signal void and geometrical distortion. In vivo test was performed with one volunteer who had a cochlear implant device fixed to the surface of the skin with a bandage. All the in vitro tests were in compliance with standard EN 45502-2-3 relating to Cochlear Implants. In vivo MRI scans demonstrated an image distortion for spin echo sequences of 7 cm maximum around the internal magnet. Magnetic resonance imaging with the Neurelec Digisonic SP cochlear implant is possible with no measurable adverse effects for either the patient or the device. Image artefact around the internal magnet, however, is unavoidable.