[Nuclear magnetic resonance and cochlear implant].
Chou underlined that ive potential effects may be anticipated if MRI is realized on implantees: 1) force on the implant by strong magnetic field, 2) current induced by the implant in the radiofrequency (RF) field, 3) damage of implant by RF exposure, 4) MRI image distortion caused by the implant, 5) implant and adjacent tissue heating due to the absorption of RF energy. We studied the reality of the four first of these risks on the Digisonic cochlear implant from MXM using the Siemens Magneton 42 SP, which supplied the implants during 10 minutes with 1 Tesla magnetic field, RF 42 MHz, maximum intensity 10 kV. During T1 and T2 sequences we could notice that: 1) Provided the receiver is strongly attached in its skull niche as requested by normal surgical procedure, no deplacement may be observed: 2) No adverse current may been observed as well on the implanted electrodes as in the internal circuitry; 3) No damage or adverse magnetisation have been detected in the 3 studied receivers; 4) Cerebral imaging of the animal is moderately darkened by the implant. The volume of the shadow involved by the implant is approximately three times the volume of the implant. As Chou demonstrated that no observable heating could be detected after a long MRI sequence, and as Portnoy using Nucleus device observed also that neither adverse current nor implant damage could be detected, we estimate that there are no real contraindication to perform MRI on implantees, provided the surgical attachment has been correctly realised. Practical attitudes will be evoked and discussed.