Cochlear implant is an established auditory prosthesis for children and adults with severe to profound sensorineural hearing loss. With the expansion of the use of cochlear implants, the number of cochlear implant users needing magnetic resonance imaging (MRI) is also increasing.
We report a case of magnet displacement after 1.5 T MRI in a 68-year-old female patient who was using the Hi-Res 90KTM cochlear implant. The patient complained of severe pain during the MRI. On physical examination, the skin over the internal magnet was found to be swollen. Because of severe tenderness in the region, the patient could not wear the receiver-stimulator. A CT scan showed that the lower end of the internal magnet in the implant had become dislodged from the silicone sheath. In this case, the magnet was repositioned by a non-invasive approach via a percutaneous closed reduction maneuver. Immediately after the repositioning procedure, the tenderness and the bulging of the skin disappeared. At present, 6 months since the procedure, the cochlear implant continues to function well.
The objective of this research was to investigate how the spike trains in response to sinusoidally rate-modulated electric stimuli would be characterized in an auditory nerve fiber model using computer simulations.
In this study, in order to understand the properties of the spike trains in response to sinusoidally rate-modulated pulsatile stimuli, the post-stimulus time histogram of the spike trains was generated, and then the parameters of the intensity function in inhomogeneous Poisson process of von Mises type were estimated on the basis of the maximum likelihood method.
The results of computer simulations suggest that the parameters estimated from the spike trains in response to rate-modulated pulsatile electric stimuli are agreed well with those observed in animal experiments.
In conclusion, the rate-modulated pulsatile stimuli may be expected to play a key role in the better design of cochlear implant (CI) and further in restoring auditory functions for CI users.