fMRI for Cochlear Implantation

Overview

fMRI is used to detect activity in various parts of the brain. In this project the auditory cortex is examined. Specifically, an electrical pulse is used to stimulate the cochlear nerves of deaf patients, and activity in the auditory cortex is measured. The main equipment used is a 3T head scanner.

The long term aim of the research is to increase the success rate of cochlear implantations. Currently, deaf patients being considered for an implant are tested by a number of medical techniques to investigate their physiology. These include audiological assessment, diagnostic medical imaging, and electric response audiometry. Next an electrical impulse is applied to the inner ear to check that there is `current return'. A positive outcome of these tests, however, does not guarantee that the cochlear is properly connected to the auditory cortex and the auditory cortex is functioning. Performing fMRI scans whilst stimulating the cochear electrically allows visual evaluation of the function of the Auditory Cortex.

[top of page]

Procedure

Anatomy of the ear. The red arrow shows the path of the needle electrode

Under local anaesthetic, a needle electrode is implanted through the timpanic membrane to the cochlear, by a surgeon. This is a bit like a temporary cochlear implant which is removed after scanning is completed. An electrical pulse is passed through the electrode to stimulate the cochlear nerve. Whilst the signal is being applied, the brain is being scanned by fMRI to detect activity in the auditory cortex.

[top of page]

Results

fMRI scans of the patient's brain, showing stimulation of the auditory cortex

Initial results have been very promising. One patient has been examined, yielding a positive result first time. As expected, right cochlear stimulation led to left auditory cortex stimulation (and vice-versa). As with many parts of the brain, the right side of the brain controls the left side of the body. This is known as inverse-lateral control.

Before tests on human subjects were started the safety of the experiment was carefully investigated. This was particularly important since metallic objects within the scanner can be moved by the magnetic forces, and conducting objects can have currents induced in them by the magnetic field (which could lead to the object getting very hot and burning the patient's ear). Either of these could be dangerous. Detailed checks proved that the apparatus being used would be safe.

[top of page]

Researchers

The following people are involved in the project:

Adnan Alwatban, Magnetic Resonance Centre
Peter Morris, Magnetic Resonance Centre
Andrew Peters, Magnetic Resonance Centre

Catherine Ludman, Radiology
Steve Mason, Medical Physics
Gerry O'Donoghue, Paediatrics

This work is funded by the Medical Research Council