In cochlear implant surgery an electrode array is permanently implanted to stimulate the auditory nerve and allow
deaf people to hear. Current surgical techniques require wide excavation of the mastoid region of the temporal bone
and one to three hours time to avoid damage to vital structures. Recently a far less invasive approach has been
proposed-percutaneous cochlear access, in which a single hole is drilled from skull surface to the cochlea. The drill
path is determined by attaching a fiducial system to the patient's skull and then choosing, on a pre-operative CT, an
entry point and a target point. The drill is advanced to the target, the electrodes placed through the hole, and a
stimulator implanted at the surface of the skull. The major challenge is the determination of a safe and effective drill
path, which with high probability avoids specific vital structures-the facial nerve, the ossicles, and the external ear
canal-and arrives at the basal turn of the cochlea. These four features lie within a few millimeters of each other, the
drill is one millimeter in diameter, and errors in the determination of the target position are on the order of 0.5mm
root-mean square. Thus, path selection is both difficult and critical to the success of the surgery. This paper presents
a method for finding optimally safe and effective paths while accounting for target positioning error.
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