 Magnetic Resonance Imaging MRI. Subjects will undergo a T1- and T2-weighted MRI scan at the T10-S2 levels. Standard sagittal and axial T1-weighted images as well as sagittal T2-weighted turbo inversion recovery spin-echo images will be obtained. The scan will be performed a few days prior to the surgical procedure to determine incision location for appropriate placement in more detail. The decision to implant one or two electrodes will be based on anthropometrical data derived from this scan. If one 16-electrode array does not span across sufficient number or segments a second array will be implanted. 