Combined diffuse light reflectance and electrical impedance measurements as a navigation aid in deep brain surgery.

Aim: The aim of this study is to assess reflected light intensity combined with impedance as a navigation aid during stereotactic neurosurgery.

Methods: During creation of 21 trajectories for stereotactic implantation of deep brain stimulation electrodes in the globus pallidus internus or subthalamus (zona incerta or subthalamic nucleus), impedance at 512 kHz and reflected light intensity at 780 nm were measured continuously and simultaneously with a radio frequency electrode containing optical fibres. The signals were compared with the anatomy, determined from pre- and post-operative MRI and CT. The measurements were performed within minutes, and signal analysis was done post-operatively.

Results: Reflected light intensity was low from the cortex, lateral ventricle, caudate nucleus and putamen; intermediate from the globus pallidus and thalamus; while it was high from the subcortical white matter, internal capsule and subthalamus. The electrical impedance was less consistent, but generally low in the cortex, intermediate in the subcortical white matter, putamen, globus pallidus and thalamus, and high in the internal capsule and subthalamus.

Conclusion: Reflected light intensity and electrical impedance give complementary information about passed tissue, and the combination seems promising as a navigation aid during stereotactic neurosurgery.