In-vivo reflection spectroscopy measurements in pig brain during stereotactic surgery

• Radiofrequency (RF) lesioning in the human brain is a commonsurgical therapy for relieving severe pain as well as formovement disorders such as Parkinsonia. During the procedure a smallelectrode is introduced by stereotactic means towards a target arealocalized by CT or MRI. An RF-current is applied throughthe electrode tip when positioned in the target area. Thetissue in the proximity of the tip is heated bythe current and finally coagulated.The overall aim of this studywas to improve the RF-technique and its ability to estimatelesion size by means of optical methods. Therefore, the opticaldifferences between white and gray matter, as well as lesionedand unlesioned tissue were investigated. Reflection spectroscopy measurements in therange of 450-800 nm were conducted on fully anesthetized pigsduring stereotactic RF-lesioning (n=6). Light from a tungsten lamp wasguided to the electrode tip through optical fibers, inserted alonga 2 mm in diameter monopolar RF-electrode. Measurements were performedin steps of 0-10 mm from the target in eachhemisphere towards the entry point of the skull. In thecentral gray of the porcine brain measurements were performed bothbefore and after the creation of a lesion. A totalof 55 spectra were collected during this study. Correlation totissue type was done using post-operative MR-images. The spectral signaturefor white and gray matter differs significantly for the entirespectral range of 450-800 nm. Pre- and post-lesioning reflection spectroscopyshowed the largest differences below 600 and above 620 nm,which implies that lasers within this wavelength range may beuseful for in-vivo measurements of tissue optical changes during RF-lesioning.

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