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

Radio frequency (RF) lesioning in the human brain is a common surgical therapy for relieving severe pain as well as for movement disorders such as Parkinsonia. During the procedure a small electrode is introduced by stereotactic means towards a target area localized by CT or MRI. An RF-current is applied through the electrode tip when positioned in the target area. The tissue in the proximity of the tip is heated by the current and finally coagulated. The overall aim of this study was to improve the RF-technique and its ability to estimate lesion size by means of optical methods. Therefore, the optical differences between white and gray matter, as well as lesioned and unlesioned tissue were investigated. Reflection spectroscopy measurements in the range of 450-800 nm were conducted on fully anesthetized pigs during stereotactic RF-lesioning (n=6). Light from a tungsten lamp was guided to the electrode tip through optical fibers, inserted along a 2 mm in diameter monopolar RF-electrode. Measurements were performed in steps of 0-10 mm from the target in each hemisphere towards the entry point of the skull. In the central gray of the porcine brain measurements were performed both before and after the creation of a lesion. A total of 55 spectra were collected during this study. Correlation to tissue type was done using post-operative MR-images. The spectral signature for white and gray matter differs significantly for the entire spectral range of 450-800 nm. Pre- and post-lesioning reflection spectroscopy showed the largest differences below 600 and above 620 nm, which implies that lasers within this wavelength range may be useful for in-vivo measurements of tissue optical changes during RF-lesioning.