227. MR Diffusion Tensor Imaging fiber tractography of thalamocortical and optical radiation tracts: Comparison between probabilistic fiber tracking and evoked potential recorded in epileptic patients

Abstract

Purpose The purpose of this study was to evaluate the accuracy of the probabilistic tracking method of diffusion tensor imaging fiber tractography (DTI-FT), compared to imaging-represented electrophysiology data in epileptic patients who underwent stereoelectroncephalography (SEEG) for neurosurgical planning. Methods We identified 17 epileptic patients (mean age 26 ± 11) who underwent DTI acquisition on a 1.5T Philips Achieva scanner by using echo planar imaging and a Receive Coil Head SENSE 8 channels. Sequence details include: 64 non collinear diffusion gradient directions, b-value = 1000 s/mm2, TR/TE = 6522/86 ms, FA = 90°, SENSE factor = 2 and voxel-size = 2 × 2 × 2.6 mm. In addition, a three-dimensional T1-weighted Fast Field Echo (FFE) image was acquired with a TR/TE = 7.22/3.24 ms and FA = 8° and voxel size = 0.46 × 0.46 × 0.90 mm. These data were obtained with other brain MR sequences, used for SEEG planning. Depending on electrodes location, we recorded tibial and median somatosensory-evoked potentials (SEP) in 11 patients and flash-visual evoked potential (VEP) in 12. The thalamocortical (THC) and optical radiation (OR) tracts were blindly reconstructed using a probabilistic algorithm implemented in FSL 5.0.6, using two ROIs corresponding to the sensory thalamus and white matter (WM) lying underneath the somatosensory cortex for the THC, and the lateral geniculate body and WM lying next to the calcarine cortex for the OR. The 3D tractographies were then compared to the position of SEEG electrodes contacts, on which evoked potentials (EPs) were recorded. Results Comparison between DTI-FT and EPs shown that a superposition of the neurophysiological recording contacts and the tracts resulted in 15 out of 17 patients (88%). In particular, we obtained correspondence in the reconstruction of 9 out of 11 THC and 8 out of 12 OR. Conclusions This study is a preliminary one, suggesting that EPs recorded during SEEG monitoring can be considered as a valuable tool to validate the probabilistic tracking method in the reconstruction of THC and OR tracts.