P115. The predictive value of FAT and MFL for deterministic, NTMS-based fibre tracking using a multiple-ROI approach

Abstract

Introduction Imaging of the course of the corticospinal tract (CST) by diffusion tensor imaging (DTI) is useful for function-preserving tumour surgery especially of gliomas infiltrating the white matter. The integration of functional data such as navigated transcranial magnetic stimulation (nTMS) for the delineation of starting ROIs has improved the fibre tracking results in a multiple-ROI approach. However, alterations of MRI signals in and adjacent to brain tumours often lead to spurious tracking results. Parameters such as the minimal fibre track length (MFL) and the fractional anisotropy threshold (FAT) may reflect an unfavourable signal-to-noise ratio and, thus, the risk for non-plausible tractography results. Methods The CST of 32 patients with intracranial tumours was investigated by deterministic DTI (iPlanNet) and nTMS. The cortical seeds were defined by the nTMS hot spots of the primary motor area (M1) of the hand, the foot and the tongue representation. The CST originating from the contralesional M1 hand area was mapped as intra-individual reference. As subcortical region of interests (ROI), we used the anterior inferior pontine region (aiP). The plausibility of the fibre trajectories was assessed by a-priori defined anatomical criteria by two independent raters. As potential co-factors i.a. the FAT and the MFL were analysed. Results Low FAT values (cut-off of 0.105) and long MFL (cut-off 121.5 mm) led to less plausible fibre tracking results ( Figure ). In addition, there was a strong effect of somatotopic location of the seed ROI; best plausibility was obtained for the contralateral hand CST (100%), followed by the ipsilesional hand CST (>95%), the ipsilesional foot (>85%) and tongue (>75%) CST. Conclusions In summary, we found excellent plausibility rates using a deterministic multiple-ROI approach with a cortical, nTMS-derived ROI and an additional ROI in the anterior pontine region. However, due to the technical limitations of the method, the results should always be interpreted with caution, especially when dealing with the FAT values lower than 0.105 or the MFL exceeding 121.5 mm.