Neuro 3d

Three-tesla MRI and DTI sequences were performed on all subjects (including the patient and controls) at Bilkent University. The examinations were performed by using a 3T unit (Trio with Tim; Siemens Healthcare AG, Erlangen, Germany) with 32-channel birdcage head coil. Multiplanar and curved reformatted images were obtained with Leonardo software (Neuro 3D, Siemens Healthcare AG, Germany). An experienced neuroradiologist evaluated the MRI data during acquisition. Details of the routine anatomical imaging sequences (except DTI sequence) are given in Table 1. The diffusion tensor and tractography images were acquired using a high-resolution diffusion tensor sequence (named as Diffusion High-Res, TE = 83 ms, and TR = 8200 ms). A DTI diffusion scheme was used, and a total of 49 diffusion sampling directions were acquired. The b-value was 700 s/mm 2 . The in-plane resolution was 2.16 mm. The slice thickness was 1.8 mm. DTI data were analyzed with FSL, Medinria, and Leonardo programs for obtaining tractography images.

Tractography was performed on a commercially available workstation (software 'Neuro 3D', syngo Leonardo, Siemens Healthcare, Erlangen, Germany) by two readers (LF and DK). One seed ROI, which served as starting point for the automatic fibre tracking, was placed at the level of the pisiform bone. In contrast to the aforementioned ROIs for FA/MD measurements, this ROI was drawn exactly along the borders of the nerve to ensure the inclusion of all nerve fibres [13] . Based on the findings of a previous study on optimal fibre tracking of the median nerve at 3 Tesla [12] , the FA threshold value and the angulation threshold were set to 0.2 and 10°, respectively.
The tractography performance depending on the slice acceleration factor chosen was assessed in terms of (1) number of tracks, (2) average track length and (3) fibre density index (FDi, i.e. the number of tracts divided by the area of the seed ROI) [28] . Furthermore, a qualitative 4-point-scale assessment was performed with regard to the track homogeneity (1 = poor, 2 = fair, 3 = good, 4 = excellent) and the anatomical accuracy (i.e. the correspondence of the track to the anatomical fibre course: 1 = poor, 2 = fair, 3 = good, 4 = excellent).