Symmetry of the fornix using diffusion tensor imaging.

PURPOSE: To: 1) Present fornix tractography in its entirety for 20 healthy individuals to assess variability. 2) Provide individual and groupwise whole tract diffusion parameter symmetry assessments prior to clinical application. 3) Compare whole tract diffusion parameter assessments with tract-based spatial statistics (TBSS). MATERIALS AND METHODS: Diffusion tensor imaging (DTI) data were acquired on a 3T Siemens magnetic resonance imaging (MRI) system using a single-shot spin echo planar imaging (EPI) sequence. Individual fornix tractography was conducted and whole tract diffusion parameter symmetries assessed. Whole tract results were compared with asymmetry contrasts conducted with voxelwise statistical analysis of diffusion parameters using TBSS. RESULTS: The fornix tract could be visualized in its entirety including the columns, body, crura, and fimbria. Contrary to the crus and body, there were some tractography inconsistencies of the columns and fimbria across subjects. Although whole tract diffusion parameter asymmetries were nonsignificant, fractional anisotropy (FA) values bordered on statistical significance (P = 0.052). Using TBSS, significant FA asymmetries were identified (P ≤ 0.01, corrected). CONCLUSION: The findings demonstrate consistency of fornix tractography as well as some variability in the columns and fimbria. While parametric assessment demonstrates diffusion parameter symmetry, permutation-based TBSS analysis reveals significant FA asymmetries in the crura and fimbriae.

Tractography of Meyer's Loop asymmetries.

PURPOSE: The purpose of the current study was to use diffusion tensor imaging (DTI) to conduct tractography of the optic radiations (OR) and its component bundles and to assess both the degree of hemispheric asymmetry and the inter-subject variability of Meyer's Loop (ML). We hypothesized that there are significant left versus right differences in the anterior extent of ML to the temporal pole (TP) in healthy subjects. MATERIALS AND METHODS: DTI data were acquired on a 3T Siemens MRI system using a single-shot Spin Echo EPI sequence. The dorsal, central and ML bundles of the OR were tracked and visualized in forty hemispheres of twenty healthy volunteers. The uncinate fasciculus (UF) was also tracked in these subjects so that it could be used as a distinct anatomical reference. Measurements were derived for the distance between ML-TP, ML and the temporal horn (ML-TH) and ML and the uncinate fasciculus (ML-UF). Paired difference t-tests were carried out with SPSS 14.0. RESULTS: ML and the UF were successfully tracked and visualized in all 20 volunteers. Significant hemispheric asymmetries were found for all measurements with left distances shorter than the right (P<0.005). In 50% of the subjects the left ML-UF distance was ≤1.9 mm. CONCLUSION: The results support our hypothesis and demonstrate that left ML-TP distances are significantly shorter than right ML-TP distances. These asymmetries are also reflected in shorter left distances between ML-TH and ML-UF. Moreover, these results are of interest to left-sided temporal lobe epilepsy surgery because it is not only more likely to disturb the anterior extent of ML but also renders the often closely located posterior aspect of the left UF more vulnerable to potential surgical impact.