title: Tractography of Meyer's Loop asymmetries.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: National Research Council Institute for Biodiagnostics, Magnetic Resonance Technology, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada.
authors.forename: Patricia
authors.initials: P
authors.lastname: Dreessen de Gervai
authors.affiliation: Alberta Innovates Technology Futures, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada. Electronic address: UtaFrankenstein@sboto.com.
authors.forename: Uta N
authors.initials: UN
authors.lastname: Sboto-Frankenstein
authors.affiliation: National Research Council Institute for Biodiagnostics, Magnetic Resonance Technology, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada; Biopsychology Program, Department of Psychology, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: Bolster
authors.affiliation: National Research Council Institute for Biodiagnostics, Magnetic Resonance Technology, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada.
authors.forename: Sunny
authors.initials: S
authors.lastname: Thind
authors.affiliation: National Research Council Aquatic and Crop Resource Development, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada.
authors.forename: Marco L H
authors.initials: ML
authors.lastname: Gruwel
authors.affiliation: National Research Council Institute for Biodiagnostics, Magnetic Resonance Technology, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada; Biopsychology Program, Department of Psychology, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Smith
authors.affiliation: Alberta Innovates Technology Futures, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada; Multimodal and Functional Imaging Group, Central Europe Institute of Technology, Kamenice 753, Brno CZ-62500, Czech Republic.
authors.forename: Boguslaw
authors.initials: B
authors.lastname: Tomanek
mesh_terms: D000328:Adult; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D056324:Diffusion Tensor Imaging / Q000379:methods; D005260:Female; D005625:Frontal Lobe / Q000033:anatomy & histology; D007839:Functional Laterality; D005829:Geniculate Bodies / Q000033:anatomy & histology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008032:Limbic System / Q000033:anatomy & histology; D008297:Male; D009434:Neural Pathways / Q000033:anatomy & histology; D013702:Temporal Lobe / Q000033:anatomy & histology*; D014793:Visual Cortex / Q000033:anatomy & histology*; D066127:White Matter / Q000033:anatomy & histology; D055815:Young Adult
keywords: Asymmetry; Diffusion tensor imaging; Meyer's Loop; Optic radiations