title: Diffusion tensor fiber tractography of the optic radiation: analysis with 6-, 12-, 40-, and 81-directional motion-probing gradients, a preliminary study.
abstract: OBJECTIVE
  Knowing the exact location of the optic radiation preoperatively is important for surgery of the temporal lobe. We hypothesized that a greater number of motion-probing gradients (MPGs) would provide better results of diffusion tensor (DT) fiber tractography of the optic radiation. To test this hypothesis, this study evaluated differences in DT fiber tractography of the optic radiation under different MPG settings.
  
  
  METHODS
  DT images were obtained in 12 healthy volunteers (7 men, 5 women) with a mean age of 32 years (range, 22-45 years) by using a 3T MR imaging scanner with single-shot echo-planar imaging with parallel acquisition (reduction factor = 2). MPG was applied in 6, 12, 40, and 81 independent directions. The first region of interest (ROI) was placed in the occipital lobe, and the second ROI was placed in the lateral geniculate body. Fibers penetrating both ROIs were considered as the optic radiation. Anteroposterior distance between the tip of the Meyer loop and the lateral geniculate body on an axial section was defined as a loop index. Numbers of fibers and loop indices in both cerebral hemispheres were evaluated statistically.
  
  
  RESULTS
  The optic radiation was well visualized in full length by DT fiber tractography in 20 of 24 hemispheres (83%). No significant differences were noted in number of fibers and loop indices among different MPG settings.
  
  
  CONCLUSIONS
  DT fiber tractography can frequently depict almost the entire optic radiation. MPG number does not exert any significant effect on visualization of the optic radiation, and 6-directional MPG is thus sufficient for this purpose.
authors.affiliation: Department of Diagnostic Imaging and Nuclear Medicine, Kyoto University, Kyoto, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Miki
authors.forename: S
authors.initials: S
authors.lastname: Urayama
authors.forename: Y
authors.initials: Y
authors.lastname: Fushimi
authors.forename: T
authors.initials: T
authors.lastname: Okada
authors.forename: T
authors.initials: T
authors.lastname: Hanakawa
authors.forename: H
authors.initials: H
authors.lastname: Fukuyama
authors.forename: K
authors.initials: K
authors.lastname: Togashi
mesh_terms: D000328:Adult; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004292:Dominance, Cerebral / Q000502:physiology; D005260:Female; D005829:Geniculate Bodies / Q000033:anatomy & histology; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000648:ultrastructure*; D009778:Occipital Lobe / Q000033:anatomy & histology; D009900:Optic Nerve / Q000033:anatomy & histology*; D011446:Prospective Studies; D012016:Reference Values; D014795:Visual Pathways / Q000033:anatomy & histology