title: Visualizing Meyer's loop: A comparison of deterministic and probabilistic tractography.
abstract: BACKGROUND
  Diffusion tensor tractography of the anterior extent of the optic radiation - Meyer's loop - prior to temporal lobe resection (TLR) may reduce the risk for postoperative visual field defect. Currently there is no standardized way to perform tractography.
  
  
  OBJECTIVE
  To visualize Meyer's loop using deterministic (DTG) and probabilistic tractography (PTG) at different probability levels, with the primary aim to explore possible differences between methods, and the secondary aim to explore anatomical accuracy.
  
  
  METHODS
  Twenty-three diffusion tensor imaging exams (11 controls and 7 TLR-patients, pre- and post-surgical) were analyzed using DTG and PTG thresholded at probability levels 0.2%, 0.5%, 1%, 5% and 10%. The distance from the tip of the temporal lobe to the anterior limit of Meyer's loop (TP-ML) was measured in 46 optic radiations. Differences in TP-ML between the methods were compared. Results of the control group were compared to dissection studies and to a histological atlas.
  
  
  RESULTS
  For controls and patients together, there were statistically significant differences (p<0.01) for TP-ML between all methods thresholded at PTG ≤1% compared to all methods thresholded at PTG ≥5% and DTG. There were no statistically significant differences between PTG 0.2%, 0.5% and 1% or between PTG 5%, 10% and DTG. For the control group, PTG ≤1% showed a closer match to dissection studies and PTG 1% showed the best match to histological tracings of Meyer's loop.
  
  
  CONCLUSIONS
  Choice of tractography method affected the visualized location of Meyer's loop significantly in a heterogeneous, clinically relevant study group. For the controls, PTG at probability levels ≤1% was a closer match to dissection studies. To determine the anterior extent of Meyer's loop, PTG is superior to DTG and the probability level of PTG matters.
authors.affiliation: Ear, Nose and Throat Clinic, Sahlgrenska University Hospital, Gröna Stråket 5, 41345 Gothenburg, Sweden; Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, University of Gothenburg, Per Dubbsgatan 14, 41345 Gothenburg, Sweden. Electronic address: ylva.lilja@neuro.gu.se.
authors.forename: Ylva
authors.initials: Y
authors.lastname: Lilja
authors.affiliation: Department of Medical Physics and Medical Engineering, Sahlgrenska University Hospital, 41345 Gothenburg, Sweden. Electronic address: maria.ljungberg@vgregion.se.
authors.forename: Maria
authors.initials: M
authors.lastname: Ljungberg
authors.affiliation: Department of Medical Physics and Medical Engineering, Sahlgrenska University Hospital, 41345 Gothenburg, Sweden. Electronic address: goran.starck@vgregion.se.
authors.forename: Göran
authors.initials: G
authors.lastname: Starck
authors.affiliation: Department of Neurology, Sahlgrenska University Hospital, 41345 Gothenburg, Sweden; Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, University of Gothenburg, Per Dubbsgatan 14, 41345 Gothenburg, Sweden. Electronic address: Kristina.malmgren@neuro.gu.se.
authors.forename: Kristina
authors.initials: K
authors.lastname: Malmgren
authors.affiliation: Department of Neurosurgery, Sahlgrenska University Hospital, 41345 Gothenburg, Sweden; Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, University of Gothenburg, Per Dubbsgatan 14, 41345 Gothenburg, Sweden. Electronic address: bertil.rydenhag@neuro.gu.se.
authors.forename: Bertil
authors.initials: B
authors.lastname: Rydenhag
authors.affiliation: Department of Neurosurgery, Sahlgrenska University Hospital, 41345 Gothenburg, Sweden; Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, University of Gothenburg, Per Dubbsgatan 14, 41345 Gothenburg, Sweden. Electronic address: daniel.nilsson@neuro.gu.se.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Nilsson
mesh_terms: D000293:Adolescent; D000328:Adult; D038481:Anterior Temporal Lobectomy / Q000009:adverse effects*; D001931:Brain Mapping; D056324:Diffusion Tensor Imaging; D004833:Epilepsy, Temporal Lobe / Q000601:surgery; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D010468:Perceptual Disorders / Q000175:diagnosis / Q000209:etiology*; D011336:Probability; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult
keywords: Diffusion tensor imaging; Epilepsy surgery; Meyer's loop; Optic radiation; Temporal lobe; Tractography