title: Diffusion tensor imaging and colored fractional anisotropy mapping of the ventralis intermedius nucleus of the thalamus.
abstract: BACKGROUND
  The ventralis intermedius (VIM) nucleus of the thalamus is the primary surgical target for treatment of tremor. Most centers rely on indirect targeting based on atlas-defined coordinates rather than patient-specific anatomy, making intraoperative physiological mapping critical. Detailed identification of this target based on patient-specific anatomic features can help optimize the surgical treatment of tremor.
  
  
  OBJECTIVE
  To study colored fractional anisotropic images and diffusion tensor imaging (DTI) tractography to identify characteristic magnetic resonance appearances of the VIM nucleus.
  
  
  METHODS
  Four patients undergoing stereotactic surgery for essential tremor (ET) were retrospectively studied with analysis of magnetic resonance imaging-based colored fractional anisotropy (FA) images and fiber tractography. All were scanned with a 1.5-T magnetic resonance imaging unit, and all sequences were obtained before frame placement. Because the goal of this study was to identify the DTI characteristics of physiologically defined VIM nucleus, we selected and studied patients who had undergone DTI and had efficacious tremor control with intraoperative microlesioning effect and tremor reduction with less than 2.0-V stimulation.
  
  
  RESULTS
  Analysis of color FA maps, which graphically illustrate fiber directionality, revealed consistent anatomic patterns. The region of the VIM nucleus can be seen as an intermediate region where there is a characteristic transition of color. Presumptive VIM nucleus interconnectivity with sensorimotor cortex and cerebellum was identified via the internal capsule and the superior cerebellar peduncle, respectively. FA maps could also be used to distinguish segments of gray matter, white matter, and gray-white matter boundaries.
  
  
  CONCLUSIONS
  Analysis of DTI and FA maps on widely available 1.5-T magnetic resonance imaging yields clear identification of various structures key to neurosurgical targeting. Prospective evaluation of integrating DTI into neurosurgical planning may be warranted.
authors.affiliation: The Permanente Medical Group, Inc., Redwood City, California 94063, USA. msedrak@gmail.com
authors.forename: Mark
authors.initials: M
authors.lastname: Sedrak
authors.forename: Alessandra
authors.initials: A
authors.lastname: Gorgulho
authors.forename: Andrew
authors.initials: A
authors.lastname: Frew
authors.forename: Eric
authors.initials: E
authors.lastname: Behnke
authors.forename: Antonio
authors.initials: A
authors.lastname: DeSalles
authors.forename: Nader
authors.initials: N
authors.lastname: Pouratian
mesh_terms: D001931:Brain Mapping / Q000379:methods*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D006801:Humans; D009434:Neural Pathways / Q000502:physiology / Q000601:surgery; D012189:Retrospective Studies; D020651:Ventral Thalamic Nuclei / Q000033:anatomy & histology* / Q000502:physiology / Q000601:surgery