title: Diffusion tensor imaging and fiber tractography of the median nerve at 1.5T: optimization of b value.
abstract: OBJECTIVE
  The objective of this study was to systematically assess the optimal b value for diffusion tensor imaging and fiber tractography of the median nerve at 1.5 T.
  
  
  METHODS
  This is a prospective study which was carried out with institutional review board approval and written informed consent from the study subjects. Fifteen healthy volunteers (seven men, eight women; mean age, 31.2 years) underwent diffusion tensor imaging of the wrist. A single-shot spin-echo-based echo-planar imaging sequence (TR/TE, 7000/103 ms) was performed in each subject at eight different b values ranging from 325 to 1,550 s/mm(2). Number and length of reconstructed fiber tracts, fiber density index (FDi), fractional anisotropy (FA), and apparent diffusion coefficient (ADC) were calculated for the median nerve. Signal-to-noise ratio (SNR) was also calculated for each acquisition. The overall image quality was assessed by two readers in consensus by ranking representative fiber tract images for each subject using a scale range from 1 to 8 (1 = best to 8 = worst image quality).
  
  
  RESULTS
  Longest fibers were observed for b values between 675 and 1,025 s/mm(2). Maximum FDi was found at b values of 1,025 s/mm(2). FA was between 0.5 and 0.6 for all b values. ADC gradually decreased from 1.44 x 10(-3) to 0.92 x 10(-3) mm(2)/s with increasing b values. Maximum SNR +/- standard deviation (175.4 +/- 72.6) was observed at the lowest b value and decreased with increasing b values. SNR at b values of 1,025 s/mm(2) was 48.5% of the maximum SNR. Optimal fiber tract image quality was found for b values of 1,025 s/mm(2).
  
  
  CONCLUSIONS
  The optimal b value for diffusion tensor imaging and fiber tractography of the median nerve at 1.5 T was 1,025 s/mm(2).
authors.affiliation: Division of Musculoskeletal Imaging, Department of Medical Imaging, Mount Sinai Hospital and the University Health Network, University of Toronto, 600 University Ave, Toronto, Ontario, Canada, M5G 1X5. gustav@andreisek.de
authors.forename: Gustav
authors.initials: G
authors.lastname: Andreisek
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: White
authors.forename: Andrea
authors.initials: A
authors.lastname: Kassner
authors.forename: George
authors.initials: G
authors.lastname: Tomlinson
authors.forename: Marshall S
authors.initials: MS
authors.lastname: Sussman
mesh_terms: D000328:Adult; D016880:Anisotropy; D003430:Cross-Sectional Studies; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008475:Median Nerve / Q000033:anatomy & histology*; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure*; D009434:Neural Pathways / Q000033:anatomy & histology*; D011446:Prospective Studies
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