title: In vivo diffusion tensor imaging of human calf muscle.
abstract: OBJECTIVE
  To investigate a tetrahedral diffusion gradient encoding scheme to measure the diffusion tensor in vivo for human calf muscle.
  
  
  METHODS
  The theoretical TE which maximizes the signal-to-noise ratio (SNR) of the diffusion images was derived for both the orthogonal and tetrahedral sampling strategies and the SNR advantage verified experimentally. A diffusion echo-planar imaging (EPI) sequence was used to image five volunteers. Gradient cycling and geometric averaging was performed to eliminate cross-terms between the imaging and diffusion gradients.
  
  
  RESULTS
  Trace diffusion coefficients in human muscle are spatially invariant and have low intersubject variability (<4%). Images of the off-diagonal terms confirm the anisotropy of muscle, and fiber orientation maps were derived from these off-diagonal images. A noninvariant index of anisotropy, A(ratio) (average value: 1.28), was found to be less susceptible to noise than the invariant index.
  
  
  CONCLUSIONS
  This technique is robust and can be readily implemented on clinical scanners with EPI capabilities.
authors.affiliation: Department of Radiological Sciences, UCLA School of Medicine, Los Angeles, California, USA.
authors.forename: Usha
authors.initials: U
authors.lastname: Sinha
authors.forename: Lawrence
authors.initials: L
authors.lastname: Yao
mesh_terms: D016880:Anisotropy; D002138:Calibration; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007866:Leg / Q000033:anatomy & histology*; D008433:Mathematics; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D019047:Phantoms, Imaging