title: Intravoxel partially coherent motion technique: characterization of the anisotropy of skeletal muscle microvasculature.
abstract: OBJECTIVE
  To propose a reformulation of the intravoxel incoherent motion (IVIM) technique exploiting the low b-value diffusion-weighted imaging regime that can characterize microcirculation of tissues perfused with partially coherent blood flow.
  
  
  METHODS
  The new methodology, termed intravoxel partially coherent motion (IVPCM) technique, is suitable for probing microcirculation in tissues with ordered microvasculature, such as skeletal muscle. We employ a subvoxel model utilizing a randomly oriented bundle of straight vessels whose orientation statistics are characterized by a Fisher axial distribution with concentration parameter K quantifying the anisotropy of the distribution (K = 0 indicates isotropic capillary orientation). The methodology is first validated with a proof-of-principle phantom experiment and is then applied to analyze the microvasculature of human calf muscle at rest.
  
  
  RESULTS
  The microcirculatory part of the diffusion-weighted signal at b < 200 s/mm(2) is anisotropic. The variation of the diffusion-weighted signal with b-value exhibits stronger deviation from the expected monoexponential decay when the diffusion encoding gradient is applied parallel to the mean myofiber direction in the calf muscle of three healthy volunteers. The application of the model to data from the medial gastrocnemius and the soleus of the three volunteers gives results within the expected range for the mean microvascular volume fraction, the mean microflow velocity, and the parameter K.
  
  
  CONCLUSIONS
  The proposed methodology has the capability of characterizing the anisotropy of the capillary network in vivo in a manner analogous to the capability of high b-value diffusion to characterize the anisotropy of muscle fibers.
authors.affiliation: Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA. dimitrios.karampinos@radiology.ucsf.edu
authors.forename: Dimitrios C
authors.initials: DC
authors.lastname: Karampinos
authors.forename: Kevin F
authors.initials: KF
authors.lastname: King
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Sutton
authors.forename: John G
authors.initials: JG
authors.lastname: Georgiadis
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D002196:Capillaries / Q000473:pathology; D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007866:Leg / Q000473:pathology; D008833:Microcirculation; D055806:Microvessels / Q000473:pathology*; D015233:Models, Statistical; D009038:Motion; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000473:pathology*; D019047:Phantoms, Imaging