title: Muscle kinematics during isometric contraction: development of phase contrast and spin tag techniques to study healthy and atrophied muscles.
abstract: OBJECTIVE
  To develop and compare phase-contrast (PC) and spin-tag (ST) MR imaging techniques for accurate quantification of velocity and displacement distribution in the muscle tendon complex of the lower leg during isometric contractions under in vivo conditions, in healthy subjects and subjects with atrophy.
  
  
  METHODS
  Techniques were developed to acquire PC and ST dynamic images, gated to the force exerted by a subject during isometric contraction. Algorithms were optimized for correction of phase shading errors. Flow velocity quantification was validated in phantoms and ex vivo rabbit muscles. Trajectories of pixels calculated from PC images were compared with those in ST images. Velocity distributions were determined in healthy muscles, those atrophied by four weeks of suspension, and during physiotherapy-induced recovery.
  
  
  RESULTS
  The technique developed allowed acquisition of images retrospectively gated to the isometric contraction performed with the subject in the scanner. Significant phase shading errors in PC images (approximately 3 cm/second over the field of view) were reduced to the background noise level by the correction algorithm. Tissue trajectories calculated from PC images agreed very well with those from ST images both in human and excised animal tissues. Peak velocities in atrophied muscles were significantly lower compared to the preatrophy state but recovered to baseline values after six weeks of therapy.
  
  
  CONCLUSIONS
  We show the feasibility of monitoring muscle velocity and tissue displacement during voluntary contractions in humans under in vivo conditions using MR tissue motion mapping methods. The clinical feasibility of this technique in monitoring atrophied muscle is also demonstrated.
authors.affiliation: Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 900095-1721, USA. ssinha@mednet.ucla.edu
authors.forename: Shantanu
authors.initials: S
authors.lastname: Sinha
authors.forename: John A
authors.initials: JA
authors.lastname: Hodgson
authors.forename: Taija
authors.initials: T
authors.lastname: Finni
authors.forename: Alex M
authors.initials: AM
authors.lastname: Lai
authors.forename: John
authors.initials: J
authors.lastname: Grinstead
authors.forename: V Reggie
authors.initials: VR
authors.lastname: Edgerton
mesh_terms: D000328:Adult; D000818:Animals; D001696:Biomechanical Phenomena; D005260:Female; D006614:Hindlimb; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007537:Isometric Contraction; D007866:Leg; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000503:physiopathology*; D019047:Phantoms, Imaging; D011817:Rabbits