title: Muscle velocity and inertial force from phase contrast MRI.
abstract: OBJECTIVE
  To evaluate velocity waveforms in muscle and to create a tool and algorithm for computing and analyzing muscle inertial forces derived from 2D phase contrast (PC) magnetic resonance imaging (MRI).
  
  
  METHODS
  PC MRI was performed in the forearm of four healthy volunteers during 1 Hz cycles of wrist flexion-extension as well as in the lower leg of six healthy volunteers during 1 Hz cycles of plantarflexion-dorsiflexion. Inertial forces (F) were derived via the equation F = ma. The mass, m, was derived by multiplying voxel volume by voxel-by-voxel estimates of density via fat-water separation techniques. Acceleration, a, was obtained via the derivative of the PC MRI velocity waveform.
  
  
  RESULTS
  Mean velocities in the flexors of the forearm and lower leg were 1.94 ± 0.97 cm/s and 5.57 ± 2.72 cm/s, respectively, as averaged across all subjects; the inertial forces in the flexors of the forearm and lower leg were 1.9 × 10(-3) ± 1.3 × 10(-3) N and 1.1 × 10(-2) ± 6.1 × 10(-3) N, respectively, as averaged across all subjects.
  
  
  CONCLUSIONS
  PC MRI provided a promising means of computing muscle velocities and inertial forces-providing the first method for quantifying inertial forces.
authors.affiliation: Department of Medical Physics, University of Wisconsin School of Medicine & Public Health, Madison, Wisconsin, USA.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Wentland
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: McWalter
authors.affiliation: Department of Biomedical Engineering, California Polytechnic State University, San Luis Obispo, California, USA.
authors.forename: Saikat
authors.initials: S
authors.lastname: Pal
authors.affiliation: Department of Bioengineering, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.|Department of Bioengineering, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
mesh_terms: D000054:Acceleration; D000328:Adult; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical; D014955:Wrist Joint / Q000502:physiology
keywords: PC MRI; biomechanical models; force; muscle motion; muscle velocity; velocimetry