title: Assessment of trabecular bone yield and post-yield behavior from high-resolution MRI-based nonlinear finite element analysis at the distal radius of premenopausal and postmenopausal women susceptible to osteoporosis.
abstract: OBJECTIVE
  To assess the performance of a nonlinear microfinite element model on predicting trabecular bone yield and post-yield behavior based on high-resolution in vivo magnetic resonance images via the serial reproducibility.
  
  
  METHODS
  The nonlinear model captures material nonlinearity by iteratively adjusting tissue-level modulus based on tissue-level effective strain. It enables simulations of trabecular bone yield and post-yield behavior from micro magnetic resonance images at in vivo resolution by solving a series of nonlinear systems via an iterative algorithm on a desktop computer. Measures of mechanical competence (yield strain/strength, ultimate strain/strength, modulus of resilience, and toughness) were estimated at the distal radius of premenopausal and postmenopausal women (N = 20, age range 50-75) in whom osteoporotic fractures typically occur. Each subject underwent three scans (20.2 ± 14.5 days). Serial reproducibility was evaluated via coefficient of variation (CV) and intraclass correlation coefficient (ICC).
  
  
  RESULTS
  Nonlinear simulations were completed in an average of 14 minutes per three-dimensional image data set involving analysis of 61 strain levels. The predicted yield strain/strength, ultimate strain/strength, modulus of resilience, and toughness had a mean value of 0.78%, 3.09 MPa, 1.35%, 3.48 MPa, 14.30 kPa, and 32.66 kPa, respectively, covering a substantial range by a factor of up to 4. Intraclass correlation coefficient ranged from 0.986 to 0.994 (average 0.991); CV ranged from 1.01% to 5.62% (average 3.6%), with yield strain and toughness having the lowest and highest CV values, respectively.
  
  
  CONCLUSIONS
  The data suggest that the yield and post-yield parameters have adequate reproducibility to evaluate treatment effects in interventional studies within short follow-up periods.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, 3400 Spruce St, Philadelphia, PA 19104.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Jeremy F
authors.initials: JF
authors.lastname: Magland
authors.forename: Chamith S
authors.initials: CS
authors.lastname: Rajapakse
authors.forename: ShingChun Benny
authors.initials: SB
authors.lastname: Lam
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000368:Aged; D005260:Female; D020342:Finite Element Analysis / Q000706:statistics & numerical data*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data; D008875:Middle Aged; D010024:Osteoporosis / Q000175:diagnosis*; D015663:Osteoporosis, Postmenopausal / Q000175:diagnosis; D017698:Postmenopause / Q000502:physiology*; D011237:Predictive Value of Tests; D017697:Premenopause / Q000502:physiology*; D011884:Radius / Q000473:pathology*; D015203:Reproducibility of Results
keywords: Finite element analysis; MRI; reproducibility and reliability; trabecular bone mechanics