title: Performance of the MRI-based virtual bone biopsy in the distal radius: serial reproducibility and reliability of structural and mechanical parameters in women representative of osteoporosis study populations.
abstract: Serial reproducibility and reliability critically determine sensitivity to detect changes in response to intervention and provide a basis for sample size estimates. Here, we evaluated the performance of the MRI-based virtual bone biopsy in terms of 26 structural and mechanical parameters in the distal radius of 20 women in the age range of 50 to 75 years (mean=62.0 years, S.D.=8.1 years), representative of typical study populations in drug intervention trials and fracture studies. Subjects were examined three times at average intervals of 20.2 days (S.D.=14.5 days) by MRI at 1.5 T field strength at a voxel size of 137×137×410 μm(3). Methods involved prospective and retrospective 3D image registration and auto-focus motion correction. Analyses were performed from a central 5×5×5 mm(3) cuboid subvolume and trabecular volume consisting of a 13 mm axial slab encompassing the entire medullary cavity. Whole-volume axial stiffness and sub-regional Young's and shear moduli were computed by finite-element analysis. Whole-volume-derived aggregate mean coefficient of variation of all structural parameters was 4.4% (range 1.8% to 7.7%) and 4.0% for axial stiffness; corresponding data in the subvolume were 6.5% (range 1.6% to 13.0%) for structural, and 5.5% (range 4.6% to 6.5%) for mechanical parameters. Aggregate ICC was 0.976 (range 0.947 to 0.986) and 0.992 for whole-volume-derived structural parameters and axial stiffness, and 0.946 (range 0.752 to 0.991) and 0.974 (range 0.965 to 0.978) for subvolume-derived structural and mechanical parameters, respectively. The strongest predictors of whole-volume axial stiffness were BV/TV, junction density, skeleton density and Tb.N (R(2) 0.79-0.87). The same parameters were also highly predictive of sub-regional axial modulus (R(2) 0.88-0.91). The data suggest that the method is suited for longitudinal assessment of the response to therapy. The underlying technology is portable and should be compatible with all general-purpose MRI scanners, which is appealing considering the very large installed base of this modality.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA. shinglam@mail.med.upenn.edu
authors.forename: Shing Chun Benny
authors.initials: SC
authors.lastname: Lam
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wald
authors.forename: Chamith S
authors.initials: CS
authors.lastname: Rajapakse
authors.forename: Yinxiao
authors.initials: Y
authors.lastname: Liu
authors.forename: Punam K
authors.initials: PK
authors.lastname: Saha
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000368:Aged; D001706:Biopsy; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009929:Organ Size; D010024:Osteoporosis / Q000473:pathology*; D011884:Radius / Q000473:pathology*; D015203:Reproducibility of Results; D014584:User-Computer Interface