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Quantitation of T 2 ′ anisotropic effects on magnetic resonance bone mineral density measurement
Author(s) -
Yablonskiy Dmitriy A.,
Reinus William R.,
Stark Helmut,
Haacke E. Mark
Publication year - 1997
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910370213
Subject(s) - imaging phantom , anisotropy , isotropy , nuclear magnetic resonance , radius , relaxation (psychology) , materials science , perpendicular , orientation (vector space) , bone mineral , magnetic resonance imaging , biomedical engineering , anatomy , physics , optics , geometry , osteoporosis , medicine , mathematics , radiology , computer security , computer science , endocrinology
Abstract In this paper, the authors quantitate the anisotropy of susceptibility effects in an uniaxial trabecular bone model and show its relevance to clinical MR bone mineral density measurements. A physical model is described that quantitates the anisotropic MR behavior of uniaxial trabecular bone. To test the model, a phantom of parallel polyethylene filaments was scanned every 15° between 0° and 90° with respect to the system's main magnetic field ( B 0 ). The distal radial metaphysis of a healthy female volunteer was scanned in orthogonal projections. The signal from each phantom image and each radial image was separated in a pixel‐wise fashion into R 2 and R 2 ′ maps. As predicted, R 2 ′ relaxation showed anisotropic behavior and changed according to sin 2 (ϕ), confirming that columnar structures parallel with B 0 will cause no MR susceptibility effects. Scans of the distal radius showed that R 2 ′ relaxation was twice as great with the forearm perpendicular to B 0 as when it was parallel to it, demonstrating different contributions from struts and columns. For both phantom and radial bone scans, R 2 relaxation was isotropic and did not change with object orientation.