Relaxation time measurements of bone marrow protons in the calcaneus using a compact MRI system at 0.2 Tesla field strength

Relaxation times (T 1 and T 2 ) of the bone marrow protons and trabecular bone volume fraction (TBVF) in the calcaneus were measured for 100 female volunteers using a compact MRI system at 0.2 T field strength. The speed of sound (SOS) through the calcaneus was measured also for the same subjects using a quantitative ultrasound system. Both relaxation times were found to have positive correlations with age (R = 0.40; P < 0.0001 and R = 0.31; P < 0.002, respectively) and negative correlations with SOS (R = −0.38; P < 0.0001 and R = −0.38; P < 0.0001, respectively). Although TBVF had a fairly high positive correlation with the SOS (R = 0.67), neither T 1 nor T 2 were correlated with TBVF (R = −0.062 and −0.024, respectively). These results suggest that the age dependence of both T 1 and T 2 is caused by the microdynamic properties of the lipid molecules in bone marrow observed using acoustic or elastic modalities. Magn Reson Med 60:485–488, 2008. © 2008 Wiley‐Liss, Inc.