MR relaxometry of lumbar spine, hip, and calcaneus in healthy premenopausal women: relationship with dual energy X-ray absorptiometry and quantitative ultrasound.

This study evaluates if the reversible transverse relaxation rate (R2') assessed in vivo by MR of lumbar vertebrae, hip, and calcaneus is correlated with dual energy X-ray absorptiometry (DXA) and to quantitative ultrasound (QUS) of the calcaneus. Fifteen healthy premenopausal women aged 23-47 years were studied by DXA, QUS, and MR relaxometry. The GESFIDE sequence was used to separate the FID rate (R2*) into its two components, the non-reversible transverse relaxation rate (R2) and the reversible transverse relaxation rate (R2'). Long-term reproducibility was obtained by repeated measurements of hip and calcaneus in nine individuals after 300+/-89 days. R2' and R2* of the calcaneus had a relationship to broad-band ultrasound attenuation (BUA; r = 0.46, both p<0.05), but not to other US or DXA parameters of the calcaneus. Both R2' and R2* were correlated with bone mineral per area (BMA) of the hip (r>0.73, p<0.001 and r>0.66, p<0.01, respectively). R2 was correlated with BMA(L1-L4) (r = 0.52, p<0.05). R2' and R2* were not correlated with BMA(L1-L4). When the right and left sides were compared in calcaneus and hip the correlation coefficient for R2' and R2* ranged from 0.76 to 0.86 (p<0.001). The long-term reproducibility expressed in coefficient of variation (CV%) was approximately 5 % for R2' and approximately 4% for R2*. Differences in R2 between individuals were not reproducible. The results of this study indicate that R2' and R2* measurements are reproducible and might be of value when evaluating bone quality of the hip and foot.