Optimization of MR-Relaxometry for BMD-measurements and its Correlation with DEXA

The aim of this study was to optimize MRI conventional protocols for BMD measurements using MR-relaxometry in systems not facilitated with special multi echo protocols. Since, cortical and trabecular bone separation can not be performed in DEXA, so the results might lead to erroneous interpretation of BMD values. One method for bone quality determination is MR relaxometry that derives R2(=1/T2), R2*(=1/T2*) and R2´(=R2*-R2). This study was performed by 1.5T MRI system (Picker Vista-Q800), a uniformity phantom(1.25gr/l CuSO₄, with T2=200 ms for calibration), a body RF-Coil, 7 normal, 7 osteopenia, 7 osteoporosis volunteers and Lunar DEXA system (DPX-MD). To determine R2* and R2, multi GE and SE protocols with different TE/TR were used. Then in phantom and in coronal section of femoral-neck, relaxation rates were compared with BMD. The slope of neperian-logarithm of signal vs. TE in GE as -R2* used for protocol optimization. Therefore, for phantom calibration, optimized GE parameters of TE=13.42/18/26.8 ms, TR=800ms and ST=8mm used for the measurement of R2*, while, the measurement of R2 required the optimized SE parameters of TE=30/60/90/ 120ms, TR=800ms and ST=8mm, with CV(R2*)=2.96%, CV(R2)=3%, respectively. In volunteers for SE, TE of 36/54/63/72ms and TR=800ms were used, while, for GE the TEs/TR were the same as those of phantom study. R2* and R2´ showed a significant positive correlation with BMD, r=0.62(p<0.05) & r=0.62(p<0.05) respectively. Finally, in accordance with DEXA values, the results showed that MR-relaxometry is a proper tool for BMD-measurements in femoral-neck. Also it may be used as a complement method for DEXA failure in BMD-assessments