Ultrashort echo time bi‐component analysis of cortical bone—a field dependence study

Purpose The purpose of this study is to investigate the effect of differing field strength on theT 2 *of cortical bone at 1.5 T and 3 T. Methods Ultrashort echo time pulse sequences were used to study six bovine and nine human bone samples at 1.5 T and 3 T using single‐ and bi‐componentT 2 *analysis. Results On average, the bound waterT 2 *of bovine bone decreased by 16% (from 0.32 ms at 1.5 T to 0.27 ms at 3 T, P  < 0.01) and the bound waterT 2 *of human bone decreased by 21% (from 0.42 ms at 1.5 T to 0.33 ms at 3 T, P  < 0.01) at the higher field strength. The free waterT 2 *of bovine bone decreased by 50% (from 4.23 ms at 1.5 T to 2.12 ms at 3 T, P  < 0.001) and the free waterT 2 *of human bone decreased by 68% (from 7.65 ms at 1.5 T to 2.46 ms at 3 T, P  < 0.001) at the higher field strength. Bound and free water fractions showed only minor change with field strength in bovine (< 2%, P  > 0.05) and human bone (< 4%, P  > 0.05). Conclusion Ultrashort echo time bi‐component analysis provides consistent bound and free water fractions at 1.5 T and 3 T, thereby allowing field‐independent comparisons. Magn Reson Med 71:1075–1081, 2014. © 2013 Wiley Periodicals, Inc.