Chemical Shift magnetization transfer magnetic resonance imaging

Purpose The purpose of this work was to develop a chemical shift magnetization transfer (CSMT) magnetic resonance imaging (MRI) method to provide accurate magnetization transfer ratio (MTR) measurements in the presence of fat. Methods Numerical simulations were performed to compare MTR measurements at different echo times (TEs) for voxels with varying fat/water content. The CSMT approach was developed using water fraction estimates to correct for the impact of fat signal upon observed MTR measurements. The CSMT method was validated with oil/agarose phantom and animal studies. Results Simulations demonstrated that the observed MTRs vary with water fraction as well as with the TE-dependent phase difference between fat and water signals; simulations also showed that a linear relationship exists between MTR and water fraction when fat and water signals are in phase. For phantom studies, observed MTR decreased with increasing oil fraction: 42.41 ± 0.54, 38.12 ± 0.33, 32.93 ± 0.56, and 26.08 ± 0.87 for 5% to 40% oil fractions, respectively, compared to 42.63 ± 1.04 for phantom containing 4% agarose only. These offsets were readily corrected with the additional acquisition of a water fraction map. Conclusion Fat fraction and TE can significantly impact observed MTR measurements. The new CSMT approach offers the potential to eliminate the effects of fat upon MTR measurements. Magn Reson Med 78:656–663, 2017. © 2016 International Society for Magnetic Resonance in Medicine