Comparison of the effectiveness of saturation pulses in the heart at 3T

Cardiac MRI at 3T provides a means to increase the contrast-to-noise ratio (CNR) for first-pass perfusion MRI. However, both the static magnetic field (B₀) and radio frequency (RF) field (B₁) variations within the heart are comparatively higher at 3T than at 1.5T. The increased field variations can degrade the performance of a single rectangular saturation pulse that is conventionally used for magnetization preparation. The accuracy of T₁-weighted signal measurement depends on the uniformity of the magnetization saturation. The purpose of this study was to assess the relative effectiveness of the rectangular, pulse train, and adiabatic composite (BIR-4) saturation pulses in the human heart at 3T. In volunteers, after nominal saturation, the mean residual magnetization within the left ventricle (LV) was different between all three pulses (0.13 ± 0.06 vs. 0.03 ± 0.02 vs. 0.03 ± 0.01, respectively; P < 0.001). Within paired groups, the mean residual magnetization was significantly higher for the rectangular pulse than for either the pulse train and BIR-4 pulses (P < 0.001), but not different between the pulse train and BIR-4 pulses. The performances of all three saturation pulses were comparatively poorer in the right ventricle (RV) than in the LV, respectively.