A novel spectrally selective fat saturation pulse design with robustness to B and B inhomogeneities: A demonstration on 3D T-weighted breast MRI at 3 T.

PURPOSE

Spectrally selective fat saturation (FatSat) sequence is commonly used to suppress signal from adipose tissue. Conventional SINC-shaped pulses are sensitive to B off-resonance and B offset. Uniform fat saturation with large spatial coverage is especially challenging for the body and breast MRI. The aim of this study is to develop spectrally selective FatSat pulses that offer more immunity to B/B field inhomogeneities than SINC pulses and evaluate them in bilateral breast imaging at 3 T.

MATERIALS AND METHODS

Optimized composite pulses (OCP) were designed based on the optimal control theory with robustness to a targeted B/ B conditions. OCP pulses also allows flexible flip angles to meet different requirements. Comparisons with the vendor-provided SINC pulses were conducted by numerical simulation and in vivo scans using a 3D T-weighted (Tw) gradient-echo (GRE) sequence with coverage of the whole-breast.

RESULTS

Simulation revealed that OCP pulses yielded almost half of the transition band and much less sensitivity to B inhomogeneity compared to SINC pulses with B off-resonance within ±200 Hz and B scale error within ±0.3 (P < 0.001). Across five normal subjects, OCP FatSat pulses produced 25-41% lower residual fat signals (P < 0.05) with 27-36% less spatial variation (P < 0.05) than SINC.

CONCLUSION

In contrast to conventional SINC-shaped pulses, the newly designed OCP FatSat pulses mitigated challenges of wide range of B/ B field inhomogeneities and achieved more uniform fat suppression in bilateral breast Tw imaging at 3 T.