Slice‐selective adiabatic magnetization T2‐preparation (SAMPA) for efficient T2‐weighted imaging at ultrahigh field strengths

Abstract

At high field, T2 -weighted (T2 w) imaging is limited by transmit field inhomogeneity and increased radiofrequency power deposition. In this work, we introduce SAMPA (Slice-selective Adiabatic Magnetization T2 PrepAration) and demonstrate its use for efficient brain T2 w imaging at 7 Tesla (T). SAMPA was designed by subsampling an optimized B1 insensitive rotation (BIR4) waveform with small tip angle linear subpulses. To perform T2 w imaging, SAMPA was inserted before a fast gradient echo acquisition. The off-resonance behavior, B1 robustness, and slice selectivity of the novel T2 preparation module were analyzed using Bloch simulations. The performance of SAMPA for T2 w imaging was demonstrated in phantom experiments as well as in the brains of healthy volunteers at 7T. Based on simulations, the proposed design operates at peak B1 of 15 μT and higher, within a 400 Hz bandwidth. T2 values were in strong agreement with spin echo-based T2 mapping in phantom experiments. Whole brain, interleaved multislab three-dimensional imaging could be acquired with 0.8 mm3 isotropic resolution in 5:36 min per T2 weighting. Compared with previous adiabatic T2 preparation techniques, SAMPA allows for slice-selectivity, which can lead to efficient and robust acquisitions for T2 w imaging at high field. Magn Reson Med 76:1741-1749, 2016. © 2015 International Society for Magnetic Resonance in Medicine.