Saturation pulse design for quantitative myocardial T1 mapping

Background: quantitative saturation-recovery based t1 mapping sequences are less sensitive to systematic errors than the modified look-locker inversion recovery (molli) technique but require high performance saturation pulses. we propose to optimize adiabatic and pulse train saturation pulses for quantitative t1 mapping to have <1 % absolute residual longitudinal magnetization (|mz/m0|) over ranges of b0 and b1 (b1 scale factor) inhomogeneity found at 1.5 t and 3 t. methods: design parameters for an adiabatic bir4-90 pulse were optimized for improved performance within 1.5 t b0 (±120 hz) b1 (0.7-1.0) ranges. flip angles in hard pulse trains of 3-6 pulses were optimized for 1.5 t and 3 t,with consideration of t1 values,field inhomogeneities (b0∈=∈±240 hz and b1 =0.4-1.2 at 3 t),and maximum achievable b1 field strength. residual mz/m0 was simulated and measured experimentally for current standard and optimized saturation pulses in phantoms and in-vivo human studies. t1 maps were acquired at 3 t in human subjects and a swine using a saturation recovery single-shot acquisition (sasha) technique with a standard 90°-90°-90° and an optimized 6-pulse train. results: measured residual mz/m0 in phantoms had excellent agreement with simulations over a wide range of b0 and b1. the optimized bir4-90 reduced the maximum residual |mz/m0| to <1 %,a 5.8× reduction compared to a reference bir4-90. an optimized 3-pulse train achieved a maximum residual |mz/m0| <1 % for the 1.5 t optimization range compared to 11.3 % for a standard 90°-90°-90° pulse train,while a 6-pulse train met this target for the wider 3 t ranges of b0 and b1. the 6-pulse train demonstrated more uniform saturation across both the myocardium and entire field of view than other saturation pulses in human studies. t1 maps were more spatially homogeneous with 6-pulse train sasha than the reference 90°-90°-90° sasha in both human and animal studies. conclusions: adiabatic and pulse train saturation pulses optimized for different constraints found at 1.5 t and 3 t achieved <1 % residual |mz/m0| in phantom experiments,enabling greater accuracy in quantitative saturation recovery t1 imaging. © 2015 chow et al.