Rapid 3D absolute B(1) (+) mapping using a sandwiched train presaturated TurboFLASH sequence at 7 T for the brain and heart

PURPOSE: To shorten the acquisition time of magnetization‐prepared absolute transmit field (B(1) (+)) mapping known as presaturation TurboFLASH, or satTFL, to enable single breath‐hold whole‐heart 3D B(1) (+) mapping. METHODS: SatTFL is modified to remove the delay between the reference and prepared images (typically 5 T(1)), with matching transmit configurations for excitation and preparation RF pulses. The new method, called Sandwich, is evaluated as a 3D sequence, measuring whole‐brain and gated whole‐heart B(1) (+) maps in a single breath‐hold. We evaluate the sensitivity to B(1) (+) and T(1) using numerical Bloch, extended phase graph, and Monte Carlo simulations. Phantom and in vivo images were acquired in both the brain and heart using an 8‐channel transmit 7 Tesla MRI system to support the simulations. A segmented satTFL with a short readout train was used as a reference. RESULTS: The method significantly reduces acquisition times of 3D measurements from 360 s to 20 s, in the brain, while simultaneously reducing bias in the measured B(1) (+) due to T(1) and magnetization history. The mean coefficient of variation was reduced by 81% for T(1)s of 0.5–3 s compared to conventional satTFL. In vivo, the reproducibility coefficient for flip angles in the range 0–130° was 4.5° for satTFL and 4.7° for our scheme, significantly smaller than for a short TR satTFL sequence, which was 12°. The 3D sequence measured B(1) (+) maps of the whole thorax in 26 heartbeats. CONCLUSION: Our adaptations enable faster B(1) (+) mapping, with minimal T(1) sensitivity and lower sensitivity to magnetization history, enabling single breath‐hold whole‐heart absolute B(1) (+) mapping.