Comparison of Amplitude- and Amplitude-Frequency-Modulated Pulses for Outer Volume Suppression in Cardiac MRI:...

To evaluate single- and dual-band pulse modules for suppressing extra-cardiac signal in cardiac MRI, and test their applicability for time-efficient imaging with reduced FOV in myocardial $T_2$ mapping at 3 T.

Outer Volume Suppression (OVS) was implemented using two regional saturation slabs, along the phase-encoding direction. Different Amplitude-Modulated (AM) and Amplitude-Frequency-Modulated (AM-FM) pulses were explored. AM sinc and AM-FM Hyperbolic Secant (HS) pulses, as single- (S:1b and HS:1b) and dual-band (S:2b and HS:2b) versions, were chosen for full evaluation. Pulses were individually optimized for minimal residual signal and optimal suppression-band profiles. Pulse performance was assessed through simulations and phantom experiments, and evaluated in seven healthy subjects using residual signal and quantitative myocardial $T_2$ mapping with rFOV.

In simulations, optimized HS pulses demonstrated superior suppression-band profile homogeneity and $B_0$ robustness, while both pulse classes showed comparable $B_1^{+}$ sensitivity. Phantom data revealed better signal suppression with HS pulses (S:1b: 19.22% ± 3.23%, S:2b: 16.85% ± 6.80%, HS:1b: 4.66% ± 1.04%, HS:2b: 2.85% ± 1.01%). The residual difference across slabs was slightly reduced using simultaneous dual-band compared with sequential single-band approaches (S:1b: 3.81% vs. S:2b: 0.92%; HS:1b: 4.56% vs. HS:2b: 0.66%). In vivo, despite significantly lower residual with HS pulses (p = 0.0015) and visually observed artifacts with sinc pulses, no significant difference in $T_2$ was observed across all configurations (p = 0.087) in myocardial $T_2$ mapping.

AM-FM pulses achieved robust suppression of extra-cardiac signals, with dual-band implementations minimizing suppression-band differences. This can enable artifact-free rFOV imaging, for improved image quality in myocardial $T_2$ mapping.