Weiss, Robert G.

ABSTRACT Purpose Standard spatial‐spectral excitation pulses apply a fly‐back gradient between sub‐pulses, limiting, for example, how thin the slices can be (> 4 mm). Without fly‐back gradients, slices can be as thin as 1.7 mm but require a phase calibration for the sub‐pulses with inverted gradients due to system imperfections. Here we propose and test a fast (< 1 s), localized pre‐scan enabling thin‐slice frequency‐selective excitation. Methods The calibration pre‐scan determines the correction phase between even and odd sub‐pulses by measuring the phase difference of two FIDs excited with either the last or second‐to‐last RF sub‐pulse of the spatial‐spectral pulse. Non‐localized and localized versions of the calibration pre‐scan are tested and validated for water‐only excitation in phantoms and the human heart. As an example, breath‐held coronary MR angiography is performed with a spiral multi‐slice sequence employing the proposed pulses with a slice thickness of 1.7 mm. Results The proposed calibration pre‐scan takes 11.1 ms per slice, whether it is localized or not. Localized calibration phases are validated with an image‐based calibration map. Slice profiles are visualized for pulses with different time‐bandwidth products. Fat is suppressed to below 20% and 25% of the surrounding water signal in both phantoms and the human heart, respectively. High‐quality coronary angiograms are demonstrated in all test subjects. Conclusion Spatial‐spectral pulses without fly‐back gradients can be calibrated quickly (up to 90 slices in 1 s), enabling thinner slices, higher excitation angles, or pulses with sharper slice profiles using waveforms with higher time‐bandwidth products.