Fast and motion‐robust saturation transfer MRI with inherent B₀ correction using rosette trajectories and compressed sensing

Abstract

PurposeTo implement rosette readout trajectories with compressed sensing reconstruction for fast and motion‐robust CEST and magnetization transfer contrast imaging with inherent correction of B0 inhomogeneity.MethodsA pulse sequence was developed for fast saturation transfer imaging using a stack of rosette trajectories with a higher sampling density near the k‐space center. Each rosette lobe was segmented into two halves to generate dual‐echo images. B0 inhomogeneities were estimated using the phase difference between the images and corrected subsequently. The rosette‐based imaging was evaluated in comparison to a fully sampled Cartesian trajectory and demonstrated on CEST phantoms (creatine solutions and egg white) and healthy volunteers at 3 T.ResultsCompared with the conventional Cartesian acquisition, compressed sensing reconstructed rosette images provided image quality with overall higher contrast‐to‐noise ratio and significantly faster readout time. Accurate B0 map estimation was achieved from the rosette acquisition with a negligible bias of 0.01 Hz between the rosette and dual‐echo Cartesian gradient echo B0 maps, using the latter as ground truth. The water‐saturation spectra (Z‐spectra) and amide proton transfer weighted signals obtained from the rosette‐based sequence were well preserved compared with the fully sampled data, both in the phantom and human studies.ConclusionsFast, motion‐robust, and inherent B0‐corrected CEST and magnetization transfer contrast imaging using rosette trajectories could improve subject comfort and compliance, contrast‐to‐noise ratio, and provide inherent B0 homogeneity information. This work is expected to significantly accelerate the translation of CEST‐MRI into a robust, clinically viable approach.