Simultaneous Time Interleaved MultiSlice (STIMS) for Rapid Susceptibility Weighted acquisition

Abstract

T2* weighted 3D Gradient Echo (GRE) acquisition is the main sequence used for Susceptibility Weighted Imaging (SWI) and Quantitative Susceptibility Mapping (QSM). These applications require a long echo time (TE) to build up phase contrast, requiring a long repetition time (TR), and leading to excessively lengthy scans. The long TE acquisition creates a significant amount of unused time within each TR, which can be utilized for either multi-echo sampling or additional image encoding with the echo-shift technique. The latter leads to significant saving in acquisition time while retaining the desired phase and T2* contrast. In this work, we introduce the Simultaneous Time Interleaved MultiSlice (STIMS) echo-shift technique, which mitigates slab boundary artifacts by interleaving comb-shaped slice groups with Simultaneous MultiSlice (SMS) excitation. This enjoys the same SNR benefit of 3D signal averaging as previously introduced multi-slab version, where each slab group is sub-resolved with kz phase encoding. Further, we combine SMS echo-shift with Compressed Sensing (CS) Wave acceleration, which enhances Wave-CAIPI acquisition/reconstruction with random undersampling and sparsity prior. STIMS and CS-Wave combination thus yields up to 45-fold acceleration over conventional full encoding, allowing a 15 sec full-brain acquisition with 1.5 mm isotropic resolution at long TE of 39 ms at 3T. In addition to utilizing empty sequence time due to long TE, STIMS is a general concept that could exploit gaps due to e.g. inversion modules in magnetization-prepared rapid gradient- echo (MPRAGE) and fluid attenuated inversion recovery (FLAIR) sequences.

Whole mouse brain structural connectomics using magnetic resonance histology

“…A ten-day scan cannot serve as a routine protocol. In recent years, compressed sensing (CS) has emerged as a new accelerated imaging technique, which enables reconstruction of under sampled data by exploiting image sparsity (Lustig et al 2007;Liang et al 2009;Wu et al 2014;Bilgic et al 2017;Wang et al 2018). There are three essential aspects for CS: sparsity, sampling pattern, and reconstruction (Lustig et al 2007).…”

Validation of Highly Accelerated Wave–CAIPI SWI Compared with Conventional SWI and T2*-Weighted Gradient Recalled-Echo for Routine Clinical Brain MRI at 3T

“…The resulting decrease in acquisition time may facilitate broader clinical application of SWI, especially in motionprone populations (eg, children, elderly, and acutely ill patients). Wave-CAIPI has shown the potential to accelerate susceptibilityweighted acquisitions in healthy volunteers 8,9 but has not been systematically evaluated in a clinical setting.…”

Wave‐CAIPI ViSTa: highly accelerated whole‐brain direct myelin water imaging with zero‐padding reconstruction

“…We should also make allowance for the specific absorption rate when optimizing the profile, because the specific absorption rate is already relatively large for adiabatic inversion‐recovery pulses. After this part is done, a 2D interleaved ViSTa, or a SMS interleaved ViSTa (similar to the recently reported STIMS sequence, is applicable. Our initial experiment revealed that at least 6 SMS slice groups could fit in the current timing configuration. To mitigate the wrap‐around part of the imperfect slab excitation profile, the presented study slightly reduced (by a factor of 0.9) the excitation thickness of the RF, which is in the same principle of oversampling along the partition direction, but was still capable to cover the whole brain.…”