The Compressed Sensing MP2RAGE as a Surrogate to the MPRAGE for Neuroimaging at 3 T

Abstract

Objectives: The magnetization-prepared 2 rapid acquisition gradient echo (MP2RAGE) sequence provides quantitative T 1 maps in addition to high-contrast morphological images. Advanced acceleration techniques such as compressed sensing (CS) allow its acquisition time to be compatible with clinical applications. To consider its routine use in future neuroimaging protocols, the repeatability of the segmented brain structures was evaluated and compared with the standard morphological sequence (magnetization-prepared rapid gradient echo [MPRAGE]). The repeatability of the T 1 measurements was also assessed. Materials and Methods: Thirteen healthy volunteers were scanned either 3 or 4 times at several days of interval, on a 3 T clinical scanner, with the 2 sequences (CS-MP2RAGE and MPRAGE), set with the same spatial resolution (0.8-mm isotropic) and scan duration (6 minutes 21 seconds). The reconstruction time of the CS-MP2RAGE outputs (including the 2 echo images, the MP2RAGE image, and the T 1 map) was 3 minutes 33 seconds, using an open-source in-house algorithm implemented in the Gadgetron framework.Both precision and variability of volume measurements obtained from CAT12 and VolBrain were assessed. The T 1 accuracy and repeatability were measured on phantoms and on humans and were compared with literature.Volumes obtained from the CS-MP2RAGE and the MPRAGE images were compared using Student t tests ( P < 0.05 was considered significant). Results: The CS-MP2RAGE acquisition provided morphological images of the same quality and higher contrasts than the standard MPRAGE images. Similar intravolunteer variabilities were obtained with the CS-MP2RAGE and the MPRAGE segmentations. In addition, high-resolution T 1 maps were obtained from the CS-MP2RAGE. T 1 times of white and gray matters and several deep gray nuclei are consistent with the literature and show very low variability (<1%). Conclusions: The CS-MP2RAGE can be used in future protocols to rapidly obtain morphological images and quantitative T 1 maps in 3-dimensions while maintaining high repeatability in volumetry and relaxation times.

Rapid whole brain 3D T2 mapping respiratory‐resolved Double‐Echo Steady State (DESS) sequence with improved repeatability

“…The reconstruction of the binned k ‐spaces' pseudorandom sparse sampling was resolved easily by virtue of the CS approach, which consequently helped reach the desired acquisition time. The undersampling factor 8 was empirically chosen after having been validated in previous works 30 and compared to factors 6, 10, and 12 on one healthy volunteer (data not shown). The comparison did not yield any notable differences, which was to be expected as the NR would also change accordingly to maintain the same acquisition time.…”

“…Consequently, the overall objective of the current study was to implement rapid 3D DESS sequences that incorporated none, one, two, or all of the previously mentioned techniques 25,30,34 (self-gating, CS, and spiral profile ordering) for brain imaging and to subsequently estimate their efficiency with respect to the respiratory correction as well as their T 2 estimates' repeatability.…”

“…Gating implies selecting the data according to the subjects' breathing in order to reconstruct time‐resolved images, leading to either longer acquisition times or under sampled data. Compressed‐sensing (CS) 30,31 presents a set of advantages that accommodate such a compromise quite well. Not only does it provide high‐quality images with interesting acceleration factors but it also enables handling undersampled k ‐spaces adeptly with parallel imaging reconstruction as well as spatial and temporal regularizations 32,33 …”

Simultaneous Optimization of MP2RAGE T1‐weighted (UNI) and FLuid And White matter Suppression (FLAWS) brain images at 7T using Extended Phase Graph (EPG) Simulations

“…Similarly, Mussard et al used CS‐MP2RAGE at 3T in healthy subjects using a trajectory based on a jittered Cartesian spiral phyllotaxis pattern 37–39 . Trotier et al were able to obtain images in healthy humans at 3T with 0.8 mm isotropic resolution in 6:21 (min:s) using CS‐MP2RAGE 40 . Whereas the CS approaches are very promising to reduce the scan time, optimizing the parameters both on the acquisition and reconstruction side is challenging 39 .…”

“… 37 , 38 , 39 Trotier et al were able to obtain images in healthy humans at 3T with 0.8 mm isotropic resolution in 6:21 (min:s) using CS‐MP2RAGE. 40 Whereas the CS approaches are very promising to reduce the scan time, optimizing the parameters both on the acquisition and reconstruction side is challenging. 39 In this work, the focus was on contrast optimization using the standard MP2RAGE sequence with simple linear phase‐encode ordering.…”