Abstract
Using quantitative multi-parameter mapping (MPM), studies can investigate clinically relevant microstructural changes with high reliability over time and across subjects and sites. However, long acquisition times (20 min for the standard 1-mm isotropic protocol) limit its translational potential. This study aimed to evaluate the sensitivity gain of a fast 1.6-mm isotropic MPM protocol including post-processing optimized for longitudinal clinical studies. 6 healthy volunteers (35±7 years old; 3 female) were scanned at 3T to acquire the following whole-brain MPM maps with 1.6 mm isotropic resolution: proton density (PD), magnetization transfer saturation (MT), longitudinal relaxation rate (R1), and transverse relaxation rate (R2*). MPM maps were generated using two RF transmit field (B1+) correction methods: (1) using an acquired B1+ map and (2) using a data-driven approach. Maps were generated with and without Gibb's ringing correction. The intra-/inter-subject coefficient of variation (CoV) of all maps in the gray and white matter, as well as in all anatomical regions of a fine-grained brain atlas, were compared between the different post-processing methods using Student's t-test. The intra-subject stability of the 1.6-mm MPM protocol is 2–3 times higher than for the standard 1-mm sequence and can be achieved in less than half the scan duration. Intra-subject variability for all four maps in white matter ranged from 1.2–5.3% and in gray matter from 1.8 to 9.2%. Bias-field correction using an acquired B1+ map significantly improved intra-subject variability of PD and R1 in the gray (42%) and white matter (54%) and correcting the raw images for the effect of Gibb's ringing further improved intra-subject variability in all maps in the gray (11%) and white matter (10%). Combining Gibb's ringing correction and bias field correction using acquired B1+ maps provides excellent stability of the 7-min MPM sequence with 1.6 mm resolution suitable for the clinical routine.
Highlights
Quantitative magnetic resonance imaging has the potential to revolutionize neuroradiology by deriving absolute measures in physical units that are independent of technical confounders and provide insight into physiologically meaningful properties of tissue (Tofts, 2010)
High quality multi-parameter mapping (MPM) parameter maps with absolute values comparable to those previously reported in healthy participants (Weiskopf et al, 2013; Callaghan et al, 2014; Lommers et al, 2019) were generated using the multi-subject protocol acquired with 1.6 mm resolution
Using the data-driven B1+ correction (UNICORT) resulted in small deviations from the absolute values reported in Table 1 for gray/white matter (MT: −0.27/−0.81%, R1: 6.79/6.69%)
Summary
Quantitative magnetic resonance imaging (qMRI) has the potential to revolutionize neuroradiology by deriving absolute measures in physical units that are independent of technical confounders and provide insight into physiologically meaningful properties of tissue (Tofts, 2010). 20 min (Weiskopf et al, 2013) These maps are sensitive to microstructural tissue properties of high clinical relevance, such as myelin and iron content (Weiskopf et al, 2015), and have been shown to be sensitive to pathology, for example in multiple sclerosis (Jurcoane et al, 2013; Gracien et al, 2017; Lommers et al, 2019) and spinal cord injury (Grabher et al, 2015). Despite the high validity of MPM (Weiskopf et al, 2013; Leutritz et al., 2020), the widely used standard MPM protocol with 1 mm resolution (Weiskopf et al, 2013; Callaghan et al, 2014; Grabher et al, 2015; Ziegler et al, 2018; Lommers et al, 2019; Leutritz et al, 2020; Taubert et al, 2020) has a relatively long acquisition time, limiting its translational potential (Bagnato et al, 2020).
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