Abstract
ObjectThis study evaluates inter-site and intra-site reproducibility at ten different 7 T sites for quantitative brain imaging. Material and MethodsTwo subjects – termed the “traveling heads” – were imaged at ten different 7 T sites with a harmonized quantitative brain MR imaging protocol. In conjunction with the system calibration, MP2RAGE, QSM, CEST and multi-parametric mapping/relaxometry were examined. ResultsQuantitative measurements with MP2RAGE showed very high reproducibility across sites and subjects, and errors were in concordance with previous results and other field strengths. QSM had high inter-site reproducibility for relevant subcortical volumes. CEST imaging revealed systematic differences between the sites, but reproducibility was comparable to results in the literature. Relaxometry had also very high agreement between sites, but due to the high sensitivity, differences caused by different applications of the B1 calibration of the two RF coil types used were observed. ConclusionOur results show that quantitative brain imaging can be performed with high reproducibility at 7 T and with similar reliability as found at 3 T for multicenter studies of the supratentorial brain.
Highlights
In 2016, a multicenter magnetic resonance imaging (MRI) study at ultra-high magnetic field strength (UHF) was published (Voelker et al, 2016)
We evaluated the reproducibility of brain volumetry and T1 mapping with the Magnetization Prepared 2 Rapid Acquisition Gradient Echoes (MP2RAGE) approach (Marques et al, 2010), quantitative susceptibility mapping based on multi-echo gradient-echo (GRE) imaging (Li et al, 2014, Wu et al, 2012, Wei et al, 2015), chemical exchange saturation transfer based on the GRE snapshot approach (Zaiss et al, 2018), and relaxometry of T1, T2∗, as well as mapping of proton density (PD) based on a multi-parametric mapping technique (Weiskopf et al, 2013, Kirilina et al, 2020)
The 3rd-order shimming routines of the C5 sites allowed higher field homogeneity than the 2nd-order shimming at the C1-C4 sites, where the mean full width at half maximum (FWHM) of the peak of the whole-brain B0 distribution was about 1.7 times broader than at the C5 sites for both subjects (Fig. 3: Histogram, Inline Supplementary Table 3)
Summary
In 2016, a multicenter magnetic resonance imaging (MRI) study at ultra-high magnetic field strength (UHF) was published (Voelker et al, 2016). 2017), which are available as FDA-approved and CE-labeled medical devices for brain and musculoskeletal applications, a follow-up of the previous study seems timely and shall focus on the reproducibility of state-of-the-art quantitative MR imaging across all three generations of 7 T MR systems. Quantification of physical imaging parameters promises the inherent advantage that physical tissue properties, e.g. the longitudinal or transversal relaxation time or the tissue susceptibility value are examined that are not based on arbitrary units as in conventional weighted MRI. Quantification of imaging properties has the potential to increase diagnostic specificity and sensitivity due to its standardized nature and due to its sensitivity to micro-structural properties of brain tissue such as axons, myelin, iron or water concentration (Weiskopf et al, 2015, Langkammer et al, 2012, MacKay et al, 2006, Harkins et al, 2016)
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