PT - JOURNAL ARTICLE AU - Roy AM Haast AU - Jonathan C Lau AU - Dimo Ivanov AU - Ravi S Menon AU - Kâmil Uludağ AU - Ali R Khan TI - Effects of MP2RAGE B<sub>1</sub><sup>+</sup> sensitivity on inter-site T<sub>1</sub> reproducibility and morphometry at 7T AID - 10.1101/2020.02.13.947382 DP - 2020 Jan 01 TA - bioRxiv PG - 2020.02.13.947382 4099 - http://biorxiv.org/content/early/2020/02/14/2020.02.13.947382.short 4100 - http://biorxiv.org/content/early/2020/02/14/2020.02.13.947382.full AB - Most neuroanatomical studies are based on MR images, whose intensity profiles are not solely determined by the tissue’s longitudinal relaxation times (T1) but also affected by varying non-T1 contributions, hampering data reproducibility. In contrast, quantitative imaging using the MP2RAGE sequence, for example, allows direct characterization of the brain based on the tissue property of interest. Combined with 7 Tesla (7T) MRI, this offers unique opportunities to obtain robust high-resolution brain data characterized by a high reproducibility, sensitivity and specificity. However, specific MP2RAGE parameters choices – e.g., to emphasize intracortical myelin-dependent contrast variations – can substantially impact image quality and cortical analyses through remnants of B1+-related intensity variations, as illustrated in our previous work. To follow up on this: we (1) validate this protocol effect using a dataset acquired with a particularly B1+ insensitive set of MP2RAGE parameters combined with parallel transmission excitation; and (2) extend our analyses to evaluate the effects on hippocampal and subcortical morphometry. The latter remained unexplored initially but will provide important insights related to generalizability and reproducibility of neurodegenerative research using 7T MRI. We confirm that B1+ inhomogeneities have a considerably variable effect on cortical T1 and thickness estimates, as well as on hippocampal and subcortical morphometry depending on MP2RAGE setup. While T1 differed substantially across datasets initially, we show inter-site T1 comparability improves after correcting for the spatially varying B1+ field using a separately acquired Sa2RAGE B1+ map. Finally, as for cortical thickness, removal of B1+ residuals affects hippocampal and subcortical volumetry and boundary definitions, particularly near structures characterized by strong intensity changes (e.g. cerebral spinal fluid and arteries). Taken together, we show that the choice of MP2RAGE parameters can impact T1 comparability across sites and present evidence that hippocampal and subcortical segmentation results are modulated by B1+ inhomogeneities. This calls for careful (1) consideration of sequence parameters when setting acquisition protocols; as well as (2) interpretation of results focused on neuroanatomical changes due to disease.HighlightsPreviously observed effects of B1+ inhomogeneities on cortical T1 and thickness depend strongly on MP2RAGE parametersInter-site comparability of cortical T1 and thickness greatly improves after removal of B1+ residualsPost-hoc MP2RAGE B1+ correction affects hippocampal (and subcortical) size and shape analysesNeuroradiological research would benefit from careful examination of imaging protocols and their impact on results, especially when B1+ maps are not acquired