• Nashwan Naji, Hongfu Sun, and Alan H Wilman.
• Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada.
• Magn Reson Med. 2020 Sep 1; 84 (3): 1486-1500.

PurposeQuantitative susceptibility mapping (QSM) has been employed for both iron evaluation and segmentation of deep gray matter (DGM), but QSM sequences are not typically used in standard brain volumetric studies, which use T1-weighted magnetization-prepared rapid acquisition with gradient echo (MPRAGE) with short TE. Here, QSM produced directly from standard MPRAGE phase ( QSM MPRAGE ) is evaluated for segmentation and quantification of highly iron-rich DGM regions.MethodsSimulations were used to explore quality and possible limitations. In addition, QSM from a standard multi-echo gradient-echo ( QSM GRE ) was compared to QSM MPRAGE in 40 healthy adults at 3T. DGM structures with weak contrast on MPRAGE magnitude were evaluated for improving segmentation with QSM MPRAGE , with focus on the iron-rich globus pallidus (GP). Furthermore, susceptibility quantification was assessed on six DGM nuclei and compared to standard QSM GRE .ResultsLimited by TE and signal-to-noise ratio, only iron-rich regions like GP and dentate nucleus produced adequate contrast on QSM MPRAGE , confining applications to such regions. QSM MPRAGE improved GP segmentation with mean Dice scores raised by 9.0%, and mean volumetric differences reduced by 9.7%. Simulations suggested that phase contrast-to-noise ratio (CNR) should be above 3.0 to attain segmentation improvement. For quantification purposes, higher CNR is required, and typical QSM MPRAGE provided comparable estimates to QSM GRE in large iron-rich DGM nuclei.ConclusionDespite the short TE of standard MPRAGE, QSM MPRAGE can improve GP segmentation over the use of MPRAGE magnitude alone and roughly quantify high-iron regions in DGM. Thus, reconstructing QSM MPRAGE can be a useful addition to volumetric studies that rarely include standard QSM GRE .© 2020 International Society for Magnetic Resonance in Medicine.

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