On the value of QSM from MPRAGE for segmenting and quantifying iron-rich deep gray matter

Quantitative 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 ( $$ ) is evaluated for segmentation and quantification of highly iron-rich DGM regions.

Simulations were used to explore quality and possible limitations. In addition, QSM from a standard multi-echo gradient-echo ( $$ ) was compared to $$ in 40 healthy adults at 3T. DGM structures with weak contrast on MPRAGE magnitude were evaluated for improving segmentation with $$ , with focus on the iron-rich globus pallidus (GP). Furthermore, susceptibility quantification was assessed on six DGM nuclei and compared to standard $$ .

Limited by TE and signal-to-noise ratio, only iron-rich regions like GP and dentate nucleus produced adequate contrast on $$ , confining applications to such regions. $$ 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 $$ provided comparable estimates to $$ in large iron-rich DGM nuclei.

Despite the short TE of standard MPRAGE, $$ can improve GP segmentation over the use of MPRAGE magnitude alone and roughly quantify high-iron regions in DGM. Thus, reconstructing $$ can be a useful addition to volumetric studies that rarely include standard $$ .