QSMxT: Robust masking and artifact reduction for quantitative susceptibility mapping

Abstract

Purpose: Quantitative susceptibility mapping (QSM) estimates the spatial distribution of tissue magnetic susceptibilities from the phase of a gradient-echo signal. QSM algorithms require a signal mask to delineate regions with reliable phase for subsequent susceptibility estimation. Existing masking techniques used in QSM have limitations that introduce artifacts, exclude anatomical detail, and rely on parameter tuning and anatomical priors that narrow their application. Here, a robust masking and reconstruction procedure is presented to overcome these limitations and enable automated QSM processing. Moreover, this method is integrated within an open-source software framework: QSMxT. Methods:A robust masking technique that automatically separates reliable from less reliable phase regions was developed and combined with a two-pass reconstruction procedure that operates on the separated sources before combination, extracting more information and suppressing streaking artifacts.

Multisite reproducibility of quantitative susceptibility mapping and effective transverse relaxation rate in deep gray matter at 3 T using locally optimized sequences in 24 traveling heads

“…Alternatively, more advanced techniques can be applied to exclude unreliable regions in each echo by utilizing both magnitude and phase information in the masking process and performing two-pass susceptibility inversion. 64 In addition, restricting QSM reconstruction to comparable echo times found in all scans reduced variability further (mean SDw reduced from 4.83 to 4.16 ppb), which is consistent with findings in previous work. 33 This ensures similar field content within the VOI, including regions of high susceptibility gradients.…”

“…This also reduced mask variations between scans of different flip angles/TRs without the need for tuning mask extraction parameters for each protocol. Alternatively, more advanced techniques can be applied to exclude unreliable regions in each echo by utilizing both magnitude and phase information in the masking process and performing two‐pass susceptibility inversion 64 . In addition, restricting QSM reconstruction to comparable echo times found in all scans reduced variability further (mean SDw reduced from 4.83 to 4.16 ppb), which is consistent with findings in previous work 33 .…”

Improved dynamic distortion correction for fMRI using single‐echo EPI and a readout‐reversed first image (REFILL)

“…Signal inhomogeneity due to B 1 inhomogeneity and EPI distortion make the use of magnitude‐based masking methods, such as BET, problematic. Instead, we generated masks for DDC field maps by thresholding an image quality map (Dymerska et al, 2021) which incorporated phase coherence; a method adopted by others recently in QSM (Bachrata, Trattnig, & Robinson, 2022; Hagberg et al, 2022; Stewart et al, 2022). These generated low‐noise field maps.…”

Maximum spherical mean value filtering for whole‐brain QSM

“…[22][23][24] Dipole inversion-based techniques that use SMV-filtered field in the data-fidelity term to reduce shadow artifacts introduce erosion. 13,25 Other methods reduce shadow artifacts with smoothing regularization terms but result in underestimation in ROIs. 26,27 Here, an algorithm based on the maximum value property of harmonic functions is proposed to perform SMV-filtered dipole inversion while preserving the brain mask.…”

“…Shadows also persist near features with large susceptibility gradients such as hemorrhages. Dipole inversion algorithms such as streaking artifact reduction 12 QSM and QSMxT (robust masking and artifact reduction) 13 have been developed to suppress these artifacts.…”