Purpose: To introduce a new method for removing background artifacts in field maps and apply it to enhance the accuracy of susceptibility mapping.Methods: A field artifact removal method is introduced that is based on the sophisticated harmonic artifact reduction for phase data (SHARP) method exploiting the harmonic mean value property. The new method uses Tikhonov regularization at the deconvolution stage and is referred to as regularization enabled SHARP (RESHARP). RESHARP was compared with SHARP in a field‐forward susceptibility simulation and in human brain experiments, considering effects on both field maps and the resulting susceptibility maps.Results: From the simulation, RESHARP was able to reduce error in the field map by 17.4% as compared with SHARP, resulting in a more accurate single‐angle susceptibility map with 6.5% relative error (compared with 48.5% using SHARP). Using RESHARP in vivo, field and susceptibility maps of the brain displayed fewer artifacts particularly at the brain boundaries, and susceptibility measurements of iron‐rich deep gray matter were also more consistent than SHARP across healthy subjects of similar age.Conclusion: Compared with SHARP, RESHARP removes background field artifact more effectively, leading to more accurate susceptibility measurements in iron‐rich deep gray matter. Magn Reson Med 71:1151–1157, 2014. © 2013 Wiley Periodicals, Inc.

Concomitant gradient fields are transverse magnetic field components that are necessarily present to satisfy Maxwell's equations when magnetic field gradients are utilized in magnetic resonance imaging. They can have deleterious effects that are more prominent at lower static fields and/or higher gradient strengths. In diffusion tensor imaging schemes that employ large gradients that are not symmetric about a refocusing radiofrequency pulse (unlike Stejskal–Tanner, which is symmetric), concomitant fields may cause phase accrual that could corrupt the diffusion measurement. Theory predicting the error from this dephasing is described and experimentally validated for both Reese twice‐refocused and split gradient single spin‐echo diffusion gradient schemes. Bias in apparent diffusion coefficient values was experimentally found to worsen with distance from isocenter and with increasing duration of gradient asymmetry in both a phantom and in the brain. The amount of error from concomitant gradient fields depends on many variables, including the diffusion gradient pattern, pulse sequence timing, maximum effective gradient amplitude, static magnetic field strength, voxel size, slice distance from isocenter, and partial Fourier fraction. A prospective correction scheme that can reduce concomitant gradient errors is proposed and verified for diffusion imaging. Magn Reson Med, 2012.

Longitudinal evolution of intracranial hemorrhage by using quantitative susceptibility mapping demonstrated susceptibility differences in different disease stages, which are not found at conventional MRI. PurposeTo follow the evolution of intracranial hemorrhage (ICH) by using quantitative susceptibility mapping (QSM).Materials and MethodsThirty-six patients with ICH confirmed at CT were enrolled to follow ICH evolution on day 2, 7, and 30 after symptom onset between August 2013 and April 2017. QSM was reconstructed from MRI gradient-echo phase images acquired at 1.5 T or 3.0 T. ICH regions were manually drawn on two-dimensional sections of co-registered CT and MR images independently by two raters. The ICH areas and mean values were compared between CT and MRI by using Bland-Altman plots and Pearson correlation. QSM time evolution of ICH was assessed by using paired t tests and was compared with conventional T2-weighted fluid-attenuated inversion recovery, or T1-weighted or T2*-weighted magnitude intensities.ResultsSignificant reductions in ICH susceptibility were found between day 2 and day 7 (P < .001) and between day 7 and day 30 (P = .003), corresponding to different disease stages. The ICH areas meas...

Purpose: To investigate subcortical gray matter segmentation using transverse relaxation rate (R₂*) and quantitative susceptibility mapping (QSM) and apply it to voxel‐based analysis in multiple sclerosis (MS).Materials and Methods: Voxel‐based variation in R₂* and QSM within deep gray matter was examined and compared to standard whole‐structure analysis using 37 MS subjects and 37 matched controls. Deep gray matter nuclei (caudate, putamen, globus pallidus, and thalamus) were automatically segmented and morphed onto a custom atlas based on QSM and standard T₁‐weighted images. Segmentation accuracy and scan–rescan reliability were tested.Results: When considering only significant regions as returned by the multivariate voxel‐based analysis, increased R₂* and QSM was found in MS subjects compared to controls in portions of all four nuclei studied (P < 0.002). For R₂*, regional analysis yielded at least 66‐fold improved P‐value significance in all nuclei over standard whole‐structure analysis, while for QSM only thalamus benefited, with 5‐fold improvement in significance. Improved segmentation over standard methods, particularly for globus pallidus (2.8 times higher Dice score), was achieved by incorporating high‐contrast QSM into the atlas. Voxel‐based reliability was highest for QSM (<1% variation).Conclusion: Automatic segmentation of iron‐rich deep gray matter can be improved by incorporating QSM. Voxel‐based evaluation yielded increased R₂* and QSM in MS subjects in all four nuclei studied with R₂*, benefiting the most from localized analysis over whole‐structure measures. J. MAGN. RESON. IMAGING 2015;42:1601–1610.

Purpose To perform quantitative susceptibility mapping (QSM) in negligible acquisition time and apply it to measuring iron-rich subcortical gray matter. Methods Whole brain QSM was performed using single-shot gradient echo-planar imaging (EPI) in under 7 seconds on a standard 1.5 T system for imaging brain iron in subcortical gray matter. The method was compared to a standard 6-minute gradient recalled echo (GRE) QSM acquisition in healthy subjects. Region-of-interest QSM measurements were compared between methods in six subcortical gray-matter nuclei and two white matter territories. Results EPI-QSM provided similar mean susceptibility values to standard GRE-QSM in iron-rich subcortical gray matter regions, while providing greater than 50-fold scan time reduction. Blurring from the low spatial resolution and transverse relaxation decay of EPI affected edges but had negligible effect on whole subcortical nuclei measurements, which had a high correlation (R² = 0.96) to estimated iron content. Conclusion EPI-QSM can be performed in several seconds, which enables expansion of brain iron studies of subcortical gray matter to cases where time is limited and to existing MRI studies that already uses gradient echo EPI. Magn Reson Med 73:1932–1938, 2015.