Background: Accurate measurement of the liver iron concentration (LIC) is needed to guide iron-chelating therapy for patients with transfusional iron overload. In this work, we investigate the feasibility of automated quantitative susceptibility mapping (QSM) to measure the LIC. Purpose: To develop a rapid, robust and automated liver QSM for clinical practice. Study Type: Prospective Population: 13 healthy subjects and 22 patients. Field strength/Sequences 1.5T and 3T / 3D multi-echo gradient-recalled echo (GRE) sequence. Assessment: Data were acquired using a 3D GRE sequence with an out-of-phase echo spacing with respect to each other. All odd echoes that were in-phase (IP) were used to initialize the fat-water separation and field estimation (T2*-IDEAL) before performing QSM. Liver QSM was generated through an automated pipeline without manual intervention. This IP echo-based initialization method was compared with an existing graph cuts initialization method (SPURS) in healthy subjects (n=5). Reproducibility was assessed over 4 scanners at 2 field strengths from 2 manufacturers using healthy subjects (n=8). Clinical feasibility was evaluated in patients (n=22). Statistical Tests: IP and SPURS initialization methods in both healthy subjects and patients were compared using paired t-test and linear regression analysis to assess processing time and ROI measurements. Reproducibility of QSM, R2*, and proton density fat fraction (PDFF) among the four different scanners was assessed using linear regression, Bland-Altman analysis, and the intraclass correlation coefficient (ICC). Results: Liver QSM using the IP method was found to be approximately 5.5 times faster than SPURS (P< 0.05) in initializing T2*-IDEAL with similar outputs. Liver QSM using the IP method were reproducibly generated in all four scanners (average coefficient of determination 0.95, average slope 0.90, average bias 0.002 ppm, 95% limits of agreement between −0.06 to 0.07 ppm, ICC 0.97). Conclusion: Use of IP echo-based initialization, enables robust water/fat separation and field estimation for automated, rapid and reproducible liver QSM for clinical applications.
In vivo cardiac QSM is feasible and can be used to measure SvO , but improvements in data acquisition are needed. Magn Reson Med 79:1545-1552, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Purpose The Sophisticated Harmonic Artifact Reduction for Phase data (SHARP) method has been proposed for the removal of background field in MRI phase data. It relies on the spherical mean value (SMV) property of harmonic functions, and its accuracy depends on the radius of the sphere used for computing the SMV and truncation threshold needed for deconvolution. The goal of this work is to develop an alternative SMV based background field removal method with reduced dependences on these parameters. Methods The proposed background field removal method (termed iterative SMV or iSMV) consists of applying the SMV operation repeatedly on the field map and it was validated in a phantom and in vivo brain data of five healthy volunteers. Results The iSMV method demonstrates accurate background field removal in the phantom. Compared to SHARP, the iSMV method shows a significantly reduced dependence on the SMV radius both in phantom and in human data. Because a smaller radius can be chosen, the iSMV method allows retaining a larger part of the region of interest, compared to SHARP. Conclusion The iSMV method is an effective background field removal method with a reduced dependence on method parameters.
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