Rosette Trajectories Enable Ungated, Motion-Robust, Simultaneous Cardiac and Liver T 2 * Iron Assessment.

Background: Quantitative T ₂ * MRI is the standard of care for the assessment of iron overload. However, patient motion corrupts T ₂ * estimates.
Purpose: To develop and evaluate a motion-robust, simultaneous cardiac and liver T ₂ * imaging approach using non-Cartesian, rosette sampling and a model-based reconstruction as compared to clinical-standard Cartesian MRI.
Study Type: Prospective.
Phantom/population: Six ferumoxytol-containing phantoms (26-288 μg/mL). Eight healthy subjects and 18 patients referred for clinically indicated iron overload assessment.
Field Strength/sequence: 1.5T, 2D Cartesian and rosette gradient echo (GRE) ASSESSMENT: GRE T ₂ * values were validated in ferumoxytol phantoms. In healthy subjects, test-retest and spatial coefficient of variation (CoV) analysis was performed during three breathing conditions. Cartesian and rosette T ₂ * were compared using correlation and Bland-Altman analysis. Images were rated by three experienced radiologists on a 5-point scale.
Statistical Tests: Linear regression, analysis of variance (ANOVA), and paired Student's t-testing were used to compare reproducibility and variability metrics in Cartesian and rosette scans. The Wilcoxon rank test was used to assess reader score comparisons and reader reliability was measured using intraclass correlation analysis.
Results: Rosette R2* (1/T ₂ *) was linearly correlated with ferumoxytol concentration (r ² = 1.00) and not significantly different than Cartesian values (P = 0.16). During breath-holding, ungated rosette liver and heart T ₂ * had lower spatial CoV (liver: 18.4 ± 9.3% Cartesian, 8.8% ± 3.4% rosette, P = 0.02, heart: 37.7% ± 14.3% Cartesian, 13.4% ± 1.7% rosette, P = 0.001) and higher-quality scores (liver: 3.3 [3.0-3.6] Cartesian, 4.7 [4.1-4.9] rosette, P = 0.005, heart: 3.0 [2.3-3] Cartesian, 4.5 [3.8-5.0] rosette, P = 0.005) compared to Cartesian values. During free-breathing and failed breath-holding, Cartesian images had very poor to average image quality with significant artifacts, whereas rosette remained very good, with minimal artifacts (P = 0.001).
Data Conclusion: Rosette k-sampling with a model-based reconstruction offers a clinically useful motion-robust T ₂ * mapping approach for iron quantification. J. MAGN. RESON. IMAGING 2020;52:1688-1698.
(© 2020 International Society for Magnetic Resonance in Medicine.)