Hepatic Iron Quantification Using a Free‐Breathing 3D Radial Gradient Echo Technique and Validation With a 2D Biopsy‐Calibrated R2 Relaxometry Method

Background Hepatic iron content (HIC) is an important parameter for the management of iron overload. Non‐invasive HIC assessment is often performed using biopsy‐calibrated two‐dimensional breath‐hold Cartesian gradient echo (2D BH GRE) R2*‐MRI. However, breath‐holding is not possible in most pediatric patients or those with respiratory problems, and three‐dimensional free‐breathing radial GRE (3D FB rGRE) has emerged as a viable alternative. Purpose To evaluate the performance of a 3D FB rGRE and validate its R2* and fat fraction (FF) quantification with 3D breath‐hold Cartesian GRE (3D BH cGRE) and biopsy‐calibrated 2D BH GRE across a wide range of HICs. Study Type Retrospective. Subjects Twenty‐nine patients with hepatic iron overload (22 females, median age: 15 [5–25] years). Field Strength/Sequence Three‐dimensional radial and 2D and 3D Cartesian multi‐echo GRE at 1.5 T. Assessment R2* and FF maps were computed for 3D GREs using a multi‐spectral fat model and 2D GRE R2* maps were calculated using a mono‐exponential model. Mean R2* and FF values were calculated via whole‐liver contouring and T2*‐thresholding by three operators. Statistical Tests Inter‐ and intra‐observer reproducibility was assessed using Bland–Altman and intraclass correlation coefficient (ICC). Linear regression and Bland–Altman analysis were performed to compare R2* and FF values among the three acquisitions. One‐way repeated‐measures ANOVA and Wilcoxon signed‐rank tests, respectively, were used to test for significant differences between R2* and FF values obtained with different acquisitions. Statistical significance was assumed at P 0.99, respectively for both R2* and FF. The 3D FB rGRE R2* and FF values were not significantly different (P > 0.44) and highly correlated (R2 ≥ 0.98) with breath‐hold Cartesian GREs, with mean biases ≤ ±2.5% and slopes 0.90–1.12. In non‐breath‐holding patients, Cartesian GREs showed motion artifacts, whereas 3D FB rGRE exhibited only minimal streaking artifacts. Data Conclusion Free‐breathing 3D radial GRE is a viable alternative in non‐breath‐hold patients for accurate HIC estimation. Level of Evidence 3 Technical Efficacy Stage 2