Hepatic Iron Quantification Using a <scp>Free‐Breathing 3D</scp> Radial Gradient Echo Technique and Validation With a <scp>2D</scp> Biopsy‐Calibrated <scp>R₂</scp>^* Relaxometry Method

Abstract

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) R 2 * ‐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 R 2 * 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 R 2 * and FF maps were computed for 3D GREs using a multi‐spectral fat model and 2D GRE R 2 * maps were calculated using a mono‐exponential model. Mean R 2 * and FF values were calculated via whole‐liver contouring and T 2 * ‐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 R 2 * 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 R 2 * and FF values obtained with different acquisitions. Statistical significance was assumed at P &lt; 0.05. Results The mean biases and ICC for inter‐ and intra‐observer reproducibility were close to 0% and &gt;0.99, respectively for both R 2 * and FF. The 3D FB rGRE R 2 * and FF values were not significantly different ( P &gt; 0.44) and highly correlated ( R 2 ≥ 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

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