Whole liver phase‐based R2 mapping in liver iron overload within a breath‐hold

Abstract Purpose Diagnosis and treatment monitoring of iron overload increasingly relies on non‐invasive MRI‐based measurement of liver iron concentration (LIC). Liver R 2 mapping is known to correlate well with LIC. However, traditional spin‐echo based R 2 mapping methods have drawbacks such as long acquisition times and limited volumetric coverage. In this work, we present an optimized phase‐based R 2 mapping method to quantify whole‐liver R 2 in iron overload patients within a single breathhold. Theory and Methods A recently developed phase‐based R 2 mapping method is optimized in this study to improve estimation of high R 2 values using reduced TR, spatial averaging, and R 1 correction. Using Bloch equation simulations, the proposed optimization method was evaluated. Furthermore, the impact of fat on R 2 bias was investigated through simulations. The feasibility of the optimized phase‐based R 2 method was assessed in healthy volunteers and patients with iron overload and compared to reference STEAM‐MRS R 2 measurements. Results Simulations demonstrate that a shorter TR extends the dynamic range of R 2 estimation to higher values and that averaging of signal phase before R 2 estimation is necessary when R 2 is high. Phantom experiments also demonstrate reduced phase‐based R 2 bias using R 1 correction. Good agreement (1.5 T: r 2  = 0.76, 3.0 T: r 2  = 0.70) between the modified phase‐based R 2 method and reference STEAM R 2 was found in healthy volunteers and iron overload patients over a wide range of LIC values. Conclusion This study demonstrates the feasibility of the proposed phase‐based R 2 method to accurately measure whole‐liver R 2 mapping in severe iron overloaded patients during a single breathhold.