This multi-center, multi-vendor study will validate a rapid magnetic resonance-based confounder-corrected R2* mapping method as a quantitative imaging biomarker of liver iron concentration (LIC). Excessive accumulation of iron in various organs, including the liver, which affects both adult and pediatric populations, is toxic and requires treatment aimed at reducing body iron stores. Measurement of LIC is critical for detection and staging of iron overload, and for monitoring iron-reducing chelator therapies that are expensive and have side effects. Magnetic Resonance Imaging (MRI) is a widely available, accessible, and safe technology, and it is very sensitive to the presence of iron in tissue. Translation of an MRI biomarker of liver iron concentration into broad clinical use requires that it is clinically feasible, precise, robust to changes in scan parameters, calibrated to a validated reference standard of LIC, and is reproducible across sites and manufacturers. There are currently no available MRI methods that meet these requirements. R2*-MRI holds the greatest promise to meet these requirements. R2* mapping can be performed very rapidly with whole-liver 3D coverage in a single 20s breath-hold.