What does liver R2* mean when iron levels are not elevated? Understanding the variation in R1 and R2* in the healthy liver

Motivation: The influence of liver iron concentration (LIC) on liver R1 and R2* has been well described. However, in healthy subjects, R1 and R2* may be predominantly influenced by liver water content (LWC). The expected variability in R1 and R2* due to changes in LWC is not well understood. Goal(s): Our goal was to model the expected variability in liver R1 and R2* due to changes in both LWC and LIC. Approach: We developed a model, and tested the predictions against measured R1/R2* values in healthy subjects. Results: The model predictions showed good agreement with the measured data in the majority of healthy subjects. Impact: This work explains the variability in liver R1 and R2* due to changes in liver water content (LWC) and iron. This could aid our interpretation of changes in these parameters in subjects where LWC is clinically relevant.