Fig. 1: Non-invasive assessment of normal and impaired iron homeostasis in the brain.
From: Non-invasive assessment of normal and impaired iron homeostasis in the brain

a MRI theory: Early in vitro and postmortem works suggest that different iron environments can be distinguished by their iron relaxivity, i.e. the dependency of MR relaxation rates on the iron concentration. This approach requires direct estimation of the tissue iron concentration, which can only be acquired in vitro or postmortem. Here we propose an in vivo iron relaxivity approach. We exploit the distinct iron relaxivities of the MR relaxation rates, R1 and R2*, to construct a biophysical model of their linear interdependency, which we label the r1-r2* relaxivity. Using the r1-r2* relaxivity, we argue that the state of iron homeostasis in the brain can be estimated in vivo. b In vitro, the r1-r2* relaxivity distinguishes between different synthetic iron environments (ferritin, transferrin and ferrous iron ions). c Comparison between in vivo MRI scans of the healthy human brain and published postmortem histology. The r1-r2* relaxivity varies with the iron mobilization capacity across brain regions and in aging. d Direct comparison between in vivo MRI scans of meningioma patients and transcriptomics and proteomics of the resected tumor tissues. The r1-r2* relaxivity reveals tumors’ iron homeostasis and separates tumor tissue from healthy tissue.