For the noninvasive liver iron quantification by MRI in human iron overload diseases, fundamental proton relaxation mechanisms were studied in aqueous solutions with ferritin and other iron compounds, in experimentally iron overloaded rats, and in patients with iron overload diseases. MR-relaxation rates as a function of iron concentrations in the range of 0-7.5 mg Fe/g aqueous iron solutions, 0-5.4 mg Fe/g rat liver in vivo, and 0.16-4.9 mg Fe/g human liver in vivo were determined from multi- and sets of single-spin echo sequences (1.5 T imager). As predicted by theory, transverse relaxation rates (1/T2) in aqueous iron solutions, in liver tissue of rats, and in human liver tissue increased linearly with the iron concentration. A preliminary calibration for the liver iron quantification by MRI was performed from in vivo measurements of liver 1/T2-relaxation rates and liver iron quantification by atomic absorption spectroscopy in biopsies from 13 patients. With the single spin-echo method, precise in vivo liver iron quantification in humans also above 2.0 mg Fe/g liver tissue (T2 <15 ms) should be accomplished on any imager with shortest spin-echo time available, at least TE <20 ms.
