Magnetic resonance imaging and spectroscopy of hepatic iron overload.

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Abstract
Experimental animals given excess Fe in their diet were studied by magnetic resonance (MR) imaging in vivo and by MR spectroscopy in vitro. Hepatic Fe overload in patients with transfusional Fe excess was studied by MR imaging, and isolated Fe protein fractions were studied in vitro by MR spectroscopy. The spin echo image intensity of livers with Fe overload was decreased because of the extreme decreases in T2 [transverse relaxation time of tissue] compared with normal; T1 was decreased only moderately. The relaxation rates 1/T2 and 1/T1 [1/longitudinal relaxation time of tissue] both showed a linear relationship to hepatic Fe levels. Ferritin solutions showed moderate decreases in T2 and mild decreases in T1. The T2 relaxivity of ferritin, which is due to the Fe core rather than the apoferritin protein shell, does not appear sufficient to account for the extreme decrease in T2 observed in hepatic Fe overload. Low MW cytosol Fe is present in lower concentrations than ferritin but potentially has much greater relaxivity and may contribute to the MR findings. These techniques may be useful in other studies of Fe metabolism.