Hepatic hemosiderosis in non-human primates: Quantification of liver iron using different field strengths

Using a non-human primate model of idiopathic hemochromatosis, hemosiderin-induced T₂ shortening of the liver was assessed at nine different field strengths over a range of 0.05 to 1.5 Tesla. The 1/T₂ values increased linearly with field strength, with all specimens having approximately the same zero-field intercept. The slope of the field increase, termed 'field-dependent T₂ proton relaxation enhancement (PRE)', appeared to be proportional to the chemically determined tissue iron content, viz. 10.8 s^-1T^-1 (mg Fe/g wet tissue)^-1. The correlation between iron content and field-dependent T₂ PRE (r = 0.94) was better than the correlation between iron content and 1/T₂ values obtained at single field strengths. For livers containing ≤ 2 mg Fe/g wet weight, biexponential T₂ relaxation behavior emerged at higher field strengths, with the short T₂ component (intracellular water) exhibiting a linear dependence of 1/T₂ on field, while T₂ of the long component (extracellular/sinusoidal water) was nearly field- independent. After maceration of the specimens, all T₂ relaxation curves became monoexponential, including those for high iron content at high field strengths. The present data suggest that the use of double-field MR imaging to assess the field-dependent T₂ PRE has potential for specific quantification of (liver) tissue iron stores.