A constant relationship was found between the mean CT numbers of the liver and spleen in 100 normal adults. This relationship was characterized by a mean CT number consistently higher for the liver (24.9 +/- 4.6) than for the spleen (21.1 +/- 4.1). The range for liver CT numbers was 16.7-37.2, and for the spleen it was 14.9-34.3. The mean liver-spleen CT number difference for all subjects was 3.8 +/- 2.1 (p < 0.001); in every instance, the livers exhibiting the high mean CT numbers were in subjects with high mean spleen CT numbers, with the same concordance for low mean CT numbers. This relationship between liver and spleen may be useful in the clinical setting in which a normal liver with low CT numbers must be differentiated from one in which the CT number is low because of fatty infiltration; the fatty liver will exhibit a lower mean CT number than the spleen.

No abstract

Experimental animals that had been given excess iron in their diet were studied by magnetic resonance (MR) imaging in vivo and by magnetic resonance (MR) spectroscopy in vitro. Hepatic iron overload in patients with transfusional iron excess was studied by MR imaging, and isolated iron protein fractions were studied in vitro by MR spectroscopy. The spin echo image intensity of livers with iron overload was decreased because of the extreme decreases in T2 compared with normal; T1 was decreased only moderately. The relaxation rates 1/T2 and 1/T1 both showed a linear relationship to hepatic iron levels. Ferritin solutions showed moderate decreases in T2 and mild decreases in T1. The T2 relaxivity of ferritin, which is due to the iron core rather than the apoferritin protein shell, does not appear sufficient to account for the extreme decrease in T2 observed in hepatic iron overload. Low molecular weight cytosol iron 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 iron metabolism.

CT was more accurate than MR imaging in detection and characterization of transmural penetration of rectal tumors. Recent technologic advances in MR imaging may affect these results.

Experimental animal models of hepatitis, fatty liver, and hepatic iron overload were evaluated using a 3.5-kGauss nuclear magnetic resonance (NMR) imaging system. Increases in image intensity measurements and in T2 relaxation times equalled the sensitivity of histologic findings for the detection of early stages of hepatitis. A significant shift in T1 relaxation times characterized the early stages of hepatic necrosis. Liver triglyceride content correlated significantly with increases in NMR intensity measurements (p less than 0.01); however, changes in liver water content had a much greater influence on intensity, T1, and T2. Thus, it may be possible to distinguish hepatitis from benign fatty liver. Liver iron content correlated with decreases in NMR intensity measurements (p less than 0.001), and iron levels as low as 1.2 mg/g were detected. NMR may more specifically identify hepatocellular iron overload than do other techniques that do not distinguish hepatocellular from reticuloendothelial iron.