To evaluate its potential as a tissue-specific hepatobiliary magnetic resonance (MR) contrast agent, manganese chloride was orally administered to rats in increasing doses of 100-1,500 μmol/kg MnCl2, and the relaxation times of liver, pancreas, kidney, and heart were measured with ex vivo relaxometry and in vivo MR imaging. Two hours after ingestion of 200 μmol/kg MnCl2, liver T1 was decreased by 48%, whereas tumor T1 decreased by only 9%. On spin-echo MR images, the signal-to-noise ratio in liver increased by 54%; the contrast-to-noise ratio in tumor, by 375%. The T1 of pancreas, kidney, and heart decreased by 8%, 23%, and 13%, respectively. At subjective assessment, the signal intensity of the upper gastrointestinal tract was reduced, likely because of the high concentration of manganese in the lumen, and delineation of the intestine from other abdominal structures was improved. These results indicate that orally administered MnCl2 causes substantial, reproducible, and tissue-specific enhancement of liver. Because enhancement of tumor was minimal, orally administered MnCl2 may potentially be used to improve detection of hepatic tumors.
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