Evaluation of hepatocyte‐specific paramagnetic contrast media for MR imaging of hepatitis

The hepatocyte‐specific paramagnetic magnetic resonance (MR) contrast agents manganese‐DPDP [N,N′‐dipyridoxylethylenediamine‐N,N′‐diacetate 5,5′ bis‐(phosphate)] and gadobenate dimeglumine were used for diagnosing chemically induced hepatitis in rats. Ex vivo liver tissue relaxation times and in vivo MR image signal‐to‐noise ratios were compared before and after contrast agent administration. Ex vivo relaxometry and in vivo MR imaging showed that Mn‐DPDP enhanced normal and diseased livers to the same degree at all time points from 5 to 120 minutes. Gadobenate dimeglumine showed reduced T1 and T2 enhancements in hepatitis relative to those of normal liver, in the early phase (5–30 minutes). However, these effects are offsetting, and as a result, MR imaging failed to allow distinction of diseased from normal livers. This surprising result observed in vivo was in fact predicted by applying the Bloch equation to our ex vivo data. Our results show that detection and quantitation of hepatitis with MR imaging enhanced with paramagnetic cellspecific contrast agents will be more difficult than anticipated.