MR imaging of blood-borne liver metastases in mice: contrast enhancement with Fe-EHPG. To determine whether iron(III)ethylenebis-(2-hydrophenylglycine) (Fe-EHPG), a prototype hepatobiliary magnetic resonance imaging agent, can enhance the liver-to-tumor contrast-to-noise ratio (C/N) in models of liver tumors in mice, two types of cell inoculation were used: intrahepatic implantation of M5076 sarcoma and intrasplenic injection of colon tumor (C-26) or M5076 sarcoma. Significant enhancement of the liver-to-tumor C/N and/or improved visualization of small lesions was consistently observed on T1-weighted images obtained after injection of the contrast material. For intrahepatic implants, the C/N on postinjection T1-weighted images was superior to that on T1- and T2-weighted preinjection images. For the C-26 metastatic liver lesions of larger diameter (greater than 5 mm), the C/N on postinjection T1-weighted studies was superior to that on preinjection T1-weighted images but was comparable to that on preinjection T2-weighted images. However, higher C/N after administration of Fe-EHPG improved visualization of medium-sized (3-5 mm) and small (1-3-mm) metastatic lesions in both M5076 and C-26 models. These results demonstrate that MR imaging with appropriate hepatobiliary agents appears promising for early detection of liver metastases. 