Conventional MR imaging with non-specific
gadolinium contrast agents is useful in the detection and staging of
malignancies. With the development of organ-specific MR
contrast agents, MR imaging is assuming an even larger role in body imaging. Two different classes of liver-specific agents, hepato-biliary agents targeted to the hepatocytes, and reticulo-endothelial agents (or Kupffer cell agents) targeted to the reticuloendothelial system in the liver and spleen, have been developed. MRI with liver-specific
contrast agents is superior to helical CT for detection of liver
metastases.
Mangafodipir, which was originally developed as a liver-specific agent, has been shown to accumulate in the pancreas as well. Recent studies have revealed that
mangafodipir-enhanced MRI is at least equal to spiral CT in the staging of
pancreatic cancer and may be superior to CT in the detection of small
cancers. Blood-pool
contrast agents with a long blood half-life, such as ultrasmall
iron oxide particles (
USPIO), have been developed for MR angiography. After the clearance from the vascular system,
USPIO are taken up by phagocytes and accumulate in normal lymph, but not in metastatic nodes. This effect can be exploited to increase the accuracy of MRI in lymph node staging of
cancer of head-neck, lung or pelvis. In conclusion, various organ-specific MR
contrast agents with a wide range of clinical applications have been developed. Future studies will demonstrate the role of contrast-enhanced MRI in comparison with multi-detector array CT.