Intravascular (blood pool) MRI contrast agents

Intravascular MRI contrast agents normally remain confined to the intravascular space, compared to Gd-DTPA which distributes throughout the extracellular fluid space. This is a result of intravascular agents having a molecular weight of approximately 70,000 and above, compared to a molecular weight of 590 for Gd-DTPA. 

There are several advantages of intravascular agents:

• they can assess perfusion in areas of ischemia and provide information about capillary permeability in areas of reperfusion
• they can show the extent of tumor neovascularity and associated permeability changes
• they are useful in studies requiring prolonged imaging. 

These types of intravascular contrast agents will be discussed separately: 

• Gd-DTPA labeled albumin
• Gd-DTPA labeled dextran
• chromium-labeled red blood cells
• superparamagnetic iron oxide (SPIO)