Short name: AMI-25, generic name: Ferumoxide (SPIO)
Ferumoxides are superparamagnetic (T2*) MRI contrast agents, so the largest signal change is on T2 and T2* weighted images.
The agent distributes relatively rapidly to organs with reticuloendothelial cells primarily the liver, spleen and bone marrow. The liver shows decreased signal intensity, as does the spleen and marrow. The agent is taken up by the normal liver, resulting in increased CNR between tumor and normal liver. Hepatocellular lesions, such as adenoma or focal nodular hyperplasia, contain reticuloendothelial cells, so they will behave similar to the liver, with decreased signal on T2 weighted images. On T1 images, there is typically some circulating contrast agent, and blood vessels show increased signal intensity.
Current MRI protocols involve T1 weighted breath-hold gradient echo images of the liver, and fast spin echo T2 weighted pictures. This requires about 15 minutes. The patient is then removed from the scanner, and the contrast agent administered. After contrast administration, the same pulse sequences are again repeated.

(GastroMARK®, Lumirem®) A superparamagnetic MRI contrast agent for the gastrointestinal tract.

See also Oral Contrast Agents.

GastroMARK® belongs to the negative oral contrast agents (same as Lumirem®, another brand name for ferumoxsil). GastroMARK® is used to distinguish the loops of the bowel from other abdominal structures and physiology. When GastroMARK® is ingested, it flows through and darkens the stomach and the small intestine in 30 to 45 minutes. By more clearly identifying the intestinal loops, GastroMARK® improves visualization of adjacent abdominal tissues such as the pancreas.

After a bleeding, blood goes through several transitions regarding magnetic properties, intra- and extracellular distribution and content of proteins and water. Oxyhaemoglobin is degraded to deoxyhaemoglobin and further to methaemoglobin, ferritin and haemosiderin. These molecules can be characterized by their magnetic susceptibility effect. Oxyhaemoglobin is diamagnetic with no practical influence on the magnetic field. All degradation products are paramagnetic (deoxyhaemoglobin, methaemoglobin) or even superparamagnetic (ferritin, haemosiderin).

See also Haemoglobin, Blood Oxygenation Level Dependent Contrast.

Generic name: Liposomes, central moiety: different, contrast effect: paramagnetic, distribution: different
Liposomes are lipid containing nanoparticles, or fat molecules, surrounding a water core. Liposomes were the first type of nanoparticles created to be used as carriers for lipophilic MRI contrast agents with novel characteristics.
Liposomes loaded with gadolinium-containing chelates have potential as blood pool agents, caused by modifications of the surface (e.g., with polyethylene glycol) leading to longer blood retention times.
The incorporation of contrast agents into either the the bilayer membrane or the aqueous inner cavity is possible. These MRI contrast agents has been used to image the lymph nodes using liposomes containing Gd-DTPA as well as dextran coated iron oxide particles.
To image the liver or the hepatobiliary system, liposomes containing Gd-HPDO3A, or MnDPDP, have been tested.
Liposomes containing gadolinium were conjugated to antibodies and targeted to a specific organ system.
A method of targeting tumors with ultrasound that also uses MRI to watch the cell destroying, uses liposomes loaded with cytotoxic drugs and also with gadolinium to make them show up in MRI. As well as used as an imaging technique, ultrasound can also be used to destroy cancer cells. Once the drugs have been administered, focusing the ultrasound on the target area makes blood vessels permeable. The liposomes leak out of the blood vessel into the target area, watched by MRI, where the cytotoxic drug can then go to work.

See also Memosomes, Superparamagnetic Iron Oxide, Classifications, Characteristics, etc. and Mangafodipir Trisodium.