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.

Short name: Mn-EDTA-PP, generic name: Liposomes, central moiety: Mn2+, preclin. trade name: Memosomes
Memosomes are taken up by healthy Kupffer cells of the liver. Once in this cells, manganese (Mn+2) release slowly and diffuses into the adjoining hepatocytes. Normal liver tissue (not malignancies) is enhanced after application of this type of liposomes.

See also Liposomes, Hepatobiliary Contrast Agents, and Reticuloendothelial Contrast Agents.

See also Classifications, Characteristics, etc.

Contrast agent with a preferential intracellular distribution.
Intracellular agents (such as manganese derivatives and ultrasmall superparamagnetic iron oxide), exhibit a flow- and metabolism-dependent uptake. These properties may allow delayed imaging, similar to isotopic methods.
Phospholipid liposomes are rapidly sequestered by the cells in the reticuloendothelial system (RES), primarily in the liver. For imaging of the liver, liposomes may be labeled with MR contrast medium, both positive (T1-shortening) paramagnetic media, and negative (T2-shortening) superparamagnetic media.
Several other nonliposome MR contrast media are also taken up by the RES, e.g.:
Other MR contrast agents accumulate selectively in the hepatocytes, e.g.:

Liver imaging with gadolinium contrast enhanced MRI is sometimes not sufficient for a reliable diagnosis of liver lesions. For this reasons, special liver Contrast agents that are targeted to the reticuloendothelial system (RES), have been developed to improve both detection and characterization of liver and spleen lesions. Reticuloendothelial Contrast Agents, as e.g. superparamagnetic iron oxides (SPIO), are taken up by healthy liver tissue but not tumors.
These RES targeted contrast agents provide a prolonged imaging window and enough time for high spatial resolution or multiple breath hold images. Reticuloendothelial contrast agents have an increased sensitivity for the detection of small liver lesions (e.g., metastases), compared with gadolinium enhanced MRI and spiral CT. At higher field strengths with an increased signal to noise ratio the susceptibility effect with iron oxide particles may be enhanced.
Other new agents (Gadobenate Dimeglumine, Gadoxetic Acid) have both an initial extracellular circulation and a delayed liver-specific uptake. Since a considerable part of these contrast agents is excreted in the bile, functional biliary imaging can diagnose biliary anomalies, postoperative bile leaks, and anastomotic strictures. Other agents, such as liposomes (with encapsulated Gd-DTPA) or DOTA complexes are in different development stages.

See also Hepatobiliary Contrast Agents, Gadolinium Oxide, Superparamagnetic Iron Oxide and Liposomes.

Contrast agents are chemical substances introduced to the anatomical or functional region being imaged, to increase the differences between different tissues or between normal and abnormal tissue, by altering the relaxation times. MRI contrast agents are classified by the different changes in relaxation times after their injection.
The design objectives for the next generation of MR contrast agents will likely focus on prolonging intravascular retention, improving tissue targeting, and accessing new contrast mechanisms. Macromolecular paramagnetic contrast agents are being tested worldwide. Preclinical data shows that these agents demonstrate great promise for improving the quality of MR angiography, and in quantificating capillary permeability and myocardial perfusion.
Ultrasmall superparamagnetic iron oxide (USPIO) particles have been evaluated in multicenter clinical trials for lymph node MR imaging and MR angiography, with the clinical impact under discussion. In addition, a wide variety of vector and carrier molecules, including antibodies, peptides, proteins, polysaccharides, liposomes, and cells have been developed to deliver magnetic labels to specific sites. Technical advances in MR imaging will further increase the efficacy and necessity of tissue-specific MRI contrast agents.

See also Adverse Reaction and Nephrogenic Systemic Fibrosis.

See also the related poll result: 'The development of contrast agents in MRI is'