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Superparamagnetic Iron OxideInfoSheet: - Contrast Agents - 
Intro, Overview, 
Characteristics, 
Types of, 
etc.
 
(SPIO) Relatively new types of MRI contrast agents are superparamagnetic iron oxide-based colloids (median diameter greater than 50nm). These compounds consist of nonstoichiometric microcrystalline magnetite cores, which are coated with dextrans (in ferumoxide) or siloxanes (in ferumoxsil). After injection they accumulate in the reticuloendothelial system (RES) of the liver (Kupffer cells) and the spleen. At low doses circulating iron decreases the T1 time of blood, at higher doses predominates the T2* effect.
SPIO agents are much more effective in MR relaxation than paramagnetic agents. Since hepatic tumors either do not contain RES cells or their activity is reduced, the contrast between liver and lesion is improved. Superparamagnetic iron oxides cause noticeable shorter T2 relaxation times with signal loss in the targeted tissue (e.g., liver and spleen) with all standard pulse sequences. Magnetite, a mixture of FeO and Fe2O3, is one of the used iron oxides. FeO can be replaced by Fe3O4.
Use of these colloids as tissue specific contrast agents is now a well-established area of pharmaceutical development. Feridex®, Endorem™, GastroMARK®, Lumirem®, Sinerem®, Resovist® and more patents pending tell us that the last word in this area is not said.
Some remarkable points using SPIO:
A minimum delay of about 10 min. between injection (or infusion) and MR imaging, extends the examination time.
Cross-section flow void in narrow blood vessels may impede the differentiation from small liver lesions.
Aortic pulsation artifacts become more pronounced.
See also Superparamagnetism, Superparamagnetic Contrast Agents and Classifications, Characteristics, etc..
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Further Reading:
  Basics:
Progress Report: MRI Contrast Agents and AtherosclerosisOpen this link in a new window
2006   by www.ncbi.nlm.nih.gov    
Generation of the MR Images from the MR-signalsOpen this link in a new window
   by www.es.oersted.dtu.dk    
  News & More:
Optimized Labelling of Human Monocytes with Iron Oxide MR Contrast AgentsOpen this link in a new window
Sunday, 30 November 2003   by rsna2003.rsna.org    
 •• There are 3 news about 'Superparamagnetic Iron Oxide'.
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