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MRI Contrast Agents
• Classifications, Characteristics, etc. •
• Contrast Agents For Intravenous Use / Magnetic Characteristics
• Contrast Agents For Intravenous Use / Pharmacokinetics
• Contrast Agents For Intravenous Use / Distribution
• Contrast Agents For Oral Use / Magnetic Characteristics
• Contrast Agents For Oral Use / Signal Characteristics
  
Radiology Contrast Agents Open this link in a new window Ultrasound Imaging Contrast Agents Open this link in a new window
Contrast Agents For Intravenous Use / Magnetic Characteristics
Paramagnetic Contrast Agents 
Magnetic relaxation in tissues can be enhanced using contrast agents. The most commonly used for MRI are the paramagnetic contrast agents, which have their strongest effect on the T1, by increasing T1 signal intensity in tissues where they have accumulated.
MRI collects signal from the water protons, but the presence of these contrast agents enhances the relaxation of water protons in their vicinity. Paramagnetic contrast agents contain magnetic centers that create magnetic fields approximately one thousand times stronger than those corresponding to water protons. These magnetic centers interact with water protons in exactly the same way as the neighboring protons, but with much stronger magnetic fields, and therefore, have a much greater impact on relaxation rates, particularly on T1. In MRI, contrast agents are routinely injected intravenously to help identify areas of hypervascularity, as in malignant tumors.
See also Contrast Agents, Gadovist®, MultiHance®, Omniscan®, OptiMARK®.

See also the related poll result: 'The development of contrast agents in MRI is'
 
Images, Movies, Sliders:
 MRI Upper Abdomen T1 with Contrast  Open this link in a new window
    
 MRI Orbita T1  Open this link in a new window
 MRI Orbita T1 with Contrast  Open this link in a new window
    
 

• View the NEWS results for 'Paramagnetic Contrast Agents' (1).Open this link in a new window.

• View the DATABASE results for 'Paramagnetic Contrast Agents' (22).Open this link in a new window

 
Further Reading:
Superparamagnetic Contrast Agents 
Small particles of ferrite are used as superparamagnetic contrast medium in MR imaging (appearing predominantly dark on MRI). These agents exhibit strong T1 relaxation properties, and due to susceptibility differences to their surroundings also produce a strongly varying local magnetic field, which enhances T2 relaxation to darken the contrast media containing structures.
Superparamagnetic contrast agents are also known by the abbreviation SPIO's (small particle iron oxide or superparamagnetic iron oxide) and USPIO's (ultrasmall particle iron oxide or ultrasmall superparamagnetic iron oxide).
Two types of USPIO will be available on the market as blood pool agents, while SPIO's have been used as darkening contrast agents for liver imaging. As particulate matter they are taken up by the RES. Very small particles of less than 300 nanometers also remain intravascular for a prolonged period of time and thus can serve as blood pool agents.

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

• View the DATABASE results for 'Superparamagnetic Contrast Agents' (12).Open this link in a new window

 
MR-TIP Forum - Related Threads 
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• 'Omniscan Distribution Rate'
• 'CE MRA of the Liver'
• 'CE-MRA Vasovist protocol'

Superparamagnetic Iron Oxide  
(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..

• View the NEWS results for 'Superparamagnetic Iron Oxide ' (3).Open this link in a new window.

• View the DATABASE results for 'Superparamagnetic Iron Oxide' (32).Open this link in a new window

 
Ultrasmall Superparamagnetic Iron Oxide  
(USPIO) The class of the ultrasmall superparamagnetic iron oxide includes several chemically and pharmacologically very distinct materials, which may or may not be interchangeable for a specific use. Some ultrasmall SPIO particles (median diameter less than 50nm) are used as MRI contrast agents (Sinerem®, Combidex®), e.g. to differentiate metastatic from inflammatory lymph nodes. USPIO shows also potential for providing important information about angiogenesis in cancer tumors and could possibly complement MRI helping physicians to identify dangerous arteriosclerosis plaques.
Because of the disadvantageous large T2*//T1 ratio, USPIO compounds are less suitable for arterial bolus contrast enhanced magnetic resonance angiography than gadolinium complexes. The tiny ultrasmall superparamagnetic iron oxides do not accumulate in the RES system as fast as larger particles, which results in a long plasma half-life. USPIO particles, with a small median diameter (less than 10 nm), will accumulate in lymph nodes after an intravenous injection by e.g. direct transcapillary passage through endothelial venules. Once within the nodal parenchyma, phagocytic cells of the mononuclear phagocyte system take up the particles.
As a second way, USPIOs are subsequently taken up from then interstitium by lymphatic vessels and transported to regional lymph nodes. A lymph node with normal phagocytic function takes up a considerable amount and shows a reduction of the signal intensity caused by T2 shortening effects and magnetic susceptibility. Caused by the small uptake of the USPIOs in metastatic lymph nodes, they appear with less signal reduction, and permit the differentiation of healthy lymph nodes from normal-sized, metastatic nodes.
See also Superparamagnetic Contrast Agents, Superparamagnetic Iron Oxide, Very Small Superparamagnetic Iron Oxide Particles, Blood Pool Agents, Intracellular Contrast Agents.

• View the NEWS results for 'Ultrasmall Superparamagnetic Iron Oxide ' (2).Open this link in a new window.

• View the DATABASE results for 'Ultrasmall Superparamagnetic Iron Oxide' (16).Open this link in a new window

 
MRI Knowledge Resources from Universities, Companies, Agencies, etc. 
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  Contrast Agents For Intravenous Use / Pharmacokinetics top
Radiology Contrast Agents Open this link in a new window Ultrasound Imaging Contrast Agents Open this link in a new window
 
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