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Contrast Agents
Intro

  • Intro
 
 
 
 
 
Magnetic Resonance Imaging Contrast Agents Open this link in a new window Ultrasound Imaging Contrast Agents Open this link in a new window
'Contrast Agents' in Radiology News (6) and in Radiology Resources (8) 
Contrast Agents 
(CA) Contrast agents are used to change the imaging characteristics, resulting in additional information about anatomy, morphology or physiology of the human body. Radiocontrast agents (also called photon-based imaging agents) are used to improve the visibility of internal body structures in x-ray and CT procedures. Contrast agents are also used to increase the contrast between different tissues in MRI (magnetic resonance imaging) and ultrasound imaging. The ideal imaging agent provides enhanced contrast with little biological interaction.
First investigations with radiopaque materials are done shortly after the discovery of x-rays. These positive contrast agents attenuate x-rays more than body soft tissues due to their high atomic weight. Iodine and barium have been identified as suitable materials with high radiodensity and are used until today in x-ray and CT contrast agents. Iodine-based contrast agents are water-soluble and the solutions are used nearly anywhere in the body. Iodinated contrast materials are most administered intravenous, but can also be introduced intraarterial, intrathecal, oral, rectal, intravesical, or installed in body cavities. Barium sulfate is only used for opacification of the gastrointestinal tract. Negative contrast agents attenuate x-rays less than body soft tissues, for example gas.

Iodinated contrast media are differentiated in:
point ionic contrast agents:
ionic dimer;
ionic monomer (high-osmolar contrast media).
point nonionic contrast agents:
nonionic dimer (low- or iso-osmolar contrast media);
nonionic monomer (low-osmolar contrast media).
Intravascular iodinated contrast agents are required for a large number of x-ray and CT studies to enhance vessels and organs dependent on the blood supply. Injectable contrast agents are diluted in the bloodstream and rapidly distributed throughout the extracellular fluid. The main route of excretion is through the kidneys, related to the poor binding of the agent to serum albumin. The liver (gall bladder) and small intestine provide alternate routes of elimination particularly in patients with severe renal impairment. The use of special biliary contrast agents is suitable for gallbladder CT and cholecystograms because they are concentrated by the liver to be detectable in the hepatic bile.
The introduction of fast multi-detector row CT technology, has led to the development of optimized contrast injection techniques. The amount of contrast enhancement depends on the contrast agent characteristics, such as iodine concentration, osmolality, viscosity, and the injection protocol, such as iodine flux and iodine dose. Adverse reactions are rare and have decreased with the introduction of nonionic contrast agents.
See also Contrast Enhanced Computed Tomography and Abdomen CT.

• View the NEWS results for 'Contrast Agents' (4).Open this link in a new window. 

• View the DATABASE results for 'Contrast Agents' (46).Open this link in a new window.



  Further Reading:
  Basics:
POSITIVE CONTRAST MATERIAL: IODINATEDOpen this link in a new window
by www.e-radiography.net    
  News & More:
Contrast Medium Reactions, Recognition and TreatmentOpen this link in a new window
by www.emedicine.com    
Guidelines for Contrast Media from the European Society of Urogenital RadiologyOpen this link in a new window
'This perspective will present all guidelines produced to date by the Contrast Media Safety Committee of the European Society of ...'
Wednesday, 2 July 2003 by www.ajronline.org    
Biliary Contrast Agents 
The molecular structure of some iodinated contrast agents makes them suitable for the computer-tomographic examination of the biliary tract. Organic iodine compounds increase the attenuation of x-rays and the contrast between body tissues containing iodine and those tissues that do not contain iodine. The degree of opacification is directly proportional to the concentration and volume of the iodinated contrast agent (the total amount of iodine).
Biliary contrast agents can be taken orally, for example calcium iopodate, or intravenous meglumine iotroxate. The contrast media are excreted by the liver and concentrate in the gallbladder after passing the intrahepatic biliary tree and cystic duct.
Oral biliary contrast agents usually opacify the gallbladder after a few hours. If the gallbladder is removed, an intravenous cholegraphic agent is required and gallbladder CT can start 60 minutes after the beginning of contrast medium infusion.
The main limitation of the use of biliary contrast agents is the high rate of allergic reactions and of renal or hepatic toxicity. Caused by the potential for systemic toxicity with intravenous cholangiography, ultrasonography should be the preferred method for evaluation of the gallbladder and the bile ducts.

• View the DATABASE results for 'Biliary Contrast Agents' (4).Open this link in a new window.



  Further Reading:
  News & More:
Liver-Specific Contrast Media: A Magic Bullet or a Weapon for Dedicated Targets??(.pdf)Open this link in a new window
'I N an editorial on hepatic contrast matenial enhancement in magnetic resonance (MR) imaging published in 1993, Mitchell (1) ...'
November 1997 by radiology.rsnajnls.org    
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- Sir Francis Darwin
 
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