MRI contrast agents
MRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in magnetic resonance imaging (MRI). The most commonly used compounds for contrast enhancement are gadolinium-based. MRI contrast agents alter the relaxation times of tissues and body cavities where they are present. Depending on the image weighting, this can give a higher or lower signal.
Most clinically used MRI contrast agents work through shortening the T1 relaxation time of protons located nearby. The T1 shortening is due an increase in rate of stimulated emission from high energy states (spin anti-aligned with the main field) to low energy states (spin aligned). The source of the stimulation is thermal vibration of the strongly magnetic metal ions, which create oscillating electromagnetic fields at frequencies corresponding to the energy difference between the spin states (via E = hν).
MRI contrast agents may be administered by injection into the blood stream or orally, depending on the subject of interest. Oral administration is well suited to G.I. tract scans, while intravascular administration proves more useful for most other scans. A variety of agents of both types enhance scans routinely.
Intravascular
MRI contrast agents delivered through the blood stream are chelated metals.
Gadolinium (Gd): Paramagnetic
Effect of contrast agent on images: Defect of the blood-brain barrier after stroke shown in MRI. T1-weighted images, left image without, right image with contrast medium administration.
Gadolinium contrast MRI contrast agents are the most commonly used for enhancement of vessels in MR angiography or for brain tumor enhancement associated with the degradation of the blood-brain barrier. For large vessels such as the aorta and its branches, the gadolinium dose can be as low as 0.1 mmol per kg body mass. Higher concentrations are often used for finer vasculature[1]. Due to their hydrophilic character, Gd chelates do not pass the blood-brain barrier. Thus, these are useful in enhancing lesions and tumors where the Gd leaks out. In the rest of the body, the Gd initially remains in the circulation but then distributes into the interstitial space or is eliminated by the kidneys.
As a free ion, gadolinium is highly toxic. It was generally regarded as safe when administered as a chelated compound before the use of some Gd chelates was linked to a rare but severe complication, nephrogenic systemic fibrosis (NSF)[2][3][4], which causes fibrosis in various tissues and organs in the body. Patients with poor renal function are considered to be more at risk for NSF.[5][6]
The compounds can be classified by whether they are macro-cyclic or have linear geometry and whether they are ionic or not. Cyclical ionic Gd compounds are considered the least likely to release the Gd ion and hence the safest[7].
Different ranges of gadolinium-containing contrast agents are available in different territories. In the United States of America, Gd chelated contrast agents approved by the U.S. Food and Drug Administration (FDA) include:[8]
- gadodiamide (Omniscan)
- gadobenic acid (Multihance)
- gadopentetic acid (Magnevist)
- gadoteridol (Prohance]
- gadofosveset (Ablavar)
- gadoversetamide (OptiMARK)
- gadoxetic acid (Eovist in the USA, Primovist in other parts of the world)
Apart from the gadolinium-containing contrast agents that have been approved by the FDA and other regulatory bodies for marketing, there are some others that have been assigned international non-proprietary ("generic") names by the World Health Organization:[9][citation needed]
- gadobutrol (Gadavist in the USA, Gadovist in Canada and Europe)
- gadocoletic acid
- gadodenterate
- gadomelitol
- gadopenamide
- gadoteric acid (Dotarem)
Iron oxide: Superparamagnetic
Two types iron oxide contrast agents exist: Superparamagnetic Iron Oxide (SPIO) and Ultrasmall Superparamagnetic Iron Oxide (USPIO). These contrast agents consist of suspended colloids of iron oxide nanoparticles and when injected during imaging reduce the T2 signals of absorbing tissues. SPIO and USPIO contrast agents have been used successfully in some instances for liver tumor enhancement[10]. Available iron oxide contrast agents include:
Manganese: Paramagnetic
Manganese chelates such as Mn-DPDP enhance the T1 signal and have been used for the detection of liver lesions. The chelate dissociates in-vivo into manganese and DPDP where the former is absorbed intra-cellularly and excreted in bile, while the latter is eliminated via the renal filtration.[11]
Oral
A wide variety of oral contrast agents can be used for enhancement of the gastrointestinal tract. They include gadolinium and manganese chelates, or iron salts for T1 signal enhancement. SPIO, barium sulfate, air and clay have been used to lower T2 signal. Natural products with high manganese concentration such as blueberry and green tea can also be used for T1 increasing contrast enhancement.[12]
Perflubron, a type of perflorocarbon, has been used as a gastrointestinal MRI contrast agent for pediatric imaging.[13] This contrast agent works by reducing the amount of protons (as hydrogen) in a body cavity, thus causing it to appear dark in the images.
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SIDE EFFECT
http://fayetteville.injuryboard.com/toxic-substances/warning-contrast-dye-used-in-mri-test-can-be-dangerous.aspx?googleid=249844
Warning: Contrast Dye Used In MRI Test Can Be Dangerous
Brent Adams
Contributor
October 21, 2008 11:34 PM
Magnetic Resonance Imaging tests, MRIs and Magnetic Resonance Angiography, and MRAs are commonly used by physicians to study and diagnose numerous conditions of the body. Contrast material commonly used for these tests help the physician get a clear and detailed picture of the patient’s internal organs, tissues, bones and vessels. The contrast material, are commonly known as dye, is injected into the blood stream.In recent years, the contrast agent of choice for most doctors contains a metal known as Gadolinium. This substance is a metal. It is extremely harmful to the body. Because of the adverse effect this metal has on the body, the Gadolinium is coated with chelating agents to coat the metal and thereby protect the body from the dangerous effects of the metal.Some of the manufacturers of the Gadolinium containing contrast agents have used inferior chelating agents. The effect of these inferior chelating agents is to expose the body to the harmful metal Gadolinium.In order to rid the body of the contrast material after an MRI or MRA, the contrast material containing Gadolinium is transferred to the kidneys before it is urinated out of the body. Gadolinium is especially harmful to the patients with kidney insufficiency.Unfortunately, Gadolinium is also used to make CD discs, computer memory, and television tubes.Unfortunately, Gadolinium exposure causes a rare and debilitating and potentially fatal disease known as Nephrogenic Systemic Fibrosis (NSF). This disease causes a thickening of the skin, connective tissues, muscles and internal organs throughout the body. The disease causes the body to harden from the outside in.Symptoms from NSF include swelling, tightening, or thickening of the skin, colored patches, bumps or blisters; burning, itching or severe sharp pain in the effected areas, changes of skin texture; difficulty extending arms or legs, muscle weakness, deep bone pain in the hips or ribs and swelling of the hands and feet.The United States Food and Drug Administration began issuing health advisory warnings concerning Gadolinium dyes as early as June of 2006. On May 23, 2007, the FDA ordered that a black box warning be added to all Gadolinium-based contrast agent labels concerning the life-threatening risk associated with the use of contrast dyes containing Gadolinium. The warning states that patients with severe kidney insufficiency who received Gadolinium-based agents are at risk for developing debilitating, a potentially fatal disease known as Nephrogenic Systemic Fibrosis (NSF). The required warning includes advice to “avoid the use of GBCA’s (Contrast agents containing Gadolinium) unless the diagnostic information is essential and not available with non-contrast enhanced magnetic resonance imaging (MRI). Although the FDA requires the warning, this use of Gadolinium containing contrast agents is still allowed and is frequently used. If you or someone you know has developed Nephrogenic Systemic Fibrosis (NSF) or symptoms after having an MRI or an MRA contact lawyer who handles cases to see if you have a claim.
Tags: Nephrogenic Systemic Fibrosis, Gadolinium, MRI, MRA, contrast material, NSF, kidney insufficiency, Magnetic Resonance Imaging
As many people know, those who undergo MRI procedures often take gadolinium, a rare-earth metal that enhances MRI images. Since 1997, a growing number of patients with kidney disorders who have taken gadolinium have reported a serious, sometimes fatal condition called nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). People suffering from NSF/NFD experience a gradual tightening of the skin and connective tissue. NSF/NFD can lead to extreme pain, paralysis, and even death. You can obtain a free legal consultation and or learn more about gadolinium and NSF at More ... The damaging and potentially fatal side effects of gadolinium mean that you deserve an in-depth legal review.
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