Rabu, 21 Disember 2011

MRI contrast agents

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.

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]
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]
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]
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.

Water soluble
high osmolar

low osmolar


Water insoluble




Warning: Contrast Dye Used In MRI Test Can Be Dangerous

Brent Adams
Posted by Brent AdamsOctober 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.

Posted by Patrick Thronson
October 28, 2008 7:28 PM
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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Magnetic Resonance Imaging MRI

Magnetic Resonance Imaging
MRI or Magnetic Resonance Imaging is a technology that revolutionized several fields. This method of scanning was developed primarily for use in medicine, but it has also been used to study fossils and historical artifacts. Early doctors were only able to gather data about a patient through observation and rudimentary tests. X-rays provided doctors with one of the first ways of peering within a living person. The MRI was one of the exciting successors to the X-ray.
To perform a MRI scan, the patient is securely placed on an imaging table within a large MRI scanner. Powerful magnetic fields are administered to align the nuclei within the atoms of the patient's body. Next, radio frequency pulses are applied; finally, the nuclei release some of the radio frequency energy and these emissions are detected by the MRI equipment. With this data, a computer generates a surprisingly detailed view of tissues within the body.
Earlier imaging technologies, such as X-rays, were able to detect dense tissues, particularly bones. MRIs give doctors the ability to view all sorts of body structures including soft tissues.
MRIs are frequently used to detect cancers that would otherwise be difficult to diagnose, such as mesothelioma. The ability to detect abnormalities, such as cancers at their early stages, has brought these scanners to the forefront of the battle against many diseases. It is generally believed that patients are not harmed by undergoing the procedure, since MRIs do not use radiation. There are not any side effects, but patients with pacemakers or other metallic implants are not eligible for these scans.
Exams typically take between 30 minutes and one hour. Early models of MRI scanners required patients to be placed in confined positions; newer versions of these machines, however, are based on an open design that is much more spacious and comfortable. The images themselves are often available immediately after the scan and the patient is able to resume normal activity.
I work at an MRI center. There are many metal objects that can safely go into an MRI scanner. The issue is what kind of metal is it. If it is attracted to a magnet, it should not even go into the room, much less into the scanner. Items that are real gold or real silver are not attracted to magnets, therefore safe to be in the room. (Like your wedding ring.) Also, implants such as knee implants, hip implants, staples and many other surgically implanted items often can be safely entered into the magnetic field. Since the advent of MRI and it being used so much, most surgical implants are of titanium, and not a problem. NO implants are put into the machine without documentation that the implant has been tested(endlessly and carefully in thorough research) that it is safe in a particular strength machine. Another consideration is that there are different 'strengths' (called 'Tesla') of machines. And a 3T machine is exponentially stronger than a 1.5T (which is common).
Bottom line - don't try to figure it out yourself. If you have anything that you weren't born with in or around your body, tell the technologist performing your scan before going into the room!!! They are responsible for your being safe. They have endless books and studies they can reference to know if an item is safe to be in the scanner room or not. Consider all the kinds of implants people can have now; stents, portacaths, staples, pins and rods, joint replacements, plates, etc, etc. If you tell the tech everything in or around your body, trust me, they will not Let you enter the room unsafely.
That said, you may have something like a 'safe to go into the room' pin in your leg, but they can't do your scan. That's because while the pin in your leg is safe to be in the machine, if you're getting a scan of the same part of the body where the metal is, it will distort the imaging, making it undiagnostic. (unable to give you information about the injury or reason you were scanned.) The metal distorts the imaging/picture.
Your safety is in the hands of you and your technologist. You - to let them know about anything on you that you weren't born with; and them - to make sure they don't put anything unsafe into the machine. In the 19 years I've worked in MRI - the only errors were made by people not letting the techs know about something. Never an error of a tech putting something into the machine that should not be there.
MRI procedures aren't like surgery, so the staples can't be ripped out of you. Though I don't know, I'd predict that the doctors intentionally used staples that wouldn't cause problems in an MRI. As for the wedding ring, I'm guessing that since it's probably not made out of magnetic material, it won't have a huge effect on the results of the MRI either.
If I were you, I'd trust the MRI technician.
hello , my name is lori and i am scheduled for an mri on the 18 of this month and i know from having done this before that you are suppose to take off all jewlery and when i called the mri department and told them i can not take off my wedding ring and i asked then if i had to cut it off in order to have the test and she told me no it is ok i could leave it on.is that true or due i have it cut off? won't it mess up the machine? also i had gastric by-pass 1yr. ago and surgical staples are still in me and they will be there for life what about them? will the machine rip them out of me? please find out for me .it is very important that i find out right away. thank you very much. lori
MRI stands for magnetic resonance imaging; it basically uses powerful magnets and radio waves to create detailed images of the interior of your body. It can be done with or without contrast. Contrast is a type of dye that is injected intravenously either right before, or during the procedure. Certain abnormalities, such as tumors, will absorb the dye and show up very clearly on the MRI with contrast. Your doctor will determine whether you need an MRI with contrast or without, and may order both tests.
An MRI scan is different than a regular x-ray or a CT scan, which both use ionizing radiation to create images. MRI scans generally produce clearer images with much more detail than an x-ray or CT scan. Small tumors, which may be invisible on an x-ray or CT scan, may be detected by MRI. In the case of most cancers, the earlier treatment is begun, the better the outcome of treatment, so an early MRI scan of any suspicious area can literally mean the difference between life and death.
As good as a standard MRI image is, the image can be improved even further by adding contrast. Tumors and other abnormalities will absorb the contrast dye as it progresses through your blood vessels, and on the MRI scan this area will glow. This allows for the detection of even the smallest tumors, and it also gives your doctor a clearer idea about the location and size of a tumor and which organs or tissues are involved. In addition, contrast allows a doctor to observe functional abnormalities that are not visible on a regular scan, particularly problems with how well your blood is flowing through your vessels.
The contrast medium used in MRI, generally gadolinium, is different than the contrast dyes used in x-rays or CT scans. Adverse reactions to gadolinium are much rarer than iodine-based dyes. However, if you have abnormal kidney function, you may be at increased risk for nephrogenic systemic fibrosis caused by the MRI dye. This complication is extremely rare, but always be sure your doctor and radiology technician are aware of any medical problems or allergies you may have, before you are injected with any type of contrast dye. Most people tolerate MRI with contrast just fine, and the benefits of early tumor detection generally outweigh the minor risks associated with the dye.
An MRI with contrast is generally painless, but you may experience some discomfort with the IV or needle used to inject the dye. You will be placed on a table and positioned so that the scan will show the affected area most clearly. You may be slid inside a long narrow tube in a closed MRI, or you may have an open MRI, in which the scanning equipment is shaped like a large doughnut and only scans a certain portion of your body at a time. The imaging process itself may take 45 minutes up to two hours, and you may be offered headphones so you can listen to music during the scan. Once the scanning is complete, a radiologist will read and interpret the scan and your doctor will discuss the results with you.