The sensor detects the time it takes for the atoms to return to their original alignment. In essence, MRI measures the water content or fluid characteristics of different tissues, which is processed by the computer to create a black and white image. The image is highly detailed and can show even the smallest abnormality. Similar to CT, MRI allows your doctor to see your body in narrow slices, each about one quarter of an inch thick.
For example, imagine that you are slicing a loaf of bread and taking a picture of each slice. It can view slices from the bottom axial , front coronal , or sides sagittal , depending on what your doctor needs to see. A dye contrast agent may be injected into your bloodstream to enhance certain tissues. The dye contains gadolinium, which has magnetic properties. It circulates through the blood stream and is absorbed in certain tissues, which then stand out on the scan. MR angiogram MRA. MRI can be used to view arteries and veins.
Contrast dye gadolinium injected into the bloodstream helps the computer "see" the arteries and veins. Contrast is also used to view tumors and arteriovenous malformations AVMs. Nearly every part of the body may be studied with MRI. MRI gives very detailed pictures of soft tissues like the brain. Air and hard bone do not give an MRI signal so these areas appear black. Bone marrow, spinal fluid, blood and soft tissues vary in intensity from black to white, depending on the amount of fat and water present in each tissue and the machine settings used for the scan.
The radiologist compares the size and distributions of these bright and dark areas to determine whether a tissue is healthy. A radiology technologist will perform the test in the MRI suite of the Radiology department of the hospital or outpatient imaging center. It is used to advance the understanding of brain organization and offers a potential new standard for assessing neurological status and neurosurgical risk.
Although MRI does not emit the ionizing radiation that is found in x-ray and CT imaging, it does employ a strong magnetic field. The magnetic field extends beyond the machine and exerts very powerful forces on objects of iron, some steels, and other magnetizable objects; it is strong enough to fling a wheelchair across the room. Patients should notify their physicians of any form of medical or implant prior to an MR scan.
Replacing Biopsies with Sound Chronic liver disease and cirrhosis affect more than 5. NIBIB-funded researchers have developed a method to turn sound waves into images of the liver, which provides a new non-invasive, pain-free approach to find tumors or tissue damaged by liver disease.
It then pulses sound waves through the liver, which the MRI is able to detect and use to determine the density and health of the liver tissue. This technique is safer and more comfortable for the patient as well as being less expensive than a traditional biopsy.
Since MRE is able to recognize very slight differences in tissue density, there is the potential that it could also be used to detect cancer. New MRI just for Kids MRI is potentially one of the best imaging modalities for children since unlike CT, it does not have any ionizing radiation that could potentially be harmful. Back to Health A to Z. Magnetic resonance imaging MRI is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body.
An MRI scanner is a large tube that contains powerful magnets. You lie inside the tube during the scan. The results of an MRI scan can be used to help diagnose conditions, plan treatments and assess how effective previous treatment has been. Depending on the part of your body being scanned, you'll be moved into the scanner either head first or feet first.
The MRI scanner is operated by a radiographer, who is trained in carrying out imaging investigations. They control the scanner using a computer, which is in a different room, to keep it away from the magnetic field generated by the scanner.
Maybe you're concerned about the long-term impact of having all your atoms mixed about, but once you're out of the magnetic field, your body and its chemistry return to normal. There are no known biological hazards to humans from being exposed to magnetic fields of the strength used in medical imaging today.
Most facilities prefer not to image pregnant women, due to limited research of the biological effects of magnetic fields on a developing fetus. The decision of whether or not to scan a pregnant patient is made on a case-by-case basis with consultation between the MRI radiologist and the patient's obstetrician.
However, the MRI suite can be a very dangerous place if strict precautions are not observed. Credit cards or anything else with magnetic encoding will be erased. Metal objects can become dangerous projectiles if they are taken into the scan room. For example, paperclips, pens, keys, scissors, jewelry, stethoscopes and any other small objects can be pulled out of pockets and off the body without warning, at which point they fly toward the opening of the magnet at very high speeds.
Big objects pose a risk, too -- mop buckets, vacuum cleaners, IV poles, patient stretchers, heart monitors and countless other objects have all been pulled into the magnetic fields of the MRI. In , a young boy undergoing a scan was killed when an oxygen tank was pulled into the magnetic bore [source: McNeil]. Once, a pistol flew out of a policeman's holster, the force causing the gun to fire.
No one was injured. To ensure safety, patients and support staff should be thoroughly screened for metal objects prior to entering the scan room. Often, however, patients have implants inside them that make it very dangerous for them to be in the presence of a strong magnetic field.
These include:. Most modern surgical implants, including staples, artificial joints and stents are made of non-magnetic materials, and even if they're not, they may be approved for scanning. But let your doctor know, as some orthopedic hardware in the area of a scan can cause distortions in the image. Sign up for our Newsletter! Mobile Newsletter banner close.
Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. How MRI Works. MRI Developments. Hydrogen Atoms and Magnetic Moments " ". MRI Safety Concerns " ". Metallic fragments in the eye, which are very dangerous as moving these fragments could cause eye damage or blindness Pacemakers, which may malfunction during a scan or even near the machine Aneurysm clips in the brain , which could tear the very artery they were placed on to repair if the magnet moves them Dental implants, if magnetic.
Sources Berman, Phyllis. Coyne, Kristen Eliza. Hornak, Joseph P. May 8, June
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