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What is mra for?

Updated: 9/27/2023
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MRI?

DefinitionMagnetic resonance imaging (MRI) is a noninvasive way to take pictures of the body.Unlike x-raysand computed tomographic (CT) scans, which use radiation, MRI uses powerful magnets and radio waves. The MRI scanner contains the magnet. The magnetic field produced by an MRI is about 10 thousand times greater than the earth's.The magnetic field forces hydrogen atoms in the body to line up in a certain way (similar to how the needle on a compass moves when you hold it near a magnet). When radio waves are sent toward the lined-up hydrogen atoms, they bounce back, and a computer records the signal. Different types of tissues send back different signals.Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces dozens or sometimes hundreds of images.For more information, see the specific MRI topics:Abdominal MRIChest MRICranial MRIHeart MRILumbosacral spine MRISpine MRIAlternative NamesMagnetic resonance imaging; Nuclear magnetic resonance (NMR) imagingHow the test is performedYou may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt). Certain types of metal can cause inaccurate images.You will lie on a narrow table, which slides into the middle of the MRI machine. If you fear confined spaces (have claustrophobia), tell your doctor before the exam. You may be prescribed a mild sedative, or your doctor may recommend an "open" MRI, in which the machine is not as close to the body.Small devices, called coils, may be placed around the head, arm, or leg, or other areas to be studied. These devices help send and receive the radio waves, and improve the quality of the images.Some exams require a special dye (contrast). The dye is usually given before the test through a vein (IV) in your hand or forearm. The dye helps the radiologist see certain areas more clearly.During the MRI, the person who operates the machine will watch you from another room. Several sets of images are usually needed, each taking 2 - 15 minutes. Depending on the areas being studied and type of equipment, the exam may take 1 hour or longer.How to prepare for the testDepending on the area being studied, you may be asked not to eat or drink anything for 4 - 6 hours before the scan. Other preparations are usually not needed.The strong magnetic fields created during an MRI can interfere with certain implants, particularly pacemakers. Persons with cardiac pacemakers cannot have an MRI and should not enter an MRI area.You may not be able to have an MRI if you have any of the following metallic objects in your body:Brain aneurysm clipsCertain artificial heart valvesInner ear (cochlear) implantsRecently placed artificial jointsSome older types of vascular stentsTell your health care provider if you have one of these devices when scheduling the test, so the exact type of metal can be determined.Before an MRI, sheet metal workers or any person that may have been exposed to small metal fragments should receive a skull x-ray to check for metal in the eyes.Because the MRI contains a magnet, metal-containing objects such as pens, pocketknives, and eyeglasses may fly across the room. This can be dangerous, so they are not allowed into the scanner area.Other metallic objects are also not allowed into the room:Items such as jewelry, watches, credit cards, and hearing aids can be damaged.Pins, hairpins, metal zippers, and similar metallic items can distort the images.Removable dental work should be taken out just before the scan.How the test will feelAn MRI exam causes no pain. Some people may become anxious inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. You can wear ear plugs to help reduce the noise.An intercom in the room allows you to speak to the person operating the scanner at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.There is no recovery time, unless you need sedation. After an MRI scan, you can resume your normal diet, activity, and medications.Why the test is performedCombining MRIs with other imaging methods can often help the doctor make a more definitive diagnosis.MRI images taken after a special dye (contrast) is delivered into the body may provide additional information about the blood vessels.An MRA, or magnetic resonance angiogram, is a form of magnetic resonance imaging, that creates three-dimensional pictures of blood vessels. It is often used when traditional angiography cannot be done.Normal valuesResults are considered normal if the organs and structures being examined are normal in appearance.What abnormal results meanResults depend on the part of the body being examined and the nature of the problem. Different types of tissues send back different MRI signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue. Consult your health care provider with any questions and concerns.What the risks areMRI contains no ionizing radiation. To date, there have been no documented significant side effects of the magnetic fields and radio waves used on the human body.The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.MRI is usually not recommended for acute trauma situations, because tractionand life-support equipment cannot safely enter the scanner area and the exam can take quite a bit of time.People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.ReferencesBeller GA, Kramer CM. Nuclear cardiology and computed tomography. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 54.Wilkinson ID, Paley MNJ. Magnetic resonance imaging: basic principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. New York, NY: Churchill Livingstone; 2001:chap 5.


Head MRI?

DefinitionA magnetic resonance imaging (MRI) scan of the head is a noninvasive method to create detailed pictures of the brain and surrounding nerve tissues.Unlike x-raysand computed tomographic (CT) scans, which use radiation, MRI uses powerful magnets and radio waves. The MRI scanner contains the magnet. The magnetic field produced by an MRI is about 10 thousand times greater than the earth's.The magnetic field forces hydrogen atoms in the body to line up in a certain way (similar to how the needle on a compass moves when you hold it near a magnet). When radio waves are sent toward the lined-up hydrogen atoms, they bounce back, and a computer records the signal. Different types of tissues send back different signals.Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces dozens or sometimes hundreds of images.See: MRIAlternative NamesNuclear magnetic resonance - cranial; Magnetic resonance imaging - cranial; MRI of the head; MRI - cranial; NMR - cranial; Cranial MRI; Brain MRI; MRI - brain; MRI - headHow the test is performedYou may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt). Certain types of metal can cause inaccurate images.You will lie on a narrow table, which slides into the middle of the MRI machine. If you fear confined spaces (have claustrophobia), tell your doctor before the exam. You may be given a medicine to help you feel sleep and less anxious, or your doctor may recommend an "open" MRI, in which the machine is not as close to the body.Small devices, called coils, are placed around the head. These devices help send and receive the radio waves, and improve the quality of the images.Some exams require a special dye (contrast). The dye is usually given before the test through a vein (IV) in your hand or forearm. The dye helps the radiologist see certain areas more clearly.During the MRI, the person who operates the machine will watch you from another room. Several sets of images are usually needed, each taking 2 - 15 minutes. Depending on the areas being studied and type of equipment, the exam may take 1 hour or longer.How to prepare for the testDepending on the area being studied, you may be asked not to eat or drink anything for 4 - 6 hours before the scan. Other preparations are usually not needed.The strong magnetic fields created during an MRI can interfere with certain implants, particularly pacemakers. Persons with cardiac pacemakers cannot have an MRI and should not enter an MRI area.You may not be able to have an MRI if you have any of the following metallic objects in your body:Brain aneurysm clipsCertain artificial heart valvesInner ear (cochlear) implantsRecently placed artificial jointsSome older types of vascular stentsTell your health care provider if you have one of these devices when scheduling the test, so the exact type of metal can be determined.Before an MRI, sheet metal workers or any person that may have been exposed to small metal fragments should receive a skull x-ray to check for metal in the eyes.Because the MRI contains a magnet, metal-containing objects such as pens, pocketknives, and eyeglasses may fly across the room. This can be dangerous, so they are not allowed into the scanner area.Other metallic objects are also not allowed into the room:Items such as jewelry, watches, credit cards, and hearing aids can be damaged.Pins, hairpins, metal zippers, and similar metallic items can distort the images.Removable dental work should be taken out just before the scan.How the test will feelAn MRI exam causes no pain. Some people may become anxious inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. You can wear ear plugs to help reduce the noise.An intercom in the room allows you to speak to the person operating the scanner at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.There is no recovery time, unless you need sedation. After an MRI scan, you can resume your normal diet, activity, and medications.Why the test is performedMRI provides detailed pictures of the brain and nerve tissues. It also provides clear pictures of parts of the brain that are difficult to see clearly on CT scans.MRI can also show:Blood flowBlood vesselsFluid that surrounds the brain and spinal cordMRI can be used to diagnose and monitor many diseases and disorders that affect the brain, including:Abnormal brain developmentBleeding in the brain (subarachnoid or intracranial hemorrhage)Brain infectionBrain tumorsHormonal disorders (such as acromegaly, galactorrhea, and Cushing syndrome)Multiple sclerosisAn MRI scan of the head can also help:Determine the cause of headachesDetermine the cause of vision problems, hearing loss, speaking difficulties, muscle weakness, or numbness and tinglingDiagnose a new strokeEvaluate changes in thinking or behaviorTell the difference between tumors and normal tissuesMRI is sometimes used to avoid the dangers of angiography or of repeated exposure to radiation.What abnormal results meanThe sensitivity of an MRI depends, in part, on the experience of the radiologist.Abnormal results may be due to:Abnormal blood vessels in the brain (arteriovenous malformations of the head)Acoustic neuromaBleeding in the brainBrain abscessBrain aneurysmsBrain tissue swellingBrain tumorsDamage to the brain from an injuryHydrocephalus (fluid collecting around the brain)Infection of the bones (osteomyelitis)Loss of brain tissueMultiple sclerosisOptic gliomaPituitary tumorStroke or transient ischemic attack (TIA)Structural problems in the brain, brain ventricles, and pituitary glandWhat the risks areMRI contains no ionizing radiation. To date, there have been no documented significant side effects of the magnetic fields and radio waves used on the human body.The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.MRI is usually not recommended for acute trauma situations, because tractionand life-support equipment cannot safely enter the scanner area and the exam can take quite a bit of time.People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.Special considerationsTests that may be done instead of an MRI of the head include:Cranial CT scanPositron emission tomography (PET) scan of the brainSkull x-rayA CT scan may be preferred in the following cases, since it is faster and usually available right in the emergency room:Acute trauma of the head and faceBleeding in the brain (within the first 24 to 48 hours)Early symptoms of strokeSkull bone disorders and disorders involving the bones of the earReferencesWilkinson ID, Paley MNJ. Magnetic resonance imaging: basic principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 5.Saunders D, Jager HR, Murray AD, Stevens JM. Skull and brain: methods of examination and anatomy. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 55.


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