magnetic resonance imaging(redirected from Magnetic resonance tomography)
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Magnetic Resonance Imaging
- Detail. MRI creates precise images of the body based on the varying proportions of magnetic elements in different tissues. Very minor fluctuations in chemical composition can be determined. MRI images have greater natural contrast than standard x rays, computed tomography scan (CT scan), or ultrasound, all of which depend on the differing physical properties of tissues. This sensitivity lets MRI distinguish fine variations in tissues deep within the body. It also is particularly useful for spotting and distinguishing diseased tissues (tumors and other lesions) early in their development. Often, doctors prescribe an MRI scan to more fully investigate earlier findings of the other imaging techniques.
- Scope. The entire body can be scanned, from head to toe and from the skin to the deepest recesses of the brain. Moreover, MRI scans are not obstructed by bone, gas, or body waste, which can hinder other imaging techniques. (Although the scans can be degraded by motion such as breathing, heartbeat, and normal bowel activity.) The MRI process produces cross-sectional images of the body that are as sharp in the middle as on the edges, even of the brain through the skull. A close series of these two-dimensional images can provide a three-dimensional view of a targeted area.
- Safety. MRI does not depend on potentially harmful ionizing radiation, as do standard x-ray and CT scans. There are no known risks specific to the procedure, other than for people who might have metal objects in their bodies.
- Brain and head. MRI technology was developed because of the need for brain imaging. It is one of the few imaging tools that can see through bone (the skull) and deliver high quality pictures of the brain's delicate soft tissue structures. MRI may be needed for patients with symptoms of a brain tumor, stroke, or infection (like meningitis). MRI also may be needed when cognitive and/or psychological symptoms suggest brain disease (like Alzheimer's or Huntington's diseases, or multiple sclerosis), or when developmental retardation suggests a birth defect. MRI can also provide pictures of the sinuses and other areas of the head beneath the face. Recent refinements in MRI technology may make this form of diagnostic imaging even more useful in evaluating patients with brain cancer, stroke, schizophrenia, or epilepsy. In particular, a new 3-D approach to MRI imaging known as diffusion tensor imaging, or DTI, measures the flow of water within brain tissue, allowing the radiologist to tell where the normal flow of fluid is disrupted, and to distinguish more clearly between cancerous and normal brain tissue. The introduction of DTI has led to a technique known as fiber tracking, which allows the neurosurgeon to tell whether a space-occupying brain tumor has damaged or displaced the nerve pathways in the white matter of the brain. This information in turn improves the surgeon's accuracy during the actual operation.
- Spine. Spinal problems can create a host of seemingly unrelated symptoms. MRI is particularly useful for identifying and evaluating degenerated or herniated spinal discs. It can also be used to determine the condition of nerve tissue within the spinal cord.
- Joint. MRI scanning is most commonly used to diagnose and assess joint problems. MRI can provide clear images of the bone, cartilage, ligament, and tendon that comprise a joint. MRI can be used to diagnose joint injuries due to sports, advancing age, or arthritis. MRI can also be used to diagnose shoulder problems, like a torn rotator cuff. MRI can also detect the presence of an otherwise hidden tumor or infection in a joint, and can be used to diagnose the nature of developmental joint abnormalities in children.
- Skeleton. The properties of MRI that allow it to see through the skull also allow it to view the inside of bones. It can be used to detect bone cancer, inspect the marrow for leukemia and other diseases, assess bone loss (osteoporosis), and examine complex fractures.
- The rest of the body. While CT and ultrasound satisfy most chest, abdominal, and general body imaging needs, MRI may be needed in certain circumstances to provide better pictures or when repeated scanning is required. The progress of some therapies, like liver cancer therapy, needs to be monitored, and the effect of repeated x-ray exposure is a concern.
- Medical. People with implanted cardiac pacemakers, metal aneurysm clips, or who have had broken bones repaired with metal pins, screws, rods, or plates must tell their radiologist prior to having an MRI scan. In some cases (like a metal rod in a reconstructed leg) the difficulty may be overcome.
- Injury. Patients must tell their doctors if they have bullet fragments or other metal pieces in their body from old wounds. The suspected presence of metal, whether from an old or recent wound, should be confirmed before scanning.
- Occupational. People with significant work exposure to metal particles (working with a metal grinder, for example) should discuss this with their doctor and radiologist. The patient may need prescan testing-usually a single, regular x ray of the eyes to see if any metal is present.
- For the head and neck, a helmet-like hat is worn.
- For the spine, chest, and abdomen, the patient will be lying on the transmitters.
- For the knee, shoulder, or other joint, the transmitters will be applied directly to the joint.
magnetic resonance imaging(MRI)
The patient having an MRI procedure lies in the bore of the cylindrical magnetic resonance machine; therefore, the test can induce claustrophobia. Furthermore, the person must lie motionless during the test, which can last from 15 to 90 minutes. If patients are susceptible to claustrophobia or cannot tolerate the tedium of lying still in a confined space, a sedative can be given without compromising test results.
mag·net·ic res·o·nance im·ag·ing (MRI),
magnetic resonance imaging
magnetic resonance imagingImaging A noninvasive technique for imaging anatomic structures which involves placing a person in a strong magnetic field and then, using magnetic gradients and brief radiofrequency pulses, determining the resonance characteristics at each point in the area being studied; the creation of images by magnetic resonance–MR, which is a function of the distribution of hydrogen nuclei–protons in the body; the MR image is a computerized interpretation of the physical interaction of unpaired protons with electromagnetic radiation in the presence of a magnetic field; although both have multiplanar capabilities, MRI often trumps CT: no ionizing radiation; contrast between normal and pathologic tissue is greater; confounding bone artifacts do not occur; rapidly moving components appear dark, therefore blood flow through large vessels can be analyzed as a type of natural contrast; the images derive from analysis of the amplitudes and frequencies of the weak signals produced by MR, allowing deduction of the sample's chemical composition, with protons providing the best images. See Burst MRI, Diffusion-weighted imaging, Dynamic imaging, Perfusion-weighted imaging, Short-bore MRI.
mag·net·ic res·o·nance im·a·ging(MRI) (mag-net'ik rez'ŏ-năns im'ăj-ing)
magnetic resonance imagingAbbreviation: MRI
CAUTION!Magnetic resonance imaging is contraindicated in patients with cardiac pacemakers or ferromagnetic aneurysmal clips in place. Metal may become damaged during testing; therefore, health care providers must establish whether the patient has magnetizable metal anywhere on or in the body. Patients should not wear metal objects, e.g., jewelry, hair ornaments, or watches. Patients who have had surgical procedures after which magnetizable metal clips, pins, or other hardware remain in the body should not have this imaging. Some patients with tattoos or permanent cosmetics should also avoid MRI because of the risk of burns.
During imaging, the patient lies on a flat surface that is moved inside a tube encompassed by a magnet (the bore of the gantry). The patient must lie as still as possible. No discomfort occurs as a result of the MRI. Sounds heard during the imaging come from the pulsing of the magnetic field as it scans the body. Confinement during the 30 to 90 min required for scanning may frighten the patient, but the patient can talk to staff by microphone. Relaxation techniques may help claustrophobic patients endure MRI. Comfort measures and analgesics (as necessary and prescribed) should be provided before beginning the scan to offset the discomfort related to prolonged positioning in the scanner. Claustrophobic patients may require a mild sedative, or be better managed in an open MRI scanner which is less confining, however open MRI devices, which use weaker magnetic fields than closed systems may take longer to obtain images and may reveal less detail. Right angle eyeglasses, which divert the patient's gaze outside the bore of the MRI gantry, provide a helpful diversion for some patients. Most patients, however, are able to tolerate the close confinement of the gantry. A nurse or MRI technologist should maintain verbal contact with the patient throughout the procedure. An IV line with no metal components should be in place if the patient’s condition is unstable. See: illustration; brain for illus.; positron emission tomography
magnetic resonance imagingAn important method of body scanning offering a degree of resolution of detail unequalled by any other method. The body is exposed to an intense magnetic field which forces spinning atomic nuclei into a standard orientation. Brief radio waves (electromagnetic signals) applied to the body cause certain atoms, especially the hydrogen in water, to take up a new alignment. In returning to the standard orientation these atoms emit small radio waves that can be picked up and their origin computed. The MRI scanner then reconstitutes images of cross-sections of the body in much the same way as does the CT scanner. The MRI scanner is capable of resolving subtle abnormalities in soft tissue such as brain and nerves. The characteristic plaques of multiple sclerosis, for instance, are clearly revealed as is an area of brain deprived of its blood supply. No ionizing radiation is involved. See also CT SCANNING.
magnetic resonance imaging (MRI)
functional MRI (fMRI) A non-invasive method used to map the various areas of the cortex, as well as brain tumour mapping, by observing brain activity in response to performing a task that engages a specific behaviour (e.g. tests of colour vision, face perception, motion perception, solving a mathematical problem). This is accomplished, within a conventional MRI scanner, by detecting the change in magnetic susceptibility of blood haemoglobin (and thus blood oxygenation) in various areas of the brain. During task execution when a brain region is active there is an increase in blood flow, which is more oxygenated and has a lower concentration of haemoglobin. This leads to a focal increase in MR image intensity, of around 1-5%, which can be detected using appropriate statistical methods. See visual association areas; radiology; positron emission tomography.
mag·net·ic res·o·nance im·a·ging(mag-net'ik rez'ŏ-năns im'ăj-ing)
Patient discussion about magnetic resonance imaging
Q. Anybody to tell me more about MRI scan? had an MRIscan and this has snown adenocarcinoma of endometrium early stage There is no lymphatic involvement but is it possible an MRIscan to miss some tumor?
Q. Can I have a MRI of the knee if I have hemostatic clips in the brain?(also called aneurysm clips)?
Q. i lost a lot of hearing in my ears a couple of years ago,and i had a mri done,the mri said i had ETD, the ETD caused my eushation tube to close,its very uncomfortable,i dont feel the wind or air in my ears no more,i also feel fluid behind my ear drum,i lost a lot of inner hearing,its hard to hear my own voice,and nothing sounds clear,i also feel presser behind my ear drum from the fluid,i went to several doctors for this and i tryed medican and nothing worked,i tryed steriods for the influmation in my ears,that didnt work,i asked many doctors to drain my ears and give me venteling tubes,no doctor will do it,is there anyone out there that has the same ear problem that i do,and the doctors wont give them the tubes?why are the doctors not puting tubes in ears anymore?is it just me.or is everyone getting turned down for the tubes in there ears?i just feel so alone in this does anyone have the same problem and if they do could you share your experence,it would be nice to talk to someone that has the ETD ear problem like me,im in content discomfort,and i dont understand why nobody will help.