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Get the facts. And the help you need.

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is a superior technique that uses radio waves and a strong magnetic field to provide remarkably clear pictures. As such, it offers an alternative to patients who react to radiopaque intravenous dye. Because of its ability to show soft tissues in exquisite detail, this technology can detect disease and detail blood vessels or other structures. In the kidney system, for example, an MRI can distinguish a hollow cyst from a solid mass, producing excellent three-dimensional images of any tumor's shape. In particular, its super sensitivity can help urologists identify and measure the spread of kidney cancer into the renal vein and inferior vena cava, the large vessel that returns blood to the heart. But while useful in evaluating kidney transplant donors, MRI has limited applicability for the urinary tract since the non-specificity of its signals makes it ineffective in detecting calcifications and bladder abnormalities.

MRI is unique among imaging methods because, unlike radiographs (X-rays,), CT scan and even radioisotope studies, it does not use ionizing radiation. Instead, MRI uses a strong magnet, radio waves and computers to create detailed images of the body. More specifically, lying inside a massive hollow magnet, a patient is exposed to short bursts of powerful non-ionizing radio wave energy, directed at protons, the nuclei of hydrogen or water atoms, in the body. Radio signals generated by first "exciting" and then "relaxing" those protons, are computer-processed to form digital images, reflecting different types of tissue. Typical MRI examinations consist of multiple imaging sequences, each lasting from two to 15 minutes. While these techniques continue to evolve, the beauty of current MRI is that it can be tailored for any clinical question.

This test is performed in a hospital radiology department or in a health care provider's office by a technician under the supervision of a physician. No patient preparation is necessary prior to this test. The patient will be asked to lie on a narrow table, which slides into a large tunnel-like tube within the scanner. The patient's head will be placed in a padded plastic cradle or on a pillow and the table will then slide into the scanner. The patient will be instructed to breathe quietly and normally but to refrain from any movement, coughing or wiggling. The technician will be able to communicate with the patient during this test through the use of an intercom. While the scanner is taking images, the patient will hear rapidly repeating, loud thumping noises coming from the walls of the scanner, so earplugs are usually provided to the patient to reduce the noise. The entire test usually takes between 30 and 60 minutes to complete. Following the test, the patient may resume their normal daily activities.

For generally healthy individuals, MRI poses no risk. But patients with pacemakers, aneurysm clips, ear implants and metallic pieces in vital body locations cannot be imaged safely.

Reviewed January 2011

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Magnetic Resonance Imaging (MRI) Glossary
  • aneurysm: An abnormal widening of a portion of a blood vessel.

  • bladder: The bladder is a thick muscular balloon-shaped pouch in which urine is stored before being discharged through the urethra.

  • calcification: Abnormal hardening or stiffening of a body part.

  • cancer: An abnormal growth that can invade nearby structures and spread to other parts of the body and may be a threat to life.

  • CT scan: Also known as computerized tomography, computerized axial tomography or CT scan. A diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce cross-sectional images of the body. Shows detailed images of any part of the body, including bones, muscles, fat and organs. CT scans are more detailed than general X-rays.

  • cyst: An abnormal sac containing gas, fluid or a semisolid material. Cysts may form in kidneys or other parts of the body.

  • gene: The basic unit capable of transmitting characteristics from one generation to the next.

  • inferior vena cava: A large vein that receives blood from the lower extremities, pelvis and abdomen and empties it into the right atrium of the heart.

  • inferior vena cava: A large vein that receives blood from the lower extremities, pelvis and abdomen and empties it into the right atrium of the heart.

  • intravenous: Also referred to as IV. Existing or occurring inside a vein.

  • ionizing radiation: Electromagnetic radiation that produces ionization in a medium through which it passes.

  • ions: Electrically charged atoms.

  • kidney: One of two bean-shaped organs that filter wastes from the blood and discharge these waste products in urine. The kidneys are located on either side at the level of the 12th ribs toward the back. The kidneys send urine to the bladder through tubes called ureters.

  • kidney cancer: The most common type of urologic cancer. The kidneys are two large organs that sit in the back part of the abdominal cavity. The kidney's main function is to filter the blood and clean the body of excess water, salt, and waste products. Tumors of the kidney occur twice as often in men as in women and usually occur between the ages of 50 and 70.

  • MRI: Also referred to a magnetic resonance imaging. A diagnostic procedure that uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs and structures within the body.

  • non-ionizing: Not able to produce ions.

  • nuclei: Plural of nucleus, which is the central part of a living cell that contains chromosomes and other genetic information necessary to control cell growth and reproduction.

  • radiation: Also referred to as radiotherapy. X-rays or radioactive substances used in treatment of cancer.

  • radio waves: Electromagnetic waves.

  • radioisotope: A particular form of chemical element that is radioactive.

  • radiopaque: Blocking the passage of X-rays and other forms of electromagnetic radiation.

  • renal: Pertaining to the kidneys.

  • renal vein: Short, thick vein which returns blood from the kidneys to the vena cava.

  • tissue: Group of cells in an organism that are similar in form and function.

  • transplant: Replacement of a diseased organ with a healthy one. A kidney transplant may come from a living donor or from someone who has just died.

  • tumor: An abnormal mass of tissue or growth of cells.

  • urinary: Relating to urine.

  • urinary tract: The system that takes wastes from the blood and carries them out of the body in the form of urine. Passageway from the kidneys to the ureters, bladder and urethra.

  • urologist: A doctor who specializes in diseases of the male and female urinary systems and the male reproductive system. Click here to learn more about urologists. (Download the free Acrobat reader.)

  • vas: Also referred to as vas deferens. The cordlike structure that carries sperm from the testicle to the urethra.

  • vein: Blood vessel that drains blood away from an organ or tissue.

  • vena cava: Vein carrying blood to the heart.

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