Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) uses radiofrequency waves and a strong magnetic field to generate images of the body. Electromagnetic energy is released from a person when he or she is exposed to radiofrequency waves in the magnetic field of the MRI machine. This energy is measured and analyzed by a computer, which creates two- or three-dimensional cross section (slices) images of tissue.
MRI is valuable in providing clear pictures of soft-tissue structures of the body, such as the heart, lungs, liver and other organs. It is used to diagnose a broad range of diseases including cancer, heart and vascular disease, stroke, and joint and musculoskeletal disorders. MRI is often used to detect cancer in the brain and spinal cord, head, neck and musculoskeletal system. MRI is also used in imaging gynecologic and breast cancer.
Specialized MRI Scans
Cardiac magnetic resonance imaging (cardiac MRI) is a noninvasive method to diagnose heart muscle disease and provides detailed images of the beating heart. Cardiac magnetic resonance angiography (cardiac MRA) is a study of blood vessels to detect heart disorders, stroke and blood vessel diseases. Neither procedure uses X-rays or radiation.
Functional MRI (fMRI)
Functional MRI provides detailed images of moment-to-moment changes in brain activity. fMRI measures brain function to determine where vital areas, such as movement or speech, are located in relation to a tumor, epilepsy activity or other diseased part of the brain. fMRI takes detailed pictures of the brain very quickly, identifying areas where nerves become active in response to different tasks. For example, a patient may be asked to perform a task that activates his or her memory. At the same time, an MRI image of his or her brain is taken to provide a detailed picture of the exact brain activation during this memory task.
Magnetic Resonance Spectroscopy (MRS)
MRS is a type of MRI that aids in determining a tumor’s cellular density and rate of growth. MRS measures chemicals within the body and brain without removing tissue or blood samples and without using radioactive tracers. MRS relies on the fact that different chemicals produce energy at different frequencies when stimulated in a magnetic field.
Diffusion MRI assesses how easily water moves across minute distances — a process called diffusion. Healthy cells have unbroken outer membranes that slow the movement of water. The membranes around dying or dead cells break down, allowing water to move or diffuse freely. In diffusion MRI, an MRI machine is programmed to be sensitive to water movement in tissue. For example, in diagnosing a stroke, diffusion MRI can rapidly view regions in the brain where blood flow is cut off by a hemorrhage or clot.
Regional Cerebral Blood Volume (RCBV)
RCBV uses MRI to assess blood flow in the brain to detect tumors, blood vessel disease, central nervous system problems and other disorders. RCBV is also performed to check blood volume in the brain before and after various treatments.