magnetic field gradient - In magnetic resonance imaging, a magnetic field that varies with location, superimposed on the uniform field of the magnet, to alter the resonant frequency of nuclei and allow recovery of their spatial position. -

magnetic resonance angiography (MRA) - (an-jE-Ogra-fE) - A method of angiography utilizing the magnetic properties of tissues and body fluids rather than x-rays to record images. For details see the MR Angiography page.

magnetic resonance cholangiopancreatography - (kO-langE-O-pan-KrE-a-tog-ra-fE) - Magnetic Resonance Cholangiopancreatography (MRCP) is an examination of the bile ducts and pancreas using magnetic resonance imaging.

magnetic resonance imaging (MRI) - A diagnostic radiological modality, using nuclear magnetic resonance technology, in which the magnetic nuclei (especially protons) of a patient are aligned in a strong, uniform magnetic field, absorb energy from tuned radiofrequency pulses, and emit radiofrequency signals as their excitation decays. These signals, which vary in intensity according to nuclear abundance and molecular chemical environment, are converted into sets of tomographic (selected planes) images by using field gradients in the magnetic field, which permits 3-dimensional localization of the point sources of the signals.

malignant - (mu-lig-nant) - Cancerous cells, also called a tumor, able to grow into surrounding tissue, spread to other parts of the body and destroy normal cells. Malignant is also used to describe other medical conditions that are severe and becoming progressively worse.

mammography - (mamog-ru-fE) - Imaging examination of the breast by means of x-rays, used for screening and diagnosis of breast disease. Ultrasound and magnetic resonance may also be used to image the breast. For details see the Mammography page. -

mantle Field Radiation - Radiation therapy to the parts of the body above the diaphragm to the neck, chest and/or underarm areas. -

mask - An immobilization device fitting over a patient's head and face to allow accurate repositioning from day to day. -

mastectomy - Mastectomy is surgical removal of the entire breast. -

mediastinum - The central part of the chest cavity, behind the sternum and between the two lungs. -

medical Oncologist - A cancer doctor who specializes in giving drugs (called chemotherapy or targeted agents) to kill cancer cells or slow down their growth. Some medical oncologists are also hematologists, meaning they have experience treating blood disorders. -

medical radiation physicists - Qualified medical physicists work directly with the doctor in the treatment planning and delivery. They oversee the work of the dosimetrist and help ensure that complex treatments are properly tailored for each patient. Qualified medical physicists are responsible for developing and directing quality control programs for equipment and procedures. They are responsible for making sure the equipment works properly. Medical radiation physicists take precise measurements of radiation beam characteristics and do other safety tests on a regular basis. Qualified medical physicists have doctorates or master's degrees. Qualified medical physicists have completed four year of college. They also have had two to four years of graduate school and typically one to two years of clinical physics training. They are certified by the American Board of Radiology or the American Board of Medical Physics. -

melanocytes - Cells located in the epidermis responsible for the production of melanin. The can suffer malignant transformation giving rise to a tumor known as malignant melanoma. -

melanoma - A malignant tumor, usually in the skin, that develops from a pigmented lesion over a period of months or years. -

membrane - A thin layer of tissue that covers a surface, lines a cavity, or divides space in the body. -

meninges - (me-nin-jEs, plural of mE-ninks) - Thin layers of tissue, or membrane, that surround and cover the brain and spinal cord. -

meningitis - Inflammation in the meninges, the covering of the brain and spinal cord, caused by a virus or bacteria. -

menopause - The point in a woman's life when she stops menstruating, or having periods. -

mesentery - Abdominal membrane that connects the intestines to the abdominal cavity. -

metabolic rate - The amount of energy or heat expended by the body in a given unit of time as a result of the body's metabolism, or all of its chemical processes. -

metabolism - The sum total of all chemical processes in the body that result in growth, energy, waste elimination and other body functions following food digestion and the distribution of nutrients in the blood. -

metastases - The spread of cancer from one part of the body to another. Tumors formed from cells that have spread are called "secondary tumors" and contain cells that are like those in the original (primary) tumor. -

metastases - (met-a-stA-sEs) - The spread of a disease process from one part of the body to another, as in the appearance of abnormal tissue growths (malignant or nonmalignant) in parts of the body remote from the site of the primary tumor. -

metastasize - To spread to another part of the body, usually through the blood vessels, lymph channels, or spinal fluid. -

metastatic tumor - A cancerous tumor formed when cancer cells located elsewhere in the body break away and spread to a new site. -

metformin - See Glucophage. -

microstent - A small wire mesh tube-like device used to hold open an artery following balloon angioplasty.

midline catheter - A special type of catheter used in a vascular access procedure that is inserted inside a major vein for a period of weeks so that blood can be repeatedly drawn or medication and nutrients can be injected into the patient’s bloodstream on regular basis. Unlike a standard intravenous catheter (IV) which is for short term use, a vascular access catheter is more durable and does not easily become blocked or infected. The midline catheter is 4-6 inches in length.

milk ducts - Small tubes that carry breast milk from the lobule to the nipple. -

milliroentgens - (mil-E-rentgen) - One-thousandth of a roentgen (the international unit of exposure dose for x-rays or gamma rays).

minimal and moderate sedation - See sedation, minimal and moderate. -

minimally invasive - A minimally invasive procedure requires a small skin puncture or very limited incision to perform the intervention, which typically involves the insertion of miniaturized instruments. Common examples of minimally invasive procedures would be heart catheterization or temporary placement of an implanted port for chemotherapy. -

modality - (mO-dali-tE) - A form of application or employment of a therapeutic agent or regimen. -

mohs Surgery - Also known as chemosurgery, created by a general surgeon, Dr. Frederic E. Mohs, microscopically controlled surgery that is highly effective for common types of skin cancer and squamous cell carcinoma. -

monoclonal Antibodies - Monoclonal antibodies target certain cells in the body by attaching themselves to those molecules. This causes some cancer cells to die and makes other cells more likely to be killed by radiation and chemotherapy. -

monoclonal antibodies - Proteins composed of laboratory-developed identical molecules used to treat disease. Also called genetically engineered antibodies.

mortality - The rate of death from a particular disease or condition in a defined population. -

mR or MRI Scan - An imaging study using a magnetic field and a computer to create cross-sectional pictures of the body.

mR spectroscopy - A form of magnetic resonance imaging that provides chemical information on an organ or structure of the body at the cellular level. -

multileaf Collimator or MLC - Located in the head of the linear accelerator, it is used to shape the radiation beam. -

multiple myeloma - An uncommon disease that occurs more frequently in men than in women and is associated with anemia, hemorrhage, recurrent infections, and weakness. -

multiple sclerosis - A degenerative disease affecting the central nervous system in which the sheaths around nerve fibers in the brain and spinal cord are damaged. -

musculoskeletal - (mus-kyU-lO-skel-a-tal) - Relating to muscles and to the skeleton, as, for example, the musculoskeletal system.

mV or MeV - Abbreviation for million electron volts, a measure of radiation beam energy . -

myelogram - An x-ray taken after injecting contrast material into the space surrounding the spinal cord. Its purpose is to identify spinal lesions caused by disease or injury.

myelography - A radiographic procedure using contrast material to visualize the spinal column and its contents. See the Myelography page for more information. -

myeloma - A tumor of the bone marrow. -

myocardial infarction - A sudden insufficiency of blood supply that produces the death on the cellular level of a section of the heart wall. -

myocardial perfusion scan - The most common Cardiac Nuclear Medicine procedure, which results in imaging of blood-flow patterns to the heart muscles.

myomas - Masses of fiber and muscle tissue in the wall of the uterus, also known as fibroid tumors. Although these tumors are not cancerous, they may cause heavy menstrual bleeding, pain in the pelvic region and pressure on the bladder or bowel. -

myometrium - The muscular walls of the uterus. -