narcotic - A substance that is used medically to relive pain and/or produce a state of drowsiness or sleep. -

nasal cavity - A system of air channels connecting the nose with the back of the throat. -

natural background exposure - Radiation is a natural part of life. It has existed since the beginning of time and is an integral part of the universe in which we live. Life as we know it on earth has evolved in the presence of radiation. Radiation comes to us from many sources both natural and man-made. These sources include cosmic radiation from outer space, radiation from the soil and buildings, and natural isotopes in our own bodies. Cosmic radiation and terrestrial radiation vary with location.

necrosis - The death of living tissue. -

needle aspiration - The removal of living tissue for microscopic examination by suction through a fine needle attached to a syringe. The procedure is used primarily to obtain cells from a lesion containing fluid. -

needle biopsy - Removal of tissue or suspensions of cells from living patients through a small needle for diagnostic examination. -

needle electrode - A fine wire through which electrical current may flow in or out when attached to a power source. There are two types of needle electrodes: simple straight needles and a straight, hollow needle that contains several retractable electrodes that extend when needed. A needle electrode is used to carry high frequency electrical currents that create heat to ablate or destroy diseased tissue (called radiofrequency ablation) or seal blood vessels. -

neoplasm - (nE-O-plaz-um) - An abnormal tissue that grows by cellular proliferation more rapidly than normal and continues to grow after the stimuli that initiated the new growth cease. Neoplasms show partial or complete lack of structural organization and functional coordination with the normal tissue, and usually form a distinct mass of tissue, which may be either benign (benign tumor) or malignant (cancer). -

nephrogenic - Of or related to the kidney. -

nephrogenic systemic fibrosis - A rare complication in patients with kidney disease that undergo an MRI with contrast material that causes a thickening of the skin, organs and other tissues. -

nephropathy - Damage to or disease of the kidney. -

neuro -oncologist - A doctor who specializes in diagnosing and treating brain tumors and other tumors of the nervous system.

neurologic - Pertaining to the nervous system and its disorders. -

neurologist - A physician who specializes in the diagnosis and treatment of diseases and conditions related to the brain and nervous system. -

neuroradiology - (nUr-rO-rA-dE-ol-O-jE) - The clinical subspecialty concerned with the diagnostic radiology of diseases of the central nervous system, head, and neck.

neurostimulators - Devices that are implanted into the spine and connected to internal or external generators to stimulate the nerves as a means of disrupting pain signals or causing organs to function more efficiently. -

neurosurgeon - A physician trained in surgery of the nervous system and who specializes in surgery on the brain and other parts of the nervous system. Sometimes called a "brain surgeon." -

neutron Beam Therapy - A specialized type of external beam radiation therapy using neutrons to treat tumors. -

nodule - A small, solid lump. -

non-hodgkin's Lymphoma - Also called NHL, it is a cancerous growth of the cells that make up the lymph nodes. It is eight times more common than Hodgkin's lymphoma.

non -pharmacological sedation - See sedation, non-pharmacological.

noninvasive - (nonin-vA-siv) - A noninvasive procedure does not require any skin incision or the insertion of any instruments or medical devices. Examples include CT and MR scanning and ultrasound. -

nonradiologic - Not related to radiology. -

nonrepudiation - Nonrepudiation ensures that a party cannot argue the validity of a statement or contract, that a transferred message has been sent and received by the parties claiming to have sent and received the message; methods include digital signature, the use of public and private keys, and auditing of all user activity. -

nSAID - A non-steroidal antiinflammatory drug that reduces swelling and pain, such as aspirin and ibuprofen.

nuclear medicine - The clinical discipline concerned with the diagnostic and therapeutic uses of radionuclides (an isotope of artificial or natural origin that exhibits radioactivity), excluding the therapeutic use of sealed radiation sources. -

nucleus - The center part of intervertebral discs, sponge-like cushions between the vertebrae, or bones, of the spine. The nucleus is filled with a soft, rubber-like material.

numbing agent - See local anesthetic ("numbing agent") -