|Medical Dictionary - Dictionary of Medicine and Human Biology|
1. The science of high-energy radiation and of the sources and the chemical, physical, and biologic effects of such radiation; the term usually refers to the diagnosis and treatment of disease. 2. The scientific discipline of medical imaging using ionizing radiation, radionuclides, nuclear magnetic resonance, and ultrasound. SYN: diagnostic r.. [radio- + G. logos, study] cardiovascular r. the clinical subspecialty of r. concerned with diagnosis and treatment of diseases of the vascular system. chest r. the clinical subspecialty concerned with the diagnostic r. of diseases of the thorax, especially of the heart and lungs. diagnostic r. SYN: r. (2) . interventional r. the clinical subspecialty that uses fluoroscopy, CT, and ultrasound to guide percutaneous procedures such as performing biopsies, draining fluids, inserting catheters, or dilating or stenting narrowed ducts or vessels. pediatric r. the clinical subspecialty concerned with the radiologic manifestations of diseases of children. therapeutic r. SYN: radiation oncology.
A region of a radiograph showing increased exposure, either because of greater transradiancy of the corresponding portion of the subject or because of inhomogeneity in the source of radiation, such as off-center positioning.
Relatively penetrable by x-rays or other forms of radiation. Cf.:radiopaque. [radio- + L. lucens, shining]
A probe or sound. [L. dim. of radius, spoke]
A device for determining the penetrative power of x-rays. SYN: roentgenometer. [radio- + G. metron, measure]
A sensitive thermopile designed for the measurement of minute changes in radiant energy.
Imitating the biologic effects of radiation, as in the case of chemicals such as nitrogen mustards. [radio- + G. mimetikos, imitative]
Relating to the radius and the neighboring muscles; denoting certain nerves and muscular branches of the radial artery.
Necrosis due to radiation; e.g., after excessive exposure to x- or gamma rays. See radiation burn.
Neuritis caused by prolonged or repeated exposure to x-rays or radium.
A radioactive isotope of nitrogen; e.g., 13N.
An isotope of artificial or natural origin that exhibits radioactivity.
The x-ray shadow of a radiopaque object. SYN: radiodensity.
Relating to the radial or lateral side of the palm.
Exhibiting relative opacity to, or impenetrability by, x-rays or any other form of radiation. Cf.:radiolucent. SYN: radiodense. [radio- + Fr. opaque fr. L. opacus, shady]
A branch of radiology or pathology concerned with the effects of radiation on cells and tissues. Cf.:radiobiology.
Radiographic measurement of the pelvis. See pelvimetry.
A radioactive chemical or pharmaceutic preparation, labeled with a radionuclide in tracer or therapeutic concentration, used as a diagnostic or therapeutic agent.
Morbid fear of radiation, as from x-rays or nuclear energy. [radio- + G. phobos, fear]
A radioactive isotope of phosphorus; e.g., 32P.
SYN: radiotelemetering capsule.
A radioactive isotope of potassium; e.g., 40K.
Substance that prevents or lessens the effects of radiation.
1. A receptor that normally responds to radiant energy such as light or heat. 2. A receptor used as a binding agent for unlabeled and radiolabeled analyte in a type of competitive binding assay called r. assay.
Indicates cells or tissues that are less affected than average mammalian cells on exposure to radiation; when applied to neoplasms, indicates less susceptibility to damage from therapeutic radiation than the surrounding host tissues.
Obsolete term for fluoroscopy. [radio- + G. skopeo, to view]
Readily affected by radiation. Cf.:radioresistant.
The condition of being readily affected by radiant energy.
The use of chemotherapy or other agents that increase the sensitivity of tissue to the effects or radiation therapy, usually by inhibiting cellular repair or increasing the percentage of cells in mitotic phases of the growth cycle.
A chemical substance that increases the radiosensitivity of tissues; restoring normal tissue oxygen tension to an anoxic region is also an effective r..
A radioactive isotope of sodium; e.g., 24Na.
Simultaneous viewing of two radiographs made in slightly different projections, usually with a device that reflects the image of one on each eye, allowing three-dimensional visualization of an object in relation to others. See stereoradiography, stereoscope. [radio- + G. stereos, solid, + skopeo, to view]
A radioactive isotope of strontium; e.g., 90Sr.
A radioactive isotope of sulfur; e.g., 35S.
Radiotherapy with a sharply delimited field, optimistically considered to be equivalent to resecting the irradiated region.
See telemetry, biotelemetry.
Relating to radiotherapy or to radiotherapeutics.
The study and use of radiotherapeutic agents.
One who practices radiotherapy or is versed in radiotherapeutics. SYN: radiation oncologist.
SYN: radiation oncology. mantle r. r. with shielding of uninvolved radiosensitive structures or organs.
Diathermy effected by heat from radiant sources. [radio- + G. therme, heat]
The destruction of thyroid tissue by administration of radioactive iodine.
SYN: radioactive thyroxine.
Radiation sickness caused by the products of disintegration produced by the action of x-rays or other forms of radioactivity and by the depletion of certain cells and enzyme systems from the organism. [radio- + G. toxikon, poison, + haima, blood]
A radionuclide or radiolabeled chemical; a radioactive tracer.
Allowing relatively free transmission of radiant energy. Cf.:radiolucent.
Affected by radiation. [radio- + G. trope, a turning]
Relating to both radius and ulna.
SYN: root amputation. [L. radix, root, + G. ektome, excision]
radium (Ra) (ra′de-um)
A metallic element, atomic no. 88, extracted in very minute quantities from pitchblende; 226Ra, its longest-lived isotope, is produced as an intermediate in the uranium series by the emission of an α particle from thorium-230 (ionium); 226Ra emits α particles and gamma rays with a half-life of 1,599 years breaking down to 222Rn; chemically, it is an alkaline earth metal with properties similar to those of barium. Its therapeutic action is similar to that of x-rays, since the α emission is filtered out. [L. radius, ray]
radius, gen. and pl. radii (ra′de-us, ra′de-i) [TA]
1. [NA] The lateral and shorter of the two bones of the forearm. 2. A straight line passing from the center to the periphery of a circle. SYN: radio- (3) . [L. spoke of a wheel, rod, ray] r. fixus a line passing from the hormion to the inion. radii of lens [TA] 9–12 faint lines on the anterior and posterior surfaces of the lens that radiate from the poles toward the equator; they mark the lines along which the ends of lens fibers abut. SYN: radii lentis [TA] , lens stars (1) , lens sutures. radii lentis [TA] SYN: radii of lens.
radix, gen. radicis, pl .radices (ra′diks, ra-di′sis, ra′di-sez or ra-di′sez) [TA]
1. SYN: root (1) . 2. SYN: root of tooth. 3. The hypothetical size of the birth cohort in a life table, commonly 1,000 or 100,000. [L.] r. accessoria [TA] SYN: accessory root of tooth. r. anterior nervi spinalis [TA] SYN: anterior root of spinal nerve. r. arcus vertebrae SYN: pedicle of arch of vertebra. r. brevis ganglii ciliaris SYN: parasympathetic root of ciliary ganglion. r. buccalis [TA] SYN: buccal root of tooth. r. clinica dentis [TA] SYN: clinical root of tooth. r. cranialis nervi accessorii [TA] SYN: cranial root of accessory nerve. r. dentis [TA] SYN: root of tooth. r. dorsalis nervi spinalis SYN: posterior root of spinal nerve. r. facialis SYN: nerve of pterygoid canal. r. inferior ansae cervicalis [TA] SYN: inferior root of ansa cervicalis. r. inferior nervi vestibulocochlearis SYN: cochlear root of VIII nerve. r. lateralis nervi mediani [TA] SYN: lateral root of median nerve. r. lateralis tractus optici [TA] SYN: lateral root of optic tract. r. linguae [TA] SYN: root of tongue. r. longa ganglii ciliaris SYN: sensory root of ciliary ganglion. r. medialis nervi mediani [TA] SYN: medial root of median nerve. r. medialis tractus optici [TA] SYN: medial root of optic tract. r. mesenterii [TA] SYN: root of mesentery. r. motoria nervi spinalis anterior root of spinal nerve. r. motoria nervi trigemini [TA] SYN: motor root of trigeminal nerve. r. nasi [TA] SYN: root of nose. r. nasociliaris ganglii ciliaris sensory root of ciliary ganglion. r. nervi facialis SYN: root of facial nerve. r. nervi oculomotorii ad ganglion ciliare parasympathetic root of ciliary ganglion. radices nervi trigemini SYN: roots of trigeminal nerve, under root. r. oculomotoria ganglii ciliaris parasympathetic root of ciliary ganglion. r. parasympathica ganglii submandibularis SYN: chorda tympani. radices parasympathicae gangliorum pelvicorum pelvic splanchnic nerves, under nerve. r. parasympathica ganglii ciliaris [TA] SYN: parasympathetic root of ciliary ganglion. r. parasympathica ganglii otici lesser petrosal nerve. r. penis [TA] SYN: root of penis. r. pili SYN: hair root. r. posterior nervi spinalis [TA] SYN: posterior root of spinal nerve. r. pulmonis [TA] SYN: root of lung. r. sensoria ganglii ciliaris [TA] SYN: sensory root of ciliary ganglion. r. sensoria ganglii pterygopalatini [TA] SYN: sensory root of pterygopalatine ganglion. r. sensoria ganglii sublingualis [TA] SYN: sensory root of sublingual ganglion. r. sensoria ganglii submandibularis [TA] SYN: sensory root of submandibular ganglion. r. sensoria nervi spinalis posterior root of spinal nerve. r. sensoria nervi trigemini [TA] SYN: sensory root of trigeminal nerve. r. spinalis nervi accessorii [TA] SYN: spinal root of accessory nerve. r. superior ansae cervicalis [TA] SYN: superior root of ansa cervicalis. r. superior nervi vestibulocochlearis SYN: vestibular root. r. sympathica ganglii ciliaris [TA] SYN: sympathetic root of ciliary ganglion. r. sympathica ganglii otici [TA] SYN: sympathetic root of otic ganglion. r. sympathica ganglii pterygopalatini deep petrosal nerve. r. sympathica ganglii sublingualis [TA] SYN: sympathetic root of sublingual ganglion. r. sympathica ganglii submandibularis [TA] SYN: sympathetic root of submandibular ganglion. r. unguis SYN: root of nail. r. ventralis nervi spinalis SYN: anterior root of spinal nerve. r. vestibularis SYN: vestibular root.
radon (Rn) (ra′don)
A gaseous radioactive element, atomic no. 86, resulting from the breakdown of radium; of the isotopes with mass numbers between 198 and 228, only 222Rn is medically significant as an alpha-emitter, with a half-life of 3.8235 days; it is used in the treatment of certain malignancies. Poorly ventilated homes in some parts of the country accumulate a dangerous amount of naturally occurring r. gas. [from radium]
Georg Johann, Norwegian ophthalmologist, 1889–1956. See R. paratrigeminal syndrome.
A dextrorotatory trisaccharide, occurring in cotton seed and in the molasses of beet root, composed of d-galactose, d-glucose, and d-fructose and formed by transfer of d-galactose from UDP-d-galactose to sucrose; many seeds are rich in r.. SYN: gossypose, melitose, melitriose.
Violent anger; a total discharge of the sympathetic portion of the autonomic nervous system. [Fr., fr. L. rabies, violent anger, fr. rabo, to rave] sham r. a quasiemotional state, characterized by manifestations of fear and anger upon trifling provocation; produced in animals by the removal of the cerebral cortex (decortication).
Richard H., U.S. psychiatrist, *1936. See Holmes-R. questionnaire.
Hermann, U.S. respiratory physiologist, 1912–1990. See R.-Otis sample.
A genus of tapeworms (family Davaineidae, order Cyclophyllidea), three species of which, R. madagascariensis or R. demerariensis, R. asiatica, and R. formsana, have been found in humans. However, the identification of many of these worms found in humans has been questioned.
Infection of rodents and monkeys, and occasionally humans, with tapeworms of the genus Raillietina.
George, English anatomist, 1801–1884. See R. corpuscles, under corpuscle.
Ambiguous term for an added sound heard on auscultation of breath sounds; used by some to denote rhonchus and by others for crepitation. SYN: crackle. [Fr. rattle] amphoric r. sound heard through the stethoscope associated with the movement of fluid in a lung cavity communicating with a bronchus. atelectatic r. transitory light crackling sound that disappears after deep breathing or coughing. bubbling r. moist sound heard through the stethoscope as a result of air entering portions of lung tissue containing exudate and thus creating bubbles; sometimes associated with resolving pneumonia or small lung cavities. cavernous r. a resonating, bubbling sound caused by air entering a cavity partly filled with fluid. SYN: cavernous rhonchus. clicking r. short, sticking sound usually associated with opening of small bronchi on deep breathing, sometimes heard in early pulmonary tuberculosis. consonating r. a resonant r. produced in a bronchial tube and heard through consolidated lung tissue. crackling r. (krak′ling) very fine sounds produced by fluid in very small airways in pneumonia or congestive heart failure. crepitant r. a fine bubbling or crackling sound produced by air mixing with very thin secretions in the smaller bronchial tubes. SYN: vesicular r.. dry r. a harsh or musical breath sound produced by a constriction in a bronchial tube or the presence of a viscid secretion narrowing the lumen. gurgling r. coarse sound heard over large cavities or over trachea nearly filled with secretions. guttural r. sound heard over the lung but resulting from upper airway obstruction. metallic r. a r. of metallic quality caused by resonance in a large cavity. moist r. a bubbling r. caused by air mixing with a fluid exudate in the bronchial tubes or a cavity. mucous r. a bubbling r. heard on auscultation over bronchial tubes containing mucus. palpable r. a vibration that can be felt accompanying a low-pitched, hard, musical, or sonorous r.. pleural r. SYN: pleural rub. sibilant r. a whistling sound caused by air moving through a viscid secretion narrowing the lumen of a bronchus. SYN: whistling r.. Skoda r. a r. in a bronchus heard through an area of consolidated tissue in pneumonia. sonorous r. a cooing or snoring sound often produced by the vibration of a projecting mass of viscid secretion in a large bronchus. subcrepitant r. a very fine crepitant r.. vesicular r. SYN: crepitant r.. whistling r. SYN: sibilant r..
A selective estrogen receptor modulator (SERM) that has estrogen-agonistic effects on bone and lipid metabolism but estrogen-antagonistic effects on breast and uterus; used in the prophylaxis of osteoporosis after menopause.R. is a benzothiophene derivative that binds to estrogen receptor sites. Besides conferring protection against osteoporosis after menopause, it has been shown to improve bone mineral density and reduce the risk of fractures in established osteoporosis. The reduction in fracture risk is greater than would be expected from the increase in bone density. Unlike tamoxifen, which also reduces osteoporosis risk, r. does not heighten the risk of endometrial cancer. Although r. increases bone mineral density to a lesser degree than estrogen, it reduces the risk of breast cancer rather than increasing it as estrogen may perhaps do. Hence it may be preferred for women who fear breast cancer or are at high risk for it. Like hormone replacement therapy with estrogen-progestogen, r. decreases LDL cholesterol, fibrinogen, and lipoprotein(a), increasing HDL cholesterol without raising triglycerides. It does not relieve hot flashes; in fact, it causes them in 25% of patients. Like estrogen replacement therapy, it is contraindicated in pregnancy and in women with a history of thromboembolism. Whether it protects against cardiovascular disease and Alzheimer dementia as estrogen does has not yet been determined.
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