R
racemose resembling a bunch of grapes.
radial associated with the radius. Applied to the nerve, artery and vein.
radiation the process of heat loss from a body in the form of electromagnetic radiation; this is the only heat transfer process that can take place in a vacuum. Emanation of radiant energy in the form of electromagnetic waves, including gamma rays, infrared, ultraviolet rays, X-rays and visible light rays. Subatomic particles, such as neutrons or electrons, may also be radiated. Radiation may be non-ionizing or ionizing and has many diagnostic and therapeutic uses. See also ionizing radiation.
radiation dosimetry the method of measuring the amount of radiation received by an individual. Also called radiation monitoring.
radiation nephritis inflammation of the renal nephrons; acute associated with hypertension and proteinuria occurring 6–13 months after radiotherapy. chronic associated with urinary protein and casts, nocturia and loss of the ability to concentrate and occurs 1.5–4 years after radiotherapy.
radiation oncologist medical specialist in the treatment of disease by X-rays and other forms of radiation.
radiation pneumonitis inflammation of the lungs caused by the radiation dosage received by the patient.
radiation protection equipment and rules to ensure that staff and patient’s experience safe working practices. See also local rules, dosimetry.
radiation protection advisor a suitably qualified and experienced person whose role is to advise staff on the safe use of ionizing radiation.
radiation protection supervisor a person directly involved with ionization who is responsible for ensuring safe working practices in a specific department and is appointed by the radiation protection advisor.
radiation safety committee a local group of radiation users, advisors and management who discuss matters related to radiation safety.
radiation sickness tissue damage from exposure to ionizing radiation leads to diarrhoea, vomiting, anorexia and bone marrow failure.
radiation treatment planning the method required to graphically display the isodose distribution that results when one or more radiation beams converge on the target volume in external beam therapy.
radical associated with the root of a thing.
radical mastectomy rarely performed operation that involves removal of the breast, pectoralis major muscle and clearance of the axillary lymph nodes.
radical surgery usually extensive surgery which aims to be curative, not palliative.
radical treatment aimed at attempting to kill or remove all malignant cells present.
radiculography radiography of the spinal nerve roots after the introduction of a positive contrast agent via a lumbar puncture to locate the site and size of a prolapsed intervertebral disc. Superseded by CT and MRI.
radioactive exhibiting radioactivity. Describes an unstable atomic nucleus which emits charged particles as it disintegrates. See also radioisotope.
radioactive decay the process by which a nucleus of a radioactive atom spontaneously transforms by one or more discrete energy steps until a stable state is reached. See also half-life.
radioactive disintegration when a stable nuclide, the parent, changes to another nuclide, the daughter, which may be either stable or unstable and therefore radioactive.
radioactive equilibrium equilibrium reached, after radioactive disintegration, when the weight of each nuclide in the atom is inversely proportional to the half-life of the nuclide.
radioactive fallout release of radioactive particles into the atmosphere. Results from industrial processes or accidents, and the testing or use of nuclear weapons.
radioactive source a radioactive substance sealed, in a capsule, which, when inserted into the body, delivers a predetermined dose of radiation.
radiobiology the study of the effects of radiation on living organisms. The use of radioactive tracers to study biological processes.
radiocarbon a radioactive form of the element carbon, such as carbon-14 (14C), used for investigations, for example, absorption tests and research.
radiodermatitis skin inflammation caused by exposure to ionizing radiation.
radiograph a photographic image formed by exposure to X-rays; the correct term for an ‘X-ray’.
radiographer there are two distinct professional disciplines within radiography, diagnostic and therapeutic; they are health professionals qualified in the use of ionizing radiation and other techniques, either in diagnostic imaging or radiotherapy.
radiographic contrast the photographic differences between two adjacent areas on a film.
radiography the use of X-radiation (a) to create images of the body from which medical diagnosis can be made (diagnostic radiography); or (b) to treat a person suffering from a (malignant) disease, according to a medically prescribed regimen (therapeutic radiography). See also radiotherapy.
radioimmunoassay the use of radioactive substances to measure the amount of concentration of an antigen, antibody or protein or substances such as hormones and drugs in the blood.
radioiodinated human serum albumin (RIHSA) used for detection and localization of brain lesions, determination of blood and plasma volumes, circulation time and cardiac output.
radioisotope (radionuclide) any isotope that is radioactive. Forms of an element which have the same atomic number but different mass numbers, exhibiting the property of spontaneous nuclear disintegration. When taken orally or by injection, can be traced by a Geiger counter.
radioisotope scan pictorial representation of the amount and distribution of radioactive isotope present in a particular organ.
radiolabel the modification of a substance to make it radioactive so that it can be used to target a particular organ or body part so that it can be detected in radionuclide imaging.
radiologist a medical specialist in diagnosis by using X-rays and other allied imaging techniques.
radiology the study of the diagnosis of disease by using X-rays and other allied imaging techniques.
radiolucent a substance that has minimal effect on an X-ray beam and therefore the beam does not change as it passes through the substance.
radiomimetic exerting effects similar to those of ionizing radiation, for example, nitrogen mustards.
radionecrosis tissue death caused by radiation.
radionuclide (radioisotope) any nuclide that is radioactive. Forms of an element which have the same atomic number but different mass numbers, exhibiting the property of spontaneous nuclear disintegration. When taken orally or by injection, can be traced by a Geiger counter.
radionuclide generator a system containing a long-lived parent radionuclide which decays to a short-lived daughter radionuclide.
radionuclide therapy the introduction of a radionuclide either orally or by injection; this is then taken up by a targeted organ which receives a calculated radiation dose to maximize the dose of radiation to the treatment area in a patient and minimize the dose to normal tissue.
radiopaque having the property of significantly absorbing X-rays, thus becoming visible on a radiograph. Barium and iodine compounds are used, as contrast agents, to produce artificial radiopacity.
radiosensitivity the relative susceptibility of cells, tissues, organs, organisms, or any other substances to the effects of ionizing radiation.
radiosurgery (stereotactic radiotherapy) a radiotherapy treatment based on a 3D coordinate system designed to achieve a high concentration of absorbed dose to an intracranial target.
radiotherapist (oncologist) medical specialist in the treatment of disease by X-rays and other forms of radiation.
radiotherapy a method of treating disease and eradicating tumour cells by aiming to deliver a therapeutic dose of radiation while preserving normal tissue function and structure.
radiotracer the modification of a substance to make it radioactive so that it can be used to target a particular organ or body part so that it can be detected in radionuclide imaging.
radium (Ra) a radioactive element occurring in nature.
radius the lateral bone of the forearm.
radon seeds capsules containing radon – a radioactive gas produced by the disintegration of radium atoms.
raised intracranial pressure (RIP) an elevation in intracranial pressure is a serious situation. Causes include: tumours, intracranial haemorrhage, trauma causing oedema or haematoma and obstruction to the flow of cerebrospinal fluid. The features depend on the cause, but there may be headache, vomiting, papilloedema, fits, bradycardia, arterial hypertension and changes in the level of consciousness. See also benign intracranial hypertension.
RAM (Random Access Memory) the part of the memory of a computer which can be accessed by the user; the amount of RAM available determines how much data can be stored by the user.
randomized controlled trial (RCT) research study using two or more randomly selected groups: experimental and control. It produces high-level evidence for practice.
random sampling in research. The selection process whereby every person in the population has an equal chance of being selected.
random variable background factors such as environmental conditions that may affect any conditions of the independent variables equally. See also independent variable.
range describes the span of values (lowest – highest) observed in a sample.
range of motion (ROM) the movements possible at a joint.
rank in statistics, the method of organizing data.
raphe a seam, suture, ridge or crease.
rare earths metals having two electrons in the outer shell and either 8 or 9 electrons in the penultimate shell; they are used for the phosphors in television monitors, lasers and modern intensifying screens. Examples include lanthanum, europium, gadolinium, terbium, yttrium.
rarefaction less dense, as applied to diseased bone. In ultrasound the opposite of compression.
raster lines the lines formed when a beam of electrons scans a phosphor to form an image. See also phosphor.
rating the rating of an X-ray unit is the combination of exposure settings which can occur without unacceptably damaging the unit.
ratio data measurement data with a numerical score, for example, height, that has a true zero of 0. It is interval data with an absolute zero. See also interval data.
raw data original received information.
raw data matrix in magnetic resonance imaging it is the initial image before analysis. The points at the centre of the matrix represent areas of low spatial frequencies and the frequencies become higher the further away from the centre.
Rayleigh scattering see coherent scattering.
reactance the opposition to current flow and is produced by capacitors and inductors but not by resistors.
reactionary haemorrhage bleeding that occurs a few hours after an injury but within 24 hours; shock and/or drugs can inhibit the blood flow.
reactive arthritis (Reiter’s syndrome) arthritis that develops in response to infection, usually urogenital, gastrointestinal or throat infection. See also sexually acquired reactive arthritis.
real time a computer controlling, or recording, events as they are actually happening.
real time scanning a method of producing a moving image on a screen.
real-time ultrasonography an ultrasound imaging technique involving rapid pulsing to enable continuous viewing of movement to be obtained, rather than stationary images.
reasonable doubt to secure a conviction in criminal proceedings, the prosecution must establish beyond reasonable doubt the guilt of the accused.
receiver the part of the ultrasonic transducer that detects returning sound waves and converts them to electrical signals.
receiver bandwidth the measure of a range of frequencies within which a magnetic resonance system is tuned to receive the signal. Alteration affects the signal-to-noise ratio, by narrowing the bandwidth the ratio is increased and by broadening it the ratio is decreased.
receiver operating characteristics a method of measuring the ability of an observer to make a diagnosis.
receptaculum receptacle, often forms a reservoir.
receptor sensory afferent nerve ending capable of receiving and transmitting stimuli. A protein situated on or inside a cell membrane which reacts with various molecules, drugs, hormones or cell mediators.
recipient the individual who receives something from a donor such as blood, an organ such as a kidney or bone marrow.
reciprocity the ability to produce an accurate range of densities over a film which reflect the structure being imaged.
