Category: R

The characteristic time it takes for a sample of atoms, whose nuclei have first been aligned along a static magnetic field and then excited to a higher energy (nuclear magnetic resonance) state by a radiofrequency signal, to return to a lower energy equilibrium state. Two time parameters are used to describe the return (relaxation) to…

A measure of the cell-killing ability of a particular radiation compared to a reference radiation. The reference is 250 keV x rays. The ratio of cells killed with the test radiation over that of the 250 keV radiation is the RBE.  

Elevation of temperature over an extended volume of tissue.  

Control of cancer in sites that represent the first stages of spread from the local origin.  

The scanning or imaging (with ultrasound, say) of an entire object, or a cross-sectional slice of the object, at a single moment. To produce such a “snapshot” image scanning data must be recorded quickly over a very short time rather than by accumulation over a longer period.  

For many years the fluorescent material calcium tungstate was used as the basis of x-ray intensifying screens. In recent years, new materials including the rare earths yttrium and gadolinium have found application in such devices. These rare earths enable lower radiation doses to be used while producing acceptable film densities.  

A radioactive substance used for most of this century to fill the needles and tubes required for brachytherapy. Radium use is now being eliminated since cesium-137 has similar energy characteristics and is not subject to hazardous leakage as radium sources sometimes are.  

Drugs that enhance the killing effect of radiation on ceils. If radiosensitizers can be selectively introduced into the cells of a tumor while being absent from the surrounding normal tissue, the effect of irradiating the tumor will be increased, presumably leading to improved survival for the patient. Radiosensitizers are being studied in clinical trials.  

That portion of the electromagnetic spectrum with frequencies lower than about 10¹⁰ Hz.  

A measure of the response of tissue to ionizing radiation.