| background radiation | <radiobiology> Level of environmental radation due to background sources. Background sources can be natural, such as cosmic rays and natural radioactive elements (principally radon, but including other elements such as isotopes of potassium (which people get substantial amounts of in foods like bananas)). They can also be man-made, such as from fossil-fuel combustion, everyday leakage from nuclear activities, and leftover from atmospheric nuclear weapons tests. Background radiation is usually distinguished from acute radiation, such as from medical X-rays, nuclear accidents, radioisotope therapy, or other short-term doses. The man-made contribution to background radiation is quite small compared to the natural contribution, medical uses dominate human exposure to acute radiation. (09 Oct 1997) |
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| background level | The average amount of a substance present in the environment. Originally referring to naturally occurring phenomena. Used in toxic substance monitoring. (05 Dec 1998) |
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| background retinopathy | <ophthalmology, pathology> Early stage of diabetic retinopathy, it usually does not impair vision. Origin: Gr. Pathos = disease (09 Oct 1997) |
| radiatio | In neuroanatomy, a term applied to any one of the thalamocortical fibre systems that together compose the corona radiata of the cerebral hemisphere's white matter (e.g., optic radiation, acoustic radiation, etc.). Synonym: radiation. Origin: L. (05 Mar 2000) |
| radiatio acustica | The fibres that pass from the medial geniculate body to the transverse temporal gyri of the cerebral cortex by way of the sublentiform part of the internal capsule. Synonym: radiatio acustica. (05 Mar 2000) |
| radiatio corporis callosi | The spreading out of the fibres of the corpus callosum in the centrum semiovale of each cerebral hemisphere. Synonym: radiatio corporis callosi. (05 Mar 2000) |
| radiatio optica | The massive, fanlike fibre system passing from the lateral geniculate body of the thalamus to the visual cortex (striate or calcarine cortex, area 17 of Brodmann); the fibres follow the retrolenticular and sublenticular limbs of the internal capsule into the corona radiata but they curve back along the lateral wall of the temporal and occipital horns of the lateral ventricle to the striate cortex on the medial surface and pole of the occipital lobe. Synonym: radiatio optica, geniculocalcarine radiation, geniculocalcarine tract, Gratiolet's fibres, Gratiolet's radiation, occipitothalamic radiation, Wernicke's radiation. (05 Mar 2000) |
| radiatio pyramidalis | Corticospinal fibres passing from the cortex into the pyramid. Synonym: radiatio pyramidalis. (05 Mar 2000) |