| X-linked ichthyosis | A form of ichthyosis, due to 3-beta-hydroxysteroidsulfate sulfatase deficiency, that appears at birth or in early infancy and affects males; characterised by scaling predominantly on the neck and trunk but not on the palms and soles; histologically, there is hyperkeratosis, a granular layer in the epidermis, and normal epidermal cell turnover. Synonym: steroid sulfatase deficiency. (05 Mar 2000) |
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| X-linked inheritance | The pattern of inheritance that may result from a mutant gene on an X chromosome. (05 Mar 2000) |
| X-linked locus | Any locus that in normal karyotypes is borne on the X chromosome. (05 Mar 2000) |
| x-omat | A trade name (of Kodak) that has become the generic designation of an automatic processor for X-ray films. (05 Mar 2000) |
| x-point | <radiobiology> Place where the poloidal magnetic field vanishes in such a way that two flux surfaces appear to cross, for example where the main plasma joins the divertor or between magnetic islands. Location where magnetic reconnection takes place. See: magnetic reconnection, divertors, O-point. (09 Oct 1997) |
| X-Pro aminopeptidase | <enzyme> Proline specific exopeptidase Registry number: EC 3.4.11.9 Synonym: x-prolyl aminopeptidase, proline-specific exopeptidase, aminopeptidase p (26 Jun 1999) |
| x-radiation | Radiant energy from an X-ray tube. See: X-ray. (05 Mar 2000) |
| X-ray | <investigation> A type of irradiation used for imaging purposes that uses energy beams of very short wavelengths (0.1 to 1000 angstroms) that can penetrate most substances except heavy metals. This is the commonest form of imaging technique used in clinical practice everywhere in the world with the image captured on photographic film. An AP film is when the beams pass from front-to-back (anteroposterior) and is used for mobile film, particularly on the ward or in casualty. This is the oposite to a PA film (posteroanterior) in which the rays pass through the body from back-to-front. Most films taken in the main radiology department are PA. (20 Jun 2000) |
| X-ray computed tomography | <radiology> Tomography using X-ray transmission and a computer to reconstruct the image. See: computed tomography. (20 Jun 2000) |
| X-ray crystallography | <investigation> A technique of determining the three-dimensional structure of a molecule by analysing the X-ray diffraction patterns of crystals made up of the molecule in question. (06 May 1997) |
| X-ray diffraction | <investigation> Basis of powerful technique for determining the three dimensional structure of molecules, including complex biological macromolecules such as proteins and nucleic acids, that form crystals or regular fibres. Low angle X-ray diffraction is also used to investigate higher levels of ordered structure, as found in muscle fibres. (18 Nov 1997) |
| X-ray dosimetry | Measurement of an administered therapeutic or diagnostic dose and the penetrating power of X-rays. Synonym: X-ray dosimetry. (05 Mar 2000) |
| X-ray film | A film base coated with an emulsion designed for use with X-rays. (12 Dec 1998) |
| X-ray generator | The electronic device that controls production of X-rays in radiography; a key function is rectification of line voltage to produce a smooth direct current voltage to the X-ray tube. (05 Mar 2000) |
| X-ray intensifying screens | Screens which absorb the energy in the X-ray beam that has penetrated the patient and convert this energy into a light pattern which has as nearly as possible the same information as the original x-ray beam. The more light a screen produces for a given input of x-radiation, the less X-ray exposure and thus shorter exposure time are needed to expose the film. In most film-screen systems, the film is sandwiched between two screens in a cassette so that the emulsion on each side is exposed to the light from its contiguous screen. (12 Dec 1998) |