| X-ray microanalysis | A technique of elemental analysis in the electron microscope based on spectral analysis of the scattered X-ray emission from the specimen induced by the electron beam. Using this technique it is possible to obtain quantitative data on, for example: the calcium concentration in different parts of a cell, but it is necessary to use ultra thin frozen sections. (18 Nov 1997) |
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| X-ray microscope | <instrument> A microscope in which images are obtained by using X-rays as an energy source that are recorded on a very fine-grained film, or the image is enlarged by projection; if film is used, it may be examined with the light microscope at fairly high magnifications. (05 Mar 2000) |
| X-ray therapy | Radiation therapy using X-rays; sometimes used ironically to refer to excessive use of diagnostic radiation. (05 Mar 2000) |
| X-ray, lateral | An X-ray picture taken from the side. (12 Dec 1998) |
| X-ray, pa | An X-ray picture in which the beams pass from back-to-front (posteroanterior). By contrast an ap (anteroposterior) film is one in which the rays pass through the body from front-to-back. (12 Dec 1998) |
| X-rays | Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release energy - in the same energy range as gamma rays (0.010-10 mev), but of non-nuclear origin, of shorter wavelength than ultraviolet; soft X-rays or grenz rays are less penetrating and longer in wavelength than hard X-rays. (12 Dec 1998) |
| X-strabismus | Strabismus in which exotropia is more marked when looking upward or downward than when looking straight ahead. (05 Mar 2000) |
| Xaa | Symbol for unspecified amino acid. (05 Mar 2000) |
| xamoterol | <chemical> A selective beta-1-adrenergic partial agonist. Because it is a partial agonist it acts like an agonist when sympathetic activity is low and as an antagonist when sympathetic activity is high. It reduces myocardial ischemia and improves ventricular function in patients with mild to moderate heart failure. In patients with severe heart failure it has been shown to produce benefits in systolic and diastolic function. Pharmacological action: adrenergic beta-agonists, cardiotonic agent, sympathomimetic. Chemical name: 4-Morpholinecarboxamide, N-(2-((2-hydroxy-3-(4-hydroxyphenoxy)propyl)amino)ethyl)-, (+-)- (12 Dec 1998) |
| Xan | <abbreviation> Xanthine. (05 Mar 2000) |
| xanchromatic | Yellow-coloured. Synonym: xanchromatic, xanthochromic. (05 Mar 2000) |
| xanthamide | <chemistry> An amido derivative of xanthic acid obtained as a white crystalline substance, C2H5O.CS.NH2. Synonym: xanthogen amide. Origin: Xanthic + amide. Source: Websters Dictionary (01 Mar 1998) |
| xanthan gum | <chemical> A polysaccharide gum often used in foods, it is synthesised (fermented) from glucose by the bacterium Xanthomonas campestris. (11 May 1997) |
| xanthate | <chemistry> A salt of xanthic; a xanthogenate. See: Xanthic. Source: Websters Dictionary (01 Mar 1998) |
| xanthelasma | <medicine> See Xanthoma. Origin: NL.; Gr. Xanqos = yellow + 'elasma a metal plate. Source: Websters Dictionary (01 Mar 1998) |