| Allen video enhanced contrast | <procedure> A method for enhancing microscopic images pioneered by R D Allen. The digitised image has the background (an out of focus image of the same microscopic field with comparable unevenness of illumination etc.) subtracted and the contrast expanded to utilise the potential contrast range. Interestingly, it is possible to produce images of objects that are below the theoretical limit of resolution microtubules for example. (18 Nov 1997) |
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| barium contrast material | This radiopaque contrast material is either swallowed or given as a enema for the purpose of demonstrating the anatomy of the gastrointestinal tract using X-rays. (27 Sep 1997) |
| radiopaque contrast | A radiopaque substance (for example metal) will be highlighted (appear white) on a plain X-ray. The use of iodine containing radiopaque contrast dyes allow enhancement of the anatomy demonstrable with conventional X-ray. (27 Sep 1997) |
| radiopaque contrast dye | A radiopaque substance (for example metal) will be highlighted (appear white) on a plain X-ray. The use of iodine containing radiopaque contrast dyes allow enhancement of the anatomy demonstrable with conventional X-ray. (27 Sep 1997) |
| radiopaque contrast material | A radiopaque substance (for example metal) will be highlighted (appear white) on a plain X-ray. The use of iodine containing radiopaque contrast dyes allow enhancement of the anatomy demonstrable with conventional X-ray. (27 Sep 1997) |
| phase-amplitude contrast | <microscopy> The separation and recombination of direct vs. Diffracted rays in a light microscope adjusted to Kohler illumination. at the lower focal plane of the condenser there is an annular diaphragm with an opaque central stop. Through this diaphragm rays are focused as a hollow cone onto the specimen. In the back focal plane of the objective there is a conjugate annular diaphragm (phase plate). If here the undiffracted rays are retarded (by a transparent film of proper thickness on the annulus of the phase plate), bright contrast results. If, instead, the phase-delay film is on the central spot, dark contrast results. With either a bright or a dark-contrast phase plate, the annulus is usually coated with a partially absorbing (very thin) film of silver (Zernike method) or carbon soot (Wilska method) to reduce the higher amplitude (intensity) of the undiffracted rays. (05 Aug 1998) |
| phase contrast | <microscopy> An optical method devised by F. Zernike for converting the focused image of a phase object (one with differences in refractive index or optical path but not in absorbance), which ordinarily is not visible in focus, into an image with good contrast. (05 Aug 1998) |
| phase-contrast microscope | <instrument> A specially constructed microscope that has a special condenser and objective containing a phase-shifting ring whereby small differences in index of refraction are made visible as intensity or contrast differences in the image; particularly useful for examining structural details in transparent specimens such as living or unstained cells and tissues. (05 Mar 2000) |
| phase contrast microscopy | <investigation> A simple nonquantitative form of interference micoscopy of great utility in visualising live cells. Small differences in optical path length due to differences in refractive index and thickness of structures are visualised as differences in light intensity. (18 Nov 1997) |
| microscopy, phase-contrast | A form of interference microscopy in which variations of the refracting index in the object are converted into variations of intensity in the image. This is achieved by the action of a phase plate. (12 Dec 1998) |
| colour-contrast microscope | <instrument> A type of microscope in which the condenser stop is of one colour and the annulus is a complement of it so that unstained objects are observed in one colour on a field of the other. (05 Mar 2000) |
| contrast | A dye injected intravenously during X-ray studies, for example CT, to enhance the image of a tumour. In MR studies, the contrast is called gadolinium. The use of contrast may rarely result in some adverse effects: it also increases the cost (but also accuracy in many cases) of the scan. (16 Dec 1997) |
| contrast agent | A substance that is introduced into or around a structure and, because of the difference in absorption of X-rays by the contrast medium and the surrounding tissues, allows radiographic visualisation of the structure. (18 Nov 1997) |
| contrast bath | A bath in which a part is immersed in hot water for a period of a few minutes and then in cold, the hot and cold periods alternated regularly at intervals, usually half-hours; used to increase the blood flow to the part. (05 Mar 2000) |
| contrast echocardiography | The injection of contrast media of high echo reflectants (e.g., bubbles) to outline a chamber or delineate a shunt within the heart. (05 Mar 2000) |