| cytometry | The counting of cells, especially blood cells, using a cytometer or haemocytometer. Flow cytometry, a method of measuring fluorescence from stained cells that are in suspension and flowing through a narrow orifice, usually in combination with one or two lasers to activate the dyes; used to measure cell size, number, viability, and nucleic acid content with the aid of acridine orange, Kasten's fluorescent Feulgen stain, ethidium bromide, trypan blue, and other selected staining reagents. Synonym: flow cytophotometry. (05 Mar 2000) |
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| cytometry, flow | Analysis of biological material by detection of the light-absorbing or fluorescing properties of cells or subcellular fractions such as chromosomes passing in a narrow stream through a laser beam. Flow cytometry is used with automated sorting devices to sort successive droplets of the stream into different fractions depending on the fluorescence emitted by each droplet. (12 Dec 1998) |
| image cytometry | A technique encompassing morphometry, densitometry, neural networks, and expert systems that has numerous clinical and research applications and is particularly useful in anatomic pathology for the study of malignant lesions. The most common current application of image cytometry is for DNA analysis, followed by quantitation of immunohistochemical staining. (12 Dec 1998) |
| flow cytometry | <technique> Flow cytometry is an emerging technique which holds great promise for the separation, classification and quantitation of blood cells and antibodies which affect blood cells. Complex computerised instruments are used to pass a monocellular stream of cells, platelets or other microscopic particulate elements through a beam of laser light. The cells are categorised first by size and then computer analysed to sort the mixture of cellular elements into cell type by size. Cells are labelled with fluorescent dye and then passed, in suspending medium, through a narrow dropping nozzle so that each cell is in a small droplet. A laser based detector system is used to excite fluorescence and droplets with positively fluorescent cells are given an electric charge. Charged and uncharged droplets are separated as they fall between charged plates and so collect in different tubes. The machine can be used either as an analytical tool, counting the number of labelled cells in a population or to separate the cells for subsequent growth of the selected population. Further sophistication can be built into the system by using a second laser system at right angles to the first to look at a second fluorescent label or to gauge cell size on the basis of light scatter. The great strength of the system is that it looks at large numbers of individual cells and makes possible the separation of populations with, for example: particular surface properties. Tabulation of counted data in conjunction with size analysis enables determination of relative percentages of each specific cellular subset for which monoclonal antibody conjugates are utilised, even when the size of the cell is identical to other subset species. Flow cytometry is a slightly imprecise but common term for the use of the Fluorescence-activated Cell Sorter (FACS). (01 Dec 1998) |
| calorimetry, differential scanning | Differential thermal analysis in which the sample compartment of the apparatus is a differential calorimeter, allowing an exact measure of the heat of transition independent of the specific heat, thermal conductivity, and other variables of the sample. (12 Dec 1998) |
| magnetic resonance scanning | A special imaging technique used to image internal stuctures of the body, particularly the soft tissues. An MRI image is often superior to a normal X-ray image. It uses the influence of a large magnet to polarize hydrogen atoms in the tissues and then monitors the summation of the spinning energies within living cells. Images are very clear and are particularly good for soft tissue, brain and spinal cord, joints and abdomen. These scans may be used for detecting some cancers or for following their progress. Acronym: MRI (11 Nov 1997) |
| ventilation perfusion scanning | <investigation, radiology> A nuclear medicine test that involves the inhalation of a radioactive gas and the injection of a radioactive compound into the bloodstream. A special camera measures the radioactive compound and generates a image of the lungs. Comparisons are made between the images generated. Pulmonary embolism can be diagnosed using this procedure. (12 Jan 1998) |
| vq scanning | A nuclear medicine test that involves the inhalation of a radioactive gas and the injection of a radioactive compound into the bloodstream. A special camera measures the radioactive compound and generates a image of the lungs. Comparisons are made between the images generated. Pulmonary embolism can be diagnosed using this procedure. (27 Sep 1997) |
| microscopy, electron, scanning | Microscopy in which the object is examined directly by an electron beam scanning the specimen point-by-point, giving the surface image a three-dimensional quality. (12 Dec 1998) |
| microscopy, electron, scanning transmission | A type of electron microscopy which scans with an extremely narrow beam that is transmitted through the sample. The detection apparatus produces an image whose brightness depends on the atomic number of the sample. It should not be confused with microscopy, electron scanning nor with microscopy, electron, transmission (see microscopy, electron). (12 Dec 1998) |
| microscopy, scanning tunneling | Electron microscopy in which a very sharp conducting needle is swept just a few angstroms above the surface of a sample. The tiny tunneling current that flows between the sample and the needle tip is measured and from this are produced three-dimensional topographs, with a lateral resolution often as good as 1-2 angstroms and a vertical resolution of less than 1 angstrom. Due to their composition, biological samples are usually coated with a conductive layer, e.g., by depositing a thin metal or carbon film on top of the sample, to enhance their conductivity. (12 Dec 1998) |
| scanning | The act of imaging by traversing with an active or passive sensing device, often identified by the technology or device employed. (05 Mar 2000) |
| scanning electron microscope | <instrument> An electron microscope in which the image is formed by a beam synchronised with an electron probe scanning the object. The intensity of the image forming beam is proportional to the scattering or secondary emission of the specimen where the probe strikes it (05 Aug 1998) |
| scanning electron microscopy | <procedure> Technique of electron microscopy in which the specimen is coated with heavy metal and then scanned by an electron beam. The image is built up on a monitor screen (in the same way as the raster builds a conventional television image). The resolution is not so great as with transmission electron microscopy, but preparation is easier (often by fixation followed by critical point drying), the depth of focus is relatively enormous, the surface of a specimen can be seen (though not the interior unless the specimen is cracked open) and the image is aesthetically pleasing. (18 Nov 1997) |
| scanning equalization radiography | An electronically enhanced method of radiography in which a small X-ray beam is scanned over the patient while its attenuation is measured, providing feedback to modulate beam intensity in order to equalise average X-ray film exposure. (05 Mar 2000) |