| 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) |
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| 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) |
| Scanning Probe Microscopy | <technique> Initially called Atomic Force Microscopy, this technique is now more typically termed Scanning Force Microscopy or Scanning Probe Microscopy. This instrument is essentially an extremely high resolution profilometre. A sharp tip, typically fabricated from silicon nitride, is scanned across the surface of a sample at a constant force by three piezoelectric ceramics. The piezoelectric ceramics are computer controlled via a feedback loop which monitors the position of the tip by means of an optical lever. (A laser is focused on the top of the tip support and the beam reflected into a position sensitive detector). The changes in height of the tip are used to form an image as the tip is scanned across the sample. Acronym: SPM (26 Mar 1998) |
| scanning speech | Measured or metered, often slow speech. (05 Mar 2000) |
| scanning transmission electron microscopy | <procedure> Method of electron microscopy in which image formation depends upon analysis of the pattern of energies of electrons that pass through the specimen. Has comparable resolving power to conventional transmission EM. (18 Nov 1997) |
| scanning tunnelling microscopy | <procedure> A form of ultra high resolution microscopy of a surface in which a very small current is passed through a surface and is detected by a microprobe of atomic dimnensions at its tip that scans the surface by use of a piezodrive. In the simplest form the current transferred to the probe is recorded as an indication of the contours of molecules on the surface above the local plane. In more complex forms feedback is used to hold the probe at a constant difference and the signal in the feedback loop indicates the contours of the molecule. Capable of resolving single atoms and known to work for nonconducting molecules as well as conducting ones. (18 Nov 1997) |
| Environmental Scanning Electron Microscopy | <technique> Scanning electron microscopy is performed by scanning a focused probe across the surface of the sample to be studied. In the environmental scanning electron microscopy the composition and pressure of the atmosphere around the specimen may be controlled. In favourable cases non-conductive specimens may be examined without coating, and hydrated specimens may be examined with the water still in place. Acronym: ESEM (05 Aug 1998) |
| linker scanning | A type of deletion mutagenesis where the distance and/or reading frame between potentially important regions is maintained by replacement with a synthetic oligonucleotide of known sequence. (05 Mar 2000) |