| HD | Haab-Dimmer [syndrome]; Hajna-Damon [broth]; Hansen disease; hearing distance; heart disease; helix ... |
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| HEP | hemolysis end point; hepatoerythropoietic porphyria; high egg passage [virus]; high-energy phosphate... |
| HFD | hemorrhagic fever of deer; high-fiber diet; high forceps delivery; hospital field director; human fa... |
| HFHV | high frequency, high volume |
| HFO | high-frequency oscillator; high-frequency oscillatory [ventilation] |
| microscopy, video | Microscopy in which television cameras are used to brighten magnified images that are otherwise too dark to be seen with the naked eye. It is used frequently in telepathology. (12 Dec 1998) |
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| confocal microscopy | <procedure> A system of (usually) epifluorescence light microscopy in which a fine laser beam of light is scanned over the object through the objective lens. The technique is particularly good at rejecting light from outside the plane of focus and so produces higher effective resolution than is normally achieved. (18 Nov 1997) |
| Conventional Transmission Electron Microscopy | <technique> A term applied to 'normal' transmission electron microscopy imaging. The electron beam is passed through a thin film sample (typically ~1-200 nm thick). Bright field diffraction contrast images are formed with the direct (undiffracted) beam. Dark field images are formed with a selected diffracted beam. CTEM imaging is used in the general observation of samples and careful selection of the diffracting conditions of the sample will allow the analysis of defect structures within the sample. (05 Aug 1998) |
| polarization microscopy | <procedure> Any form of microscopy capable of detecting birefringent objects. Usually performed with a polarizing element below the stage to produce plane polarized light and an analyser that is set to give total extinction of the background and thus to detect any birefringence. (18 Nov 1997) |
| 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 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 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) |
| holographic microscopy | <technique> A mode of light microscopy in which a highly coherent, laser beam is split into a reference and main beam, with the reference beam (usually travelling outside of the microscope) being made to interfere with the main beam that has passed through the specimen. The interference of the two mutually coherent beams forms a hologram. The depth of field gained by viewing the hologram is essentially infinitely great, and the contrast mode or observation can be switched to dark field, phase contrast, interference contrast, etc., after the hologram has been formed by the microscope in bright field. (05 Aug 1998) |
| nanovid microscopy | <procedure> Technique of bright field light microscopy using electronic contrast enhancement and maximum numerical aperture. (18 Nov 1997) |
| dark field microscopy | <procedure> A system of microscopy in which particles are illuminated at a very low angle from the side so that the background appears dark and the objects are seen by diffracted and reflected patches of light against a dark background. (18 Nov 1997) |
| immune electron microscopy | Electron microscopy of biological specimens to which specific antibody has been bound. (05 Mar 2000) |
| immunoelectron microscopy | <technique> A technique for using an electron microscope to locate specific antigensin cells or tissue. (09 Oct 1997) |
| interference microscopy | <procedure> Although all image formation depends on interference, the term is generally restricted to systems in which contrast comes from the recombination of a reference beam with light that has been retarded by passing through the object. Because the phase retardation is a consequence of the difference in refractive index between specimen and medium and because the the refractive increment is almost the same for all biological molecules, it is possible to measure the amount of dry mass per unit area of the specimen by measuring the phase retardation. Quantification of the phase retardation is usually done by using a compensator to reduce the bright object to darkness (see Senarmont and Ehrlinghaus compensators). Two major optical systems have been used the Jamin Lebedeff system and the Mach Zehnder system. These instruments are often referred to as interferometers, since they are designed for measuring phase retardation. Although their use has passed out of fashion, it may be that they will be employed more frequently in future in conjunction with image analysing systems. (18 Nov 1997) |
| interference reflection microscopy | <procedure> An optical technique for detecting the topography of the side of a cell in contact with a planar substrate and for providing information on the separation of the plasmalemma from the substrate. Interference between the reflections from the substrate medium interface and the reflections from the plasmalemma medium interface generate the image. (18 Nov 1997) |