filter

1. A porous substance through which a liquid or gas is passed in order to separate it from contained particulate matter or impurities to sterilize. SYN: filtrum. 2. To use or to subject to the action of a f.. 3. In diagnostic or therapeutic radiology, a plate made of one or more metals such as aluminum and copper which, placed in the x- or gamma ray beam, permits passage of a greater proportion of higher-energy radiation and attenuation of lower-energy and less desirable radiation, raising the average energy or hardening the beam. 4. A device used in spectrophotometric analysis to isolate a segment of the spectrum. 5. A mathematical algorithm applied to image data for the purpose of enhancing image quality, usually by suppression or enhancement of high spatial frequencies. 6. A passive electronic circuit or device that selectively permits the passage of certain electrical signals. 7. A device placed in the inferior vena cava to prevent pulmonary embolism from low extremity clot. There are many variants. [Mediev. L. filtro, pp. -atus, to strain through felt, fr. filtrum, felt]

- bandpass f. a device that allows a limited range of frequencies to pass.

- Berkefeld f. a bacterial f. used in 1891, made of earth known as Kieselguhr taken from the name of the mine in Hanover, Germany, from which the earth was found. Ground water at this mine had a clear blue color suggesting the use of the earth as a f.. [Berkefield, name of owner of the mine]

- bird's nest f. a wire mesh inferior vena cava f..

- Greenfield f. a multistrutted, spring-style vena cava f..

- high-pass f. a device or material that allows high frequency signals to pass while attenuating other signals.

- low-pass f. a device or material with the opposite effect from a high-pass f.; most tissues act as low-pass filters of ultrasound signals.

- nitinol f. a vena cava f. made with a metal that springs into shape when warmed to body heat by the blood after catheter insertion.

- vena cava f. a f. used for interruption of inferior vena cava to prevent pulmonary embolism; e.g., Greenfield f.. SYN: venocaval f..

- venocaval f. SYN: vena cava f..

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fil·ter 'fil-tər n

1) a porous article or mass (as of paper or sand) through which a gas or liquid is passed to separate out matter in suspension

2) an apparatus containing a filter medium

3 a) a device or material for suppressing or minimizing waves or oscillations of certain frequencies (as of electricity, light, or sound)

b) a transparent material (as colored glass) that absorbs light of certain wavelengths or colors selectively and is used for modifying light that reaches a sensitized photographic material called also color filter

filter vb, fil·tered; fil·ter·ing -t(ə-)riŋ vt

1) to subject to the action of a filter

2) to remove by means of a filter vi to pass or move through or as if through a filter

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fil·ter (filґtər) [L. filtrum] 1. a membrane or other porous substance or device for the separation of impurities or particulate matter from liquid or gas. 2. to pass liquid or gas through such a device or material. 3. a device used to absorb electromagnetic radiation, particularly light, of specific wavelengths. 4. in radiology, a solid screen usually of varying thickness of metal (aluminum, copper, tin, lead, etc.) which when placed in the pathway of the radiation beam prevents transmission of beta particles and photons of longer wavelengths.