| attenuation | <radiobiology> Process by which a beam of radiation is reduced in intensity when passing through material - combination of absorption and scattering processes, leading to a decrease in flux density of beam when projected through matter. (16 Dec 1997) |
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| attenuation coefficient | 1. <radiobiology> Compton: The fractional number of photons removed from a beam of radiation per unit thickness of material through which it is passing as a result of Compton effect interactions. 2. Linear: The fractional number of photons removed from a beam of radiation per unit thickness of material through which it is passing due to all absorption and scattering processes. 3. Pair Production: That fractional decrease in the intensity of a beam of ionising radiation due to pair production in a medium through which it passes. 4. Photoelectric Effect: That fractional decrease in the intensity of a beam of ionising radiation due to photoelectric effect in a medium through which it passes. (16 Dec 1997) |
| attenuation compensation | In ultrasonography, an increase in receiver gain with time to compensate for loss in echo amplitude with depth, usually due to attenuation. Synonym: attenuation compensation, depth compensation, time compensation gain, time-compensated gain, time-varied gain control, time-varied gain. (05 Mar 2000) |
| attenuation factor | <radiobiology> A measure of the opacity of a layer of material for radiation transversing it, the ratio of the incident intensity to the transmitted intensity. It is equal to Io/I, where Io and I are the intensities of the incident and emergent radiation, respectively. In the usual sense of exponential absorption (I = Ioe- m x), the attenuation factor is e- m x, where x is the thickness of the material and m is the absorption coefficient. (16 Dec 1997) |
| mass attenuation coefficient | <physics> The mass attenuation coefficient, u/p, of a material for uncharged ionising particles is the quotient of DN/N by pdl, where DN/N is the fraction of particles that experience interactions in traversing a distance dl in a material of density p. (16 Dec 1997) |
| back pain, low | Symptoms in the low back can relate to the bony lumbar spine, discs between the vertebrae, ligaments around the spine and discs, spinal cord and nerves, muscles of the low back, internal organs of the pelvis and abdomen, and the skin covering the lumbar area. The low back, or lumbar area, functions in structural support, movement, and protection of certain body tissue. (12 Dec 1998) |
| blood sugar, low | The sugar here is glucose. Low blood glucose constitutes hypoglycaemia. Hypoglycaemia is only significant when it is associated with symptoms. It has many causes including drugs, liver disease, surgical absence of the stomach, pre-diabetes, and rare tumours that release excess insulin. (12 Dec 1998) |
| cardiac output, low | A state of subnormal or depressed cardiac output, usually seen in patients with heart failure secondary to coronary artery, hypertensive, primary myocardial, valvular, or pericardial disease. (12 Dec 1998) |
| very low density lipoprotein | <biochemistry> A lipoprotein substances (combination of a fat and a protein) which acts as a carrier for cholesterol and fats (particularly triglycerides) in the bloodstream. Elevations in very low density lipoprotein in the bloodstream are associated with an increased risk of atherosclerosis and coronary artery disease. Acronym: VLDL (18 Nov 1997) |
| Castellani-Low sign | <clinical sign> A fine tremor of the tongue observed in sleeping sickness. (05 Mar 2000) |
| mean lower low water | <marine biology> The average height of the lower low waters over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value. (09 Oct 1997) |
| mean low water | <marine biology> The average height of the low waters over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value. All low-water heights are included in the average where the type of tide is either semidiurnal or mixed. Only the lower low-water heights are included in the average where the type of tide is diurnal. So determined, mean low water in the latter case is the same as mean lower low water. (09 Oct 1997) |
| placenta, low | Location of the placenta in the lower part of the uterus (womb) so that the placenta partially or completely covers the cervix. Also known as a placenta previa. (12 Dec 1998) |
| heparin, low-molecular-weight | <chemical> Heparin fractions with a molecular weight usually between 4000 and 6000 kD. These low-molecular-weight fractions are effective antithrombotic agents. Their administration reduces the risk of haemorrhage, they have a longer half-life, and their platelet interactions are reduced in comparison to unfractionated heparin. They also provide an effective prophylaxis against postoperative major pulmonary embolism. Pharmacological action: anticoagulant, fibrinolytic agent. (12 Dec 1998) |
| infant, low birth weight | An infant having a birth weight of 2500 gm. (5.5 lb.) or less but infant, very low birth weight is available for infants having a birth weight of 1500 grams (3.3 lb.) or less. (12 Dec 1998) |