| PSD | particle size distribution; peptone, starch, and dextrose; periodic synchronous discharge; phase-sen... |
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| DPA | Dual Photon Absorptiometry |
| DPX | Dual Photon X-Ray |
| SPA | 1) Single Photon Absorptiometry 2) Sperm Penetration Assay |
| SPECT | Single Photon Emission Computed Tomography = SET |
| DPA | Dual Photon Absorptiometry |
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| PCS | Photon Correlation Spectroscopy |
| PPF | Photosynthetic photon flux |
| SPA | Single Photon Absorptiometry |
| SPECT | Single Photon Emission CT |
| photon density | The number of counted events recorded in scintigraphy per square centimeter or per square inch of imaged area. Synonym: count density. (05 Mar 2000) |
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| absorptiometry, photon | A noninvasive method for quantitating bone mineral content. It is used especially in the diagnosis of osteoporosis and also in measuring bone mineralization in infants. (12 Dec 1998) |
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| photon | <physics> A quantum unit of light energy. (09 Oct 1997) |
| single photon emission computed tomography | <radiology> Tomographic imaging of metabolic and physiological functions in tissues, the image being formed by computer synthesis of photons of a single energy emitted by radionuclides administered in suitable form to the patient. The method uses radionuclides which emit a single photon of a given energy. The camera is then rotated 180 or 360 degrees around the patient to capture images at multiple positions along the arc. The computer then reconstructs the transaxial, sagittal, and coronal images from the 3-dimensional distribution of radionuclides in the target area scanned. The advantages of SPECT are that it can be used to observe biochemical and physiological processes as well as the size and volume of the organ. The disadvantage is that, unlike positron emission tomography where the positron-electron annihilation results in the emission of 2 photons at 180 degrees from each other, SPECT requires physical collimation to line up the photons, which results in the loss of available photons and hence degrades the image. Acronym: SPECT (20 Jun 2000) |
| bone density | Bone density is the amount of bone tissue in a certain volume of bone. It can be measured using a special X-ray called a quantitative computed tomogram. (12 Dec 1998) |
| bulk density | Weight per unit of volume, usually specified in pounds per cubic foot. (05 Dec 1998) |
| buoyant density | The density that allows a substance to float in some standard fluid. (05 Mar 2000) |
| vapor density | The mass per unit volume of a vapor; since the vapor density changes with temperature and pressure, it is commonly expressed as a specific gravity, i.e., the weight of the vapor divided by the weight of an equal volume of a reference gas (e.g., oxygen or hydrogen) at the same temperature and pressure. (05 Mar 2000) |
| 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) |
| centrifugation, density gradient | Separation of particles according to density by employing a gradient of varying densities. at equilibrium each particle settles in the gradient at a point equal to its density. (12 Dec 1998) |
| count density | The number of counted events recorded in scintigraphy per square centimeter or per square inch of imaged area. Synonym: count density. (05 Mar 2000) |
| population density | <epidemiology> Number of individuals in a population relative to space. (12 Dec 1998) |
| current density | <radiobiology> Amount of current flowing through a substance, per unit area perpendicular to the direction of current flow. (See also density) (09 Oct 1997) |
| high density lipoprotein | <biochemistry> These lipoproteins acts to carry cholesterol in the bloodstream. Raised high density lipoprotein levels have been correlated with a lower risk for heart disease. Less than 35 mg/dl is considered a positive risk factor for coronary artery disease, over 60 mg/dl is considered a negative risk factor (reduces your risk of heart disease). Recent studies show a low high density lipoprotein level is the strongest predictor of cardiovascular death in women. Acronym: HDL (18 Nov 1997) |
| spin density | The number of nuclear dipoles per unit volume. (05 Mar 2000) |
| stand density | The number or mass of trees occupying a site. It is usually measured in terms of stand density index or basal area per acre. (05 Dec 1998) |
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