| half register | <molecular biology> A misalignment between two identical sets of repeating units of nucleotides within two copies of the same chromosome (one set of repeating units per copy of the chromosome), where repeating unit A from one set is inappropriately aligned with repeating unit B on the other set, so that ABABAB on one set would be aligned with BABABA on the other set instead of the correct ABABAB with ABABAB. (13 Nov 1997) |
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| half-tetrad analysis | <genetics> The analysis of tetrad chromosomes (a pair of homologous chromosomes, thus four total chromosomes) after recombination when only half of the tetrad (two of the four chromosomes) can be analysed. (13 Nov 1997) |
| half-time | The time, in a first-order chemical (or enzymic) reaction, for half of the substance (substrate) to be converted or to disappear. Compare: half-life. (05 Mar 2000) |
| half-value layer | <radiobiology> The thickness of a specified material (usually a specific absorber), which attenuates a beam of radiation so that the exposure rate or absorbed dose rate at a specified point is reduced by half. (20 Sep 2002) |
| drug half-life | The amount of time it takes for one-half of an administered drug to be lost through biological processes (metabolism and elimination). (27 Sep 1997) |
| effective half-life | <radiobiology> Time required for a radioactive substance contained in a biological system (such as a person or an animal) to reduce its radioactivity by half, as a combination result of radioactive decay and biological elimination from the system. (09 Oct 1997) |
| elimination half-life | <pharmacology> The time it takes for the body to eliminate or breakdown half of a dose of a pharmacologic agent. (09 Oct 1997) |
| adrenal imaging | <radiology> Cortex, I-131 iodo-cholesterol, not widely used due to high rad dose and 4-15 day delayed imaging, medulla, search for pheo, MIBG (I-131 meta-iodobenzylguanidine) (12 Dec 1998) |
| adrenal medullary imaging | <investigation, radiology> A nuclear scan that images the adrenal glands after a radioactive tracer is injected into the bloodstream. This test is useful in detecting a pheochromocytoma, particularly if it not within the adrenal gland. (27 Sep 1997) |
| backscattered electron imaging | <microscopy> The production of backscattered electrons from a sample varies directly with the specimen's average atomic number, higher atomic number elements produce more backscattered electrons than lower atomic number ones. Detection of Backscattered Electrons is achieved by using a donut shaped solid state saemiconductor device mounted on the bottom of the objective lens. When Backscattered Electrons strike the detector electron-hole pairs are created which are then counted. This quantity is translated into a pixel intensity and displayed on the CRT, forming the image. By splitting the detector into halves (or quadrants) differences in the signal level on the individual detector segments provide surface topography information. (05 Aug 1998) |
| blood pool imaging | Nuclear medicine study using a radionuclide that is confined to the vascular compartment. (05 Mar 2000) |
| bone: gallium imaging | <radiology> Increased activity in: active osteomyelitis (90% sensitivity: better than Tc-99m MDP), sarcoma, cellulitis, septic arthritis, rheumatoid arthritis, Paget disease, metastases (65% sensitivity: than for bone agents) see: gallium: indications (12 Dec 1998) |
| bright field imaging | <microscopy> An imaging mode in a transmission electron microscopy that uses only unscattered Electrons to form the image. Contrast in such an image is due entirely to mass-thickness variations in amorphous samples, and may include diffraction contrast in crystalline samples. (05 Aug 1998) |
| cardiac blood pool imaging | This noninvasive test uses radioactive tracers to delineate the hearts chambers and major vessels. It may be used to detect a heart attack, heart muscle function and coronary artery disease. The patient receives a radioactive tracer by injection (into a vein) and then the heart is imaged using a gamma camera. The heart is imaged before and after exercise. This test may be used to detect and evaluate atrial septal defect, dilated cardiomyopathy, congestive heart failure, cardiomyopathy, Lyme disease (secondary), mitral stenosis and superior vena cava syndrome. (27 Sep 1997) |
| radionuclide imaging | Process whereby a radionuclide is injected or measured (through tissue) from an external source, and a display is obtained from any one of several rectilinear scanner or gamma camera systems. The image obtained from a moving detector is called a scan, while the image obtained from a stationary camera device is called a scintiphotograph. (12 Dec 1998) |