differential absorption

differential absorption

Etymology: L, differentia, difference

the difference in absorption of x-rays by different body tissues. In a radiograph of a body part, such as an arm, the image of the bone is produced because more x-rays are absorbed by bone than by the surrounding soft tissue. Lowering the kilovolt peak of an x-ray beam increases differential absorption, but it also increases the patient dose. Also called selective absorption.

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absorption

1. the act of taking up or in by specific chemical or molecular action; especially the passage of liquids or other substances through a surface of the body into body fluids and tissues, as in the absorption of the end products of digestion into the villi that line the intestine.

2. in radiology, uptake of energy by matter with which the radiation interacts.

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chemical absorption

any process by which one substance in liquid or solid form penetrates the surface of another substance.

Compton absorption effect

see compton effect.

differential absorption

the difference in the absorption of x-rays by different tissues.

digestive absorption

the passage of the end products of digestion from the gastrointestinal tract into the blood and lymphatic vessels and the cells of tissues. Absorption of this kind can take place either by diffusion or by active transport.

percutaneous absorption

a passive process in which noxious or therapeutic substances pass through the skin into the body.

radiation absorption

the dissipation of radiant energy as it passes through matter. This phenomenon is of particular importance in diagnostic and therapeutic radiology, which depends on the interaction between ionizing radiations and matter. As radiation passes through matter, it is absorbed by an amount dependent on the atomic and molecular structure and thickness of the substance, and the energy of the primary photons. If radiations pass through a medium of living or nonliving material without absorption (loss of energy), no biological or photographic effects can occur. In true absorption the photons of radiation waves give up or transfer all of their energy to electrons within the atoms of the matter through which they are passing.

absorption tests

are used to assess absorptive function of the small intestine. Glucose, d-xylose and fats are substances administered orally and at timed intervals later measured in the blood. See also digestive absorption (above), fat absorption test.

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differential

exhibiting or depending on a difference.

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differential absorption

see differential absorption.

differential cell count

see differential count.

differential diagnosis

the differences between diseases in terms of clinical signs and epidemiological parameters; used as a basis for selecting as a diagnosis the one with the best fit to those seen in the subject.

differential leukocyte count

see differential count.

differential milk cell counts

count of cells in a milk sample including individual counts of somatic cells and individual leukocyte types.

differential thromboplastin time

used in differentiating the cause of hemophilia. Reagents containing either factor VIII or factor IX are added in the partial thromboplastin time test to demonstrate which factor corrects the prolonged clotting time.