8. Glossary
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Barracuda & QABrowser Reference Manual
CT
See Computed Tomography
CT number
One of a set of numbers on a linear scale which are related to the linear attenuation
coefficients calculated by a computed tomographic device. One of the specific set of
CT numbers on a scale from -1000 for air to +1000 for bone, with water equal to zero,
which is called a Hounsfield unit.
Curie (Ci)
The previously used special unit of activity equal to 3.7 × 1010 per second. 1 Ci =
3.7 × 10
10
Bq.
Dead man switch
A switch so constructed that a circuit-closing contact can be maintained only by
continuous pressure on the switch.
Dental panoramic radiographic
Direct radiography of a part of or the complete dentition by the use of an intra-oral
X-ray tube. See also Orthopantomography.
Diagnostic source assembly
A diagnostic source housing (X-ray tube housing) assembly with a beam limiting
device attached. This assembly shall be so constructed that the leakage radiation air
kerma measured at a distance of one meter from the source does not exceed 1 mGy
(0.1 rad) in one hour when the source is operated at its leakage technique factors.
(See definition).
Digital radiography
A diagnostic procedure using an appropriate radiation source and an imaging system
which collects processes, stores, recalls, and presents image information in a digital
rather than analogue fashion.
Digital subtraction
An image processing procedure used to improve image contrast by subtracting one
digitized image from another.
Dose equivalent (H)
A quantity, defined for radiation protection purposes, which is the product of the
absorbed dose to the tissue and a quality factor "Q" determined by the properties of
the radiation that produced the absorbed dose. For X-rays, gamma rays, and
electrons, Q = 1 and dose equivalent values are numerically equal to absorbed dose
values when consistent units are used for both quantities. The SI unit for dose
equivalent is joule per kilogram. The special name for the SI unit of dose equivalent is
sievert (Sv). The previous special unit of dose equivalent was the rem. One sievert
equals 100 rem.
SI unit: Sv = J/kg
Dose rate meter
Radiation meter intended to measure absorbed dose per unit time.
Dosemeter
Radiation meter intended to measure absorbed dose.
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