8. Glossary
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Barracuda & QABrowser Reference Manual
Target
The part of an X-ray tube anode assembly impacted by the electron beam to produce
the useful X-ray beam.
Tenth value layer (TVL)
Thickness of a specified substance which, when introduced into the path of a given
beam of radiation, reduces the kerma rate to one-tenth of its original rate.
Tomography
A special technique to show in detail images of structures lying in a predetermined
plane of tissue, while blurring or eliminating detail in images of structures in other
planes.
Topogram
For CT, prior to making the cross-sectional scans, the CT scanner is normally used to
obtain one or more radiograph-like reference images, as a way of identifying and
documenting where the scans are to be made. These so-called topograms are
prepared by keeping the X-ray source and the detectors stationary, and dragging the
specimen through the fan-beam by moving the table. Also called scout scans, pilot
scans, or scanograms.
Total filtration
The total of inherent filtration and additional filtration.
User
Physicians and other responsible for the radiation exposure of patients.
Voxel
A volume element in the object being imaged. The mean attenuation coefficient of the
voxel determines the CT (Hounsfield) number of the pixel.
Whole body dose equivalent (Hwb)
The dose equivalent associated with the uniform irradiation of the whole body.
Workload (W)
The degree of use of a radiation source. For X-ray machines operating at tube
potentials below 500 kV, the workload is usually expressed in milliampere minutes per
week. For gammabeam therapy sources and for photon-emitting equipment operation
at 500 kV or above, the workload is usually stated in terms of the weekly kerma of the
useful beam at one meter from the source and is expressed in grays per week at one
meter.
Xeroradiography
The production of an image on a xerographic plate (e.g., electrically charged selenium)
by the action of X-rays transmitted through the patient. (xeromammography:
Mammography carried out by the xeroradiographic process.)
X-ray tube
Evacuated vessel for the production of x-radiation by the bombardment of a target,
usually contained in an anode, with electrons accelerated from a cathode by an electric
field. Thus: Rotating anode X-ray tube. Double focus X-ray tube.
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