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41 terms

Radiology Chapter 2

Anatomy of the X-Ray Machine
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Acceleration
the increase in speed over time
Actual Focal Point
the area of the focal spot consisting of coiled wire that is perpendicular to the surface of the target
Alloy
a mixture of metals
Anode
a positively charge electrode that acts as a target for the electrons from the cathode. Electrons interacting with the anode produce heat and x-rays
Arcing
a phenomenon in which metal deposits on the inner wall of the envelope act as a secondary anode, thereby attracting electrons from the cathode.
Autotransformer
provides a variable yet predetermined voltage to the high-voltage step-up transformer. It acts as the kilovoltage selector
Cathode
a negatively charged electrode that provides a source of electrons
Collimator
a restricting device used to control the size of the primary beam
Effective Focal Spot
the area of the focal spot that is visible through the x-ray tube window and directed toward the x-ray film
Filament
part of a lower-energy circuit in the cathode that, when heated, releases electrons from their orbit
Focal Spot
the small area of the target that with which electrons collide on the anode
Focusing Cup
a recessed area where the filament lies, directing the electrons toward the anode
Full-wave rectification
creates an almost constant electrical potential across the x-ray tube, converting the positive electrical current pulses to 120 times per second compared with the normal rate of 60 times per second
Glass Envelope
a glass vacuum tube that contains the anode and cathode of the x-ray tube
Half-wave rectification
a method of converting alternating to direct current in which half of the current is lost
Heel Effect
a decrease of x-ray intensity on the anode side of the x-ray beam caused by the anode target angle
Kilovoltage
the amount of electrical energy being applied to the anode and cathode to accelerate the electrons from the cathode to the anode
1 kilovolt=
1000 volts
Line-focus principle
the effect of making the actual focal spot size appear smaller when viewed from the position of the film because of the angle of the target to the electron stream
Line-voltage compensator
adjusts the incoming line voltage to the autotransformer so that the voltage remains constant
Milliamperage (mA)
the amount of electrical energy being applied to the filament. Milliamperage describes the number of x-rays produced during the exposure.
Molybdenum
a metal commonly used in focusing cups because of its high melting point and poor conduction of heat
Penumbra
partial outer shadow of an object being imaged by illumination
Rectification
process of changing alternating current to direct current
Rotating anode
an anode that turns on an axis to increase x-ray production while dissipating heat
Stationary anode
a nonmoving anode, usually found in dental and small portable radiography units
Step-down Transformer
reduces the x-ray machine input voltage from 110 to 220 V to thousands of volts (i.e kilovolts)
Target
anode
Timer Switch
controls the length of exposure
Tungsten
a common metal used in the filament of a cathode
Valve tubes
allow the flow of electrons in one direction only. Commonly called self-rectifiers
X-ray tube
a mechanism consisting of an anode and a cathode in a vacuum that produces a controlled x-ray beam
Filaments located in an x-ray tube
emit electrons when heated
The anode's target
is composed of tungsten
reaches temperatures in excess of 1000C during x-ray production
usually has a copper base
Limitations of the stationary anode
it is unable to withstand large amounts of heat
How can the technician help to prolong the life of the filament in the x-ray tube
enter the proper exposure settings in the control panel before the final positioning of the animal
Which of the following are possible effects of excessive heat within an x-ray tube
bearing failure and decreased anode speed
roughened target surface
arcing
Veterinary patients have a tendency to move while being positioned for radiographs to be taken. The radiographer should help to safely prevent artifacts of movement by
using the shortest exposure time possible
Recommendation to reduce unnecessary irradiation of the patient or persons restraining the patient and to decrease scatter radiation
adjustment of the collimator so that the smallest field size possible is used
X-ray tube ratings are based on target angle, focal spot size, electrical current
rectification
the advantages of using an x-ray machine with a three-phase generator as opposed to a single-phase generator include
use of shorter exposure times because more power is available to the x-ray tube per unit time