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56 terms

Equipment operation & quality control

STUDY
PLAY
Screen Speed mAs Conversion Factor
50 =4
100 =2
200 =1
400= 0.5
800= 0.25
Which of the following is (are) characteristics of a 16:1 grid?
1. It absorbs more primary radiation than an 8:1 grid.
2. It has less centering latitude than an 8:1 grid.
3. It is used with higher kVp exposures than an 8:1 grid.
In which type of equipment does kVp decrease during the actual length of the exposure?
1. Battery operated mobile equipment
2. Fixed x-ray equipment
Mobile x-ray machines
are compact and cordless and are either the battery-operated type or the condenser discharge type
Condenser discharge mobile x-ray units
do not use batteries; this type mobile unit requires that it be charged before each exposure
A condenser (or capacitor)
is a device that stores electrical energy.
the stored energy is used
to operate the x-ray tube only. Because this machine does not carry many batteries, it is much lighter and does not need a motor to drive or brake it
The major disadvantage of the capacitor discharge unit is
that, as the capacitor discharges its electrical charge, the kVp gradually decreases throughout the length of the exposure, therefore limiting tube output and requiring recharging between exposures.
A light-absorbing dye is frequently incorporated during the manufacture of screens to
reduce the diffusion of fluorescent light
Remnant radiation emerging from the patient causes
fluorescence of the cassette's intensifying screens.
When activated by x-ray photons, the individual phosphors
emit light isotropically.
. Fluorescent light that is not perpendicular produces
a blur, resulting in geometric unsharpness and decreased resolution.
During manufacture, special dyes can be added to the active layer that will
absorb much of the diffused fluorescence and allow a greater percentage of the image density to be created by more perpendicular fluorescent light.
These dyes improve resolution but result in
a small loss of screen speed.
Although the stated focal spot size is measured directly under the actual focal spot, focal spot size in fact varies along the length of the x-ray beam. At which portion of the x-ray beam is the effective focal spot the largest?
At the cathode end
X-ray tube targets are constructed according to the
line focus principle—the focal spot is angled (usually 12° to 17°) to the vertical
As the actual focal spot is projected downward,
it is foreshortened; thus, the effective focal spot is smaller than the actual focal spot
As the focal spot is projected toward the cathode end of the x-ray beam,
it becomes larger and approaches its actual size.
As the exposed film enters the processor from the feed tray, it first enters
the developer section, where the emulsion's exposed silver bromide crystals are reduced to black metallic silver.
The film then enters the
fixer, where the unexposed silver grains are removed from the film by the clearing agent (hypo).
The film then enters the
wash section, where chemicals are removed from the film to preserve the image.
From the wash section, the film enters the
dryer section
What is the name of the device that functions to expose a film with an optical step wedge having a number of densities ranging from white to black?
Sensitometer
Two devices that are required for quality assurance evaluation purposes are
sensitometer and a densitometer
A sensitometer
is a device that functions to expose a film; when developed, that film will illustrate an optical step wedge with a number of optical densities ranging from white through several shades of gray to black.
A densitometer
is a device that reads the various densities on the film.
A penetrometer
or (usually aluminum) step wedge, can be used to demonstrate the effect of kVp on radiographic contrast.
A potentiometer
is another name for a variable resistor
Very low humidity in the darkroom can lead to
static electrical discharge.
Excessive emulsion swelling and chemical fog can be caused by
increased solution temperature or insufficient replenishment.
What determines the amount of fluorescent light emitted from a fluorescent screen?
1. Thickness of the active layer
2. Type of phosphor used
3. kV range used for exposure
The thicker the active layer of phosphors,
the more fluorescent light is emitted from the screen.
Different types of phosphors have different
conversion efficiencies
rare earth phosphors
emit more light during a given exposure than do calcium tungstate phosphors
As the kVp level is increased
so is the amount of fluoroscopic light emitted by intensifying screen phosphors
When green-sensitive rare earth screens are properly matched with the correct film, what type of safelight should be used in the darkroom?
GBX
It is essential that the darkroom safelight filter color is correctly matched with
the type/sensitivity of film emulsion being used.
The GBX is
a red filter that is safe with green-sensitive film emulsion.
The amber-colored Wratten 6B filter is safe for
blue-sensitive film only.
Which of the following functions to increase the mA?
Increasing the heat of the filament
The thoriated tungsten filament of the cathode assembly is heated by
its own filament circuit.
This circuit provides current and voltage to
heat the filament to incandescence, at which time it undergoes thermionic emission (the liberation of valence electrons from filament atoms).
The greater the number of electrons flowing between the cathode and the anode
the greater the tube current (mA)
Rectification (single- or three-phase)
is the process of changing alternating current to unidirectional current.
A greater number of secondary transformer turns functions to
increase voltage and decrease current.
The device that is used for the direct measurement of optical density is the
densitometer
A densitometer
indicates optical density by providing a digital readout of the quantity of light transmitted through an x-ray image
A sensitometer
is a device used to produce a consistent gray scale exposure on film, usually in conjunction with processor sensitometry
A penetrometer
is an aluminum step wedge that may be radiographed to produce a gray scale
H&D (Hurter & Driffield) curves
are sensitometric curves of a film emulsion's response to light and radiation.
A misaligned guide shoe in the turnaround assembly will create
evenly spaced minus-density lines as a result of emulsion scratching
Dirty rollers
cause multiple black specks on the finished radiograph
A pi line
is a plus-density artifact found 3/4 inch from the leading edge of the film.
Grid lines
appear as minus-density lines resulting from improper positioning or centering of the grid or x-ray tube
Component part(s) of x-ray film include the following:
1. Gelatin emulsion
2. Adhesive layer
x-ray film
starts with a clear polyester base that serves as support for the emulsion. Applied next is an adhesive layer that functions to hold the emulsion to the base. Next is the emulsion, consisting of silver halide grains suspended in gelatin. Finally, a supercoat of clear hard gelatin is applied as an antiabrasive layer.