77 terms

Equipment operation & quality control

The advantages of large format spot film cameras, such as 100 mm and 105 mm, over smaller format cameras, such as 70 mm and 90 mm, include
improved image quality
Spot film cameras have replaced
conventional spot film cassettes
A significant advantage of spot film cameras is
the big reduction in patient dose that their use permits
However, as the film format increases (from 70 mm to 100 mm), so do
image quality, patient dose, and heat production
Patient dose, however
is so much smaller than the dose with conventional spot film cassettes that it is almost insignificant given the small improvement in image quality afforded by cassette spot films.
A star pattern is used to measure
focal spot resolution
What is essential to high-quality mammographic examinations?
1. Small focal spot x-ray tube
2. High radiographic contrast
3. Use of a compression device
Which of the following is (are) tested as part of a quality assurance (QA) program?
1. Beam alignment
2. Reproducibility
3. Linearity
means that repeated exposures at a given technique must provide consistent intensity
means that a given mAs, using different mA stations with appropriate exposure time adjustments, will provide consistent intensity.
The brightness level of the fluoroscopic image is dependent on
1. milliamperage.
2. kilovoltage.
3. patient thickness.
Focal spot blur is greatest
toward the cathode end of the x-ray beam
Focal spot blur, or geometric blur, is caused by
photons emerging from a large focal spot.
Because the projected focal spot is greatest at the cathode end of the x-ray tube,
geometric blur is also greatest at the corresponding part (cathode end) of the radiograph
The projected focal spot size becomes progressively smaller toward the
anode end of the x-ray tube
TV camera tubes used in image intensification, such as the Plumbicon and Vidicon, function to
transfer the output phosphor image to the TV monitor
Image intensification is a process that
converts the dim fluoroscopic image into a much brighter image, much like normal daylight
As x-ray photons emerge from the patient and enter the image intensifier, they
first encounter the input phosphor, which is generally composed of cesium iodide phosphors.
At the input phosphor, x-ray photons are converted to
light photons, which in turn strike the photocathode.
The photocathode
is a photoemissive metal (usually antimony and cesium compounds); when struck by light, it emits electrons in proportion to the intensity of the light striking it
The electrons are then directed to the
output phosphor via the electrostatic focusing lenses, speeded up in the neck of the tube by the accelerating anode, and directed to the output phosphor for further amplification.
From the output phosphor, the image is
taken by the TV camera, most often a Plumbicon or Vidicon tube, and transferred to the TV monitor
A cine camera
is required to record images on 16- or 35-mm film.
Which of the following waveforms has the lowest percentage voltage ripple?
high-frequency current
is almost constant potential, having less than 1% voltage ripple.
Double-focus x-ray tubes have two
1. focal spots.
2. filaments.
These focal spots are actually two available paths on the
focal track
The effective energy of the x-ray beam is increased by increasing the
1. added filtration.
2. kilovoltage.
To maintain image clarity, the path of electron flow from photocathode to output phosphor is controlled by
electrostatic lenses
The autotransformer
controls/selects the amount of voltage sent to the primary winding of the high-voltage transformer and operates on the principle of self-induction.
The instrument that is frequently used in quality control programs to measure varying degrees of x-ray exposure is the
densities may be measured and given a numeric value with a device called a
device used in quality control programs; it is used to give a precise exposure to a film emulsion
An aluminum step wedge (penetrometer) may be used to
show the effect of kVp on contrast
Several types of exposure timers may be found on x-ray equipment. Which of the following types of timers functions to accurately duplicate radiographic densities?
synchronous timer
an older type of x-ray timer that does not permit very precise, short exposures
impulse timer
permits a shorter, more precise exposure,
electronic timer
may be used for exposures as short as 0.001 second
The important advantage of the phototimer
it can accurately duplicate radiographic densities. It is therefore very useful for providing accurate comparison in follow-up examinations, and for decreasing patient dose by decreasing the number of "retakes" required because of improper exposure.
As the CR laser scanner recognizes various tissue densities, it constructs a graphic representation of pixel value distribultion called a
a graphic representation showing the distribution of pixel values.
the radiographer has selected a processing algorithm by
selecting the anatomical part and particular projection on the computer
The CR unit matches that information with a particular
Lookup Table (LUT)—a characteristic curve that best matches the anatomical part being imaged
histogram analysis and use of the appropriate LUT together function to
produce predictable image quality in CR.
Histogram appearance can be affected by
Degree of accuracy in positioning and centering
Change is affected in
average exposure level and exposure's latitude; these changes will be reflected in the images informational numbers ("S number," "Exposure Index," etc).
Other factors affecting histogram appearance and, therefore, these informational numbers, include
selection of the correct processing algorithm (eg, chest vs femur vs cervical spine), changes in scatter, SID, OID, and collimation. In short, anything that affects scatter and/or dose
Three-phase current is obtained from
three individual alternating currents superimposed on, but out of step with, one another by 120°
All of the following statements regarding three-phase current are true
1. Three-phase equipment produces more x-rays per mAs.
2. Three-phase produces higher-average-energy x-rays than single-phase.
3. The three-phase waveform has less ripple than the single-phase.
A focal spot size of 0.3 mm or smaller is essential for which of the following procedures?
Magnification radiography
A fractional focal spot of 0.3 mm or smaller is essential for
reproducing fine detail without focal spot blurring in magnification radiography
As the object image is magnified, so will be
the associated blur unless the fractional focal spot is used
The image intensifier's input phosphor differs from the output phosphor in that the input phosphor
is much larger than the output phosphor
The image intensifier's input phosphor is
six to nine times larger than the output phosphor. It receives the remnant radiation emerging from the patient and converts it into a fluorescent light image.
Very close to the input phosphor, separated only by a thin transparent layer, is the
the fluorescent light image strikes the
photocathode and is converted to an electron image, which is focused by the electrostatic lenses to the small output phosphor
bar pattern
used to evaluate screen resolution
star pattern
used to evaluate the focal spot
Wisconsin cassette
can be used to evaluate kVp calibration.
To eject a K shell electron from a tungsten atom, the incoming electron must have an energy of at least
70 keV
Characteristic radiation makes up
only about 15% of the primary beam.
The biggest advantage of coupling the image intensifier to the TV camera or CCD via a lens coupling device is its
ability to accommodate cine and/or spot films
The image intensifier can be coupled to the TV camera via
a fiber optic bundle or via a lens coupling device
The fiber optic connection offers
less fragility, more compactness, and ease of manuverability
The big advantage of the objective lens is
that it allows the use of auxiliary imaging devices such as a cine camera or spot film camera
Which of the following x-ray circuit devices operate(s) on the principle of mutual induction?
1. High-voltage transformer
2. Filament transformer
mutual induction
two coils are in close proximity, and a current is supplied to one of the coils. As the magnetic field associated with every electric current expands and "grows up" around the first coil, it interacts with and "cuts" the turns of the second coil. This interaction, motion between magnetic field and coil (conductor), induces an emf in the second coil. This is mutual induction, the production of a current in a neighboring circuit.
Transformers such as the high-voltage transformer and the filament (step-down) transformer operate on
mutual induction
The autotransformer operates on the principle of
Both the transformer and the autotransformer require the use of
alternating current
The line focus principle refers to the fact that
the actual focal spot is larger than the effective focal spot
The effective focal spot is the
foreshortened size of the focus as it is projected down toward the image receptor
The quoted focal spot size is the
effective focal spot size
What are the advantages of photospot camera imaging over cassette spot imaging during fluoroscopy?
1. Lower patient dose
2. Less interruption of the fluoroscopic examination
Photospot camera film comes in
90- and 105-mm sizes.
Comparing these two sizes,
the larger size provides better resolution but more patient dose
when compared to cassette-loaded spot films, photospot camera film produces
less resolution than cassette-loaded film, but requires half the exposure