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507 terms

Selection of technical factors - 507

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Which of the following could be used to improve recorded detail?
1. Slower screen/film combination
2. Smaller focal-spot size
Other imaging factors such as milliampere-seconds and kilovoltage selection and correct photocell selection influence the visibility of recorded detail by affecting
density and contrast
Which of the following is (are) associated with subject contrast?
1. Patient thickness
2. Tissue density
3. Kilovoltage
Radiographic contrast is the sum of
film emulsion contrast and subject contrast
what has by far the greatest influence on radiographic contrast
Subject contrast
Several factors influence subject contrast, each as a result of
beam attenuation differences in the irradiated tissues
As patient thickness and tissue density increase, attenuation increases and subject contrast is
increased
As kilovoltage increases
higher energy photons are produced, beam attenuation is decreased, and subject contrast decreases
Using a short (25-30 inches) SID with a large size (14 x 17 inches) image receptor is likely to
increase the anode heel effect
anode angles of 10° or less
cause the anode heel effect to be much more apparent
The x-ray beam needs to diverge more to cover a
large-size image receptor
it needs to diverge even more for coverage as the SID
decreases
The x-ray beam has no problem diverging toward the cathode end of the beam, but as it tries to diverge toward the anode end of the beam, it is eventually stopped by the
anode (x-ray photons are absorbed by the anode).
This causes a decrease in beam intensity at the anode end of the beam and is characteristic of the
anode heel effect
To change nongrid exposures to grid exposures, or to adjust exposure when changing from one grid ratio to another, you must remember the factor for each grid ratio:
No grid = 1 x the original mAs
5:1 grid = 2 x the original mAs
6:1 grid = 3 x the original mAs
8:1 grid = 4 x the original mAs
12:1 grid = 5 x the original mAs
16:1 grid = 6 x the original mAs
To adjust exposure factors, you simply compare the old with the new:
(old mAs) = (old grid factor)
```````````` ```````````````````
(new mAs) = (new grid factor)
Which of the following is most likely to produce a radiograph with a long scale of contrast?
Increased photon energy
An increase in photon energy accompanies an increase in
kilovoltage
Kilovoltage regulates the
penetrability of x-ray photons; it regulates their wavelength—the amount of energy with which they are associated.
The higher the related energy of an x-ray beam, the greater its
penetrability (kilovoltage and photon energy are directly related; kilovoltage and wavelength are inversely related).
Adjustments in kilovoltage have a big impact on
radiographic contrast
As kilovoltage (photon energy) is increased
the number of grays increases, thereby producing a longer scale of contrast
as screen speed increases, so does
contrast (resulting in a shorter scale of contrast).
An increase in mAs is frequently accompanied by an appropriate decrease in
kilovoltage, which would also shorten the contrast scale.
SID and radiographic contrast are
unrelated
Grid ratio is defined as
the height of the lead strips compared to (divided by) the width of the interspace material
The width of the lead strips has no bearing on the
grid ratio.
Although the stated focal spot size is measured directly under the actual focal spot, focal spot size really 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 always smaller than the
actual focal spot
As it is projected toward the cathode end of the x-ray beam, the effective focal spot becomes larger and approaches the
actual size
As it is projected toward the anode end, it gets smaller because of the
anode "heel" effect.
How are mAs and radiographic density related in the process of image formation?
mAs and radiographic density are directly proportional.
Radiographic density is described as the
overall degree of blackening of a radiograph or a part of it.
The mAs regulates
the number of x-ray photons produced at the target, and thus regulates radiographic density
mAs and radiographic density are directly
proportional
The speed of an intensifying screen is influenced by which of the following factors?
1. Phosphor layer thickness
2.. Phosphor type used
Rare earth phosphors have a much higher conversion efficiency (and therefore speed) and have all but replaced the older
calcium tungstate screens.
The larger the phosphor and the thicker the layer of phosphors (active layer), the greater the light emission and therefore the
speed.
Antihalation backing
a component of single-emulsion film that prevents crossover of fluorescent light within an image receptor.
In radiography of a large abdomen, which of the following is (are) effective way(s) to minimize the amount of scattered radiation reaching the IR?
1. Use of close collimation
2. Use of compression devices
One way to minimize scattered radiation reaching the IR is to use
optimal kilovoltage
excessive kVp increases the production of
scattered radiation.
Close collimation is also important because
the smaller the volume of irradiated material, the less scattered radiation is produced
Using compression bands or the prone position in a large abdomen has the effect of making the abdomen "thinner"; it will therefore generate less
scattered radiation
Low-ratio grids allow a greater percentage of
scattered radiation to reach the IR.
Use of a high-ratio grid will clean up a greater amount of
scattered radiation before it reaches the IR.
The general rule is that structures measuring more than 10 cm should be radiographed with a
grid
To produce a just perceptible increase in radiographic density, the radiographer must increase the
mAs by 30%
f a radiograph lacks sufficient blackening, an increase in
mAs is required.
mAs regulates
the number of x-ray photons produced at the target.
An increase or decrease in mAs of at least
30% is necessary to produce a perceptible effect.
Increasing the kVp by 15% will have about the same effect as
doubling the mAs.
The mAs is the exposure factor governing radiographic
density.
Which of the following influences geometric unsharpness?
1. OID
2. Source-object distance
3. SID
As OID increases, so does
magnification
OID is directly related to
magnification
As focal-object distance and SID decrease, magnification
increases
Focal-object distance and SID are inversely related to
magnification
Greater latitude is available to the radiographer in which of the following circumstances?
1. Using high-kVp technical factors
2. Using a slow film-screen combination
3. Using a low-ratio grid
In the low kilovoltage ranges, a difference of just a few kVp makes a very
noticeable radiographic difference
High-kVp technical factors offer much greater margin for
error
slow film-screen combinations offer much greater margin for
error
Lower-ratio grids offer more tube-centering latitude than
high-ratio grids
Decreasing field size from 14 x 17 into 8 x 10 inches will?
decrease radiographic density and decrease the amount of scattered radiation generated within the part.
Limiting the size of the radiographic field serves to limit the amount of ?
scattered radiation produced within the anatomic part.
As the amount of scattered radiation generated within the part decreases, so does the?
resultant density within the radiographic image
beam restriction is a very effective means of reducing the quantity of non-information-carrying?
scattered radiation (fog) produced, resulting in a shorter scale of contrast with fewer radiographic densities.
Slow-speed screens are used
to image fine anatomic details.
The slower the screen speed, the smaller the quantity of?
fluorescent light emitted during x-ray exposure.
slow-speed screens require more?
x-ray exposure to provide adequate radiographic density and cannot be used when exposure reduction or fast exposure time is essential.
because they are associated with less diffusion of fluorescent light, they produce better?
recorded detail and are used to image structures requiring excellent recorded detail.
Pediatric radiography is likely to require?
fast screens to reduce exposure time and dose.
Shape distortion is influenced by the relationship between the
1. x-ray tube and the part to be imaged.
2. part to be imaged and the image recorder.
3. image recorder and the x-ray tube.
Shape distortion is caused by ?
misalignment of the x-ray tube, the part to be radiographed, and the image recorder/film.
Only one of the three need be misaligned for
distortion to occur.
Which of the following devices is used to overcome severe variation in patient anatomy or tissue density, providing more uniform radiographic density?
Compensating filter
A compensating filter is used when ?
the part to be radiographed is of uneven thickness or density (in the chest, mediastinum vs lungs)
The filter (made of aluminum or lead acrylic)
is constructed in such a way that it will absorb much of the primary radiation that would expose the low-tissue density area, while allowing the primary radiation to pass unaffected to the high-tissue density area.
A collimator is used to
decrease the production of scattered radiation by limiting the volume of tissue irradiated.
The grid functions to
trap scattered radiation before it reaches the IR, thus reducing scattered radiation fog.
If a lateral projection of the chest is being performed on an asthenic patient and the outer photocells are selected, what is likely to be the outcome?
Decreased density
The radiographic accessory used to measure the thickness of body parts in order to determine optimum selection of exposure factors is the:
caliper
A technique chart identifies?
the standardized factors that should be used with that particular x-ray unit, for various examinations/positions, of anatomic parts of different sizes.
To be used effectively, these technique charts require?
that the anatomic part in question be measured correctly with a caliper.
Exposure latitude will be reduced in which of the following situations?
1. Use of low kilovoltage technical factors
2. Use of high-speed film
In the low-kilovoltage ranges, a difference of just a few kilovolts makes a very noticeable radiographic difference; that is, there is little
exposure latitude.
The faster the speed of the film emulsion:
the less the latitude/margin of error.
What is the best way to reduce magnification distortion?
Decrease the OID.
Shape distortion relates to?
the alignment of the x-ray tube, the part to be radiographed, and the image recorder
Size distortion is magnification, and it is related to the
OID and the SID.
Magnification can be reduced by either?
increasing the SID or decreasing the OID.
an increase in SID must be accompanied by an increase in ?
mAs to maintain density.
is therefore preferable, in the interest of exposure, to reduce
OID whenever possible.
Artifacts can be a result of?
exposure, handling and storage, or processing.
Exposure artifacts include
motion, double exposure, poor screen-film contact—the effects of these are seen as a result of the exposure
Handling and storage artifacts include
static electricity discharge, crinkle marks, scratches, and light or radiation fog—all these occur as a result of improper usage or storage.
Processing artifacts occur
while the film is in the automatic processor and include pi lines, guide shoe marks, and chemical fog.
The effect described as differential absorption is
1. responsible for radiographic contrast.
2. a result of attenuating characteristics of tissue.
3. minimized by the use of high kVp.
Differential absorption refers to
the x-ray absorption characteristics of neighboring anatomic structures
The radiographic representation of these structures is referred to as
radiographic contrast
t may be enhanced with high-contrast technical factors, especially using
low kilovoltage levels.
At low kilovoltage levels
the photoelectric effect predominates.
Diagnostic x-ray photons interact with tissue in a number of ways, but mostly they are involved in the production of
Compton scatter or in the photoelectric effect
Compton scatter occurs
when a relatively high-energy (kV) photon uses some of its energy to eject an outer-shell electron. In doing so, the photon is deviated in direction and becomes a scattered photon.
Compton scatter causes
objectionable scattered radiation fog in large structures such as the abdomen and poses a radiation hazard to personnel during procedures such as fluoroscopy.
In the photoelectric effect
a relatively low-energy x-ray photon uses all its energy to eject an inner-shell electron, leaving a "hole" in the K shell. An L-shell electron then drops down to fill the K vacancy, and in so doing emits a characteristic ray whose energy is equal to the difference between the binding energies of the K and L shells.
The photoelectric effect occurs with
high-atomic-number absorbers such as bone and positive contrast media, and is responsible for the production of radiographic contrast
photoelectric effect
is helpful for the production of the radiographic image, but it contributes to the dose received by the patient (because it involves complete absorption of the incident photon).
Factor(s) that can be used to regulate radiographic density is (are)
1. milliamperage.
2. exposure time.
3. kilovoltage.
Factors that regulate the number of x-ray photons produced at the target can be used to control
radiographic density, namely milliamperage and exposure time (mAs)
Radiographic density is directly proportional to
mAs
if the mAs is cut in half, the radiographic density will decrease by
one-half
Although kilovoltage is used primarily to regulate radiographic contrast, it may also be used to regulate
radiographic density in variable-kVp techniques, according to the 15% rule.
Congestive heart failure and pleural effusion involve abnormal amounts of fluid in the chest and thus require
an increase in exposure factors.
An increase in kVp will have which of the following effects?
1. More scattered radiation will be produced.
2. The exposure rate will increase.
An increase in kilovoltage (photon energy) will result in
a greater number (ie, exposure rate) of scattered photons (Compton interaction)
These scattered photons
carry no useful information and contribute to radiation fog, thus decreasing radiographic contrast.
The relationship between the height of a grid's lead strips and the distance between them is referred to as grid
ratio
Grid frequency
refers to the number of lead strips per inch.
Focusing distance and grid radius
are terms denoting the distance range with which a focused grid may be used.
Using a 48-inch SID, how much object-image distance (OID) must be introduced to magnify an object two times?
24-inch OID
Magnification radiography may be used to?
delineate a suspected hairline fracture or to enlarge tiny, contrast-filled blood vessels.
Magnification radiography also has application in
mammography
To magnify an object to twice its actual size:
the part must be placed midway between the focal spot and the IR.
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.
The actual focal spot is always larger than the?
effective (or projected) focal spot, as illustrated by the line focus principle.
In addition, the effective focal spot size varies along the longitudinal tube axis, being greatest in size at the ?
cathode end of the beam and smallest at the anode end of the beam
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.
Which of the following is (are) classified as rare earth phosphors?
1. Lanthanum oxybromide
2. Gadolinium oxysulfide
Rare earth phosphors have a greater
conversion efficiency than do other phosphors.
Lanthanum oxybromide is
a blue-emitting rare earth phosphor,
gadolinium oxysulfide is
a green-emitting rare earth phosphor.
Cesium iodide
the phosphor used on the input screen of image intensifiers; it is not a rare earth phosphor
How is the mAs adjusted in an AEC system as the film-screen speed combination is decreased?
The mAs remains unchanged as film-screen speed decreases.
As the speed of the film-screen system decreases:
an increase in mAs is usually required to maintain radiographic density
when an automatic exposure control (phototimer or ionization chamber) is used, the system is programmed for:
the use of a particular film-screen speed
If a slower-speed screen cassette-image receptor is placed in the Bucky tray, the AEC has no way of recognizing it as different and will:
time the exposure for the system that it is programmed for
For example, if the system is programmed for a 400-speed film-screen combination, and if a 200-speed screen cassette-image receptor was placed in the Bucky tray, the resulting radiograph would
have half the required radiographic density.
SID affects recorded detail in which of the following ways?
Recorded detail is directly related to SID.
As the distance from focal spot to IR (SID) increases, so does
recorded detail.
Because the part is being exposed by more perpendicular (less divergent) rays, less
magnification and blur are produced.
Although the best recorded detail is obtained using a
long SID, the necessary increase in exposure factors and resulting increased patient exposure becomes a problem.
An optimal 40-inch SID is used for most radiography, with the major exception being
chest examinations.
If a 4-inch collimated field is changed to a 14-inch collimated field, with no other changes, the radiographic image will possess
more density
More scattered radiation is generated within a part as:
the kilovoltage is increased, the size of the field is increased, and the thickness and density of tissue increases.
As the quantity of scattered radiation increases from any of these sources,
more density is added to the radiographic image.
Insufficient milliamperage and/or exposure time will result in lack of
radiographic density
Insufficient kVp will result in
underpenetration and excessive contrast
insufficient SID will result in
increased exposure rate and radiographic overexposure.
As photon energy increases, more penetration and greater production of scattered radiation occur, producing a
longer scale of contrast
As grid ratio increases, more scattered radiation is absorbed, producing a
shorter scale of contrast.
As OID increases, the distance between the part and the IR acts as a grid, and consequently less scattered radiation reaches the IR, producing a
shorter scale of contrast
Focal spot size is related only to
recorded detail.
In the RAO position, the sternum must be visualized through the
thorax and heart
Prominent pulmonary vascular markings can hinder
good visualization
A method frequently used to overcome this problem is to use an mAs with a long
exposure time.
The patient is permitted to breathe
normally during the (extended) exposure and, by doing so, blurs out the prominent vascularities.
A focal spot size of 0.3 mm or smaller is essential for
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 any
associated blur unless a fractional focal spot is used.
Use of the fractional focal spot on a routine basis is unnecessary; it is not advised because it causes
unnecessary wear on the x-ray tube and offers little radiographic advantage.
X-ray photon beam attenuation is influenced by
1. tissue type.
2. subject thickness.
3. photon quality.
Attenuation (decreased intensity through scattering or absorption) of the x-ray beam is a result of
its original energy and its interactions with different types and thicknesses of tissue.
The greater the original energy/quality (the higher the kilovoltage) of the incident beam, the less the
attenuation
The greater the effective atomic number of the tissues (tissue type determines absorbing properties), the greater the
beam attenuation
The greater the volume of tissue (subject density and thickness), the greater the
beam attenuation.
The screen-film system and radiographic density are directly
proportional
if the system speed is doubled, the radiographic density is
doubled
mAs conversion factor formula
screen speed factor 1 = mAs 1
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screen speed factor 2 mAs 2
An increase in the kilovoltage applied to the x-ray tube increases the
exposure rate.
As the kilovoltage is increased,
a greater number of electrons are driven across to the anode with greater force.
as energy conversion takes place at the anode,
more high-energy (short-wavelength) photons are produced.
because they are higher energy photons, there will be less
patient absorption.
OID is related to recorded detail in which of the following ways?
Radiographic detail is inversely related to OID.
As the distance from the object to the IR (OID) increases, so does
magnification distortion thereby decreasing recorded detail.
Which of the following examinations might require the use of 120 kVp?
1. Chest radiograph
2. Barium-filled stomach
High-kilovoltage factors are frequently used to even out densities in anatomic parts with high
tissue contrast (eg, the chest)
as high kilovoltage produces added scattered radiation, it generally must be used with a
grid
It would be inappropriate to perform an AP abdomen with high kilovoltage because it has such low
subject contrast
Barium-filled structures are frequently radiographed using 120 kV or more to penetrate the barium—to see
through to structures behind.
Radiographic contrast is the result of
differential absorption
Differential absorption refers to
the x-ray absorption characteristics of neighboring anatomic structures—determined by the atomic number of the tissue being examined.
The radiographic representation of these various density structures is referred to as
radiographic contrast; it may be enhanced with high-contrast technical factors, especially using low kilovoltage levels.
At low kilovoltage levels,
the photoelectric effect predominates.
If photons are absorbed, there will be no
contrast
The technical factor milliampere-seconds is used to regulate
image density.
when two or more characteristic curves are being compared, the fastest film emulsion is the one furthest to the
left
sensitivity =
speed
Screen-film imaging is one example of a (n)
analog system
Screen-film imaging consists of an exposure method of converting x-ray energy to
light energy, then converting light energy to electrochemical energy in the development process.
Processing changes the invisible electrochemical image to a
visible/manifest radiographic image
This process ends with
analog data
Digital imaging is
an electronic imaging method that allows data capture and manipulation in an electron pattern.
The resulting image can be turned into an analog image after going through
several energy changes (electron to light to film or TV screen).
The direct action of x-rays has very little influence on
a radiographic image produced with intensifying screens (fluorescent light is responsible for the majority of film exposure).
If the imaging system speed is cut in half (from 400 to 200 speed), the result will be
half of the original density on the radiograph
Because the grid removes scattered (and some primary) radiation from the beam, an
increase in exposure factors is required.
Which of the following combinations will result in the most scattered radiation reaching the image receptor?
Using fewer mAs and more kVp
As x-ray photons travel through a part, they either pass all the way through to expose the film/image receptor, or they
undergo interaction(s) that may result in their being absorbed by the part or deviated in direction.
It is those that change direction (scattered radiation) that
undermine the image
Scattered radiation adds
unwanted, degrading densities to the radiographic image.
The single most important way to reduce the production of scattered radiation is to
collimate
Although collimation, use of lower kVp (with appropriately higher mAs), and compression can be used, a large amount of scattered radiation is still generated within the part being radiographed and, because it adds unwanted noninformation-carrying densities, it can have a severely degrading effect on image quality, thus the need for
grids
X-ray photon energy is inversely related to
photon wavelength
As kVp is increased,
more high-energy photons are produced and the overall energy of the primary beam is increased.
Photon energy is inversely related to
wavelength; that is, as photon energy increases, wavelength decreases.
An increase in milliamperage serves to
increase the number of photons produced at the target, but is unrelated to their energy.
Using fixed-mAs and variable-kVp technical factors, each centimeter increase in patient thickness requires what adjustment in kilovoltage?
Increase 2 kVp
When the variable-kVp method is used,
a particular mAs is assigned to each body part
As part thickness increases, the kVp (penetration) is also
increased
The body part being radiographed must be carefully measured, and for each centimeter of increase in thickness,
2 kVp is added to the exposure.
Radiographic density is directly proportional to
mAs.
All of the following are related to recorded detail
1. focal spot size
2. screen speed.
3. OID.
The focal spot size selected will determine
the amount of focal spot, or geometric, blur produced in the image
Different screen speeds will create differing degrees of
fluorescent light diffusion, affecting recorded detail.
OID is responsible for
image magnification, and hence recorded detail.
milliamperage is unrelated to recorded detail; it affects only
the quantity of x-ray photons produced and thus the radiographic density.
Types of moving grid mechanisms include
1. oscillating.
2. reciprocating.
Grids are devices constructed of
alternating strips of lead foil and radiolucent interspacing material.
They are placed between the patient and
the IR, and they function to remove scattered radiation from the remnant beam before it forms the latent image.
Stationary grids will efficiently remove scattered radiation from the remnant beam; however,
their lead strips will be imaged on the radiograph.
If the grid is made to move (usually in a direction perpendicular to the lead strips) during the exposure, the lead strips will be effectively
blurred.
The motion of a moving grid, or Potter-Bucky diaphragm, may be
reciprocating (equal strokes back and forth), oscillating (almost circular direction), or catapult (rapid forward motion and slow return).
Synchronous refers to
a type of x-ray timer.
Disadvantage(s) of using low kV technical factors include
1. insufficient penetration.
2. increased patient dose.
3. diminished latitude.
As the kilovoltage is decreased, x-ray beam energy (ie, penetration) is
decreased.
at lower kilovoltage levels
a shorter scale of contrast is obtained
at lower kilovoltage levels
there is less exposure latitude (less margin for error in exposure)
As kilovoltage is reduced
the mAs must be increased accordingly to maintain adequate density
This increase in mAs results in
greater patient dose
Radiographic density is greatly affected by changes in
the SID, as expressed by the inverse square law of radiation.
As distance from the radiation source increases, exposure rate
decreases and radiographic density decreases
Exposure rate is inversely proportional to
the square of the SID.
the following have a significant effect on density, but they are not the primary controlling factors
Aluminum filtration, kilovoltage, and scattered radiation
Which of the following factors contribute(s) to the efficient performance of a grid?
1. Grid ratio
2. Number of lead strips per inch
3. Amount of scatter transmitted through the grid
Grid ratio is defined as
the ratio of the height of the lead strips to the width of the interspace material; the higher the lead strips, the more scattered radiation they will trap and the greater the grid's efficiency.
The greater the number of lead strips per inch, the
thinner and less visible they will be on the finished radiograph.
The function of a grid is to
absorb scattered radiation in order to improve radiographic contrast.
The selectivity of a grid is determined by
the amount of primary radiation transmitted through the grid divided by the amount of scattered radiation transmitted through the grid.
Which of the following is (are) characteristic(s) of a 16:1 grid?
1. It absorbs a high percentage of scattered radiation.
2. It has little positioning latitude.
3. It is used with high-kVp exposures.
High-kilovoltage exposures produce large amounts of
scattered radiation, and therefore high-ratio grids are used in an effort to trap more of this scattered radiation.
accurate centering and positioning become more critical to avoid
grid cutoff.
High-kilovoltage exposure factors are usually required for radiographic examinations using
barium sulfate.
Positive-contrast medium is
radiopaque
negative-contrast material is
radioparent
Barium sulfate (radiopaque, positive-contrast material) is most frequently used for examinations of the
intestinal tract, and high-kVp exposure factors are used to penetrate (to see through and behind) the barium.
Water-based iodinated contrast media (Conray, Amipaque) are also
positive-contrast agents.
the K-edge binding energy of iodine prohibits the use of much greater than
70 kVp with these materials
Higher kVp values will obviate the effect of
iodinated contrast media
Air is an example of a
negative-contrast agent, and high-kVp factors are clearly not indicated.
Recorded detail can be improved by decreasing
1. the OID.
2. motion unsharpness.
Motion, voluntary or involuntary, is most detrimental to good
recorded detail.
if all other detail factors are adjusted to maximize detail, if motion occurs during exposure, detail is
lost
The most important ways to reduce the possibility of motion are
using the shortest possible exposure time, careful patient instruction (for suspended respiration), and adequate immobilization when necessary.
Minimizing magnification through the use of increased SID and decreased OID functions to improve
recorded detail.
For which of the following examinations can the anode heel effect be an important consideration?
1. Lateral thoracic spine
2. AP femur
The heel effect is characterized by a variation in beam intensity, which gradually increases from
anode to cathode
the AP thoracic spine is thicker
caudally than cranially, and so the thicker portion is best placed under the cathode
in the lateral projection of the thoracic spine, the upper portion is
thicker because of superimposed shoulders, and therefore that portion is best placed under the cathode end of the beam.
The femur is also uneven in density, particularly in the
AP position, and can benefit from use of the heel effect
The anode heel effect is most pronounced when using
large-size IRs, at short SIDs, and with an anode having a steep (small) target angle.
If the radiographer is unable to achieve a short OID because of the structure of the body part or patient condition, which of the following adjustments can be made to minimize magnification distortion?
A longer SID should be used.
An increase in SID will help decrease the effect of excessive
OID
especially with larger body parts, increased SID usually requires a significant increase in
exposure factors.
Focal spot size, screen speed, and grid ratio are unrelated to
magnification.
Which of the following would be useful for an examination of a patient suffering from Parkinson's disease?
1. High-speed screens
2. Short exposure time
Which of the following may be used to reduce the effect of scattered radiation on the finished radiograph?
1. Grids
2. Collimators
3. Compression bands
Collimators
restrict the size of the irradiated field, thereby limiting the volume of irradiated tissue, and hence less scattered radiation is produced.
Once radiation has scattered and emerged from the body, it can be trapped by
the grid's lead strips
Grids effectively remove much of the scattered radiation in the remnant beam before it reaches the
x-ray IR
Compression can be applied to
reduce the effect of excessive fatty tissue (eg, in the abdomen), in effect reducing the thickness of the part to be radiographed.
Compared to a low ratio grid, a high ratio grid will
1. absorb more primary radiation.
2. absorb more scattered radiation.
The higher the lead strips (or the smaller the distance between the strips), the greater the
grid ratio and the greater the percentage of scattered radiation absorbed
a grid does absorb some
primary radiation as well.
The higher the lead strips, the more critical the need for
accurate centering, as the lead strips will more readily trap photons whose direction do not parallel them
The reduction in x-ray photon intensity as the photon passes through material is termed
attenuation
Absorption
occurs when an x-ray photon interacts with matter and disappears, as in the photoelectric effect
Scattering
occurs when there is partial transfer of energy to matter, as in the Compton effect.
attenuation
The reduction in the intensity of an x-ray beam as it passes through matter
Which of the following is an abnormal intensifying screen action?
Lag
Luminescence
the production of energy in the form of light
Two types of luminescence are
fluorescence and phosphorescence.
Fluorescence
occurs when an intensifying (radiographic) screen absorbs x-ray photon energy, emits light, and ceases to emit light as soon as the energizing source ceases.
Fluoroscopic screens continue to emit light
for a short time after the exposure has terminated. This characteristic (phosphorescence) is a desirable quality in fluoroscopic screens.
Lag
occurs when an intensifying (radiographic) screen continues to fluoresce after the x-ray stimulation has terminated. This characteristic is undesirable and causes excessive density.
Screen speed is identified by
the amount of light emitted by the phosphors.
Which of the following technical changes would best serve to remedy the effect of widely different tissue densities?
High kVp exposure factors
When tissue densities within a part vary greatly (eg, chest x-ray), the radiographic result can be
unacceptably high contrast.
To "even out" these densities and produce a more appropriate scale of grays, exposure factors using
high kVp should be employed
Radiographic contrast generally increases with
an increase in screen speed.
The higher the grid ratio, the higher the
contrast.
Exposure factors using high mAs generally result in
excessive image density, frequently obliterating much of the gray scale.
Congestive heart failure, pneumonia, and pleural effusion, all involve abnormal amounts of fluid in the chest and would therefore require
an increase in exposure factors.
An increase in kilovoltage will serve to
produce a longer scale of contrast
An increase in kilovoltage increases
the overall average energy of the x-ray photons produced at the target, thus giving them greater penetrability. (This can increase the incidence of Compton interaction and therefore the production of scattered radiation.)
Greater penetration of all tissues serves to
lengthen the scale of contrast.
excessive scattered radiation reaching the IR will cause
a fog and carries no useful information.
Focusing distance is associated with which of the following?
Grids
Focusing distance
the term used to specify the optimal SID used with a particular focused grid.
Focusing distance is usually expressed as
focal range, indicating the minimum and maximum SID workable with that grid.
Lesser or greater distances can result in
grid cutoff
Which of the following absorbers has the highest attenuation coefficient?
Bone
The atomic number (Z) of the tissues under investigation is directly related to
its attenuation coefficient
differential absorption
contributes to the various shades of gray (scale of radiographic contrast) on the finished x-ray image.
effective Z number
Air has an effective Z number of 7.78, fat is about 6.46, water is 7.51, muscle is 7.64, and bone is 12.31.
As the object-to-image receptor distance (OID) increases, magnification of that object
increases.
The formula used to determine image width is:
iw = SID
`````` `````````
ow SOD
Osteoporosis
a condition, often seen in the elderly, marked by increased porosity and softening of bone. The bones are much less dense, and thus a decrease in exposure is required.
Osteomyelitis and osteochondritis
inflammatory conditions that usually have no effect on bone density.
Osteosclerosis
abnormal hardening of the bone, and an increase in exposure factors would be required.
Exposure rate increases with an increase in
1. mA.
2. kVp.
quantity of x-ray photons produced at the target is the function of
mAs
quality (wavelength, penetration, energy) of x-ray photons produced at the target is the function of
kVp
kVp also has an effect on exposure rate, because
an increase in kVp will increase the number of high-energy x-ray photons produced at the target.
The intensity of scattered radiation 1 m from the patient is approximately
0.1% of the intensity of the primary beam
Distortion can be caused by
1. tube angle.
2. the position of the organ or structure within the body.
3. the radiographic positioning of the part.
Increasing the grid ratio will result in a larger percentage of scattered radiation being absorbed and hence a
shorter scale of contrast.
The function(s) of automatic beam limitation devices include
reducing the production of scattered radiation.
Beam restrictors
function to limit the size of the irradiated field. In doing so, they limit the volume of tissue irradiated (thereby decreasing the percentage of scattered radiation generated in the part) and help reduce patient dose.
Beam restrictors do not affect
the quality (energy) of the x-ray beam—that is the function of kVp and filtration
Beam restrictors do not absorb scattered radiation—that is a function of
grids
The formula used to determine the amount of image magnification is:
image size = SID
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object size SOD
mAs has no effect on
the scale of contrast produced
slower screens will produce
lower (longer scale) contrast than faster screens
lower grid ratios produce
longer scale than higher grid ratios
As the volume of irradiated tissue increases, so does the amount of
scattered radiation produced and, consequently, the longer the scale of radiographic contrast
As kVp is reduced, the number of high-energy photons produced at the target is reduced; therefore, a decrease in
radiographic density occurs.
If a radiograph exhibits insufficient density, this might be attributed to
1. inadequate kVp.
2. grid cutoff.
density maintenance formula,
old mAs = old distance squared
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new mAs new distance squared
when kVp is increased by 15%
density is doubled
As screen speed is increased, exposure factors must
be decreased to maintain the original image density.
A change from 100 to 200 speed usually requires that the mAs be
reduced by one-half.
If screen speed were changed from 400 to 200 speed,
twice the mAs would be required
the effect of high kVp on iodinated contrast media
will produce excessive scattered radiation and obviate the effect of the contrast agent
when iodinated contrast media is being used low kilovoltage (about 70) is usually employed to enhance the
photoelectric effect
The factors that affect the recorded detail of traditional screen/film imaging are
focal-spot size, source-to-object distance (SID), object-to-image distance (OID), film/screen speed, and motion
Recorded detail is improved using
a small focal-spot size, largest practical SID, shortest possible OID, and slowest practical screen film combination and avoiding motion of the part being imaged.
The smaller the anode angle,
the smaller is the effective focal spot.
The greater the intensification factor, the greater is the
screen speed
Filtration affects
the overall average photon energy, that is, beam quality. Filtration is unrelated to recorded detail.
Radiographic recorded detail is directly related to
SID
SID is directly related to
recorded detail because as SID increases, so does recorded detail (because magnification is decreased)
OID is
inversely related to recorded detail because as OID increases, recorded detail decreases.
As screen speed increases, recorded detail
decreases, as a result of greater diffusion of light.
OID and screen speed are
inversely related to recorded detail.
density maintenance formula
old mAs = old distance squared
`````````````` ````````````````````````````
new mAs new distance squared
What is the single most important factor controlling size distortion?
OID
OID is the primary factor influencing
magnification, followed by SID.
Which of the following have an effect on recorded detail?
1. Focal spot size
2. SID
Focal spot size
affects recorded detail by its effect on focal spot blur: The larger the focal spot size, the greater the blur produced
Recorded detail is significantly affected by
distance changes because of their effect on magnification
As SID increases, magnification
decreases and recorded detail increases.
The line focus principle expresses the relationship between
the actual and the effective focal spot.
The line focus principle
is a geometric principle illustrating that the actual focal spot is larger than the effective (projected) focal spot.
The actual focal spot (target) is larger, to accommodate
heat over a larger area, and is angled so as to project a smaller focal spot, thus maintaining recorded detail by reducing blur.
The relationship between the exposure given the IR and the resulting density is expressed in
the reciprocity law
the relationship between the SID and resulting density is expressed by the
inverse square law.
Which of the following will influence recorded detail?
1. Screen speed
2. Screen-film contact
3. Focal spot
The faster the imaging system
the greater the sacrifice of image clarity (recorded detail).
As intensifying-screen speed increases
recorded detail decreases.
Perfect screen-film contact is essential for
good detail.
Any areas of poor contact result in
considerable blurriness in the radiographic image.
Focal spot blur is related to
focal spot size; smaller focal spots produce less blur and thus better recorded detail.
Materials that emit light when stimulated by x-ray photons are called
phosphors
Typically, for each x-ray photon absorbed,
many light photons are emitted; intensifying screens serve to amplify the action of x-rays.
Characteristics of low ratio focused grids include the following:
1. they have a greater focal range
2. they are less efficient in collecting SR
Grid ratio
compares the height of the lead strip to the distance between the lead strips
Focused grids
have their lead strips angled so as to parallel the divergent x-ray beam.
The higher the grid ratio
the greater the grid's efficiency in absorbing scattered radiation before it reaches the image receptor—but the more critical the centering and distance specifications.
Focused grids must not be accidentally inverted
to do so would cause the lead strips to be placed exactly in the path of the lead strips (grid cutoff), everywhere but in the center of the grid.
Which of the following can impact the visibility of the anode heel effect?
1. SID
2. Image recorder size
Because the focal spot (track) of an x-ray tube is along the anode's beveled edge
photons produced at the target are able to diverge considerably toward the cathode end of the x-ray tube but are absorbed by the heel of the anode at the opposite end of the tube.
This results in a greater number of x-ray photons distributed toward the
cathode end, which is known as the anode heel effect.
The effect of this restricting heel is most pronounced when
the x-ray photons are required to diverge more, as would be the case with short SID, large-size IRs, and steeper (smaller) target angles.
to compensate for every 1 inch of OID, an increase of
7 inches of SID is required.
Compression of the breast during mammographic imaging improves the technical quality of the image because
1. geometric blurring is decreased.
2. less scattered radiation is produced.
3. patient motion is reduced.
Which of the following quantities of filtration is most likely to be used in mammography?
0.5 mm Mo
Soft tissue radiography requires the use of
long-wavelength, low-energy x-ray photons.
Very little filtration is used in
mammography.
anything more than 1.0 mm of aluminum would
remove the useful soft photons, and the desired high contrast could not be achieved.
Dedicated mammographic units
usually have molybdenum targets (for the production of soft radiation) and a small amount of molybdenum filtration.
Which of the following are methods of limiting the production of scattered radiation?
1. Using the prone position for abdominal examinations
2. Restricting the field size to the smallest practical size
Beam restriction is probably the single most effective means of
reducing the production of scattered radiation.
Grid ratio affects
the cleanup of scattered radiation; it has no effect on the production of scattered radiation
Radiographic contrast is a result of
1. differential tissue absorption.
2. emulsion characteristics.
Radiographic contrast
the degree of difference between adjacent densities.
These density differences represent
sometimes very subtle differences in the absorbing properties of adjacent body tissues.
type of film emulsion used also brings with it its own
contrast characteristics
Different types of film emulsions have different degrees of
contrast "built into" them chemically.
The technical factor used to regulate contrast is
kilovoltage.
With a given exposure, as intensifying-screen speed decreases, how is radiographic density affected?
Decreases
As intensifying-screen speed decreases,
less fluorescent light is emitted from the phosphors.
If less fluorescent light strikes the film emulsion,
a smaller number of silver halide grains are changed to black metallic silver in the developer, and hence there is a decrease in radiographic density.
As intensifying-screen speed decreases, so does
radiographic density
Intensifying-screen speed and radiographic density are
directly related.
Because the anode's focal track is beveled
(angled, facing the cathode), x-ray photons can freely diverge toward the cathode end of the x-ray tube.
the "heel" of the focal track prevents x-ray photons from
diverging toward the anode end of the tube. This results in varying intensity from anode to cathode, with fewer photons at the anode end and more photons at the cathode end.
The anode heel effect is most noticeable when using
large IR sizes, short SIDs, and steep target angles.
The formula used to determine magnification factor is:
MF = SID/SOD
if MF = 1.257
The "1" represents the actual object, while the ".257" represents the degree of magnification. The percent magnification can be determined by moving the decimal two places to the right. Thus, the percent magnification is 25.7%.
As grid ratio is increased,
the scale of contrast becomes shorter.
The advantage(s) of high kilovoltage chest radiography is (are) that
1. exposure latitude is increased.
2. it produces long-scale contrast.
3. it reduces patient dose.
A grid is usually used whenever
high kilovoltage is required.
A grid is usually employed in which of the following circumstances?
1. When radiographing a large or dense body part
2. When using high kilovoltage
Significant scattered radiation is generated within the part when
imaging large or dense body parts and when using high kilovoltage.
Although a grid prevents much of the scattered radiation from reaching the radiograph, its use does necessitate a significant increase in
patient exposure.
Which of the following is most likely to result from the introduction of a grid to a particular radiographic examination?
Increased patient dose and increased contrast
The iodine-based contrast material used in intravenous (IV) urography gives optimum opacification at
60 to 70 kVp.
Use of higher kVp will negate the effect of
the contrast medium; a lower contrast will be produced, and poor visualization of the renal collecting system will result.
GI and BE examinations employ high-kVp exposure factors (about 120 kVp) to
penetrate through the barium.
In chest radiography, high-kVp technical factors are preferred for
maximum visualization of pulmonary vascular markings, made visible with long-scale contrast.
grid compensation formula
old mAs = old grid factor
``````````` ```````````````````
new mAs new grid factor
Which of the following contribute to the radiographic contrast present on the finished radiograph?
1. Atomic number of tissues radiographed
2. Any pathologic processes
3. Degree of muscle development
The atomic number of the tissues under investigation is directly related to their
attenuation coefficient.
differential absorption contributes to
the various shades of gray (scale of radiographic contrast) on the finished radiograph.
Normal tissue density may be significantly altered in the presence of
pathologic processes.
What determines the quantity of fluorescent light emitted from a fluorescent screen?
1. Thickness of the phosphor layer
2. Type of phosphor used
3. kV range used for exposure
The thicker the 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.
Why are a single intensifying screen and single emulsion film used for select radiographic examinations?
For better recorded detail
The diffusion of fluorescent light from intensifying screens is responsible for
a loss of recorded detail on double-emulsion film.
by changing the system to include only one intensifying screen and single-emulsion film, as in mammographic systems, light diffusion is reduced and better
recorded detail results.
Patient dose is somewhat greater than with a two-screen cassette system, but the advantage of significantly improved
recorded detail greatly offsets this.
The major function of filtration is to reduce
patient dose
X-rays produced at the target make up a
heterogeneous primary beam
There are many "soft," low-energy photons that, if not removed, would contribute only to
greater patient (skin) dose
They do not have enough energy to penetrate the patient and expose the film; they just
penetrate a small thickness of the patient's tissue and are absorbed.
These photons are removed by
aluminum filters
A shoulder was imaged using 300 mA, 7 ms, 70 kVp, 40-inch SID, 1.2-mm focal spot, and 100 speed screen/film combination. Which of the following changes, made to compensate for changes in optical density, would result in decreased production/visualization of blur?
1. Use of a 0.6-mm focal spot
2. Use of a 50-inch SID
Blur impairs
recorded detail
The factors that affect the recorded detail of traditional screen/film imaging are
focal-spot size, source-to-image distance (SID), object-to-image distance (OID), film/screen speed, and motion
Recorded detail is improved using
a small focal-spot size, largest practical SID, shortest possible OID, and slowest practical screen/film combination and avoiding motion of the part being imaged.
Which of the following focal spot sizes should be employed for magnification radiography?
0.2 mm
Proper use of focal spot size is of paramount importance in
magnification radiography.
A magnified image that is diagnostic can be obtained only by using
a fractional focal spot of 0.3 mm or smaller
The amount of blur or geometric unsharpness produced by focal spots that are larger in size render the radiograph
undiagnostic.
The continued emission of light by a phosphor after the activating source has ceased is termed
phosphorescence
Fluorescence
occurs when an intensifying screen absorbs x-ray photon energy, emits light, and then ceases to emit light as soon as the energizing source ceases.
Phosphorescence
occurs when an intensifying screen absorbs x-ray photon energy, emits light, and continues to emit light for a short time after the energizing source ceases.
Quantum mottle
the freckle-like appearance on some radiographs made using a very fast imaging system.
The brightness of a fluoroscopic image is amplified through
image intensification.
Which of the following materials may be used as grid interspace material?
1. Plastic
2. Aluminum
The interspace material must be
radiolucent
Cardboard was formerly used as interspace material, but it had the disadvantage of being affected by
humidity (moisture)
pneumoperitoneum
an abnormal accumulation of air or gas in the peritoneal cavity, it would require a decrease in exposure factors.
Obstructed bowel
usually involves distended, air- or gas-filled bowel loops, again requiring a decrease in exposure factors.
ascites
an abnormal accumulation of fluid in the abdominal cavity, necessitating an increase in exposure factors.
Renal colic
the pain associated with the passage of renal calculi; no change from the normal exposure factors is usually required.
Which of the following is (are) method(s) that would enable the radiographer to reduce the exposure time required for a particular radiograph?
1. Use higher mA.
2. Use higher kVp.
3. Use faster film-screen combination.
Use of a higher-speed film-screen combination also helps reduce mAs (exposure time) through
more efficient conversion of photon energy to fluorescent light energy.
Methods that help reduce the production of scattered radiation include using
1. compression.
2. beam restriction.
Limiting the size of the irradiated field is a most effective method of
decreasing the production of scattered radiation
The smaller the volume of tissue irradiated, the smaller the amount of
scattered radiation generated; this can be accomplished using compression (prone position instead of supine or a compression band)
The single most important factor regulating radiographic contrast is
kVp
The lower the kVp
the shorter the scale of contrast.
Grid ratio
defined as the ratio between the height of the lead strips and the width of the distance between them (ie, their height divided by the distance between them).
The thickness of the lead strip is unrelated to
grid ratio.
Why is a very short exposure time essential in chest radiography?
To minimize involuntary motion
All of the following affect the exposure rate of the primary beam
A. mA.
B. kVp.
C. distance.
Exposure rate is regulated by
milliamperage.
Distance significantly affects the exposure rate, according to the
inverse square law of radiation.
Kilovoltage also has an effect on exposure rate, because
an increase in kVp will increase the number of high-energy photons produced at the target.
The size of the x-ray field determines
the volume of tissue irradiated, and hence the amount of scattered radiation generated, but is unrelated to the exposure rate.
Which of the following is (are) causes of grid cutoff when using reciprocating grids?
1. Inadequate SID
If the SID is above or below the recommended focusing distance, the primary beam will not coincide with the angled lead strips at their lateral edges. Consequently, there will be absorption of the primary beam, termed
grid cutoff.
If the central ray is off-center longitudinally, there will be
no ill effects
If the central ray is off-center side-to-side, the lead strips are no longer parallel with the divergent x-ray beam, and there will be
loss of density due to grid cutoff.
Central ray angulation in the direction of the lead strips is appropriate and will not cause
grid cutoff
Central ray angulation against the direction of the lead strips will cause
grid cutoff
In comparison to 60 kVp, 80 kVp will
1. permit greater exposure latitude.
2. produce longer scale contrast.
3. produce more scattered radiation.
The higher the kVp range, the greater the
exposure latitude (margin of error in exposure)
Higher kVp is more penetrating and produces more
grays on the radiograph, lengthening the scale of contrast.
As kVp increases, the percentage of
scattered radiation also increases.
The variation in photon distribution between the anode and cathode ends of the x-ray tube is known as
the anode heel effect
Because the focal spot (track) of an x-ray tube is along the anode's beveled edge
photons produced at the target are able to diverge toward the cathode end of the tube, but are absorbed by the "heel" of the anode at the opposite anode end of the tube
This results in
a greater number of x-ray photons distributed toward the cathode end and is known as the anode heel effect.
line focus principle
is a geometric principle illustrating that the effective focal spot is always smaller than the actual focal spot.
Bohr's theory
refers to an atom's resemblance to the solar system
reciprocity law
states that a particular mAs, regardless of the mA and exposure time used, will provide identical radiographic density.
This holds true with direct exposure techniques, but it does fail somewhat with
the use of intensifying screens. However, the fault is so slight as to be unimportant in most radiographic procedures.
most likely to be the cause of quantum mottle.
Fast imaging systems (fast film and fast screens, as well as CR/DR systems) with low mAs and high kVp factors
Recorded detail is unaffected by changes in
kVp
When changing from single-phase to three-phase, six-pulse equipment,
two-thirds of the original mAs is required to produce a radiograph with similar density
When changing from single-phase to three-phase, 12-pulse equipment,
only one-half of the original mAs is required.
Which of the following affect(s) both the quantity and the quality of the primary beam?
1. Half-value layer (HVL)
2. kVp
The principal qualitative factor for the primary beam is
kVp, but an increase in kVp will also create an increase in the number of photons produced at the target.
HVL
the amount of material necessary to decrease the intensity of the beam to one half of its original value, thereby effecting a change in both beam quality and quantity.
The mAs value is adjusted to regulate
the number of x-ray photons produced at the target.
X-ray beam quality is unaffected by changes in
mAs
The use of which of the following is (are) essential in magnification radiography?
Fractional focal spot
Magnification radiography is used to
enlarge details to make them more perceptible
candidates for magnification radiography
Hairline fractures, minute blood vessels, and microcalcifications
The problem of magnification unsharpness is overcome by using a
fractional focal spot;
larger focal spot sizes will produce
excessive blurring unsharpness
Grids are usually unnecessary in magnification radiography because of
the air-gap effect produced by the OID
A direct-exposure technique would not be likely to be used because of
the excessive exposure required.
A compensating filter is used to
even out widely differing tissue densities
For example
it is difficult to obtain a satisfactory image of the mediastinum and lungs simultaneously without the use of a compensating filter to "even out" the densities. With this device, the chest is radiographed using mediastinal factors, and a trough-shaped filter (thicker laterally) is used to absorb excess photons that would overexpose the lungs. The middle portion of the filter lets the photons pass to the mediastinum almost unimpeded.
Which of the following factors influence(s) the production of scattered radiation?
1. Kilovoltage level
2. Tissue density
3. Size of field
Beam restriction is the single most important way to limit the amount of
scattered radiation produced
The absorption of useful radiation by a grid is called
grid cutoff.
contrast improvement factor.
Contrast obtained with a grid compared to contrast without a grid
he greater the percentage of scattered radiation absorbed compared to absorbed primary radiation, the greater the
"selectivity" of the grid
If a grid absorbs an abnormally large amount of useful radiation as a result of improper centering, tube angle, or tube distance
grid cutoff occurs