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Image production & evaluation

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Comparison of Technical Factors Required
Single-Phase (x mAs)
Three-Phase, 6-Pulse (2/3x mAs)
Three-Phase, 12-Pulse (1/2x mAs)
With three-phase equipment, the voltage never drops to
zero
With three-phase equipment x-ray intensity is
significantly greater.
When changing from single-phase to three-phase, six-pulse equipment,
two thirds of the original mAs are required to produce a radiograph with similar density
When going from three-phase, six-pulse to single-phase, add
one-third more mAs.
When changing from single-phase to 3-phase, 12-pulse equipment,
only one-half of the original mAs is required.
Going from three-phase, 12-pulse to single-phase requires
twice the mAs.
changing from single-phase to three-phase, 12-pulse equipment; therefore the new mAs should be
half the original
The amount of replenisher solution added as a film enters the automatic processor is related to the
1. size of the film.
2. number of films processed.
Each film passing through the processor solutions
takes with it a certain amount of solution
Replenishment is also essential for
maintaining each solution's level of concentration, to maintain solution activity and avoid chemical fog from exhausted solutions.
One way to determine the quantity of replenisher solution to be added is by
the length of the film entering the processor.
A microswitch initiates and terminates replenishment as
it senses the beginning and end of each film.
Replenishment is also determined by
the number of films (volume) processed.
The greater the number of films processed,
the lower the required replenishment rate
Greater latitude is available to the radiographer when using
1. high kVp factors.
2. a slow film-screen combination.
Which of the following adult radiographic examinations usually require(s) use of a grid?
1. Ribs
2. Vertebrae
3. Shoulder
anatomic parts measuring in excess of 10 cm require
a grid.
The major exception to this rule is
the chest
The larger the part,
the more scattered radiation is generated.
Parts generally requiring the use of a grid include
the skull, spine, ribs, pelvis, shoulder, and femur.
osteomalacia, fibrosarcoma, and paralytic ileus (obstruction), result in a
decrease in body tissue density.
The technical factors mAs, kVp, and grid ratio have no effect on
recorded detail.
A radiograph exposed using a 12:1 ratio grid may exhibit a loss of density at its lateral edges because the
SID was too great
If the grid failed to move during the exposure, there would be
grid lines throughout.
If the central ray was off-center, there would be
uniform loss of density.
If the x-ray tube is angled significantly across the lead strips of a focused grid, there is
uniform loss of density (grid cutoff)
Insufficient or excessive distance with focused grids causes
loss of density (grid cutoff) along the periphery of the image.
An increase in exposure factors is usually required in which of the following circumstances?
1. Edema
2. Ascites
3. Acromegaly
acromegaly
an increase in bone size and density
The fact that x-ray intensity across the primary beam can vary as much as 45% describes the
anode heel effect
The anode heel effect becomes more pronounced as
the SID decreases, as IR size increases, and as target angle decreases.
A higher milliamperage with a short exposure time is generally
preferable
Which of the following methods can be effectively used to decrease differential absorption, providing a longer scale of contrast in the diagnostic range?
1. Using high kVp and low mAs factors
2. Using compensating filtration
The photoelectric effect
the interaction between x-ray photons and matter that occurs at low kVp levels—levels that tend to produce short-scale contrast.
Which of the following function(s) to reduce the amount of scattered radiation reaching the IR?
1. Grid devices
2. Beam restrictors
Which portion of the characteristic curve would most likely represent a density of 1.0?
Straight-line portion
A characteristic curve is used to
predict the speed, contrast, and exposure latitude of a particular film emulsion.
A characteristic curve compares
the exposure, given the film with the resultant density
A characteristic curve has three portions:
the toe, the straight-line portion (region of correct exposure), and the shoulder
The toe
occurs immediately after base-plus fog, whose density must not exceed 0.2.
straight-line portion
follows the toe; portion of correct exposure and extends from about 0.25 to 2.5
The curve then bends and levels off at the
shoulder (Dmax) portion of the curve.
Which of the following factors affect(s) both radiographic density and intensifying screen speed?
1. Thickness of phosphor layer
2. Type of phosphors used
Factors that affect screen speed will also affect
radiographic density.
Rare earth-type phosphors
absorb x-rays more efficiently and convert their energy into fluorescent light; they therefore affect both screen speed and radiographic density
The thickness of the phosphor layer affects
speed and density similarly: As the thickness of the phosphor layer increases, speed and density increase.
The spongy layer behind each intensifying screen helps ensure
good screen-film contact and therefore good recorded detail. The spongy layer is unrelated to radiographic density.
Which of the following can affect histogram appearance?
1. Centering accuracy
2. Positioning accuracy
3. Processing algorithm accuracy
The CR laser scanner recognizes the various tissue density values and constructs a
representative gray-scale histogram
A histogram is a
graphic representation showing the distribution of pixel values
Histogram analysis and use of the appropriate LUT together function to
produce predictable image quality in CR.
Degree of accuracy in positioning and centering
can have a significant effect on histogram appearance (as well as patient dose)
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 (e.g., chest vs femur vs cervical spine), changes in scatter, SID, OID, and collimation.
How would the introduction of a 6-inch OID affect image contrast?
Contrast would be increased
ID can affect contrast when it is used as
an air gap.
If a 6-inch air gap (OID) is introduced between the part and IR
much of the scattered radiation emitted from the body will not reach the IR
The OID is thus acting as a
low-ratio grid and increasing image contrast.
A technique chart should include which of the following information?
1. Recommended SID
2. Grid ratio
3. Screen-film combination
Technique charts are
exposure factor guides that help technologists produce radiographs with consistent density and contrast
They suggest a group of exposure factors to be used at
a particular SID with a particular grid ratio, screen-film combination, focal spot size, and central ray angulation.
Technique charts do not take into account
the nature of the part (disease, atrophy, etc)
Recorded detail is directly related to
source-image distance (SID)
As SID increases, so does
recorded detail, because magnification is decreased
SID is directly related to
recorded detail.
As focal spot size increases, recorded detail
decreases because more penumbra is produced.
Focal spot size is thus inversely related to
radiographic sharpness or recorded detail.
Tube current affects
radiographic density and is unrelated to recorded detail.
In which of the following ways can higher radiographic contrast be obtained in abdominal radiography?
1. By using lower kilovoltage
2. By using a contrast medium
3. By limiting the field size
Higher contrast is
shorter scale contrast; it is present in an image that has few shades of gray between white and black.
High radiographic contrast is, in part, a result of
lower energy photons (lower kVp).
High radiographic contrast also results when
radiographing anatomic parts that have high subject contrast, such as the chest.
The abdomen has low
subject contrast, and therefore abdominal radiographs will tend to have very low contrast unless technical factors are selected to increase contrast.
To produce high radiographic contrast in abdominal radiography,
lower kVp should be used.
To better demonstrate high contrast within a viscus
a contrast medium such as barium, iodine, or air can be used.
Restricting the size of the field will also function to
increase contrast because less scattered radiation will be generated.
Which of the following pathologic conditions are considered additive conditions with respect to selection of exposure factors?
1. Osteoma
2. Bronchiectasis
3. Pneumonia
Osteoma
or exostosis, is a (usually benign) bony tumor that can develop on bone
Bronchiectasis
is a chronic dilatation of the bronchi with accumulation of fluid
Pneumonia
is inflammation of the lung(s) with accumulation of fluid.
A grid is usually employed
1. when radiographing a large or dense body part.
2. when using high kilovoltage.
The function of the developer solution chemicals is to
reduce the latent image to a manifest image
The latent image is
the invisible image produced within the film emulsion as a result of exposure to radiation
unexposed crystals are removed from the film during
the fixing process.
Penetration and contrast are a function of
kilovoltage
Inadequate penetration and high contrast are a result of insufficient
kVp
How can the radiographer reduce the amount of scattered radiation generated during a radiographic examination?
1. Use optimum kVp.
2. Collimate closely.
The amount of scattered radiation generated in a given exposure increases as three factors increase:
the kVp, the field size, and the thickness and density of the tissues.
Geometric unsharpness is influenced by which of the following?
1. Distance from object to image
2. Distance from focus to object
3. Distance from focus to image
As focal-object distance and SID decrease, so does
magnification
OID may be said to be directly proportional to
magnification.
Focal-object distance and SID are inversely proportional to
magnification
If single-emulsion film was loaded into its cassette with the emulsion facing away from the intensifying screen, the resulting image would demonstrate
decreased density
Single-emulsion film is used for particular examinations, such as
mammography
Single-emulsion film is used
with a cassette that has a single intensifying screen and provides better detail than typical double-emulsion film and two-screen cassettes
It is essential that the light-sensitive emulsion be placed against the
light-emitting screen
Single-emulsion film has an antihalation backing that
efficiently absorbs reflected (crossover) light.
if the film were loaded with the antihalation side against the light-emitting screen, the film emulsion would
receive very little exposure
The processor rollers that are out of solution and function to transfer the film from one solution to another are the
crossover rollers
Turnaround assemblies
are located at the bottom of each solution tank and function to direct the film from a downward to an upward motion
Guide shoes
also called deflector plates, serve to keep the film on its proper course by directing or guiding it around corners.
The crossover rollers
are located at the top of the processor, out of the solution, and direct the film from one solution tank to the next. These are the racks that need daily cleaning to avoid chemical or emulsion buildup on their surface. Chemical or emulsion buildup on roller surfaces can cause film artifacts.
Which type of error results in grid cutoff at the periphery of the radiographic image?
Off-focus
If the x-ray beam is not centered to the grid, or if the x-ray tube and grid surface are not parallel (level), there will be a fairly uniform decrease in
radiographic density across the entire image.
if the grid is not used within its recommended SID (focus) range (ie, if the SID is too great or too little), there will be
a decrease in density at the periphery of the image.
All of the following are related to recorded detail
A. motion.
B. film-screen contact.
C. SID.
Motion
is said to be the greatest enemy of recorded detail because it completely obliterates image sharpness
Poor screen-film contact
reduces recorded detail because of the degree of light diffusion in the areas of poor contact. Areas of poor contact appear blurry.
A decrease in source-image distance causes
magnification and blurriness of recorded detail.
Which of the following conditions require(s) a decrease in technical factors?
1. Emphysema
2. Osteomalacia
Subcutaneous emphysema
is a pathologic distention of tissues with air
pulmonary emphysema
a chronic disease characterized by overdistention of the alveoli with air.
Osteomalacia
a softening of bone so that it becomes flexible, brittle, and deformed
Atelectasis
a collapsed or airless lung; it requires an increase in exposure factors.
If the quantity of black metallic silver on a particular radiograph is such that it allows 1% of the illuminator light to pass through the image, that image has a density of
2.0
If 10% of the illuminator's light passes through the image, that image has a density of
1.0
What should be done to correct for magnification when using air-gap technique?
Increase SID
OID is used to effect
an increase in contrast in the absence of a grid, usually in chest radiography
OID acts as a
low-ratio grid and increases image contrast.
the SID needs to be increased 7 inches for every
1 inch of OID.
With a 6-inch OID, the SID is usually increased from 6 feet to
10 feet (120 inches)
Geometric unsharpness is most likely to be greater
at the cathode end of the image
The x-ray tube anode is designed according to the
line focus principle, that is, with the focal track beveled
This allows a larger actual focal spot to project a
smaller effective focal spot, resulting in improved recorded detail with less blur
because of the target angle,
penumbral blur varies along the longitudinal tube axis, being greater at the cathode end of the image and less at the anode end of the image.
Which of the following will have an effect on radiographic contrast?
1. Beam restriction
2. Grids
Radiographic contrast is described as
the difference between densities, or scale of grays, in the radiographic image.
the function of grids is to
collect scattered radiation, they serve to shorten the scale of contrast.
Beam restrictors function to
limit the x-ray field size, thereby reducing the production of scattered radiation and shortening the scale of contrast.
Focal spot size
one of the geometric factors affecting recorded detail; it has no effect on the scale of contrast.
It is the function of radiographic contrast to
make details visible
The sum of subject contrast and film contrast equals
radiographic contrast.
When the collimated field must extend past the edge of the body, allowing primary radiation to strike the tabletop, as in a lateral lumbar spine, what may be done to prevent excessive radiographic density due to undercutting?
Use lead rubber to absorb tabletop primary radiation
When the primary beam is restricted to an area near the periphery of the body, sometimes
part of the illuminated area overhangs the edge of the body
If the exposure is then made, scattered radiation from the tabletop (where there is no absorber) will undercut the part, causing
excessive image density.
If, however, a lead rubber mat is placed on the overhanging illuminated area, most of this scatter will be
absorbed.
This is frequently helpful in
lateral lumbar spines and AP shoulders
Improper spectral matching between rare earth intensifying screens and film emulsion results in
insufficient density
If, for example, a blue-sensitive emulsion were matched with green-emitting screens, the resulting radiograph would be
underexposed because the blue-sensitive film emulsion was not responsive to the green-emitting phosphors.
In which of the following examinations would a cassette front with very low absorption properties be especially desirable?
Mammography
Because mammographic techniques operate at very low kVp levels, the cassette front material
becomes especially important.
The use of soft, low-energy x-ray photons is the underlying principle of
mammography; any attenuation of the beam would be most undesirable
Special plastics that resist impact and heat softening, such as polystyrene and polycarbonate, are frequently used as
cassette front material
The presence of dust or scratches on intensifying screens will cause
decreased density in those areas of the image
If intensifying-screen phosphors are covered with dust
either they will not fluoresce or their fluorescence will not reach the IR emulsion
if the screen is scratched and phosphors are removed,
there will be no fluorescence to expose the IR.
The principal quantitative factor regulating radiographic (or optical) density is
mAs
The mAs selected is directly proportional to
radiographic density (ie, if the mAs is cut in half, radiographic density will be halved)
Although SID affects exposure rate (according to the inverse square law of radiation), and therefore affects density (according to the density maintenance formula), it is not used to regulate
radiographic density
A grid is
a thin wafer placed between the patient and the IR to collect scattered radiation. It is made of alternating strips of lead and a radiolucent material such as plastic or aluminum.
An increase in kVp with appropriate compensation of mAs will result in
increased exposure latitude
As the kilovoltage is increased
more penetration will occur and a greater range of densities (grays) will be apparent in the image
This is termed
long scale or low contrast
In addition, as the kVp and scale of grays increase,
the exposure latitude increases; the "margin for error" in technical factors becomes greater.
According to the line focus principle, an anode with a small angle provides
1. improved recorded detail.
2. improved heat capacity.
The line focus principle illustrates that as the target angle decreases,
the effective focal spot decreases (providing improved recorded detail), but the actual area of electron interaction remains much larger (allowing for greater heat capacity).
It must be remembered, however, that a steep (small) target angle increases
the heel effect, and part coverage may be compromised
The effect that differential absorption has on radiographic contrast of a high subject contrast part can be minimized by
1. using a compensating filter.
2. using high-kVp exposure factors.
Differential absorption refers to
the different attenuation, or absorption, properties of adjacent body tissues
Two parts with widely differing absorption characteristics will produce
a high radiographic contrast.
exposure factors that would properly expose one part will
severely overexpose or underexpose the neighboring part (as with lungs vs thoracic spine)
This effect can be minimized by the use of
a compensating filter or by the use of high kilovoltage (for more uniform penetration).
Increased collimation is important in
the control of patient dose and scattered radiation, not differential absorption.
Which of the following radiographic accessories functions to produce uniform density on a radiograph?
Compensating filter
Compensating filters
can be accommodated by tracks in the tube head.
Compensating filters
can be wedge-shaped (with the thicker part of the wedge paralleling the thinner body part), thus compensating for greater or lesser tissue densities (as in a large decubitus abdomen)
penetrometer (aluminum step wedge)
used to illustrate the effect of kVp on contrast
intensifying screens
amplify the action of x-rays
An overall image density arising from factors other than the light or radiation used to expose the image is called
fog
Anything other than intensifying screen light or primary x-radiation is
undesirable in terms of image exposure
Log relative exposure
the amount of exposure required to produce a given density as measured on the sensitometric graph
Optical density
normal radiographic density.
artifact
anything foreign to the image; the term could include fog, but it also covers many physical interferences.
Crescent-shaped black marks on the finished radiograph are usually due to
bending the film acutely
A black crescent usually results from bending
after exposure
white crescent occurs if the film is bent
before exposure
As kVp is increased,
x-ray photons begin to interact with atoms of tissue via the Compton scattered interaction
While Compton scatter reduces patient dose, compared to photoelectric interactions
it can pose a significant radiation hazard to personnel during fluoroscopic procedures.
optimal kVp is recommended to reduce
the production of scattered radiation
Which of the following is most likely to occur as a result of using a 30-inch SID with a 14 x 17-inch IR to radiograph a fairly homogeneous structure?
Density variation between opposite ends of the IR
Because shorter SIDs and larger IR sizes require greater divergence of the x-ray beam to provide coverage,
the anode heel effect will be accentuated.
Which of the following can affect radiographic contrast?
1. Processing
2. Pathology
3. OID
he type of chemistry used in the automatic processor and especially the temperature of the solution can have a big impact on
the resulting image contrast.
As temperature increases,
contrast decreases.
Since pathology can alter the degree of attenuation of the x-ray beam, it can affect
contrast
An additive pathology such as Paget's disease will increase
contrast
a destructive disease such as osteoporosis will decrease
contrast
OID
can affect contrast when it is used as an air gap.
Which of the following pathologic conditions require(s) a decrease in exposure factors?
1. Pneumothorax
2. Emphysema
3. Multiple myeloma
Pneumothorax
a collection of air or gas in the pleural cavity.
Emphysema
a chronic pulmonary disease characterized by an increase in the size of the air-containing terminal bronchioles.
Multiple myeloma
a condition characterized by infiltration and destruction of bone and marrow.