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
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
or exostosis, is a (usually benign) bony tumor that can develop on bone
is a chronic dilatation of the bronchi with accumulation of fluid
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
Inadequate penetration and high contrast are a result of insufficient
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
OID may be said to be directly proportional to
Focal-object distance and SID are inversely proportional to
If single-emulsion film was loaded into its cassette with the emulsion facing away from the intensifying screen, the resulting image would demonstrate
Single-emulsion film is used for particular examinations, such as
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
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
are located at the bottom of each solution tank and function to direct the film from a downward to an upward motion
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?
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.
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
is a pathologic distention of tissues with air
a chronic disease characterized by overdistention of the alveoli with air.
a softening of bone so that it becomes flexible, brittle, and deformed
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
If 10% of the illuminator's light passes through the image, that image has a density of
What should be done to correct for magnification when using air-gap technique?
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
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
This is frequently helpful in
lateral lumbar spines and AP shoulders
Improper spectral matching between rare earth intensifying screens and film emulsion results in
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?
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
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
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?
can be accommodated by tracks in the tube head.
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
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
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
normal radiographic density.
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
white crescent occurs if the film is bent
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,
Since pathology can alter the degree of attenuation of the x-ray beam, it can affect
An additive pathology such as Paget's disease will increase
a destructive disease such as osteoporosis will decrease
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
a collection of air or gas in the pleural cavity.
a chronic pulmonary disease characterized by an increase in the size of the air-containing terminal bronchioles.
a condition characterized by infiltration and destruction of bone and marrow.