3. Density Flashcards
2 photographic properties in assessing density
Density,
Visibility of detail
is one of the 2 photographic properties that comprise visibility of detail
Density
refers to the fact that the image is
visible to the human eye only because sufficient density
(and contrast) exists to permit the structural details to be
perceived
Visibility of detail
the degree of
overall blackening from the black metallic silver deposited
in the emulsion of film
traditional definition of density
describes the concept of density as it displayed
on a soft-copy monitor for digital images
Brightness
describes the digital processing that
produces changes in density/brightness, so it also appropriate to use when controlling image density
Window level
The majority consideration in assessing density is
verification that proper densities are ______ throughout the
anatomical area of interest on the image
visible
_______ and a _______ are the
primary tools of the radiographer when evaluating density
Common sense,
trained professional eye
Information is recorded on an image that is ________
but may not exist at all on a radiograph that is
________
overexposed,
underexposed
The _______ image has not received the information
in the first place and is not capable of being manipulated to
reveal details that were never recorded
underexposed
Whenever a choice must be made between excess and
insufficient density, the wise decision is always the choice
that will produce the _______ image
overexposed
device used to see details of overexposed image but makes it darker
hot/bright light
affects visibility
density
acceptance limits
diagnostic value
The effects of mAs and other influencing factors on density
are ______ because of the multiple variables that are part
of the imaging system
not exact
Density changes can sometimes be seen from only a slight
nonlinearity in the _______
intensifying screen phosphor response curve,
film silver halide response,
thermionic emission of the x-ray tube filament
When unexpected density changes exceed the ____
necessary to become visible, they seldom place the image
outside the _______
30%,
acceptance limits
2 factors affecting density
controlling factors,
influencing factors
controlling factor of density
mAs
expresses the relationship between exposure and density
D log E sensitometric curve or a digital response curve
important region of the D log E curve in assessing density
Toe,
Shoulder
overexposed region
Shoulder region
underexposed region
Toe region
it is where large changes in exposure results in small changes in OD (optical density)
Toe and shoulder region
A common misnomer on radiography is that doubling the
exposure will ____ the film density
double
For digital image receptor systems, changes in _____ no
longer control density
mAs
For digital image receptor systems, Image density/brightness on the
display monitor is controlled by ______
window levelling
are graphic representations of the
exposure to the image receptor
Digital image histograms
is use as the primary controller of
image receptor exposure and film density
mAs
is primarily determined by the amount of
exposure a receptor receives
density
is directly proportional to mAs
exposure
The minimum change necessary to cause a visible shift in
film density is _____ of mAs, or any other influencing factors
that would equal this change.
30%
Various authors over the years have set the minimum for a
visible density change at values between ______ of mAs
25-35%
The general rule of thumb for mAs changes is to make
adjustments in _______
increments or doubles or halves
mAs is incremented by
decimals
Influencing Factors of Density:
kVp, Focal Spot Size, Anode Heel Effect, Distance (SID and OID), Filtration, Beam Restriction, Anatomical Part, Grids, Image Receptor, Film processing
alters the intensity of the beam reaching the
image receptor in two ways
kVp
a change in _______ alters the intensity of
the beam when the mAs and other factors remain the same
kilovoltage
Both the quantity and quality of the x-ray beam will vary
significantly with changes in _______
kilovoltage
A visible change in film density can usually be detected
with a _____ change in kVp in the lower ranges (30-50 kVp)
but an _____ change is required in the middle ranges (50-90
kVp), and a ____ change in the higher ranges (90-130
kVp)
4-5%,
8-9%,
10-12%
the radiographer must have a method of using kilovoltage to adjust and compensate for film density changes, the rough guide known as the _______ has been developed
15 percent rule
is another important
consideration in how kVp affects image receptor exposure/film density
configuration of the generator
utilize a greater
incident electron stream than small focal spots
Larger focal spots
The actual mA for a large focal spot is ____ than the actual
mA received when set at 100 mA for a small focal spot.
less
will heat up fast but makes the image sharper
Short Focal Spot Size
takes time to heat up but creates penumbra
Large Focal Spot Size
Large focal spots tend to bloom more at _____
milliamperages and may occasionally reach a point where
they alter the image receptor exposure
higher
Because properly calibrated units will not exhibit film
density changes when focal spots are changed, differences of
this type should be reported as a ______
quality control procedure
alters the intensity of radiation and
therefore the density, between the anode and cathode ends of the x-ray tube
Anode Heel Effect
is more pronounced when the
collimator is open wide than when it is closed because of a
greater portion of the peripheral beam
Anode Heel Effect
The anode heel effect is more pronounced when the
collimator is open wide than when it is closed because of a
greater portion of the peripheral beam, and therefore a
greater portion of the intensity difference, reaches the IR
when the collimator is _____
wide open
When the anode heel effect becomes apparent, it can be ______
minimized or converted to an advantage
Anode heel effect
is _______ by collimating the beam and eliminating as
much of the intensity difference at the periphery as possible.
minimized
The anode heel effect may be _______
in examinations of objects with greater subject density at
one end than at another
converted to an advantage
alters the intensity of the beam reaching the image receptor, according to the inverse square law
Source-to-Image receptor
Distance
affects exposure in inverse
proportion to the square of the distance
inverse square law
expresses the change in
intensity when the distance changes
inverse square law formula
the most common situation in radiography is a need to maintain an _______ image receptor exposure/film density while changing the distance
acceptable
is only accurate within a
moderate acceptance range
exposure maintenance formula
The _______ of some
components in the imaging system makes it impossible to
exactly quantify the relationship between radiation beam
intensity and film density
nonlinearity
Distance doubling and halving will bring image receptor
exposure within roughly ____ of the original exposure and
usually within image acceptance limits
50%
3 Cardinal Principles of Radiation Protection
Time,
Distance,
Shielding
has an effect on image
receptor exposure/film density.
Object-to-Image receptor (OID)
increase OID can ______ density
decrease
its ability to alter beam intensity affect
image receptor exposure and film density
Filtration
reduces the total
number of photons available
Restricting the beam, collimating, or
reducing the primary beam field size
dramatically increased with large
anatomical size and high starting kVp levels
Scatter production
Technical factor compensation for changes in film density is
required only under the following circumstances:
- ) Large anatomical part
- ) High kilovoltage
- ) Low grid efficiency
- ) Nongrid examinations
is the prime
attenuator of the beam
Patient
Because the patient is the prime
attenuator of the beam, the _________ being examined has a great deal of influence on image receptor
exposure and film density
anatomical part
There is an _______ relationship between tissue thickness/type and image receptor exposure/film density
inverse
absorb scatter, which would otherwise add
exposure to the image receptor and density to the film
Grids
(Grids) factors that reduce image receptor exposure/film density
Grids with high ratios,
low frequency and dense interspace material;
moving grids and improperly used grids
HTD
Height of the grid (H),
Thickness of the grid strip (T),
Width of the Interspace material (D)
Grid ratio
h/D
the primary purpose of a grid is the _________
improvement
of contrast
compensating for film density changes by
varying the kVp is ______ because it may change
the contrast in the opposite direction, thus negating the
reason for using the grid in the first place
not recommended
when using grids, do not change ____
kVp
Both film and intensifying screens alter film density
Image Receptor
When the silver halide crystals in the film emulsion form
________, they establish the physical foundation
for the black metallic silver that is the definition of density
latent image centers
are the most useful
parameters for intensifying screen combinations
Relative Speed (RS) numbers
As relative speed increases, the amount of exposure required to maintain the same film density ______
decreases
Digital radiographic systems can be _____ in their sensitivity to the income of x-ray photons
varied
The condition of the ________ solutions can dramatically alter film density
film processing
Film density will increase when the ______ (Film processing)
developer solution temperature increases, immersion time increases or
replenishment rates increase
With Grid, _____ Contrast, _____ Density
Increase C,
Decrease D
