2. Radiographic Contrast II Flashcards
It is the range of differences in the intensity of the x-ray beam after it has been attenuated by the subject
Subject Contrast
is the primary controller of subject contrast
Kilovoltage (kVp or kilovoltage peak)
The \_\_\_\_\_ the range of photon energies, the \_\_\_\_\_ the ability of the photons to penetrate the body tissues
wider,
greater
SID
Source to Image Receptor Distance
As long as the kVp
is adequate to penetrate the part being examined,
___ kVp will produce ___ subject contrast
low,
high
It produces higher subject contrast because most of these low energy photons
are absorbed by thicker parts while more penetrate the thin
part.
Low kVP
\_\_\_\_\_ causes density differences that were previously undetectable to become visible, resulting in an increase in the diagnostic information provided by the image
Increasing kVp
In \_\_\_\_\_\_\_\_ – low kVps are used to enhance the differences between the air-filled lungs and the overlying bony structures
rib radiography
In addition to kVp, _______ has a significant effect on
contrast
radiation fog
Radiation fog is a result of x-ray interactions with matter, primarily _____
Compton scatter
These changes cause the lightest film densities to be “\_\_\_\_\_\_” so they can no longer be distinguished from one another
fogged over
Fog can be caused by factors other than scatter radiation and includes :
subjecting film to heat, low level ionizing radiation, or
chemical fumes
may also
cause objectionable fog levels.
Developer temperature, replenishment,
and developer contamination
depends on the
thickness of the body
part and the field size
Amount of Irradiated Material
Factors affecting scatter radiation
Field size
most important factor in the production of scatter radiation
Field size
a small x-ray field usually called ______ irradiate less tissue and generates fewer scattered photons
Narrow beam
As body part thickness decreases so does ______
absorption
When the difference between adjacent thicknesses of
various body parts is great, subject contrast is _______
increased
When little difference exists in the thickness of
adjacent body parts, subject contrast is ______
decreased
When the overall thickness of a body part increases when a
field size increases, the amount of scatter created will
______
increased
A decrease in overall body part thickness or field size results in ______ subject contrast
increased
Controlling factors:
kVp,
Amount of Irradiated Material,
Type of Irradiated Material
is influenced by the atomic number of the material and its tissue density
Type of Irradiated Material
Materials with a high atomic number absorb a ______ percentage of the x-ray beam
than low atomic number materials
greater
high atomic number example
Lead and iodine
low atomic number materials
hydrogen, carbon and
calcium
When the difference between the average atomic number
of adjacent tissues is great, subject contrast is ______
increased
When little difference exists between them, subject contrast
is _______
decreased
Contrast media ______ subject contrast by introducing
greater differences in atomic number variations than those
than exist naturally
increase
describes how tightly the atoms of a given
substance are packed together
Tissue density
When the difference between the densities of adjacent tissues is great, subject contrast is \_\_\_\_\_\_
increased
When little difference exists between the densities of adjacent tissues, subject contrast _____
decreased
The major consideration in evaluating visible contrast is verification that a _____ range of densities is _____ throughout the anatomical area of interest on the image
proper,
visible
Unlike the evaluation of density, contrast assessment
requires ____ than just sufficient density within the visibility range
more
Because there is more information recorded on an image
than is seen, the diagnostic importance of contrast is a
matter of how many densities are included in the ______
contrast range
visible
is limited in its ability to discern light and dark
and this essentially establishes a value for the lightest and
darkest visible shades of gray
Human eye
A____ exposure difference has been used as the minimum
change to cause a visible differenced because this
magnitude is discernible by nearly everyone.
30%
Some professionals may be able to discern as little contrast as a ____ difference which means they are capable of seeing
twice as many shades of gray as someone who can discern
only a 30% change
15%
can be made only when sufficient density exists to permit the range of contrast to be seen
Contrast evaluation
is a simple tool to help us focus on the
contrast in a selected area
contrast mask
When contrast mask is used with an image, adjacent
information is ______
eliminated
A visible change in contrast will not be perceived until kVp
is changed by _____ depending on the kVp range
4%-12%
CHANGE NECESSARY TO PRODUCE VISIBLE CHANGE:
30-50 kVp
4-5 percent
CHANGE EQUAL TO PERCENT CHANGE:
30-50 kVp
1-3 kVp
CHANGE NECESSARY TO PRODUCE VISIBLE CHANGE:
50-90 kVp
8-9 percent
CHANGE EQUAL TO PERCENT CHANGE:
50-90 kVp
4-8 kVp
CHANGE NECESSARY TO PRODUCE VISIBLE CHANGE:
90-130 kVp
10-12 percent
CHANGE EQUAL TO PERCENT CHANGE:
90-130 kVp
9-16 kVp
The effects of mAs and the influencing factors on image contrast are _____ because of the wide variety of
variables that are part of the imaging system
not exact
Both the quality and
the quantity of the x-ray beams will vary with changes in
kilovoltage
When a radiograph is outside acceptable limits, it needs to be _____
repeated
The rule for contrast changes is to make adjustments in increments of ______
15 or 8 percent
Radiographic image contrast occurs due to the ________ total absorption of photons in the subject
photoelectric effect’s
is directly related to the number of
photoelectric effect’s total absorption of photons in the
subject
High contrast
Compton interactions produce ______,
scatter
low contrast is
directly related to the amount of _____ that occurs in the subject
Compton scatter
can be determined by matching the average
incident photon energy with the average inner-shell binding energy of the predominant subject material
Contrast
FACTORS AFFECTING CONTRAST
controlling factor,
influencing factors
that affects contrast has the most direct effect on the image
controlling factor
have a less direct effect on the image or change other factors as well as
contrast
influencing factors
is the controller of contrast
kVp
Kvp increases = contrast ______and vice-versa
decreases
controls the amount of scatter radiation produced
kVp
changes the penetrability (quality) + quantity
kVp
Increasing kVp will ______ the amount of radiation fog,
thereby ______ contrast
increase,
decreasing
changes the amount of x-rays (quantity)
mAs
alters image receptor
exposure and film density of the image and therefore affects
contrast
mAs
10 INFLUENCING FACTORS OF CONTRAST
mAs, Focal Spot Size, Anode Heel Effect, SID and OID, Filtration, Beam Restriction, Anatomical part, Grids, Image Receptor, Processing
OID
Object-to-image receptor distance
possibility of the focal spot size altering
contrast enough to be visible is extremely ______
unlikely
alters the intensity of radiation and
therefore affects image receptor exposure and film density which can effect contrast
Anode Heel Effect
alters the intensity of the beam reaching the image receptor
according to the inverse square law
Source-to-Image receptor distance (SID)
has an effect
on image receptor exposure/film density and contrast
Object-to-image receptor distance (OID)
As the x-ray beam diverges, the image produced on the film is always slightly _____ than the original image
larger
As the x-ray beam diverges, the image produced on the film is always slightly larger than the original image, this effect is called _____
Magnification
increases the effect of kVp by changing the
average photon energy of the beam
Filtration
All types of filtration (_______) alter image
receptor exposure/film density and contrast
inherent, added, total
The increase in the average photon energy causes _____ Compton scatter production and this ____ contrast
more,
decreases
reduces the total
number of photons available
Restricting the beam, collimating, or
reducing the primary beam field size
Restricting the beam, collimating, or
reducing the primary beam field size
Beam Restriction
is the prime attenuator of the beam, both the amount and type of tissue being examined
greatly influence density and contrast
Patient
As tissue density increases, the amount of scatter radiation ______, which also results in a _____ in contrast
increases,
decrease
primary function is contrast improvement
Grids
Improve contrast by ______ scatter before it reaches the image receptor
removing
is the best measure of
how well a grid accomplishes this function
The contrast improvement factor (K)
“Clean up” scatter radiation
Grids
With ______
systems, the primary determinant of the shape of the D log E
curve is the physical composition of the film emulsion
Film/Screen image receptor
With _______, sufficient differences in
exposure to the receptor are necessary for the individual
pixels to exhibit different exposure values
Digital Image Receptors
Increasing film developer time, temperature, or replenishment rate from the optimal range
will increase the chemical fog on the film
Processing
shadow, space between the focal spot
Penumbra
common SID distance
40 inches
view box
Negatoscope
fastens the production of image
Intensifying screen
kVp’s increment is by __, mAs is by __
1,
decimals
