Unit 2: Chapter 6 Flashcards
2ndary exposure factors
density and contrast
What is the controlling factor for density?
mAs
What is the controlling factor for contrast?
kVp
SID
Source to Image Distance
The intensity of the x-ray beam is inversely proportional to the square of the distance from the source
inverse square law
The equation for inverse square law
I1 (d2)^2
– = ———
I2 (d1)^2
What effect does increasing the SID have on image density and brightness?
Decreases Density and Increases Brightness
Increasing distance (SID) means that you should __________ the mAs to maintain exposure to IR
increase
Decreasing distance (SID) means that you should _________ the mAs to maintain exposure to IR
decrease
mAs/Distance Compensation Formula
mAs1 (SID1)^2
——— = ———–
mAs2 (SID2)^2
As SID increases, maginifcation __________
decreases
As SID increases, recorded detail or spatial resolution _________
increases
OID
Object to Image Distance
When distance is created, the exit radiation continues to diverge, and _____ overall intensity of the beam reaches the IR
less
What effect does increased OID have on density?
decreases
What effect does increased OID have on brightness?
increases
What has the greatest effect on the
amount of size distortion?
OID
OID has the greatest effect on the
amount of what?
size distortion
As the OID increases, the diverging exit beam records the anatomic part with ____________ size distortion or magnification
increased
What indicates how much size distortion or magnification is demonstrated on a radiograph?
Magnification factor (MF)
Calculating Magnification factor
MF = SID/SOD
Calculating Source to object distance
SOD = SID - OID
MF of ___ or lower indicates no magnification
1
MF of _________ than 1 expressed as a percentage of magnification
greater
How to calculate object size
Image/MF
When time magnification increases, recorded detail or spatial resolution ___________
decreases
An increase in OID ____________ recorded detail
decreases
Shape distortion can occur in 3 ways: misalignment of….
CR/tube
part being radiographed
IR
What is the device placed between the anatomic area of interest and the IR to absorb scatter radiation exiting the patient?
grid
What limits the amount of scatter radiation that reaches the IR?
grids
When an anatomical structure measures to be more than ______, it requires a grid
10 cm
Grid Ratio: Grid conversion factor
NO GRID: _____
1
Grid Ratio: Grid conversion factor
5:1 : ______
2
Grid Ratio: Grid conversion factor
6:1 :_____
3
Grid Ratio: Grid conversion factor
8:1 :_______
4
Grid Ratio: Grid conversion factor
12:1 :________
5
Grid Ratio: Grid conversion factor
16:1 :_______
6
As focal spot increases, the unsharpness _______
increases
As focal spot increases, the recorded detail or spatial resolution __________
decreases
The _________ the focal spot, the better the detail
smaller
Focal spot size is a major controller of image resolution because it controls the _________
penumbra
Generators with more efficient output, such as three-phase or high-frequency, require _______ exposure technique settings
lower
Increasing the amount of tube filtration________the percentage of higher-penetrating x-rays to lower-penetrating x-rays
increases
Filtration _________ average photon energy
increases
Filtration________ scatter production
increases
The use of compensating filters requires an ________ in mAs to maintain the overall exposure to the IR
increase
Thicker tissue parts requires the mAs to be __________
increased
General guidelines for Part thickness: For every change in part thickness of 4 to 5 cm, Adjust mAs by a factor of ____
2
Increase in part thickness, __________ the amount of scatter
increase
Increase in part thickness, __________ the amount of contrast
decrease
Exposure factors must be modified for patients younger than __ years old (lack bone density)
6
For peds patients, it is recommended to _________ the kVp by at least ____% to compensate
decrease, 15
With a fiberglass cast, generally _____________ in exposure factors is needed
no change
For inflatable (air) and fiberglass splints, there is ____________ in exposure factors needed
no change
For wood, aluminium, and solid plastic splints, there is a(n) __________ required in the primary beam
increase
What is a diseases or conditions that increase the absorption characteristics of the part, making the part more difficult to penetrate?
additive disease
Do you increase or decrease the technique for an additive disease?
increase
What is a diseases or conditions that decrease the absorption characteristics of the part, making the part less difficult to penetrate?
destructive disease
Within a pathological condition, it is best to make a change in the ______, which affects the penetrating ability of the primary beam.
kVp
When the area of interest requires less density to visualize soft tissue, the mAs should be ___________ accordingly
decreased
What is used when imaging anatomic tissues that have low subject contrast?
contrast media
Contrast media changes the absorption characteristics of the tissues by either ____________ or _________ the attenuation of the beam
increasing, decreasing
Examples of positive contrast agents
Barium, Iodine
Examples of negative contrast agents
air
Which contrast agent produces less radiographic density or more brightness than the adjacent tissues?
positive
Positive contrast agents ___________ scatter
increase
Positive contrast agents ___________ contrast
decrease
Positive contrast agents require an ___________ in exposure factors
increase
Which contrast type produces more radiographic density or less brightness than adjacent tissues?
negative
Do negative contrast agents require a change in exposure factors?
no
Can negative contrast agents be used in conjunction with positive agents?
yes
