APPH Test 2
Which factor does not contribute to differential absorption?
Tissue thickness
Z number
Mass density
Electron binding energy
How does kVp affect Comptons?
Increases
Decreases
No effect
True/False: The IR can differentiate between a scattered photon and a directly transmitted photon
True
False
How does Z number affect Compton Scatter?
Increases
Decreases
No effect
How is the frequency of a grid calculated?
Number of lines/inch
Number of lead strips/cm
How well a grid is able to improve image contrast
What part of the circuit is controlled by kVp?
Falling load generator
Autotransformer
Primary coil
Step up transformer
When should a grid be used?
When using >60kVp and when tissue thickness exceeds 10cm
When using >50kVp and when tissue thickness exceeds 5cm
When using >60kVp and when tissue thickness exceeds 15cm
What should the backup timer for AEC be set to?
1.5 times the expected length of exposure
125% of expected length of exposure
1/2 the expected length of expposure
When using AEC what technical factor cannot be set?
AEC cell selection
mAs
kVp
Exposure time
Which beam restriction device allows for the easiest adjustments in field size?
Aperture diaphragm
Cone
Cylinder
Variable aperture collimator
What type of generator uses highest mA and shortest possible exposure time?
High frequency
Falling load
Low voltage
What will produce the greatest amount of scatter radiation leaving the patient?
Low kVp and small field size
Low kVp and large field size
High kVp and small field size
High kVp and large field size
For an AP T-spine, what happens if the area of interest is not positioned over the seleced AEC cell?
Underexposure
Overexposure
No change occurs
Optimal image contrast
What is the simplest type of beam restricting device?
Cone
Cylinder
Aperture diaphragm
Why are scattered photons absorbed by grids?
They travel at an angle to the transmitted photons
They travel parralel to the transmitted photons
They travel perpendicular to the transmitted photons
True/False: Technique charts can be used in all x-ray rooms at the same site
True
False
What aspect of the x-ray circuit controls mA stations?
Primary circuit
Secondary circuit
Filament circuit
What is the purpose of PBL?
Automatically collimates to anatomy
Automatically collimates to the IR size
Allows for improves image contrast
Why is repeat analysis important?
Decrease patient dose
Increase accountability
Increase technologist cooperation
It is not important in DI
What two main factors directly affect amount of scatter exiting a patiient?
kVp and volume of tissue irradiated
mAs and volume of tissue irradiated
Exposure time and volume of tissue irradiated
kVp and density of tissue irradiated
What type of images are not included on repeat analysis?
Quality control tests
Positioning errors
Motion errors
Underexposed images
What is the probability of a Compton interaction related to?
mAs
kVp
Energy of the x-ray photon
Angle of the incident photon
What type of timer circuit is considered to be the most accurate to 1ms?
Electronic
mAs timer
Synchronous
AEC
In comparison to a low kVp, a high kVp will result in a scattered photon with ________ energy
Higher
Lower
The same
What is the most common grid error?
Off center
Off focus
Upside down
Off angle
What factor affects probabiliy of PE interactions?
If the energy levels are close together
If the energy levels are far apart
If incident photon has low energy
If incident photon has low binding energy
What is the most common type of grid?
Linear
Oscillating
Rotating
Angled
Main characteristic of a focused grid
As photons come through, there is a more uniform image
As photons come through, there is a less uniform image
As photons come through, there is more beam divergence
As photons come through, there is less beam divergence
The recommended range of SID's that can be used with focused grids is called ______
Focal range
Focal distance
OID range
Grid range
Where are focused grids most commonly used?
Flouroscopy
CT
GR
Interventional radiography
What is the most frequent error with focused grids?
Incorrect SID
Transverse lock not engaged
Improper positioning
Not centered to AEC cell selected
What technical factor is usually adjusted for grids?
kVp
Exposure time
mAs
AEC
What does a higher K value mean in terms of contrast?
Higher contrast
Lower contrast
No change
For each cm of air gap, how much do we have to increase mAs by?
15%
25%
5%
10%
Why is the air gap techniqiue not as effective with high kVp?
Scatter is not travelling straight
Scatter is travelling straight
kVp has no effect on scatter
High kVp means more scatter
What is the purpose of the filament circuit?
To produce the appropriate electron cloud
To generate appropriate voltage
To create x-rays
Eliminate low energy photons
What must the main x-ray circuit permit the technologist to change?
Amperage, voltage, and length of exposure
Amperage, current, and length of exposure
Amperage, voltage, and mA
AEC, voltage, and length of exposure
Why is a line compensator used?
Because power cannot always be supplied to a continuous 220V
Because power cannot always be supplied to a continuous 200V
Because current cannot always be supplied to a continuous 220V
What is the purpose of a rectifier?
To convert AC to DC
To convert DC to AC
To eliminate high energy photons
To eliminate low energy photons
Is the step up transformer adjustable?
No
Yes
When do we use rectifiers?
When the anode of the x-ray tube is negative and the cathode is positive
When the cathode of the x-ray tube is negative and the anode is positive
When low energy photons need to be energized at the filament circuit
What does rectification do to voltage?
Decreases average energy
Increases average energy
Inverse voltage is removed from the supply to the x-ray tube
Inverse voltage is added to the supply to the x-ray tube
What percent waveform does 3 phase 6 pulse have?
4%, Voltage supply to x-ray tube never falls below 96%
14%, Voltage supply to x-ray tube never falls below 86%
Minimum voltage to 100%
What percent waveform does 3 phase 12 pulse have?
4%, Voltage supply to x-ray tube never falls below 96%
14%, Voltage supply to x-ray tube never falls below 86%
Minimum voltage to 100%
Why do most image repeats occur?
Improper collimation
Incorrect AEC cell selection
Incorrect technique selected
Improper positioning
How many patients are required for repeat analysis?
150
250
100
200
What does it mean when there is a repeat rate of 0%?
Radiologist is too lenient
High technologist efficiency
Equipment is damaged
Which is not an advantage of repeat analysis?
Improved department efficiency
Lower costs to department
Decreased equipment recallibration
Lower patient doses
Which does not affect repeat rate?
Staff skill level
Quality of equipment
Workload
Patient type
What should the repeat rate be in general radiography?
10-12%
8-10%
Below 5%
6-8%
What is the simplest type of grid?
Parallel
Focused
Angled
Crossed
Can you avoid grid cut off with a parallel grid?
Yes
No
What is the most common grid error?
Off focused
Upside down
Off center
Off level
Why is exposure time important?
Patient dose
Quality of photons
Energy of photons
Which does not apply to a high grid ratio?
Increased image contrast
More accurate positioning required
Prone to increased grid errors
Must be used with high kVp
What type of timer circuit is only found on falling load generator systems?
AEC
Synchonous
mAs
Electronic
What is the purpose of AEC?
Eliminate guessing for technical factors
Allow for increased patient cooperation
Eliminate possible positioning errors
By what percentage does each AEC compensation interval increase/decrease preset exposure by?
15-25%
40-55%
25-50%
10-25%
Why does positioning over the proper AEC cell matter?
Small field size will result in overexposure
Small field size will result in underexposure
Large field size will result in overexposure
It does not matter
What does not affect the amount of scatter reaching the IR?
Patient thickness
kVp
AEC cell selection
Exposure time
How does high kVp affect patient dose, scatter, and contrast?
Patient dose will decrease, scatter will increase, and contrast will decrease
Patient dose will decrease, scatter will increase, and contrast will increase
Patient dose will decrease, scatter will decrease, and contrast will decrease
Patient dose will increase, scatter will decrease, and contrast will decrease
What two types of x-rays form the image on the IR?
Transmitted and absorbed
Transmitted and attenuated
Attenuated and absorbed
Attenuated and restricted
What is least likely to occur to a scattered x-ray photon after it has undergone a Comptons interaction?
Stay in the body and undergo additional interactions
Leave the body and contribute to occupational dose
Pass through the body and contribute to IR exposure
Scatter back in the direction of the primary x-ray beam
Why does collimation affect the amount of scatter being produced?
Affects the volume of tissue being irradiated
Increases patient dose
Scatter provides helpful information to IR
Increased collimation means more photons hitting the IR
How does increasing kVp affect probability of PE interactions?
Increase
Decrease
No change
How does increasing kVp affect scatter radiation?
Increase
Decrease
No change
How does increasing mA affect scatter radiation?
Increase
Decrease
No change
How does increasing SID affect PE interactions?
Increase
Decrease
No change
How does decreasing the mAs effect scatter radiation?
Increase
Decrease
No change
With which type of grid can the x-ray beam NOT be angled?
Parallel
Crossed
Focused
Rotating
What is the fuzzy edge of an image called?
Penumbra
Absorbed photons
Blur
How is penumbra effected as beam restictor distance is increased from the tube port?
Increased
Decreased
No effect
What is the 9 penny test used to check?
Mirror alignment
Cathode function
Anode function
Current flow
What do the transformers require to function?
AC
DC
What does the x-ray tube require to function?
AC
DC
What are we adjusting when we adjust the rheostat?
kVp
mA
exposure time
beam restriction
What do the rheostat and exposure timer control?
Filament temperature
Current flow
Electron energy
Angle of deflection
Where is a falling load generator most commonly used?
CT
GR
Flouroscopy
Interventional radiography
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