Ch.6 (not Complete) Flashcards
Directly proportional to radiation quantity exiting the x-ray tube
Inversely related to exposure time to maintain exposure to image receptor (IR)
Milliamperage (mA)
Directly proportional to radiation quantity exiting the x-ray tube
Inversely related to mA to maintain exposure to IR
Exposure time (TIME)
Directly related to radiation quality and quantity exiting the x-ray tube
Inversely related to radiographic contrast
Kilovoltage (kVp)
Milliamperage and exposure time have a _______ proportional relationship when discussing quality
Direct
Increasing mA = _____ time = _______ quality
Increase, increase
**mAs is INVERSELY related to exposure but DIRECTLY related to quantity
!!!
Increasing or decreasing the mA results in a _____ change in mAs.
Proportional
T or F - MAs does not control brightness
TRUE
In order to maintain exposure, by increasing your mA you will need to ______ time
Decrease
MA and exposure time have an _____ proportional relationship when maintaining mAs.
Inverse
Increasing kVp= ______ penetration = ______ absorption = _______ contrast
Increases, decreases, decreases
Increasing kVp _____ subject contrast
Decreases
Decreasing kVp ______ subject contrast
Increases
What is the 15% rule?
By increasing your kVp by 15%, it is the equivalent of doubling your MAs.
Increase for 15% rule
1.15
Decrease by 15% rule
0.85
How to maintain exposure to the IR
- Increase mA and proportionally decrease time
- Increase time and proportionality decrease
- Increase kVp 15% and decrease MAs by half
- Decrease kVp 15% and increase MAs by two times
Image brightness is _______ on MAs and kVp
Not dependent
Image contrast is _________ on kVp
Not dependent
Image brightness and image contrast are both
Dependent on the computer
With too little MAs and/or kVp, computer processing will adjust image brightness and contrast BUT
Quantum noise is visible, therefore the image will need to be repeated.
For digital, using _____kVp and _____ MAs values.
Higher, lower
With too much kVp/mAs, computer processing with adjust the image brightness and contrast BUT
The patient is overexposed.
Increasing MAs= ______ noise
Decrease
Secondary factors include
- focal spot size
- SID
- OID
- Part/IR alignment
- Grids
- Beam restriction
- generator output
- tube filtration
- compensating filters
- patient factors
The size of the focal spot affects ______ and _______ _______ recorded in the image.
Unsharpness and spatial resolution
Increasing focal spot size, unsharpness ______ and spatial resolution _______
Increases, decreases
Decreasing focal spot size _______ unsharpness and _______ spatial resolution.
Decreases, increases
SID and radiation intensity are ______ related.
Inversely
Changing the SID requires a change in ____ to maintain consistent radiation exposure to the image receptor
MAs
SID affects _________ and __________
Distortion and recorded detail/spatial resolution
Increasing SID= ______ magnification and _____ spatial resolution
Decrease, increase
Decreasing SID= ______ magnification= ________ spatial resolution
Increases, decreases
What is the formula for the direct square law?
MAs2=mAs1x(D2/D1)^2
What is the formula for exposure maintenance?
MAs1/mAs2= (SID1/SID2)^2
OID affects
Radiation intensity reaching the IR
Amount of scatter radiation reaching the IR
Magnification
Spatial Resolution
(Increase mag.=decrease SR)
Increasing OID will have what effect on beam intensity ?
It will decrease beam intensity, hence decreasing exposure.
Once exposure to the IR is decreases, you will need to INCREASE MAS
An ________ will decrease the intensity of radiation and scatter reaching the IR without the use of a grid.
Air Gap
Increasing OID=______ IR exposure=______contrast and magnification= _______ SR
Decreases, increases, decreases
Decreasing OID= ________ IR exposure= _______ contrast and magnification= _______ SR
Increases, decreases, increases
What is the formula to find the magnification factor?
MF= SID/SOD
MF= Image size/Object size
What is the formula to solve for SOD?
SOD=SID-OID
What is the best magnification factor?
1
Shape distortion can occur from any misalignment of the CR alongside these three factors:
- X-ray tube
- Part being radiographed
- IR
Improper CR alignment causes shape distortion, as well as
(ON TEST)
- Incorrect SID
- Off centered CR
- Angled CR
What effect do grids have on spatial resolution ?
Increases spatial resolution
Less scatter=______ contrast
Increase
When using the magnification factor formula, what formula would be used in order to find the object size?
Obj. Size= image size/MF
What is the formula for Grid Conversion?
Mas1/mAs2=grid ratio 1/grid ratio 2
What is the formula for grid ratio ?
Grid ratio=height of lead strips/distance btw strips
The more effective the grid, the _______ the mAs
GREATER
