Term
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Definition
| The density on an x-ray film should remain unchanged as long as the intensity and duration of the x-ray exposure remains unchanged. |
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Term
| Definition of the 15% rule: |
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Definition
| An increase in or decrease in kVp by 15%, will result in the same density/IR exposure as doubling or halving the mAs. |
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Term
| How can the 15% rule be used in a practical setting? |
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Definition
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Term
| The definition of the inverse square law is: |
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Definition
"The intensity of the beam is inversely proportional to the square of the distance from the source." |
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Term
| Formula for Grid Conversion Factor |
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Definition
mAs with Grid
mAs without Grid |
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Term
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Definition
h (height of lead strip)
D (interspace width) |
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Term
| What is the formula to determine the new mAs when you add or take away a grid? |
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Definition
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Term
CF for no grid
5:1
6:1
8:1
10:1 or 12:1
16:1 |
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Definition
no grid=1
5:1=2
6:1=3
8:1=4
10:1 or 12:1=5
16:1=6 |
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Term
| If 30mAs is the technique needed to obtain a radiograph using an 8:1 grid, what mAs would be required if a 12:1 grid is used? |
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Definition
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Term
| If a radiograph made using a 6:1 grid had to be repeated without a grid, what mAs would be needed if the original mAs was 15? |
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Definition
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Term
| Formula for the new mAs law: |
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Definition
mAs1 = D1 (All of distance squared)
mAs1 = D2 |
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Term
Calculate the following using the new mAs formula:
Old mAs=30
New Distance=40
Old distance=72 |
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Definition
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Term
Calculate the following using the new mAs formula:
Old mAs=12
New Distance=52
Old distance=64 |
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Definition
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Term
Calculate the following using the new mAs formula:
Old mAs=200
New Distance=48
Old distance=40 |
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Definition
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Term
Use the 15% rule to find the new kVp with the change in mAs (goal: keep same density/IR exposure)
Original mAs=10
Original kVp=70
New mAs=5 |
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Definition
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Term
Use the 15% rule to find the new kVp with the change in mAs (goal: keep same density/IR exposure)
Original mAs=25
Original kVp=75
New mAs=50 |
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Definition
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Term
Use the 15% rule to find the new kVp with the change in mAs (goal: keep same density/IR exposure)
Original mAs=4
Original kVp=100
New mAs=8 |
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Definition
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Term
Use the 15% rule to find the new kVp with the change in mAs (goal: keep same density/IR exposure)
Original mAs=24
Original kVp=66
New mAs=12 |
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Definition
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Term
Use the 15% rule to find the new mAs to keep same density/IR exposure, with the given change in kVp
Original mAs=12
Original kVp=70
New kVp=80 |
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Definition
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Term
Use the 15% rule to find the new mAs to keep same density/IR exposure, with the given change in kVp
Original mAs=10
Original kVp=90
New kVp=80 |
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Definition
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Term
Use the 15% rule to find the new mAs to keep same density/IR exposure, with the given change in kVp
Original mAs=120
Original kVp=70
New kVp=80 |
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Definition
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Term
Use the 15% rule to find the new mAs to keep same density/IR exposure, with the given change in kVp
Original mAs=60
Original kVp=88
New kVp=78 |
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Definition
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Term
| Formula for Magnification |
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Definition
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Term
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Definition
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Term
Calculate the following using the Inverse Square Law
I1=90
D1= 40
D2=72 |
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Definition
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Term
Calculate the following using the Inverse Square Law
I1=120
D1= 56
D2=68 |
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Definition
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Term
Calculate the following using the Inverse Square Law
I1=5
D1= 30
D2=82 |
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Definition
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Term
Calculate the following using the Inverse Square Law
I1=250
D1= 48
D2=40 |
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Definition
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Term
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Definition
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Term
| Name the 8 influencing factors affect Receptor Exposure and state whether they are directly or inversely related. |
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Definition
- mAs-direct
- kVp-direct
- SID-indirect
- Grids-indirect
- Filtration-indirect
- Beam restriction-indirect
- Anode Heel Effect-indirect
- Patient factors-indirect
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Term
| Explain the effect of mAs on density/IR receptor. |
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Definition
Adequate mAs ensures enough photons reach the IR to capture anatomic detail of the part.
Not enough mAs= a noisy, underexposed image. |
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Term
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Definition
| The same mAs can be achieved by varying either mA or seconds. |
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Term
| Explain the effect of kVp on density/IR receptor. |
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Definition
Increasing the kVp means that more photons will make it through the body and reach the IR.
When the kVp is increased, the voltage that drives the electrons across the tube in increased. Higher voltage means electrons go faster. Electrons hitting the anode with more speed create x-ray photons with higher energy (which allow them to penetrate the tissue more easily) |
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Term
| Explain the effect of SID on density/IR receptor. |
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Definition
X-rays are electromagnetic energy and diverge (fan out) in a predictable pattern from the source.
Remember, when you double the distance, the intensity will be a quarter of it's original strength.
When you decrease the distance by half, the intensity is 4 times the strength. |
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Term
| Explain the effect of a Grid on density/IR receptor. |
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Definition
Adding a grid and not increasing mAs can result in an under-exposed IR.
The function of a grid is to clean up scatter. When a grid is used, some useful beam is absorbed within the lead strips. The grid is placed between the patient and the IR. Because the grid iss truck by x-rays before they can strike the IR, it is necessary to use more x-rays to ensure enough reach the IR |
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Term
| Explain the effect that Filtration on density/IR receptor. |
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Definition
Filtration effects IR exposure as a result of absorbing some of the useful beam.
A compensating filter can be used to ensure that too many photons do not reach the IR where an anatomic area is thinner in one area than another (An example would be a wedge filter used for a foot exposure.) |
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Term
| Explain the effect of Bream Restriction on density/IR receptor. |
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Definition
Restricting the beam (collimating), means that fewer x-ray photons strike the patient.
This also means that less scatter is produced, and fewer "stray" x-ray photos will strike the IR.
Increasing the beam restriction=less IR exposure |
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Term
| Explain the effect of the Anode Heel Effect on density/IR receptor. |
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Definition
Some of the x-rays that are created at the anode are absorbed by the "heel" of the anode.
This happens as a result of the angle of the anode. The anode is angled to create a smaller effective focal spot with a wider actual focal spot. This is known as the "line focus principle". The result is increased detail, but a side effect is fewer photons on the anode side of the beam and more photons on the cathode side of the beam. |
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Term
| Explain the effect of patient factors on density/IR receptor. |
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Definition
Patient size and pathology can affect the IR exposure because more tissue for the x-rays to penetrate.
If the kVp and/or mAs is not increased to compensate, the IR will be underexposed and vice versa for subtractive pathology. |
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