Review Stuff
Spatial resolution is determined by...
Pixel Size
What is the downside of using a grid?
Increase patient dose
Higher, Higher
or
Lower, Lower
What is the most used beam-restricting device in radiography?
Collimators or Variable-aperture collimators
200+20 = 220
10,000/220 = 45.4 lines/cm
What produces image noise, and reduces image contrast?
Compton Scatter
What removes scatter radiation from the remnant beam, thus removing image noise and improves image contrast?
Radiographic Grids
Contrast improvement factor is ______ for high-ratio grids.
Higher
Image contrast is approximately doubled when a grid is used.
An aluminum wedge is placed on a tissue phantom that is 40 cm thick and a radiograph is made. Without a grid, analysis of the radiograph shows a 2.2% contrast factor. With a 5:1 grid, radiographic contrast is 3.5%. What is the contrast improvement factor of this grid?
K = 3.5/2.2
K = 1.6 or 1.59
The patient dose ________ with high kVp techniques.
Decreases
What type of grids show less distinct grid lines on the image?
High-frequency grids
Which grid misalignment causes grid cut off toward the edge of an image?
Off-Focus
Grid cutoff is not _______ across the IR with Off Focus Grid problems.
Uniform
Using a 5:1 grid, if the required mAs is 20, how much mAs is needed with a 12:1 grid?
50 mAs
What is the air-gap technique?
An alternative to using a grid; the OID increases to improve contrast but at the cost of patient dose
Most grids have frequencies in the range of ____ to ____ lines per cm.
25 to 45
Which grid misalignment has severe grid cut off towards the edge of the image?
Upside-down
What are the three factors when it comes to choosing the correct grid ratio?
kVp, how much scatter needs to be reduced, how much radiation the patient is going to receive
A radiograph is taken without a grid used 10 mAs. How much mAs is needed with a 16:1 grid?
60 mAs
What does increasing kVp do?
More photons transmit through the patient to the IR, but Compton scatter also increases
What is the Bucky Factor for a 12:1 Grid?
5
What is an example of an Off-Level Grid?
The grid tilts during mobile radiography as the IR sinks into the patient's bed off to one side.
When using a grid, which technique factors must be increased?
If a 6:1 grid requires 30 mAs, how much mAs would be required with a 5:1 grid?
25 mAs