111- Chapter 16,17,18 Test Flashcards
What can you do to exposure field size and tissue thickness to reduce scatter production
Decrease field size, compression band, PA
Is pt thickness best reduced in the abdomen when the pt is supine or prone
Prone
How is grid ratio determined
Height of lead strips / distance between strips
For a given grid ratio, as height of strips increase, how does it effect scatter pickup
Increases
For a given grid ratio, as distance between lead strips increases, how does it effect scatter pickup
Decreases
Which type of grid is most challenging to use accurately
Cross hatched
Define grid frequency
of lead strips per inch or cm
Define grid selectivity
How much a grid allows the primary beam to transmit and how much scatter pickup
Define K or contrast improvement factor
How well the grid cleaned up scatter and improved contrast
What effect will imaging a thicker body part have on Compton and photoelectric interactions
Increase Compton decrease photoelectric
What effect will imaging a thicker body part have on scatter production
Increase
What effect will imaging a thicker body part have on image contrast
Decrease contrast
When comparing a 5:1 grid and a 16:1, what prevents scatter the best
Neither
When comparing a 5:1 grid and 16:1, which removes scatter the best
16:1
When comparing a 5:1 grid and 16:1, which requires the biggest increase in technique
16:1
When comparing a 5:1 grid and 16:1, which has the highest k factor
16:1
When comparing a 5:1 grid and 16:1, which is more selective
16:1
When comparing a 5:1 grid and 16:1, which requires more accurate positioning
16:1
Describe the design of a focused grid in relationship to the Xray beam
Strips angle out to match divergence of beam
What is the grid conversion factor formula
Mas 1 = GCF1
Mas2= GCF2
What is the grid conversion factor for no grid
1
What is the grid conversion factor for 5:1
2
What is the grid conversion factor for 6:1
3
What is the grid conversion factor for 8:1
4
What is the grid conversion factor for 10:1
4.5
What is the grid conversion factor for 12:1
5
What is the grid conversion factor for 16:1
6
What is grid cutoff and how can it occur
Undesired absorption of primary beam, off focus, level, center, upside down
When should a grid be used
Body part greater than 9-10 cm. Kvp over 60
How does air gap technique work in reducing scatter reaching IR and when might it come in handy
Greater OID drops off scatter, use when grid is unavailable
How does an off level grid error occur when using a parallel grid
Short axis of grid is angled
How does an off level grid error occur when using a focused grid
Short axis is angled
How does an off center grid error occur when using a parallel grid
No error
How does an off center grid error occur with a focused grid
Not centered on long axis
How does an off focus grid error occur with a parallel grid
No error
How does an off focus grid error occur when using a focused grid
When SID is out of focal range
How does an upside down grid error occur when using a parallel grid
No error
How does an upside down grid error occur when using a focused grid
Grid is upside down