Unit 5: Image Quality in CT (Part 1) Flashcards
T/F
The aspects that control exposure in X-ray is the same in CT
True
T/F
Increasing mA decreases the number of electrons that will produce x rays
False; Increasing mA increases the number of electrons that will produce x rays
Why is having a smaller filament better for increasing spatial resolution?
Using a smaller filament concentrates the focal spot, which in turn results in increased spatial resolution
What are the disadvantages of a smaller filament?
-Does not tolerate high mA values a well as large filaments so time must be increased to maintain mAs
In CT, what is scan time?
The time it takes for the x ray tube to make one 360 degree rotation
What is the typical scan time in CT?
2s-0.5s
T/F
Shorter scan times completely eliminate artifacts caused by motion entirely.
False; Shorter scan times reduce, but do not eliminate artifacts caused by motion entirely.
(peristalsis, cardiac motion)
T/F
As a rule, if mAs can be maintained, it is preferable to use the shortest scan times available.
True
What happens to heat produced as mAs increases?
As mAs increases, so does the amount of heat being generated within the x-ray tube.
What is the main limiting factor for exposure in all scanners?
Heat
T/F
There is no correlation between mAs levels and interscan delay
False; There is a direct correlation between mAs levels and the interscan delay.
What is Interscan Delay?
Interscan delay is the time between scans (when the tube is not energized).
T/F
The lower the mAs setting, the longer the interscan delay needed to allow for longer tube cool-off time between scanning sequences.
FALSE; The higher the mAs setting, the longer the interscan delay needed to allow for longer tube cool-off time between scanning sequences.
What 2 main factors determine the mAs levels selected?
Patient thickness and density.
