Exposure Time, mAs, and mA Flashcards
mA
determined by temperature of filament
mA is directly _______________ to the tube current
proportional
When mA increases, what also increases?
number of electrons going to anode
If you double mA, what happens?
number of electrons and number of x-rays emitted are doubled
What happens to patient dose if you cut the mA in half?
the dose will be cut in half
What does Milliampere Seconds (mAs) control?
quantity of x-rays in the beam
Does mAs have any control on the quality of beam?
no
Milliampere Seconds (mAs)
product of exposure time and x-ray tube current
higher mAs increases what proportionally?
patient dose
If mAs is doubled, does the patient dose double?
yes
Exposure time
amount of time that Potential Difference (voltage) is applied to the tube
measured in milliseconds or secs
Exposure time is _________ _________________ to the number of electrons crossing the tube and number of x-rays generated.
directly proportional
If you double exposure time, what happens?
number of electrons and quantity/intensity of x-rays is doubled
What is a reason why a shorter exposure time would be desired?
pediatric patients
What is a reason why a longer exposure time would be desired?
Lateral T spine “breather” technique
Ribs and motion are blurred out
What happens to patient dose if you double exposure time?
it’s doubled
mA x seconds =
mAs
Increasing exposure time and decreasing mA will increase what?
heat capacity
How do you convert seconds to milliseconds?
move decimal three digits to the right
How do you convert milliseconds to seconds?
move decimal three digits to the left
Calculate mAs:
50 mA
.25 sec
12.5 mAs
Calculate mAs:
200 mA
.5 sec
100 mAs
Calculate mAs:
25 mA
4000 milliseconds
100 mAs
Reciprocity Law
exposure to the IR will remain constant with adjustments in exposure time or mA if mAs remains constant
mA1s1 = mA2s2
