Exposure Time, mAs, and mA

Question 1

mA

Answer 1

determined by temperature of filament

Question 2

mA is directly _______________ to the tube current

Answer 2

proportional

Question 3

When mA increases, what also increases?

Answer 3

number of electrons going to anode

Question 4

If you double mA, what happens?

Answer 4

number of electrons and number of x-rays emitted are doubled

Question 5

What happens to patient dose if you cut the mA in half?

Answer 5

the dose will be cut in half

Question 6

What does Milliampere Seconds (mAs) control?

Answer 6

quantity of x-rays in the beam

Question 7

Does mAs have any control on the quality of beam?

Answer 7

no

Question 8

Milliampere Seconds (mAs)

Answer 8

product of exposure time and x-ray tube current

Question 9

higher mAs increases what proportionally?

Answer 9

patient dose

Question 10

If mAs is doubled, does the patient dose double?

Answer 10

yes

Question 11

Exposure time

Answer 11

amount of time that Potential Difference (voltage) is applied to the tube

measured in milliseconds or secs

Question 12

Exposure time is _________ _________________ to the number of electrons crossing the tube and number of x-rays generated.

Answer 12

directly proportional

Question 13

If you double exposure time, what happens?

Answer 13

number of electrons and quantity/intensity of x-rays is doubled

Question 14

What is a reason why a shorter exposure time would be desired?

Answer 14

pediatric patients

Question 15

What is a reason why a longer exposure time would be desired?

Answer 15

Lateral T spine “breather” technique

Ribs and motion are blurred out

Question 16

What happens to patient dose if you double exposure time?

Answer 16

it’s doubled

Question 17

mA x seconds =

Answer 17

mAs

Question 18

Increasing exposure time and decreasing mA will increase what?

Answer 18

heat capacity

Question 19

How do you convert seconds to milliseconds?

Answer 19

move decimal three digits to the right

Question 20

How do you convert milliseconds to seconds?

Answer 20

move decimal three digits to the left

Question 21

Calculate mAs:
50 mA
.25 sec

Answer 21

12.5 mAs

Question 22

Calculate mAs:
200 mA
.5 sec

Answer 22

100 mAs

Question 23

Calculate mAs:
25 mA
4000 milliseconds

Answer 23

100 mAs

Question 24

Reciprocity Law

Answer 24

exposure to the IR will remain constant with adjustments in exposure time or mA if mAs remains constant

mA1s1 = mA2s2