2a - Radiographic Quality

Question 1

mAs

Answer 1

milliamps x seconds (mAs)

• Gives the quantity of x-ray
• Responsible for the DENSITY (overall darkness) of an x-ray
  
  • Increasing mAs –> more dark x-ray

Question 2

Relationship between mA and mAs

Answer 2

there is a direct relationship between mA and mAs

• Doubling mA = doubling the mAs
  
  • 100 mA * 0.2 sec = 20 mAs
  • 200 mA * 0.2 sec = 40 mAs
• Halving mA = Halving mAs
  
  • 100 mA * 0.2 sec = 20 mAs
  • 50 mA * 0.2 sec = 10 mAs

Question 3

Relationship between time and mAs

Answer 3

there is a direct relationship between time and mAs

• doubling time = doubling the mAs
  
  • 100 mA * 0.2 sec = 20 mAs
  • 100 mA * 0.4 sec = 40 mAs
• Halving time = halving mAs
  
  • 100 mA * 0.2 sec = 20 mAs
  • 100 mA * 0.1 sec = 10 mAs

Question 4

50% mAs reciprocal rule

Answer 4

double (or ½) mAs will double (or ½) FILM DENSITY

Question 5

15% kVp rule

Answer 5

adding (or subtracting) 15% kVp, has the same effect as doubling (or halving) the mAs

Question 6

Rule of 3

Answer 6

• when going for 40” to 72” must use 3x mAs
• when going for 72” to 40 must use 1/3 mAs

Question 7

Rule of thumb for kVp

Answer 7

If you can see bone leave kVp alone

• if bone is seen, but film is too light:double mAs
• film is so light that bone cannot be seen: double mAs + increase kVp 15%

Question 8

If SID changes, how does mAs change?

Answer 8

• mAs must be adjusted to maintain DENSITY
• use “Rule of 3”
  
  • when going for 40” to 72” must use 3x mAs
  • when going for 72” to 40 must use 1/3 mAs