Physics Ch 7 CT

Question 1

adult –> CT abd –> CTDI ACR limit?

Answer 1

25 mGy

Question 2

peds –> CT abd –> CTDI ACR limit?

Answer 2

20 mGy

Question 3

adult –> CT head –> CTDI ACR limit?

Answer 3

75 mGy

Question 4

what is CT dose index (CTDI)? unit?

Answer 4

radiation dose normalized to beam width

mGy

Question 5

what is weighted CTDI?

Answer 5

1/3 central CTDI + 2/3 peripheral CTDI

Question 6

what is volume CTDI?

Answer 6

(weighted CTDI)/(pitch)

Question 7

dose length product (DLP) –> formula? unit?

Answer 7

DLP = CTDIvol x length of scan(cm)

mGy*cm

Question 8

CT –> effective dose –> formula? unit?

Answer 8

eff dose = k x DLP

k = constant for specific body part

mSv

Question 9

kVP –> inc 2x –> what happen to dose?

Answer 9

inc 4x CTDI/DLP/eff dose

Question 10

tube current (mA) –> inc 2x –> what happen to dose?

Answer 10

inc 2x CTDI/DLP/eff dose

Question 11

pitch –> inc 2x –> what happen to dose?

Answer 11

1/2x CTDI/DLP/eff dose

Question 12

rotation time –> inc 2x –> what happen to dose?

Answer 12

inc 2x CTDI/DLP/eff dose

Question 13

effective mAs –> formula?

Answer 13

Effective mAs = mAs/pitch = (tube current x rotation time) / pitch

Question 14

adult –> risk of radiation induced cancer per dose (% per Sv)?

Answer 14

5% per Sv

Question 15

ped –> risk of radiation induced cancer per dose (% per Sv)?

Answer 15

15% per Sv

Question 16

> 50yo –> risk of radiation induced cancer per dose (% per Sv)?

Answer 16

1/10th

Question 17

metal artifact –> how to improve? (4)

Answer 17

• thinner slices
• reconstruct acquired slices into thicker slices
• inc kVp
• dual-energy CT