36. CT: CTDI

Question 1

1. What is the final CTDI result?

Answer 1

• the CTDI vol

Question 2

2. What does the CTDI vol not reflect?

Answer 2

• it does not reflect the total ionising energy
  that was deposited into the scan volume

Question 3

3. Through which conditions does the CTDI vol remain unchanged?

Answer 3

• it remains unchanged regardless of the Patient
  Anatomy that is exposed

Question 4

4. What can we do with the CTDI vol to better represent the overall risk for a real Clinical Study?

Answer 4

• the dose can be integrated along the scan length

THIS ALLOWS FOR THE:
- computation of the Dose-Length Product

Question 5

5. What is the formula for working out the approximate DLP?

Answer 5

Question 6

6. Does this image make sense?

Answer 6

• yes

Question 7

7. How do we transform the DLP into an Effective Dose?

Answer 7

• we multiply the DLP by one of the two constants
• this is the simple method
• it is not fully accurate

CONSTANT ONE:
- 0.002 for the Head

CONSTANT TWO:
- 0.015 for the Abdomen

Question 8

8. What is the typical calculated effective CT dose for a head examination?

Answer 8

• 1 to 2 mSv

Question 9

9. What is the typical calculated effective CT dose for the chest?

Answer 9

• 5 to 7 mSv

Question 10

10. What is the typical calculated effective CT dose for the abdomen or the pelvis?

Answer 10

• 8 to 11 mSv

Question 11

11. Does this table make sense?

Answer 11

• yes

Question 12

12. Is the CTDI vol for a scan a good or poor measure of patient dose?

Answer 12

• it is a poor measure
• it offers a reproducible measure of device output

Question 13

13. How is the CTDl useful?

Answer 13

• it is useful in the comparison and improvement of the
  CT parameter- setting protocols

Question 14

14. What needs to be employed for accurate, patient specific measurements of dose?

Answer 14

• you need to employ something like the:
• Patient Air Kerma in Tomography
  Methodology
• (PAKT)