Questions

Answers

1. What is the main indication for ventilation perfusion scintigraphy?

1. evaluation for pulmonary embolism

2. What is the mortality rate from untreated pulmonary embolisms?

2. 30%

3. Name the two classes of radiopharmaceuticals used for ventilation scintigraphy.

3. radioactive gases and radioaerosols

4. Which three radioactive gases are available for ventilation scintigraphy?

4. ¹²⁷Xe, ¹³³Xe, and ^81mKr

5. Why can ¹²⁷Xe be used for postperfusion ventilation scanning?

5. The photon energies of ¹²⁷Xe are higher than those of ^99mTc.

6. What is the practical life of an ⁸¹Rb–^81mKr generator?

6. approximately 12 hours

7. Why is ^81mKr not more widely used for ventilation scanning?

7. due to high costs and the impracticality of daily generator replacement

8. Why can ^81mKr be used for postper-fusion imaging?

8. The energy of the principal photon (191 keV) is higher than that of ^99mTc.

9. Why does xenon accumulate in the livers of some patients?

9. Xenon is fat soluble and may accumulate in fatty livers.

10. What radiopharmaceutical is most commonly used for radioaerosol imaging?

10. ^99mTc–diethylene triamine pentacetic acid (DTPA)

11. What is the appropriate aerosol particle size for radioaerosol ventilation scanning?

11. 0.5 to 1.0 mm

12. What happens to inhaled particles whose size is less than 0.1 mm (micrometers)?

12. They are exhaled and thus not deposited in the lungs.

13. What happens to inhaled particles whose size is greater than 2 to 3 mm?

13. They settle in the large airways.

14. How can both ventilation and perfusion imaging be performed with the same isotope?

14. The dose of the second study must be substantially greater than that of the first.

15. What is the usual adult dosage for a ventilation scan with xenon?

15. 10 to 20 mCi (370 to 740 MBq)

16. What are the three phases of a xenon ventilation study?

16. wash-in (first breath), equilibrium, washout

17. What view is most commonly taken for a xenon ventilation study?

17. posterior chest

18. What does the patient breathe during the wash-in portion of a xenon ventilation study?

18. radioactive xenon mixed with air

19. What does the patient breathe during the equilibrium portion of a xenon ventilation study?

19. radioactive xenon mixed with air

20. What does the patient breathe during the washout portion of a xenon ventilation study?

20. air (without radioactive xenon)

21. How much of the activity in a nebulizer is delivered to the lungs in a radioaerosol ventilation study?

21. 5% to 10%

22. How much radioactivity is typically placed in the nebulizer for a radio-aerosol ventilation study?

22. 25 to 27 mCi (925 to 999 MBq)

23. What is the biologic half-life of inhaled ^99mTc-DTPA in the lungs?

23. approximately one hour

24. How does ^99mTc–microaggregated albumin (MAA) localize in the lungs?

24. After intravenous injection, ^99mTcMAA is trapped in the pulmonary vascular bed on the first pass.

25. Why does ^99mTc-MAA uptake in the lungs reflect lung blood flow?

25. Areas of reduced perfusion have less tracer delivered during the first-pass injection.

26. What is the biologic half-life of ^99mTcMAA in the lungs?

26. two to three hours

27. What is the differential diagnosis of systemic organ uptake of ^99mTc-MAA?

27. free pertechnetate or a right-to-left shunt

28. What is the best organ to image to detect right-to-left shunting of ^99mTcMAA?

28. the brain

29. What is the problem with administering too few particles of ^99mTcMAA?

29. The pattern of uptake is not based on a statistically valid distribution of particles to reflect blood flow.

30. What is the problem with administering too many particles of ^99mTcMAA?

30. It may cause hemodynamic obstruction.

31. What is the minimum number of particles of ^99mTc-MAA that should be injected for a perfusion scan?

31. 60,000

32. What group of patients should always get the minimum number of particles of ^99mTc-MAA?

32. patients with pulmonary hypertension, patients with a known right-to-left shunt, and children

33. How does one adjust the number of particles of ^99mTc-MAA that are administered to a patient?

33. Adjust the activity of ^99mTc-pertechnetate.

34. How will the number of particles of ^99mTc-MAA that are administered to a patient change with decay of the kit?

34. The number of particles required to give a dose increases with decay.

35. What is the usual dose of ^99mTc-MAA for a lung perfusion scan?

35. 2 to 5 mCi (74 to 185 MBq)

36. How long after injection of ^99mTcMAA can imaging for a lung perfusion scan begin?

36. immediately

37. What is the minimum number of counts that should be obtained for a lung perfusion scan?

37. 500,000

38. What may occur if blood clots form in the syringe used to inject ^99mTcMAA for a lung perfusion scan?

38. Hot spots may appear in the lung.

39. What should be done with a syringe containing ^99mTc-MAA immediately prior to injecting it into a patient?

39. The syringe should be agitated to prevent sedimentation of the particles. (If there is sedimentation of the particles, then they may remain in the syringe after injection.)

40. What is the normal pattern of uptake on the wash-in and equilibrium phases of a ¹³³Xe lung ventilation scan?

40. uniform distribution

41. What can cause diffusely delayed washout of ¹³³Xe from the lungs during the washout phase of a lung ventilation scan in a normal patient?

41. difficulty breathing through the apparatus for delivering xenon

42. What two organs outside the chest can show uptake of ¹³³Xe in a lung ventilation scan performed on a normal person?

42. the stomach (due to swallowed gas) and the liver (If uptake in the liver is prominent, then a fatty liver should be suspected.)

43. What two organs outside the chest can show uptake of ^99mTc-DTPA in a lung ventilation scan performed on a normal person?

43. the stomach (due to swallowed aerosol) and the kidneys

44. What parts of the lung may be seen on an aerosol scan but never on a lung ventilation scan performed with gas?

44. the trachea and large airways

45. What are two photopenic areas that will be seen in lung perfusion scans of normal patients?

45. the heart and the lung hila

46. What is a ventilation perfusion mismatch?

46. The perfusion defect does not correspond to a ventilation scan abnormality.

47. What is the difference between a segmental and a nonsegmental per-fusion defect on a perfusion scan?

47. A segmental defect reflects the vascular territory of a pulmonary artery branch; nonsegmental defects do not.

48.

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