Questions

Answers

1. Which element does ⁶⁷Ga most closely mimic in terms of biologic behavior?

1. iron (Fe-III)

2. How is ⁶⁷Ga produced?

2. by cyclotron bombardment of ⁶⁸Zn

3. How does ⁶⁷Ga decay?

3. by electron capture

4. What is the half-life of ⁶⁷Ga?

4. 78 hours

5. What are the energies of the principal photons of ⁶⁷Ga decay?

5. 93, 185, 300, and 394 keV

6. What photopeaks of ⁶⁷Ga are most commonly used for imaging?

6. 93 and 185 keV

7. To what serum protein does ⁶⁷Ga bind after injection?

7. transferrin

8. Why does gallium not become incorporated into heme and other similar iron-containing compounds?

8. Incorporation of iron into heme requires the reduction of Fe from the +3 to the +2 oxidation state, but gallium cannot be reduced by the body to a +2 state.

9. What percentage of a dose of ⁶⁷Ga is excreted by the kidneys in the first 24 hours after injection?

9. 15% to 25%

10. What is the biologic half-life of ⁶⁷Ga excretion beyond 24 hours after injection?

10. 25 days

11. What is the major source of ⁶⁷Ga excretion beyond 24 hours after injection?

11. the gastrointestinal tract

12. How does iron overload affect ⁶⁷Ga biodistribution?

12. It saturates transferrin and causes less liver uptake and more renal excretion and bone uptake.

13. What mechanisms cause ⁶⁷Ga up-take by tumors?

13. increased vascular permeability of tumors, transferrin receptors on tumors, and increased concentration of iron-binding proteins in tumors

14. How does ⁶⁷Ga uptake differ between viable and necrotic tumors?

14. The ⁶⁷Ga is taken up only by viable tumors, not by necrotic tumors.

15. How does the dose of ⁶⁷Ga used for tumor detection differ in general from the dose used for information detection?

15. A larger dose is given for tumor detection.

16. What is the usual dose of ⁶⁷Ga for tumor detection?

16. 10 mCi (370 MBq)

17. What is the organ for ⁶⁷Ga critical to symmetry, and what is its radiation-absorbed dose?

17. the large intestine, with a dose of 9 rads (90 mGy)/10 mCi (370 MBq)

18. Why is there great variation in the medical literature regarding the utility of ⁶⁷Ga for tumor detection?

18. Most of it was published before 1985 (using lower doses), and there was no single-photon emission computed tomography (SPECT).

19. How many photopeaks of ⁶⁷Ga should be utilized for tumor detection?

19. at least two and preferably three

20. How many counts should be obtained for planar ⁶⁷Ga images for tumor detection?

20. at least 500,000 counts for routine whole body images, and at least one million counts for the evaluation of areas of previous disease

21. When should images be obtained with ⁶⁷Ga for tumor detection?

21. at approximately 2 to 3 days and 7 to 10 days after injection

22. What is the advantage of performing sequential SPECT examinations with ⁶⁷Ga images for tumor detection?

22. Sequential SPECT examinations help to differentiate pathologic abdominal uptake from physiologic bowel localization.

23. How much time should elapse between treatment with chemotherapy and ⁶⁷Ga imaging to assess tumor response?

23. three to six weeks

24. How can one differentiate between inflammation and tumor when there is ⁶⁷Ga uptake and hilar lymph nodes?

24. ²⁰¹Tl imaging will show uptake in tumor but not in inflammation.

25. How does normal spleen uptake of ⁶⁷Ga compare with normal liver up-take of ⁶⁷Ga?

25. Spleen uptake is less than that of the liver.

26. Which organs normally take up ⁶⁷Ga?

26. liver, spleen, bone marrow, salivary glands, lacrimal glands, nasal mucosa, external genitalia, female breast

27. What physiologic condition results in markedly increased female breast uptake?

27. lactation

28. What condition can cause increased salivary gland uptake of ⁶⁷Ga that is unrelated to tumor or infection?

28. head and neck radiotherapy

29. In children, what organ in the chest may show physiologic uptake of ⁶⁷Ga?

29. thymus

30. For how long is kidney uptake normal on the ⁶⁷Ga scan?

30. 24 hours

31. What are the causes of faint liver up-take on ⁶⁷Ga imaging?

31. competition for uptake by tumor, liver dysfunction, recent administration with chemotherapy (vincristine), iron overload, and increased renal clearance

32. What are the causes of increased kidney uptake on ⁶⁷Ga imaging data that are related to infection or tumor?

32. hepatic or renal failure, recent chemotherapy (vincristine and Cytoxan), recent transfusion

33. True or false: Renal or perirenal up-take after 24 hours on a ⁶⁷Ga scan is abnormal.

33. true

34. What are the indications for ⁶⁷Ga imaging in infections?

34. spine lesions, splenic abscess, FUO (without recent surgery), lung infections, infection in cases of leukopenia, sarcoid, low-grade chronic infections

35. How long can uninfected surgical wounds have increased uptake of ⁶⁷Ga?

35. one to two weeks

36. How does lymphangiography affect ⁶⁷Ga uptake?

36. It can cause diffusely increased lung uptake.

37. What procedure increases the sensitivity of ⁶⁷Ga to the detection of affected axillary lymph nodes?

37. imaging patients with their arms raised

38. Why are large tumor deposits sometimes missed on ⁶⁷Ga imaging?

38. The larger tumors commonly undergo necrosis and no longer take up ⁶⁷Ga.

39. What procedure improves the detection of tumors in the liver or spleen by ⁶⁷Ga?

39. comparison with a sulfur colloid study to look for areas of decreased uptake on colloid scan that fill in with ⁶⁷Ga

40. What is the complication of using progressive enemas and bowel preparations for ⁶⁷Ga imaging?

40. They can cause bowel inflammation that takes up ⁶⁷Ga.

41. What is the sensitivity of ⁶⁷Ga for detecting Hodgkin lymphoma?

41. approximately 90%

42. What histologic types of Hodgkin lymphoma have the highest and lowest sensitivities for detection by ⁶⁷Ga?

42. highest: nodular sclerosing, mixed cellularity, and lymphocyte depleted; lowest: lymphocyte predominant

43. What is the sensitivity of ⁶⁷Ga imaging for detecting high-grade non-Hodgkin lymphomas?

43. approximately 85% to 90%

44. How does the sensitivity of ⁶⁷Ga to the low- and intermediate-grade non-Hodgkin lymphomas compare with its sensitivity to the higher-grade non-Hodgkin lymphomas?

44. The sensitivity of ⁶⁷Ga is less.

45. What is the main use of ⁶⁷Ga imaging in lymphoma?

45. to determine tumor viability after chemotherapy

46. How is ⁶⁷Ga imaging used to evaluate tumor viability?

46. A pretherapy scan is needed to confirm gallium uptake; posttherapy uptake indicates a persistent viable tumor.

47. How is ⁶⁷Ga useful in diagnosing hepatomas?

47. It can be used to distinguish hepatomas from the regeneration nodules.

48. What percentage of hepatomas are gallium avid?

48. 90%

49. What percentage of hepatomas show uptake greater than that of the normal liver?

49. 50%

50. What is the sensitivity of ⁶⁷Ga imaging for soft-tissue sarcomas?

50. 90% to 95%

51. What is the characteristic lung up-take on a gallium-67 scan in PCP pneumonia?

51. diffuse intense bilateral uptake without nodal or parotid activity

52. What element does ²⁰¹Tl mimic in the body?

52. potassium

53. How does ²⁰¹Tl decay?

53. by electron capture

54. What are the photopeaks of ²⁰¹Tl?

54. a cluster of X-rays from 69 to 83 keV, and gamma (γ) rays at 135 and 167 keV

55. What percentage of a dose of ²⁰¹Tl goes to the heart?

55. 3% to 5%

56. What is the critical organ for intravenous ²⁰¹Tl chloride, and what is the radiation absorbed dose?

56. the kidneys, with a dose of 3.6 rads (36 mGy)/mCi (37 MBq)

57. When should imaging begin after ²⁰¹Tl injection for tumor detection?

57. 10 to 30 minutes

58. Does ²⁰¹Tl imaging correlate with the histologic grade of primary brain glial tumors?

58. Yes—the higher the uptake, the higher the tumor grade.

59. Does ²⁰¹Tl imaging differentiate brain tumor recurrence from radiation necrosis?

59. Yes—tumor recurrence shows up-take, while radiation necrosis shows no uptake.

60. How is ²⁰¹Tl imaging useful for evaluating intracranial lesions in patients with AIDS?

60. Uptake in the brain indicates lymphoma or some other malignancy; no uptake suggests an infectious cause.

61. How is ²⁰¹Tl imaging useful in the management of primary bone tumors?

61. It accurately detects the extent of involvement and predicts and assesses the response to chemotherapy.

62. What is the advantage of ²⁰¹Tl imaging over ¹³¹I imaging for detecting thyroid cancer?

62. ²⁰¹Tl imaging does not require withdrawal of thyroid hormone treatment.

63. What is the main advantage of ¹³¹I imaging over ²⁰¹Tl imaging for the detection of thyroid cancer?

63. ¹³¹I imaging projects the potential usefulness of ¹³¹I therapy.

64. In a patient with a history of thyroid cancer and a negative ¹³¹I scan, when is a ²⁰¹Tl scan indicated?

64. when the serum thyroglobulin level is elevated

65. How is ²⁰¹Tl imaging useful in the evaluation of Kaposi sarcoma?

65. Kaposi sarcoma is usually negative on gallium imaging but is positive on thallium imaging.

66. What is the half-life of indium-111?

66. 67 hours (2.8 days)

67. True or false: Indium is cyclotron produced and decays by electron capture, emitting gamma (γ) photons of 173 and 247 keV.

67. true

68. What is the typical labeling efficiency of an ¹¹¹In-white blood cell (WBC) scan?

68. 75% to 90%

69. What is the target organ in an ¹¹¹InWBC scan?