Questions

Answers

1. What is the physiologic principle behind blood-brain barrier imaging?

1. Tracers stay within the blood pool and diffuse into the brain only when the blood-brain barrier is disrupted.

2. What three tracers are used for blood-brain barrier imaging?

2. ^99mTc-pertechnetate, ^99mTc-DTPA, and ^99mTc-glucoheptonate

3. What is the main disadvantage of ^99mTc-pertechnetate for blood-brain barrier imaging?

3. It localizes physiologically in the choroid plexus.

4. Why does ^99mTc-glucoheptonate have better uptake in brain tumors than other blood-brain barrier imaging agents?

4. As a glucose analog, it may serve as a substrate for tumor metabolism.

5. How do corticosteroids affect blood-brain barrier imaging?

5. They may diminish uptake, because corticosteroids decrease the permeability of the blood-brain barrier.

6. How is blood-brain barrier imaging performed?

6. Blood flow images are taken every two to three seconds for one minute, then 750K count immediate static images are taken in multiple views, and then, 1.5 to 2 hours later, 750K count delayed static images are obtained in multiple views.

7. On blood-brain barrier imaging, how much uptake is present in the healthy brain?

7. none

8. What structures are seen only on blood-brain barrier imaging?

8. the scalp and venous sinuses

9. What are the findings of subdural hematoma on blood-brain barrier imaging?

9. peripherally reduced flow on dynamic images, with increased up-take on delayed images

10. What are the findings of a ventriculitis on blood-brain barrier imaging?

10. bilaterally increased uptake in the region of the lateral ventricles

11. What are the findings of an abscess on blood-brain barrier imaging?

11. a focal area of increased uptake on delayed imaging, with a cold center developing as the abscess progresses

12. What are the findings of herpes encephalitis on blood-brain barrier imaging?

12. increased flow and uptake in the affected temporal lobe

13. What is the characteristic finding of an infarct on the angiogram portion of a blood-brain barrier scan?

13. reduced early perfusion with increased delayed perfusion; these symptoms are known as the “flip-flop” phenomenon

14. How long after an infarct is the “flipflop” perfusion first seen on blood-brain barrier imaging?

14. in the first few days

15. What is “luxury perfusion”?

15. increased blood flow to an infarction due to uncoupling of metabolism, typically seen about five days after an infarction

16. What is the best tracer to use to diagnose venous sinus thrombosis?

16. ^99mTc-RBCs

17. What is the typical finding of venous sinus thrombosis in ^99mTc–red blood cell (RBC) imaging?

17. abrupt termination of the midportion of sinus

18. What are the findings of an arteriovenous malformation on brain imaging with ^99mTc-RBCs?

18. intense uptake on delayed images

19. What is the advantage of radionuclide angiography over the electroencephalogram (EEG) in confirming brain death?

19. radionuclide angiography remains accurate in the face of hypothermia and drug intoxication

20. What are the scintigraphic criteria for brain death on a radionuclide angiogram?

20. presence of a good carotid bolus without intracranial arterial flow

21. What is the significance of faint visualization of the venous sagittal sinus or the transverse sinus on radionuclide angiography to confirm brain death?

21. It may be seen in 10% to 20% of patients with brain death and does not preclude the diagnosis of brain death, so long as there is no intracranial arterial flow.

22. What are the common features of tracers for imaging regional cerebral perfusion?

22. They are small, neutral lipophilic molecules; they rapidly diffuse across the blood-brain barrier; they have a high brain extraction fraction; and they remained fixed in the brain.

23. What three tracers are available for cerebral perfusion scintigraphy?

23. ¹²³I-isopropyl iodo-amphetamine (IMP), ^99mTc–hexamethyl propylene amine oxime (HMPAO), and ^99mTc–ethylcysteine dimer (ECD)

24. What percentage of a dose of ¹²³IIMP (isopropyl iodo-amphetamine) localizes in the healthy brain?

24. 6% to 9%

25. What is the usual administered dose of ¹²³I-IMP?

25. 3–6 mCi (111–222 MBq)

26. What is the main difference between ¹²³I-IMP and ^99mTc-HMPAO (hexamethyl propylene amine oxime) in brain uptake distribution?

26. ¹²³I-IMP demonstrates redistribution that is independent of brain-blood flow.

27. What is the ratio of gray-to-white matter uptake with ¹²³I-IMP?

27. 3–4:1

28. What percentage of a dose of ^99mTcHMPAO localizes in the normal brain?

28. 3.5% to 7%

29. What is the ratio of gray-to-white matter uptake with ^99mTc-HMPAO?

29. 2.5:1

30. How do images of ¹²³I-IMP and ^99mTcHMPAO differ when imaging infarction?

30. ¹²³I-IMP always shows a flow defect; ^99mTc-HMPAO may show luxury per-fusion with increased uptake.

31. How long after injection of ^99mTcHMPAO does peak brain uptake occur?

31. two minutes

32. What percentage of a dose of ^99mTcECD (ethylcysteine dimer) localizes in the healthy brain?

32. 6% to 7%

33. How long after injection of ^99mTc-ECD does peak brain uptake occur?

33. two minutes

34. How do ^99mTc-HMPAO and ^99mTc-ECD differ in terms of blood pool clearance?

34. Blood pool clearance is faster with ^99mTc-ECD.

35. How do the circumstances of injection affect cerebral perfusion imaging?

35. Stimulation (e.g., visual or auditory) during the injection can cause areas of increased uptake in the site stimulated.

36. What type of image acquisition is required for cerebral perfusion imaging?

36. SPECT acquisition

37. What is the normal cerebral blood flow in an adult?

37. approximately 50 mL/min/100 g

38. What is the normal cerebral blood flow in a 3- to 10-year-old child?

38. approximately 100 mL/min/100 g

39. How does blood flow change in the occipital lobes when the eyes are open versus when they are closed?

39. Blood flow increases by approximately 30%.

40. How does an intraictal seizure focus affect regional cerebral blood flow?

40. It causes an increase in blood flow.

41. What practical methods are available to quantify absolute regional cerebral blood flow with single-photon emission computed tomography (SPECT)?

41. none

42. What methods are available to quantify absolute regional cerebral blood flow with radionuclide imaging?

42. PET imaging with ¹⁵O water, or ¹⁵C carbon dioxide, or ¹³³Xe imaging with a multiprobe detector

43. What is the critical organ and what is its radiation dose for ¹²³I-IMP?

43. the lung, with 0.84 rads (8.4 mGy)/6 mCi (222 MBq)

44. What is the critical organ and what is its radiation dose for ⁹⁹Tc-HMPAO?

44. the lacrimal glands, with 5.2 rads (52 mGy)/20 mCi (740 MBq)

45. How long after infarction will decreased blood flow be seen on a cerebral perfusion scan?

45. immediately

46. In patients with cerebral infarcts, why are defects on cerebral perfusion images often larger than on computed tomography (CT) scans?

46. the area of infarction is surrounded by an ischemic area of decreased blood flow

47. What is the cause of crossed cerebellar diaschisis?

47. Increased activity in the cerebellum contralateral to a cerebral infarction is due to increased blood flow to the cerebellum after a loss of suppressive neural activity from the contra-lateral cortex.

48. Which two factors decrease the sensitivity of cerebral perfusion imaging for infarctions?

48. luxury perfusion, and difficulty detecting lacunar infarcts

49. True or false: 180-degree acquisitions on ⁹⁹Tc-HMPAO studies are diagnostically comparable to 360-degree acquisitions.

49. false

50. What is the typical scintigraphic pattern of Alzheimer disease on cerebral perfusion imaging?

50. bilateral posterior temporal and parietal hypoperfusion

51. What is the typical scintigraphic pattern of Pick disease on cerebral perfusion imaging?

51. bilateral frontal hypoperfusion

52. What is the typical scintigraphic pattern of multi-infarct dementia on cerebral perfusion imaging?

52. multiple asymmetric perfusion defects involving both the cortex and deep structures

53. What is the positive predictive value of brain perfusion scintigraphy for Alzheimer disease?

53. approximately 80%

54. What is the typical scintigraphic pattern of depression on cerebral perfusion imaging?

54. normal perfusion

55. What is the typical scintigraphic pattern of metabolic brain dysfunction on cerebral perfusion imaging?

55. normal perfusion

56. What is the typical scintigraphic pattern of Huntington chorea on cerebral perfusion imaging?

56. reduced perfusion of the caudate nucleus

57. What is the typical scintigraphic pattern of AIDS dementia on cerebral perfusion imaging?

57. multifocal or patchy cortical and subcortical regions of hypoperfusion

58. What is the typical scintigraphic pattern of an interictal seizure focus on cerebral perfusion imaging?

58. hypoperfusion

59. What is the typical scintigraphic pattern of an ictal seizure focus on cerebral perfusion imaging?

59. hyperperfusion

60. What is the sensitivity of brain per-fusion SPECT for the detection of interictal seizure foci?

60. approximately 65% to 75%

61. What is the relative sensitivity of brain perfusion SPECT for the detection of the ictal versus interictal seizure foci?

61. The sensitivity is greater for ictal foci.

62. How is brain perfusion SPECT useful in conjunction with the Wada test?

62. Brain perfusion SPECT can demonstrate the exact territory perfused by the pentobarbital.

63. How is ²⁰¹Tl imaging useful for the assessment of brain tumors?

63. The degree of the ²⁰¹Tl uptake is proportional to the malignant grade of the tumor, and uptake in the brain distinguishes recurrent brain tumor from radiation necrosis.

64. How is ²⁰¹Tl imaging useful for the assessment of AIDS patients with intracerebral mass lesions?

64. The ²⁰¹Tl uptake indicates the presence of brain tumors such as lymphoma; absence of ²⁰¹Tl uptake indicates the presence of infection, such as toxoplasmosis.

65. Which tracer is currently used for radionuclide cisternography?

65. intrathecal ¹¹¹In-DTPA

66. What is the critical organ, and its radiation dose, for intrathecal ¹¹¹InDTPA?

66. the surface of the spinal cord, with 5 rads (50 mGy)/0.5 mCi (18.5 MBq)

67. How can radionuclide cisternography distinguish normal-pressure hydrocephalus from cerebral atrophy?

67. Cisternography will show prolonged ventricular uptake in normal-pressure hydrocephalus.

68. How is radionuclide cisternography used for the detection of cerebrospinal fluid (CSF) leaks?

68. Imaging to visualize leaked radioactivity; pledgets placed in the nasal cavity and counted for the leaked radioactivity.

69. True or false: In the initial stage of cerebral ischemia, regional cerebral blood flow (rCBF) increases.

69. false

70.

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