Nuclear Medicine and Molecular Imaging

Question 1

Tc99m bone scan

Answer 1

Tagged Tc bound to phosphorus

Shows osteoblastic activity – not necessarily bone. Can be used to find bony metastases (prostate, breast, kidney, thyroid, lung - lead kettle PB KTL), but mostly for prostate and breast.

Bone will appear, but osteoblastic lesions (tumors, Paget’s, fractures) will be highlighted

Question 2

What kind of newly diagnosed prostate cancer patient gets a Tc99m bone scan?

Answer 2

Someone with unexplained lumbar back pain and an elevated PSA

Question 3

I¹²³ vs I¹³¹

Answer 3

I¹³¹ rapidly decays with beta radiation, depositing radiation locally

I¹²³ decays slightly more slowly and disperses, it is used for imaging/thyroid scintigraphy

Question 4

The first-line test for myocardial perfusion is a nuclear medicine perfusion scan. What other tests can be used?

Answer 4

A perfusion contrast MRI. An excellent alternative, just not readily available at current.

Stress echocardiography (with dobutamine or equivalent) – but obviously there are limitations in comparison.

Question 5

A defect on a nuclear perfusion scan could be due to . . .

Answer 5

1. Infarct
2. Hibernating myocardium
   
   • Hibernating myocardium refers to myocardial dysfunction than can occur in chronic ischemia with resultant hypo or dyskinetic myocardial segments. This is revserible with revascularization.

Question 6

Tests for evaluating myocardial viability

Answer 6

• MRI perfusion with delayed imaging
  
  • If tissue is viable, contrast will wash out after 2-4 minutes, while it gets trapped in infarcted tissue
• 201-Thallium scan
  
  • Taken up by viable myocardium, even if severely ischemic
• Cardiac PET FDG scan (gold standard)

Question 7

Where does FDG nonspecifically accumulate?

Answer 7

• The brain
• The myocardium
• The renal system (excretion)

Question 8

What are the most “radioresistant” cancers?

Answer 8

• Sarcoma
• Renal clear cell carcinoma
• Melanoma

Question 9

Why is HIDA the most sensitive and specific test for cholecystitis?

Answer 9

GB function is poor and the tracer never fully fills the GB