Nuclear Radiology
What the exam tests
Nuclear radiology covers radiopharmaceuticals, PET/CT, bone scanning, thyroid imaging and therapy, dosimetry, and radiation safety. Expect uptake patterns, indications, and therapy contraindications.
Core rules
- Radioiodine uptake is diffuse and increased in Graves disease; it is low in subacute thyroiditis and exogenous thyroid hormone use.
- I-131 therapy is contraindicated in pregnancy and lactation; pregnancy testing is required before therapy.
- FDG PET/CT reflects glucose metabolism; SUV is a semiquantitative measure, not a diagnosis by itself.
- Bone scan uses Tc-99m MDP; uptake reflects osteoblastic activity.
Worked example
A 35-year-old woman has hyperthyroidism, a diffuse goiter, and a 24-hour radioiodine uptake of 45% with diffuse uptake on scan. Reasoning: this pattern is consistent with Graves disease. Before I-131 therapy, pregnancy must be excluded. If she were pregnant, antithyroid drugs and definitive therapy after delivery would be considered. Subacute thyroiditis would show low uptake and is not treated with radioiodine.
Traps
Treating subacute thyroiditis with I-131; forgetting pregnancy testing; and interpreting a single SUV value as proof of malignancy.
Key points
- Graves disease shows diffuse increased radioiodine uptake.
- Subacute thyroiditis shows low uptake.
- I-131 is contraindicated in pregnancy and lactation.
- FDG uptake reflects metabolism, not histology.
- Bone scan detects osteoblastic activity.