Nuclear Medicine and Molecular Imaging
Nuclear Medicine and Molecular Imaging
This domain tests radiopharmaceuticals, PET/CT, bone scintigraphy, thyroid therapy, and dosimetry. The exam emphasizes indication, biodistribution, and false-positive patterns.
Core rules
- FDG PET: uptake reflects glucose metabolism; SUV is semiquantitative. Lymphoma response uses the Deauville score (1–3 negative, 4–5 positive). Fasting and glucose control matter.
- Differentiated thyroid cancer: total thyroidectomy followed by risk-adapted radioiodine; stimulated thyroglobulin and whole-body scan guide remnant ablation and detection.
- Bone scan: reflects osteoblastic activity; a superscan shows diffuse uptake with absent renal activity. A three-phase bone scan helps in osteomyelitis.
- V/Q scan: high-probability mismatched perfusion defects support pulmonary embolism when CTA is contraindicated.
Worked example
A 45-year-old after thyroidectomy for papillary carcinoma has a stimulated thyroglobulin of 15 ng/mL and a whole-body scan showing uptake only in the thyroid bed. This is likely remnant tissue; radioiodine ablation is considered based on risk. If there were distant uptake, treatment dose and staging would change.
Traps
Reading brown fat or urinary activity as metastasis; ignoring insulin or fasting status; using Deauville without the reference mediastinum; misinterpreting a superscan as normal; forgetting that iodine contrast can reduce radioiodine uptake.