1. Radiology vs. Nuclear Medicine – Radiology (X-ray, CT) gives a transmission image and is associated with increased radiation dose. Nuclear Medicine gives an emission image and is associated with decreased radiation dose.
2. PET tracers – Differentiated Ca: 18F-FDG, 68Ga-DOTATATE, 68Ga-PSMA; Medullary Ca: 18F-FDG, 68Ga-DOTATATE, 18F-DOPA; Anaplastic Ca: 18F-FDG.
3. Flip-flop phenomenon – Tumors with functional differentiation of iodine uptake have low glucose metabolism and low FDG avidity; Tumors without functional differentiation of iodine uptake show high glucose metabolism and high FDG avidity.
4. A study revealed that the diagnostic accuracy of FDG PET in radioiodine negative thyroid cancer may vary depending on serum Tg levels at imaging. The sensitivity of PET/CT according to Tg levels was 28.6% when stimulated Tg was 2-5, 57.1% when it was 5-10, 60% when it was 10-20 and 85.7% when Tg was >20 ng/mL.
5. High FDG uptake suggests more dedifferentiation, aggressive tumor, poorer prognosis and reduced survival.
6. A study evaluated the role of 68Ga-DOTANOC PET-CT in DTC patients with negative 131I-WBS along with serially increasing serum Tg, and compared the same with 18F-FDG PET-CT. Per-patient sensitivity and specificity of 68Ga-DOTANOC PET-CT was 78.4%, 100%, and for 18F-FDG PET-CT was 86.3%, 90.9%, respectively.
7. FDG PET in disease recurrence – A meta-analysis analyzed data on the diagnostic performance of 18FDG PET, and PET/CT in detecting recurrent medullary thyroid carcinoma. Pooled detection rate (DR) on a per patient-based analysis was 59%. It stated that DR of FDG PET and PET/CT increases in patients with higher calcitonin and carcino-embryonic antigen (CEA) values and lower calcitonin doubling time (CTDT) and CEA doubling time (CEADT) values.
8. ¹⁸F-DOPA PET in recurrent MTC – Sensitivity of 47-83% depending on calcitonin levels; the sensitivity is higher than FDG and 68Ga-somatostatin analog PET/CT. However, FDG PET is a better indicator of survival.
9. Indications of imaging in NET – Staging: Evaluation of metastases and localization of primary tumor; Re-staging: residual tumor, recurrence; Evaluation of receptor status and therapy monitoring. In a systematic review and meta-analysis, somatostatin receptor PET/CT (SMSR PET) was found to have good diagnostic performance for evaluation of NET in the thorax and abdomen. The pooled sensitivity was 93% and specificity 96%.
10. Ectopic Cushing syndrome – Pooled detection rates: 18F-FDG 61.1%; 68Ga-peptides 70%; 18F-DOPA 46.7%.

PET radiotracers in Endocrinology