Nuclear Medicine and Molecular Imaging
Nuclear Medicine and Molecular Imaging tests tracer selection, PET/CT interpretation, therapy indications and radiation protection.
Tracers
FDG accumulates in high-glucose-utilisation tissues and tumours, with physiological uptake in brain, myocardium, kidneys, bladder and bowel. Tc-99m bone scan is used for metastases and osteomyelitis; V/Q scan for pulmonary embolism when CT is contraindicated; Ga-68 DOTATATE for neuroendocrine tumours; PSMA PET for prostate cancer. Iodine-131 is used for thyroid ablation and therapy.
PET reporting
Deauville score compares tumour uptake with mediastinal blood pool and liver: 1 no uptake, 2 at or below mediastinum, 3 above mediastinum but at or below liver, 4 moderately above liver, 5 markedly above liver. Deauville 4-5 is positive in lymphoma response assessment. SUVmax is semi-quantitative and is not interchangeable between scanners.
Worked example
A lymphoma patient after chemotherapy has residual uptake greater than liver but not intense (Deauville 4). This is considered positive, so the multidisciplinary team should consider further therapy or biopsy rather than declaring complete remission.
Traps
Interpreting FDG uptake in brown fat or infection as tumour; ignoring hyperglycaemia, which lowers sensitivity; using SUVmax alone to diagnose malignancy; forgetting radiation precautions after iodine therapy; not checking renal function before renally excreted tracers.