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What is involved in a PET scan?

Injection of a glucose analogue (18F-FDG) which is taken up by cells with glucose transporter proteins.
Glucose is then phosphorylated by hexokinase to FDG-6 phosphate and FDG-phosphate is trapped in the cells.
Malignant cells have a high metabolic rate and high level of uptake of glucose


What can give a false negative on a PET scan?

Raised serum glucose as less FDG will be taken up by tumour cells as normal glucose is competing for receptors - patients are usually fasted before a scan to prevent this


What are sites on a PET that physiologically take up FDG?

Urinary system
Liver and spleen


What can give a false positive on a PET?

Brown fat
Infections (Tb)
Recent surgery


What are some FDG-PET negative tumours?

Bronchoalveolar carcinoma
Carcinoid tumours of lung
Renal cell carcinomas
Low grade lymphomas
Mucinous tumours of GI tract
Low sensitivity at detecting osteoblastic (sclerotic mets)