PET-CT indications

Last revised by Arlene Campos on 19 Jun 2024

PET-CT is a combination of cross-sectional anatomic information provided by CT and the metabolic information provided by positron emission tomography (PET).

PET is most commonly performed with 2-[F-18]fluoro-2-deoxy-D-glucose (FDG). Fluorine-18 (F-18) is an unstable radioisotope and has a half-life of approximately 110 minutes. More recently, radiopharmaceuticals such as gallium-68 prostate-specific membrane antigen have been developed and approved for use in PET.

F-18 FDG is a glucose analog, with broad clinical applications for the imaging assessment of certain types of cancer, as well as infection and inflammation. The indications for F-18 FDG PET-CT imaging in patients with cancer:

PET-CT can also be used as a problem-solving tool, for example:

  • occult primary lesion (e.g. non-metastatic manifestation of neoplastic disease)

  • evaluation of suspected recurrence in patients with equivocal conventional imaging 4

  • evaluation of residual disease in patients with treated differentiated thyroid carcinoma and treated medullary thyroid carcinoma with negative/equivocal conventional imaging 4

  • prior to radical nodal resection in patients with metastatic melanoma

  • suspected malignant transformation in plexiform neurofibromata (neurofibromatosis type 1)

  • differentiate between radiation-induced necrosis and tumor recurrence (e.g. primary CNS malignancy)

Timing of PET scans is of particular importance for insulin-dependent diabetic patients, as administration of exogenous insulin can decrease the image quality of certain PET scans (e.g. 18-F FDG PET). Blood sugar levels of up to 13mmol/L are accepted at some centers, where patients are then hydrated with oral or intravenous fluids. If short-acting insulin is administered, scans may have to be delayed by up to 4 hours.

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