Define PET scan? When do you say a positive and false negative result in PET CT?

Positron emission  tomography (PET) is a nuclear medicine fundamental imaging technique that is used to observed the pathology and identify based on the altered metabolism.

The scan is said to be the positive if the radioactive tracer to gets trapped in the tissue and concentrates which shows as the increase signal internally indicating the intensive uptake  by the tissue with increase metabolism e.g malignancy Abnormal area of FDG  Accumulation should be compare to the uptake by background tissue . For example In lung Focal Abnormalities that have greater uptake than the mediastinal blood pool on altercation correct images are highly suggestive of malignancy. If the standard uptake value (SUV) is ≥ 2.5 it is indicative of malignancy.

False positive result can occur by increased update due to the inflammatory process. It can be seen in

  • Sarcoidosis
  • Cryptococcus
  • Paragangliomas
  • Radiation fibrosis
  • Pneumonitis
  • Sclerosing haemangioma
  • Granulation tissue stromal tumour

False negative : low SUV score

  • Tumour with low activity
  • Tumour less than 1 cm


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