The tracer usually chosen is 18F-fluorodeoxyglucose (FDG). It is a short half-life glucose analogue. It becomes concentrated
in metabolically active tissues. PET can be combined with CT
or MRI to provide high-quality images combining anatomy with physiology
- A test that identified structures by their rate of metabolism and complements other imaging methods
- Useful in the key investigations in malignancy, but also
has a wide range of other uses.
- Positron Emission Tomography measures glucose uptake through the use of radiolabelled glucose
- Flourodeoxyglucose which is given to the patient.
- The glucose is taken up by areas of high metabolic activity
- FDG decays rapidly to produce a positron which encounters tissue
- It annihilates with an electron to produce a pair of high-energy photons which can be detected
- Areas of high metabolic uptake e.g. heart and brain are identified.
- Useful especially in identifying lung tumours and areas of acute inflammation.
- Can complement other imaging modalities such as CT or MRI.
- Lung tumours and extrathoracic metastases in bone and adrenals
- Useful for lung, melanoma, oesophageal as well as lymphoma
- Hot areas seen with TB and sarcoid
- Not useful for brain metastases as background metabolic activity too high
- Slow growing tumours e.g. bronchoalveolar carcinomas may be negative
- PET can also be used to image occult sources of infection eg. PUO
- New areas
- 11C-labelled metomidate to detect tumors of adrenocortical origin
- Somatostatin tracers in neuroendocrine tumours
- Amyloid tracers in Alzheimer’s disease
High Uptake areas normally
- Brain, liver, kidney, bladder,
- Larynx, and lymphoid tissue of pharynx
Single photon emission computed tomography (SPECT)
- This is closely similar to PET but uses a radioisotope-labelled molecule detected by gamma cameras for detection.
- The images produced are of lower resolution than PET but the isotopes used are longer lived and more easily available.
- Examples include myocardial perfusion scanning