Fluorodeoxyglucose positron emission tomography (FDG PET) has a wide range of clinical applications in oncology and to a lesser extent in neurology and cardiology. These clinical applications vary substantially in the amount of clinical experience and literature available.

The chapters on clinical topics will contain Clinical Indication sections, where a general assessment is made as to the level of evidence for specific clinical applications of FDG PET.

For quick reference, letters have been assigned for each clinical indication according to the following:

1. The use of FDG PET for this clinical indication is well established. Its value is supported by a large amount of clinical experience and literature.
   
2. FDG PET is useful for this clinical indication. However, compared with the A-level applications, the clinical experience and literature supporting the use of FDG PET for this clinical indication are less available or substantial. This may mean that more experience and research are needed to fully define the value of FDG PET in this clinical setting, or that FDG PET is useful but has a lesser degree of incremental benefit over conventional imaging techniques than the A-level applications.
   
3. FDG PET is potentially useful for this clinical indication. There is a minimal amount of clinical experience and literature supporting the use of FDG PET for this clinical indication. A substantially greater amount of experience and research is needed to fully define the value of FDG PET.
   
4. FDG PET has limited value and is not recommended as a standard imaging technique for this clinical indication. This may be because of limited accuracy, lack of cost-effectiveness, or lack of impact on clinical management. However, there may be specific situations where FDG PET can provide valuable information.

These levels are intended only as general guidelines. Practitioners may find FDG PET more or less valuable for each clinical indication based on their specific experience and patient populations. As clinical experience and research accumulate, it is likely that many of the C- and B-level applications will become A-level applications.