The foundation of PET imaging with [F-18] Fluoro-Deoxy-D-Glocose (FDG) rests with the observation as long ago as the 1920s that malignant tissue has a higher metabolic rate for glucose than the normal tissues from which those tumors arise (except for brain gray matter). It was not until the early 1980s that PET imaging with FDG was applied, initially in a variety of research and then clinical applications in the brain., It was not until approximately 1990 that scanners able to perform whole body imaging were developed. Current scanners have high resolution and can delineate focal lesions down to perhaps 5 mm (depending upon location). While CT and MRI have higher spatial resolution, they suffer from low specificity. For example, nodal involvment by tumor on those studies rests solely on node size of 1 cm or greater. Clearly, involved nodes can be smaller, and larger nodes may be nonspecific or resulting from scarring from successful tumoricidal therapy. PET has a considerable specificity advantage here, since one is actually assessing the in vivo biochemical characteristic of the area in question. It is not implied that the specificity of PET is ideal; a variety of chronic inflammatory lesions such as Tb, fungal granulomas, sarcoidosis and some pyogenic abscesses may be positive with FDG PET. Clearly, PET does not replace the anatomic imaging modalities in most situations. In some instances, PET naturally follows anatomic imaging and in others, PET is very useful in directing CT or MRI performed after the PET scan. It must be stressed that no imaging modality will detect microscopic disease and in that regard PET is not unique. Hence, for example, PET does not substitute for sentinel node biopsy in melanoma.

The assessment of the utility of PET is definitely a “works in progress”. In addition to a large number of single-institution trials at established PET centers, there are now a number of multi-institutional trials underway, many sponsored by outside organizations such as NCI, SWOG and the ACS Surgical Oncology group.

The following is a guide to the use of PET in cancer patients (PET Utilization Guide or follow links to specific tumor applications on the left menu). In addition to the specific indications listed, it is worth remembering that PET can be an excellent problem solver in a given patient at a given time. For example: What is the significance of the persistant mass on CT following radiation and chemotherapy? Is the low density liver lesion tumor or focal fatty infiltration or hemangioma? Is the CT documented adrenal enlargement due to metastasis or adrenal adenoma? PET isn’t perfect in terms of specificity but it is quite likely to aid and improve patient management in these and a wide variety of other situations. PET is especially useful in assessing the patient with known malignancy who is being considered for a major surgical procedure where knowledge of distant disease would lead to a decision not to operate or where an uncertain finding on CT may not be due to tumor, thereby allowing surgery to proceed.