Fundamentals of PET/CT

Positron emission tomography (PET) is a nuclear medicine imaging modality that can be used to create whole body images of physiological processes. In contrast, CT and MR create images of anatomy. PET/CT is a newly developed technology that combines a fully diagnostic PET scanner with a fully diagnostic CT scanner that can simultaneously create complimentary images of physiology and anatomy.

For many diseases, most notably cancer, PET can detect changes in physiology 6 months to a year before CT or MR can detect changes in anatomy. This allows PET to detect disease in normal sized structures as well as to detect early response to therapy.

Furthermore, PET can accurately detect disease in regions where post therapeutic change has distorted anatomy.

Currently, almost all PET scans are performed using the radiopharmaceutical F-18 fluorodeoxyglucose (FDG). F-18 is a positron emitter with a two hour half-life. FDG is a glucose analog that is used to create images of glucose metabolism.

Clinical indications for PET/CT include oncology, neurology and cardiology. In oncology, rapidly growing neoplasms fuel their growth with glucose making FDG PET the most sensitive and specific modality for imaging them. In Alzheimer’s disease, FDG PET can detect disease specific reductions in neuronal activity long before it can be detected with any other test. In cardiology, FDG PET can accurately assess myocardial viability in hypo-perfused regions of the myocardium.

Compared to CT or MR, the overall sensitivity and specificity of PET/CT is typically at least 10% higher. The peer-reviewed scientific literature shows that PET/CT can lead to significant changes in patient management at least 40% of the time. PET/CT is well tolerated by most patients and is routinely reimbursed by most insurance companies. For many indications, PET/CT is rapidly becoming part of standard care.