Abstract

Peter Lind
Department of Nuclear Medicine and Endocrinology, General Hospital Klagenfurt, Klagenfurt, Austria

Since 2001 dedicated PET/CT (full ring PET scanner and spiral CT), as a combined metabolic/morphologic imaging modality, has been available. With the introduction of this new modality of imaging in oncology, the question arises whether PET/CT is superior to PET and CT alone and if so, can PET/CT affect patients management better than both modalities alone. PET can assess for example metabolism, protein synthesis, gene expression and tissue hypoxia depending on the tracer used, whereas CT mainly reflects the anatomy and to some degree the perfusion status. The main tracer used for oncologic indication is Fluorine-18 labeled deoxyglucose (FDG) produced in a cyclotrone, with strict guidelines which are confined to Standards of Good Manufacturing Practice (GMP).

Method and patient preparation for PET/CT: After drawing a venous line and intravenous 20 mg furosemide injected, 4-7 MBq/kg BW F-18 FDG injected intravenously depending on the type of PET scanner (2D vs 3D aquisition mode, crystal etc) followed by a 250 ml saline infusion. Between the FDG injection and image acquisition (uptake time) the patient should be resting quietly in a quiet room and should not speak, eat or perform any activities that will activate the muscles. After an uptake time of 60 to 90 minutes a whole body CT is performed followed by the PET image acquisition (for oncology study, mostly 6-7 bed positions from the vertex to upper mid thigh). In the combined modality, CT data are used for attenuation correction and anatomical correlation. Weather CT should be performed as contrast enhanced diagnostic CT or as “low dose CT” for anatomic correlation is still a question mark that is yet to be answered. In our institution, if a full diagnostic contrast enhance CT have been acquired, PET/CT should be performed as low dose CT. There is also some debate on the use of oral contrast media for PET/CT imaging. However, using negative oral contrast media was found to increase the accuracy of PET/CT especially with respect to abdominal pathology.

Indications in oncology: The main indications today are the so-called 1a indications according to the German Consensus Conference (GCC) 2000. This includes: characterisation of solitary pulmonary nodule, staging and re-staging of lung cancer, head and neck cancer, lymphoma, staging of oesophageal and pancreatic cancer, restaging of thyroid cancer, breast cancer, colorectal cancer, melanoma and carcinoma of unknown primary.

For image interpretation, it is important to know the physiologic distribution as well as the most frequent pitfalls, which are found to be dramatically reduced using PET/CT compared to PET imaging alone.