POSITRON EMISSION TOMOGRAPHY: Malignant cells present an increased glucose consumption compared to normal pancreatic tissue. Positron emission tomography with 18F fluoro-D-deoxyglucose is a new imaging tool to in vivo assess the amount of glucose metabolism. This method provides metabolic information on tumors rather than morphological information.
Methods: In most PET centers a static emission scan of the upper abdomen is performed 45-60 minutes after intravenous administration of the radiotracer. To obtain quantitative parameter an additional transmission scan is necessary to correct for attenuation. Today, both visual analysis and semiquantitative parameters of glucose consumption as the Standardized Uptake Value (SUV) are used for image interpretation. To allow coregistration of the metabolic PET images and morphological imaging tools as CT or MRI external markers may be used. Following exact reorientation both the metabolic information (PET) and the morphologic information (MRI/CT) can be merged in one 3D data set (image fusion).
Results: In our series of patients the sensitivity for PET to detect pancreatic cancer was 85%, the specificity 84%. False negative results were obtained in patients with hyperglycemia, false positive results in patients with chronic active pancreatitis. Excluding hyperglycemic patients the sensitivity for PET increased to 98%. In a sample statistics of 305 euglycemic patients sensitivity, specificity and accuracy were 92%, 79%, and 87%, respectively. Image fusion of metabolic (PET) and morphologic data (MRI/CT) can help to better localize the focus of increased glucose consumption demonstrated with PET and to differentiate multifocal cancer from lymph node metastases.
Conclusion: 18FDG PET is a feasible diagnostic modality to differentiate benign and malignant pancreatic masses when morphological imaging is equivocal. Image fusion of PET and CT or MRI can combine the advantages of both modalities in one image-detailed anatomic information combined with accurate metabolic data.