Metabolic imaging with FDG: a primer.

The rapid advances in imaging technologies are a challenge for both radiologists and clinicians who must integrate these technologies for optimal patient care and outcomes at minimal cost. Multiple indications for functional imaging using fluorode-oxyglucose (FDG) are now well accepted in the fields of neurology, cardiology, and oncology, including differentiation of benign from malignant lesions, staging of malignant lesions, detection of malignant recurrence, and monitoring of therapy. The fusion of anatomic and molecular images (computed tomography [CT] and FDG) obtained with integrated positron emission tomography (PET)-CT systems, sequentially in time but without moving the patient from the imaging table, allows optimal co-registration of anatomic and molecular images, leading to accurate attenuation correction and precise anatomic localization of lesions with increased metabolism. This powerful technology provides a valuable new tool for diagnostic and therapeutic applications. The diagnostic accuracy is improved in approximately 50% of patients because of improvement of lesion detection on both CT and FDG PET images, better differentiation between physiologic and pathological foci of FDG uptake, and better localization of malignant foci of FDG uptake. This new technology affects the management of 10%-20% of cases by guiding further therapy. Promising clinical applications include guiding biopsy to the metabolically active sites of tumors, guiding surgery, and planning intensity-modulated radiation therapy. In addition, new PET radiopharmaceuticals are emerging for indications for which FDG has limitations. Some of the new PET tracers are labeled with (18)F, which has a practical half-life for commercial distribution. In the past few years, the clinical indications for FDG have broadened dramatically, and the rapid technical developments of integrated multimodality imaging systems and new PET tracers further extend the horizon.