Imaging techniques in diagnostic approaches.

Despite the considerable technological advances in imaging modalities which have occurred over the last years, EUS remains one of the most reliable and accurate technique for the study of gastroenteropancreatic neuroendocrine tumors. More specifically, EUS can detect very small lesions, assess the local extent and lymph node involvement and biopsy the lesion for cytophatological confirmation (EUS-FNA). In addition, nuclear medicine imaging has a relevant role in the evaluation of NET. However, its performance depends on series of patient-specific features (lesion size and uptake, depth and other anatomic features; metabolic activity, receptor expression, affinity and vacancy, tissue specificity) and technical features (choice of tracer, administered dose, and physical half-life; instrument sensitivity, acquisition technique, reader experience). In particular, current data show that PET/CT has greater intrinsic resolution and sensitivity than SPECT or SPECT/CT images resulting in improved tumor detection. However, the PET tracer of choice has not yet been identified. 18F-FDG has proved to be useful as indicator of tumor aggressiveness rather than detection of extent of disease, and 68Ga-DOTA-TOC has demonstrated good results in clinical trials. 11C-5HTP has performed well in limited trials, but the 20-min half life of 11C precludes widespread availability. Better information concerning biodistribution and further comparative data of these agent in larger clinical trials are warranted.