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Gallium 68 ((68)Ga) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-octreotate (DOTATATE, GaTate) positron emission tomography (PET)/computed tomography (CT) is an imaging technique for detecting and characterizing neuroendocrine tumors (NETs). GaTate, a somatostatin analog, has recently been accorded orphan drug status by the U.S. Food and Drug Administration, thereby increasing interest in and availability of this radiotracer. GaTate PET/CT allows whole-body imaging of cell surface expression of somatostatin receptors (SSTRs) and is rapidly evolving as the new imaging standard of reference for the detection and characterization of NETs. The authors discuss the normal appearance at GaTate PET/CT and the utility of this modality in a variety of these tumors, including gastrointestinal, pancreatic, and bronchial NETs as well as pheochromocytoma, paraganglioma, meningioma, and oncogenic osteomalacia. In addition, they discuss potential causes of false-positive findings, including pancreatic uncinate process activity, inflammation, osteoblastic activity, and splenosis. They also highlight the complementary role of 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) PET/CT, including the advantages of using both GaTate PET/CT and FDG PET/CT to evaluate sites of well- and poorly differentiated disease. The use of GaTate PET/CT together with FDG PET/CT allows identification of tumor heterogeneity, which provides prognostic information and can be pivotal in guiding biopsy. It also allows optimal patient management, including theranostic application of peptide receptor radionuclide therapy, and the restaging of patients following therapy.

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Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed in prostate cancer. Radiolabeled small molecules that bind with high affinity to its active extracellular center have emerged as a potential new diagnostic standard of reference for prostate cancer, resulting in images with extraordinary tumor-to-background contrast. Currently, gallium 68 (Ga)-PSMA-11 (or HBED-PSMA) is the most widely used radiotracer for PSMA positron emission tomography (PET)/computed tomography (CT) or PSMA PET/magnetic resonance (MR) imaging. Evolving evidence demonstrates superior sensitivity and specificity of PSMA PET compared to conventional imaging, with frequent identification of subcentimeter prostate cancer lesions. PSMA PET is effective for imaging disease in the prostate, lymph nodes, soft tissue, and bone in a "one-stop-shop" examination. There is emerging evidence for its clinical value in staging of high-risk primary prostate cancer and localization of disease in biochemical recurrence. The high sensitivity provided by PSMA PET, with frequent identification of small-volume disease, is redefining patterns of disease spread compared with those seen at conventional imaging. In metastatic castration-resistant prostate cancer, PSMA PET is frequently used for theranostic selection (eg, lutetium 177-PSMA radionuclide therapy), but its potential use for therapy monitoring is still under debate. However, evidence on its proper use to improve patient-related outcomes, particularly in the setting of early biochemical recurrence and targeted treatment of oligometastatic disease, is still missing. Despite the term prostate specific, PSMA functions as a folate hydrolase and is expressed in a range of normal tissues and in other benign and malignant processes. Knowledge of its physiologic distribution and other causes of uptake is essential to minimize false-positive imaging findings. RSNA, 2018.