Abstract Positron emission tomography (PET, including PET/CT and PET/MRI) with 18F-fluorodeoxyglucose (FDG) plays a key role in diagnosing and staging a wide variety of malignant tumors, assessing tumor grade, and evaluating response to therapy. The advent of other recently-approved tracers, particularly those with theranostic partners, is opening a new era of imaging where the uptake of PET tracers can directly predict the effectiveness of certain targeted therapies. Such theranostic tracers image different aspects of tumor function than traditional diagnostic tracers (e.g. FDG), and they provide complementary images with different detection and staging performance across different levels of tumor differentiation and grade. The ability to routinely image multiple PET tracers in each patient would provide increased diagnostic performance, improved grading and staging information, and combine predictive theranostic imaging with the diagnostic workup. However, current technology requires that separate scans be performed for each tracer—usually on separate days—resulting in high cost, scheduling and logistical challenges, and undue burden on the patient. This project will remove those obstacles by developing simultaneous dual-tracer PET tumor imaging techniques—providing accurate images of two PET tracers in a single scan, and making these techniques available for general clinical use. Multifunctional Imaging LLC (MFI) has previously developed a software medical device, mfiVerseä, which enables both rest and stress myocardial perfusion PET images to be obtained in a single scan in as little at 15 min. This SBIR project will expand the software capabilities to also support dual-tracer PET cancer imaging—a much broader set of applications that will serve many more clinical needs and markedly increase market demand for this product. A new technique for simultaneously imaging tracers such as FDG+DOTATATE and FDG+PSMA in a single, dual-tracer PET scan will be developed. Combined imaging of FDG+DOTATATE will improve imaging performance of both well- and poorly-differentiated neuroendocrine tumors (NETs) while simultaneously predicting response to targeted radionuclide therapy with Lu177 DOTATATE. Similarly, combined imaging of FDG+PSMA will improve characterization of both well- and poorly-differentiated prostate cancer tumors, while at the same time predicting response to targeted radionuclide therapy with Lu177 PSMA. This Phase II project will complete development of the new dual-tracer technique and thoroughly evaluate it in a prospective clinical study of 60 patients with prostate cancer or NETs, acquiring all of the verification and validation data necessary to demonstrate the safety and efficacy of the approach. Completion of this project will create a first-of-its-kind medical device for simultaneous dual-tracer PET imaging which, after subsequent regulatory approval, will enable routine clinical use of dual-tracer PET tumor imaging to improve dia...