Project Summary The Martinos Center at Massachusetts General Hospital (MGH) boasts a dynamic simultaneous magnetic resonance and positron emission tomography (MR-PET) imaging program. This program supports a substantial community of NIH-funded investigators, facilitates clinical trials, and offers crucial shared resources to the Institute for Innovation in Imaging (i3) and Interdepartmental Brain Center (IBC) at MGH. In 2010, an 11 MeV medical cyclotron was installed at MGH's Charlestown campus to bolster radiochemistry and translational radiotracer development and manufacturing. This cyclotron primarily produces short-lived imaging isotopes using carbon-11 and fluorine-18. The Siemens Eclipse HP cyclotron infrastructure lies at the heart of the research imaging enterprise. After 13 years of service, a reinvestment is necessary to ensure continued access to PET radioisotopes for the MGH Charlestown campus. Instead of replacing the Siemens Eclipse HP, which would result in significant operational disruption and research downtime, we propose a series of upgrades extending the cyclotron's lifespan by 10-15 years. These upgrades will stabilize maintenance-related operational elements, modernize the control software, and expand radiotracer production capacity. Furthermore, the upgrades will introduce new solid target capabilities to support the user community currently sourcing and shipping copper-64 from over a thousand miles away, thus establishing a Boston-wide source for the radioisotope. A current snapshot reveals 9 major and 19 minor users that will be positively impacted through funding this shared instrument grant application and the subsequent upgrades, but we also note that more than 60 human study protocols (3860 human imaging experiments) and more than 30 preclinical studies (675 non-human primate and >5000 rodent experiments) have relied on the cyclotron to date. With the volume of scanning growing, this SIG funding will support an extraordinarily strong scientific community. Specifically, we propose upgrading the RF system, software and control computers, vacuum system, and adding a solid target to one of the beam lines. This cost- effective, practical plan will ensure that NIH-funded investigators maintain a reliable supply of PET radioisotopes and radiotracers essential for their research.