Preclinical, translational, and clinical research projects using PET, PET/MR, and biodistribution at Massachusetts General Hospital are actively supported by the NIH and other federal agencies. These programs are addressing critical issues in oncology, psychiatry, neurology, cardiology, endocrinology, basic neuroscience, and pulmonary disease. Accurate measurement of radioactivity in blood and tissue samples is essential for quantitative PET imaging and biodistribution studies. Blood measurements are necessary for determining the pharmacokinetics of a radiolabeled compound, which provides insights into the action of that agent in the body and can be used to quantify imaging data acquired elsewhere in the body. Likewise, tissue measurements inform the investigator of the ultimate fate of a radiolabeled compound, which yields key information on targeting efficacy (e.g., ability of a drug to reach a tumor) and can be used to confirm the accuracy of imaging data in preclinical studies. In this application, we request funding for the purchase of a state-of the-art system for blood and tissue measurement that includes an automatic multi-sample counter for measurement of discrete samples and an MR-compatible pump and detection system for continuous blood sampling. This instrumentation will replace our antiquated and unreliable manual single-sample counter and provide our first continuous blood measurement device, which will facilitate ongoing projects, enable new research directions in the future, and offer modern hardware for this portion of the hands-on experience that fellows in our T32 program "Postgraduate Training Program in Medical Imaging" are exposed to.