PROJECT SUMMARY The Cancer Imaging Shared Resource (CI-SR) provides advanced preclinical imaging technologies and services for studying cancer biology, early cancer detection, monitoring disease progression, and developing novel diagnostic and theranostic agents. All major small animal imaging modalities are available, including positron emission tomography (PET), magnetic resonance imaging (MRI), x-ray computed tomography (CT), ultrasound and photoacoustics, magnetic particle imaging (MPI), and optical imaging (e.g., bioluminescence, fluorescence, Cerenkov). Since the last review, the CI-SR has acquired new and upgraded imaging instruments, including the first-of-its-kind MPI scanner. In 2020, 54% of users were SCI investigators accounting for approximately 55% of total usage. Members of the Cancer Imaging, Cancer Biology and Cancer Stem Cells, Cancer Therapeutics, Radiation Biology, Cancer Immunotherapy, and Hematologic Malignancies programs regularly use the CI-SR, with the heaviest use coming from the Cancer Imaging, Cancer Biology and Cancer Stem Cells, and Cancer Therapeutics programs. The CI-SR contributed to over 55 cancer-focused publications (15 high-impact). The annual budget of the CI-SR is $1,021,174, yet the CCSG request is $106,372. Accordingly, the CI-SR leverages extensive institutional support and seeks 10% from CCSG funds. The CI-SR is focused on two major scientific aims: (1) to provide access to state-of-the-art and first-of-its-kind in vivo imaging technologies and services pertinent to cancer research and (2) to educate, train, and consult with SCI members in basic and advanced imaging methods and data analysis through training courses, seminars, and workshops.