Effective imaging methods are critical for early detection of tumors and for monitoring tumor growth and treatment response. Previous studies have shown high levels of fibrin in the extracellular matrix of gastric tumors and fibrosis (i.e. collagen) in the extracellular matrix of gastric and pancreatic tumors. In this project, molecular PET and MRI imaging probes are being evaluated for the detection of fibrin in the extracellular matrix of subcutaneous gastric tumors in mice, and then radiolabels such as Y-90 will be attached to the probe to treat the tumors. The tumors will be imaged to evaluate the specificity of the PET probe and the treatment response, measured to monitor growth over time, and extracted from the mice at the end of the study for pathology. Similarly, novel PET and MRI imaging probes for the detection of collagen in the extracellular matrix of subcutaneous pancreatic tumors are being evaluated in mouse models for both detection of the tumors and for monitoring treatment response to chemotherapy.