Magnetic Particle Imaging (MPI) is a novel, high-contrast, and quantitative imaging modality that directly detects superparamagnetic iron oxide nanoparticle (SPIO) tracers. These SPIOs have been previously used as a MRI contrast agent. However, with MRI SPIOs are limited by poor specificity and difficulty associated with quantifying the negative signal. Due to its direct detection, high sensitivity and positive contrast, MPI is uniquely poised as a clinically translatable platform for vascular imaging, including gastrointestinal (GI) bleed detection. Here we present in vivo GI bleed detection using long-circulating SPIOs as the vascular agent in a mouse model of Familial Adenomatous Polyposis.