Imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) are valuable tools for non-invasive in vivo longitudinal assessment and quantification of physiological processes. Microcirculatory changes are an important component in the pathophysiological cascade in cancers, and detection of changes over time provides insight in progression of the disease. We wanted to investigate microcirculatory changes as well as the utility of nano-sized particles as the lesions progressed from premalignant to malignant in a mouse model of ductal carcinoma in situ (DCIS) using PET. Liposomes and albumin were labeled with 64-Cu, which allowed us to follow the fate of the tracer up to 48 hrs after injection. PET scanning was performed at multiple time-points up to 7 weeks after transplantation of premalignant tissue into the mammary pad. An image-driven pharmacokinetic model was applied to quantify microvascular parameters as the lesions progressed. Vascular volume fraction and vessel permeability of both tracers increased with tumor transition but albumin uptake preceded liposomal uptake. A comparison of the accumulation of the two tracers emphasized the heterogeneity in the effective permeability size cutoff. Further, PET facilitated direct visualization of tumor spatial heterogeneity of tracer distribution. One of the greatest challenges in developing therapeutic regiments is the inability to rapidly and objectively assess tumor response due to treatment. In vivo imaging may provide invaluable insight in early responses and longitudinal progression.