Preclinical Dynamic Contrast Enhanced Imaging for Longitudinal Biophysical Assessments of the Healthy and Malignant Vasculature after Radiotherapy

Abstract

Dynamic contrast enhanced (DCE) imaging acquires time-lapsed images of intravenously injected contrast agents to quantify changes in their delivery to and clearance from the tissue. It is widely used in clinical imaging to assess tissue perfusion and vascular permeability. However, minimal work has been done using DCE in a murine model to better understand the effects of radiotherapy on the vasculature and tissue. This is due in part to a lack of DCE imaging systems with the resolution to directly observe the underlying changes in single-vessel structure and function. In this thesis, I develop and use macroscopic dynamic fluorescent imaging (DynFI) and microscopic quantitative multiphoton microscopy (QMPM). These DCE techniques identify changes in tissue perfusion several days after radiotherapy in the healthy bone marrow, leukemic bone marrow, and solid tumor tissue. DCE imaging can be performed using QMPM while simultaneously observing changes in the single-vessel characteristics for direct correlation. Using QMPM, changes in bone marrow vasculature were observed with the onset of acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL). Changes included increased angiogenesis, permeability, decreased mean vessel diameter, decreased single-vessel blood flow, and decreased drug delivery. For mice bearing ALL, this resulted in reduced cellular uptake of a chemotherapy surrogate. The results identified potential biomarkers for leukemia using DCE imaging. Treatments ranging from 2 Gy to 10 Gy of total body irradiation (TBI) increased single-vessel blood flow and drug delivery for mice bearing AML and ALL 2 to 5 days after TBI. For mice bearing ALL, targeted 2 and 4 Gy radiotherapy resulted in improved cellular chemotherapy uptake. Additionally, increased survival was observed for mice bearing ALL when administering 4Gy TBI before chemotherapy compared to chemotherapy before 4Gy TBI. Finally, I develop DynFI with principal component analysis to rapidly identify changes in tumor vasculature before and 2 days after 10 Gy targeted radiotherapy. In conclusion, DCE analysis is an effective tool to measure tissue perfusion and vascular function. Increased availability of DCE imaging for preclinical models will allow for a better understanding of the underlying vascular changes that occur in a clinical setting.