The application of multiphoton microscopy1,2
(MPM) to the study of solid tumor biology in vivo
has elucidated pathways and mechanisms of cancer progression and has led to new therapeutic strategies3
. Current high-resolution intravital imaging techniques, however, permit visualization of tumor microstructure and vascular morphology only superficially (300–400 μm depth) and only over volumetric regions that are a fraction of the total tumor volume in small animal models. Additionally, longitudinal imaging is often limited in frequency due to the accumulation of exogenous contrast agents. Consequently, nearly a decade after the introduction of MPM to tumor biology, significant gaps remain in our understanding of the vascularization of tumors, the multifaceted interactions between tissues and vessels within the heterogeneous tumor mass, and the response of blood vessels, lymphatic vessels and cancer cells to therapy. New methods that complement existing MPM techniques by probing the tumor microenvironment over wider fields and broader timescales are needed to fill these gaps.
Optical coherence tomography4
(OCT) is an alternative approach for in vivo
microscopy that supports imaging at these expanded spatiotemporal scales. However, methods for effectively characterizing biological parameters of the tumor microenvironment and structure are lacking in OCT and existing angiographic OCT systems have not achieved the high sensitivity and the rapid imaging speeds required for large-volume vascular morphometry. Here, we overcome these limitations by developing new methods and instrumentation for a second generation OCT technology termed optical frequency domain imaging (OFDI)5
. We apply these techniques to a range of tumor models in vivo
and demonstrate the ability of OFDI to perform 1) high-resolution, wide-field, and deep imaging of tumor vasculature, 2) morphological and fractal characterization of vascular networks, 3) contrast-free functional lymphangiography and 4) characterization of tissue viability. Further, we demonstrate the application of these capabilities to reveal the responses of tumors in vivo
to vascular-targeted and cellular-targeted therapies.