Sonographic assessment of tumor response: from in vivo models to clinical applications

The advent of antiangiogenic drugs in cancer therapy necessitates an imaging modality that can longitudinally assess posttreatment changes in tumor vasculature. In this regard, microbubble contrast-enhanced ultrasonography (CEUS) offers several advantages over conventional imaging modalities. The small size of microbubbles (approximately 2-3 mum) permits their retention in the intravascular compartment and travel through the tortuous tumor vasculature. Mathematical models applied to signal intensity versus time depicting the kinetics of microbubble flow through the tumor are used to characterize tumor vascular density, blood flow velocity, and perfusion. In vivo studies using CEUS have demonstrated its comparability to dynamic contrast-enhanced magnetic resonance imaging and fluorodeoxyglucose positron emission tomography in distinguishing between diseased or malignant tissue and normal tissue. Moreover, CEUS has great potential for other novel clinical applications such as improved cancer diagnosis, enhanced medication delivery, and early antiangiogenic cancer treatment response evaluation. This review discusses the principles and potential clinical applications of CEUS in determining tumor response and its promising role in enhancing medication delivery in certain tumors.