Ultrasound is a widely available, cost-effective, real-time, non-invasive and safe imaging modality widely used in the clinic for anatomical and functional imaging. With the introduction of novel molecularly-targeted ultrasound
contrast agents, another dimension of ultrasound has become a reality: diagnosing and monitoring
pathological processes at the molecular level. Most commonly used ultrasound molecular imaging
contrast agents are micron sized, gas-containing
microbubbles functionalized to recognize and attach to molecules expressed on inflamed or angiogenic vascular endothelial cells. There are several potential clinical applications currently being explored including earlier detection, molecular profiling, and monitoring of
cancer, as well as visualization of ischemic memory in transient
myocardial ischemia, monitoring of disease activity in
inflammatory bowel disease, and assessment of
arteriosclerosis. Recently, a first clinical grade ultrasound
contrast agent (BR55), targeted at a molecule expressed in neoangiogenesis (
vascular endothelial growth factor receptor type 2; VEGFR2) has been introduced and safety and feasibility of VEGFR2-targeted ultrasound imaging is being explored in first inhuman clinical trials in various
cancer types. This review describes the design of ultrasound molecular imaging
contrast agents, imaging techniques, and potential future clinical applications of ultrasound molecular imaging.