Molecular acoustic angiography: Demonstration of in vivo feasibility for high resolution superharmonic ultrasound molecular imaging

Ultrasound molecular imaging utilizes targeted microbubbles to image molecular targets such as integrins, selectins, and other extracellular binding domains. Targeted microbubbles have typically been imaged using contrast-specific multi-pulse imaging sequences. Here we present an alternative strategy for ultrasound molecular imaging based on superharmonic signals produced by microbubbles. Bound bubbles were insonified near resonance using a low frequency (4 MHz) and superharmonic echoes were received at high frequencies (30 MHz). The feasibility of superharmonic molecular imaging was shown using microbubbles targeted to the α_vβ₃ integrin in a rat fibrosarcoma model (n=5) and combined with superharmonic images of free microbubbles to produce high contrast, high resolution 3D volumes of both microvascular anatomy and molecular targeting. Anatomical localization of molecular markers may prove easier using ultrasound-based acoustic angiography images as a reference rather than conventional B-mode images.