AbstractID: 11948 Title: Systems and probes for ultrasound molecular imaging Specialized ultrasound systems and targeted microbubbles optimized for vascular molecular imaging continue to advance. The development of methods for sensitive and selective imaging of adherent, targeted contrast agents requires improvements in both the physical systems and probes. We have developed transducers and signal processing techniques to maximize transducer bandwidth and integrated the components with a clinical ultrasound scanner. The transducer integrates low and high-frequency arrays; the center-row high-frequency array is surrounded on each side with confocally-focused low-frequency arrays. By transmitting from the low-frequency (1.6 MHz) arrays and receiving through the high-frequency (7 MHz) array, harmonic microbubble echoes can be detected and distinguished from the surrounding tissue. Further, by combining echoes over a pulse train, a targeted agent to free agent signal ratio of 15~22 dB can be obtained without waiting for agent clearance. Further, we report on radiolabeling methods to fully assess microbubble biodistribution with and without molecular targeting or insonation. We find that microbubbles are rapidly accumulated within the liver and spleen, although a small (but significant) mass of the microbubble shell accumulates as a result of local insonation. We acknowledge the support of NIH CA 103828 and CA 112356.