The NIH Resource on Medical Ultrasonic Transducer Technology was established at Penn State University in 1997 to pursue innovative research in high frequency (HF) ultrasonic transducers and arrays as well as to serve the medical ultrasound community who have a need in HF ultrasonic transducers and arrays. In 2002 the Resource was moved to USC with newly renovated space, start-up funding to purchase state-of-the-art equipment and new faculty lines. In past 5 years, significant progress has been made in transducer materials, HF single element transducers and arrays, and imaging electronics. A fully functional real-time HF imaging system equipped with two 48 element 35 MHz linear arrays and two 64 element 30 MHz linear arrays has now been completed. In the next grant period, the three internal core projects in novel transducer materials, HF single element transducers and linear arrays, and HF imaging electronics will be continued along with 10 external projects. The major thrusts of the core research will be (1) to further improve the prototype 30-35 MHz linear arrays and associated imaging electronics to achieve an image quality similar to that of current high- end low frequency scanners, (2) to develop a 35 MHz linear phased array and associated imaging electronics for cardiac imaging in small animals, (3) to initiate the development of linear arrays at 50 MHz and higher, (4) to further improve the performance of single element transducers by incorporating novel transducer materials and investigating new material fabrication technologies, and (5) to exploit new biomedical applications of these devices. Thrusts (1) and (4) are related to near-term goals whereas (2), (3) and (5) are related to long-term goals. Of the 10 external projects, 7 will be collaborative projects and 3 will be service projects. These projects cover a variety of topics ranging from applying transducers developed by the Resource to solving medical problems to importing novel