High frequency ultrasound imaging in the range of 30-100MHz is capable of resolving structures almost down to the cellular level. Developing such an imaging modality for clinical use would have tremendous impact on diagnostic and therapeutic procedures in many different clinical areas. In particular cardiovascular clinicians would be able to visualize in great detail arterial walls of the coronary arteries and interior heart structure from the tip of an interventional device. The diagnostics of cancer using biopsy would be revolutionized as in-situ microscopy would replace the traditional procedure. Image guided therapy could be developed since the diagnosed pathology could be localized at a great precision. In this R21 application we propose developing a novel optical technique for ultrasound detection and generation which has unique advantages for intravascular imaging application. The method is based on optical microresonators of very high quality factor acting as highly sensitive ultrasound receivers. These microresonators, designed using integrated optics techniques, are formed using closed-loop (ring type) shaped waveguides. A typical dimension of such a microresonator is 20 mu/m to 60mu/m depending on the optical wavelength and other design parameters. Our preliminary measurements showed extraordinarily high sensitivity giving rise to a high signal to noise ratio of about 30 using a driving acoustic signal of 60KPa. These experiments were performed using a microring resonator of moderate quality factor (Q=1000) excited using relatively low optical power of 1.5mW. These results imply that a microring array having an element spacing of less than 15mu/m would deliver high sensitivity and provide image resolution that is at least 5X better than that of any existing IVUS system. Such a system would utilize separate optical elements acting as ultrasound generators relying on photoacoustic ultrasound generation. The fundamental hypothesis of this project is that photoacoustic detector of high frequency ultrasound with integrated microring technology will enable high resolution imaging system easily integratable into interventional device. To develop this novel imaging technology several technical and scientific problems must be addressed. It is the aim, therefore, of the work proposed here to address the following issues in detail: 1. Develop a computational model fully describing the detection mechanism to optimize device design. 2. Fabricate and experimentally characterize the performances of microring elements as ultrasound receivers. 3. Design integrated optics elements acting as ultrasound generators using photoacoustic methods. 4. Integrate a prototype device consisting of a receiving microring array and a transmitting array.