With recent advances in animal models of disease, there has been great interest in capabilities for highresolution contrast-enhanced ultrasound imaging. Microbubble contrast agents are unique in that they scatter broadband ultrasound energy because of their nonlinear behavior. For optimal response, it is desirable to excite the microbubbles near their resonant frequency. To date, this has been challenging with high-frequency imaging systems because most contrast agents are resonant at frequencies in the order of several megahertz. Our team has developed a unique dual-frequency confocal transducer which enables low-frequency excitation of bubbles near their resonance with one element, and detection of their emitted high-frequency content with the second element. Using this imaging approach, we have attained an average 12.3 dB improvement in contrast-to-tissue ratios over fundamental mode imaging, with spatial resolution near that of the high-frequency element. Because this detection method does not rely on signal decorrelation, it is not susceptible to corruption by tissue motion. This probe demonstrates contrast imaging capability with significant tissue suppression, enabling high-resolution contrast-enhanced images of microvascular blood flow. Additionally, this probe can readily produce radiation force on flowing contrast agents, which may be beneficial for targeted imaging or therapy.

Most institutions now have a suite of imaging tools to follow mouse models of human disease. Micro-ultrasound is one of these tools and is second after whole-mouse fluorescence or bioluminescent imaging, in terms of installed systems. We report in this paper the first commercially available array transducer-based ultrasound imaging system that enables micro-ultrasound imaging at center frequencies between 15 and 50 MHz. At the heart of the new scanner is a laser-machined high-frequency 256 element, linear transducer array capable of forming dynamic diffraction limited beams. The power of the linear array approach is embodied in the uniform high resolution maintained over the full field of view. This leads to greatly expanded scope for real-time functional imaging that is demonstrated in this paper. The unprecedented images made with the new imaging system will enable many new applications not previously possible. These include real-time visualization of flow in the mouse placenta, visualization of flow development in the embryo, studies of embryonic to adult cardiac development/disease, and studies of real-time blood flow in mouse models of tumour angiogenesis. (E-mail: Stuart.foster@ sunnybrook.ca) Crown Copyright (C) 2009 Published by Elsevier Inc. on behalf of World Federation for Ultrasound in Medicine & Biology.

Transurethral thermal therapy of the prostate using ultrasound may be used to create a thermal lesion that matches a target volume of tissue while sparing surrounding structures. To produce multiple-element ultrasound transducers for this purpose, a fabrication method of subdicing one continuous piece of piezoceramic to isolate individual elements was employed. Finite element modeling was used to determine the required dicing cut width and depth for adequate inter-element isolation. Experimental acoustic measurements were used to evaluate device efficiency and power stability over a range of element widths (2 to 4 mm) and lengths (3 to 30 mm). Efficiencies of 50% or higher and power output suitable for thermal therapy were achievable for all element sizes tested. This method of fabrication and testing is being utilized for evaluation of prototype devices designed for prostate thermal therapy.

Photonics Research Ontario (PRO) is an Ontario Provincial Center of Excellence supporting a broad range of laser- processing activities within its photonics program. These activities are centered at the University of Toronto, and split between an industrial-user facility and the individual research programs of principal investors. The combined effort furnishes forefront laser system and advanced optical tools to explore novel processing applications in photonic, biomedical, and microelectronic areas. Facilities include laser micromachining stations, excimer-based mask-projection stations, extremely short wavelength lasers such as the molecular fluorine laser, and ultrafast laser systems. The latter two advanced laser offer interesting advantages and contrast in processing 'difficult' materials through linear and nonlinear absorption processes, respectively. These laser systems provide fine precision and strong interaction with a wide range of materials, including 'transparent' glasses, and also ceramics and metals. Applications fall broadly into several areas: wafer-level circuit trimming, high-resolution ultrasonic transducers, and the shaping of optical waveguides and Bragg-gratings for photonic components. This paper summarizes the laser-processing infrastructure and research activities at PRO.

Piezoelectric devices generally require film thicknesses in the range 2-200µm and have a response which is perturbed by the substrate. Sol gel and sol gel composite technology provide a manufacturable process for many purposes with a piezoelectric coupling coefficient for 40ptm thick PZT approaching k t = 0.34. Techniques such as laser machining or micromolding are required for patterning thick devices. Measurement and applications of piezoelectric coatings in medical imaging, high temperature ultrasonics and flexure devices are discussed.