Ultrasound-mediated drug delivery involves the application of acoustic energy to manipulate drug carrying vehicles in the microvasculature. The therapeutic goal is a sitetargeted delivery of a specific drug carried by microscopic vehicles directed by the presence of ultrasonic beam energy. In sequentially-activated modes the acoustic beam can be controlled to both push the vehicles in small blood vessels and then also deploy their drug payload at specific application target sites. Effective ultrasound mediated drug delivery and microbubble imaging require broad band arrays that can both image the targeted region and deliver a therapeutic treatment.Two array designs, have been built and tested to support drug delivery experiments. The first (the "Jupiter") is a single row phased array with each of 64 elements at 260 micron pitch. The elements in this array were made in a three piezoelectric layer stack for high power operation at 2.02 MHz and a 2-way fractional band width of 86%. Although not a "multi-frequency" array, its wide band performance has helped to contribute to initial experiments in the combination of imaging and acoustic delivery of significant low frequency (1 MHz) therapeutic pressures, with low frequency output intensity (I sppa ) on the order of 150W/cm 2 for long pulse durations.The second probe design, the "CoLinear1-6," is a novel integration of low and high frequency arrays, and is the principal subject of the results presented. The center row high frequency array is surrounded on each side with a low frequency array wired with 1.5D connectivity. The CoLinear1-6, as a multifrequency array combination, integrates more effectively high quality imaging with the therapeutic utility of a low frequency array. In this linear multi-row array construction, the center row is comprised of 128 elements at 1.1 lambda pitch operating at 5.24 MHz with a -6dB fractional bandwidth of 73%. The two outer rows are made of 64 elements and are spaced at 1.67 lambda pitch operating at 1.48MHz with a -6dB (2-way) fractional bandwidth > 50%. Beam performance was measured to assure optimal overlap at the 2 to 5 cm depth range. An array thermal model was constructed to provide a predictive internal temperature during experiments involving therapeutic protocols.

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Conventional transthoracic and transesophageal ultrasound imaging often cannot satisfy imaging requirements for many advanced catheter-based interventional cardiac procedures due to restricted access to the anatomy. Intracardiac echocardiography (ICE) can provide almost unrestricted access and has been shown to be very effective in accurately guiding interventional cardiac procedures by providing high quality visualization of intracardiac anatomy and intracardiac devices. ICE is steadily replacing transesophageal ultrasound as the preferred imaging tool for device guidance during atrial fibrillation treatment, valve repair and closure of atrial septal defects. This article provides a history of the ACUSON AcuNav™ Ultrasound Catheter, a discussion of key technologies employed and a review of the expanding range of clinical applications where ICE technology is utilized. We also discuss recent innovations in catheter-based ultrasound, such as threedimensional (3D) tools for navigation and volume rendering, new imaging modalities like acoustic radiation force imaging (ARFI) and emerging applications for catheter-based ultrasound in the field of minimally invasive surgery.