Efficient wideband linear arrays for imaging and therapy

Focused ultrasound surgery has typically been investigated with a large aperture single element dish, or narrowband transducer array, both of which preclude good ultrasound imaging. However, guidance is essential for effective therapy. The goal of this work was to develop linear arrays that have both the high transmit efficiency needed for therapy, yet the wide bandwidth associated with transducers for modern imaging systems. The authors present analysis and measurements on linear array transducers from 3 to 6 MHz, with measured transmit efficiencies up to 90 percent and pulse-echo fractional bandwidths of 45 to 65 percent. Power measurements on a 3.2 MHz, 5×5.5 mm linear array revealed unfocused continuous acoustic output in excess of 30 watts at greater than 80% efficiency while retaining the array´s performance. Human scanning results and ultrasound imaging of phantoms is shown, as well as in vitro lesion formation with the 32 to 64 element arrays. By combining these features into one transducer, several benefits result, including real time electronic imaging, therapy and monitoring, lack of spatial misregistration, low cost, multiple-frequency imaging/therapy and the power of acoustic beamforming techniques. The high efficiency allows the transducer to be small in size, enables endoscopic and catheter-based procedures, provides close access to the region of interest with less intervening tissue layers, supports higher frequencies, and yields better spatial resolution for imaging and therapy. The results of the study can help guide the design of such systems