Design and testing of an ultrasonic system with integrated diagnostic and therapy modes

Abstract

Our laboratories developed and tested a system integrating high-intensity focused ultrasound (HIFU) with diagnostic ultrasound procedures for aiming, delivering, and monitoring treatment exposures. The system employs 5-MHz, 5-element spherical-cap HIFU arrays with annular electrodes (for variable focusing) or strip electrodes (for inducing broad lesions of controlled width). Central apertures in these arrays house a coaxial diagnostic phased array (48 elements), interfaced with a custom digital system for visualization and RF echo acquisition. Several operational modes were investigated. A preexposure mode permits the HIFU focal point to be aimed at the desired location in B-mode images. It also assesses harmonic generation in the HIFU beam, using the diagnostic array to receive and spectrally analyze echoes from a short HIFU pulse aimed at targeted tissues. Radiation-force elastography uses the diagnostic array to monitor tissue displacements induced by brief exposures from the HIFU transducer; pre- and posttherapy data are compared to delineate mechanical alterations in lesioned volumes. Acquired pre- and post-RF data are also spectrally analyzed to map changes in scattering and attenuation indicative of lesion production. These modes have been successfully tested under in vitro conditions and are now entering use in animal studies aimed at treating cancer and cardiac diseases.