Characterization and monitoring of cavitation behavior induced by a dual-mode pulsed high-intensity focused ultrasound array

Abstract

Pulsed high-intensity focused ultrasound (pHIFU) is capable of inducing cavitation in tissue without the need for contrast agents, thereby enhancing permeability and passive drug penetration in tissue with poor perfusion. We have developed and characterized the performance of a 64-element linear ultrasound array for image-guided therapy, capable of generating sufficient levels of inertial cavitation at 1 MHz, along with B-mode and Doppler imaging for targeting and cavitation assessment, respectively. Cavitation behaviors induced by different pHIFU exposures were investigated using high-speed imaging in agarose and polyacrylamide phantoms in conjunction with passive cavitation detection (PCD) and plane wave Doppler imaging. Image quality assessment was performed on in vivo porcine models, and cavitation monitoring was demonstrated on ex vivo tissues. High-speed images of the induced cavitation behavior while steering the beam focus both axially and laterally (within ±1.2 cm) were in agreement with Doppler power distributions and broadband noise emissions from PCD. Destructive cavitation behaviors in both gels and tissue were induced at relatively low peak-negative pressures (3–4 MPa), provided that the pHIFU focal waveform was nonlinearly distorted. B-mode image quality is sufficient for recognizing the relative position of anatomic landmarks and targeting cm-sized regions. [Work supported by NIH grants R01EB023910 and R01EB025187.]