Deployable cylindrical phased-array applicator mimicking a concentric-ring configuration for minimally-invasive delivery of therapeutic ultrasound

A novel design for a deployable catheter-based ultrasound applicator for endoluminal and laparoscopic intervention is introduced. By combining a 1D cylindrical ring phased array with an expandable paraboloid or conical-shaped balloon-based reflector, the applicator can be controllably collapsed for compact delivery and deployed to mimic a forward-firing larger diameter concentric ring array with tight focusing and electronic steering capabilities in depth. Comprehensive acoustic and biothermal parametric studies were employed to characterize the capabilities of the applicator design as a function of transducer dimensions, phased array configuration, and balloon reflector geometry. Modeling results indicate that practical balloon sizes (43–57 mm expanded diameter), transducer array configurations (e.g. 1.5 MHz, 10 mm OD  ×  20 mm length, 8 or 16 array elements), and sonication durations (30 s) are capable of producing spatially-localized acoustic intensity focal patterns and ablative thermal lesions (width: 2.8–4.8 mm; length: 5.3–40.1 mm) in generalized soft tissue across a 5–100 mm depth range. Larger focal intensity gain magnitudes and narrower focal dimensions are attainable using paraboloid-shaped balloon reflectors with natural geometric focal depths of 25–55 mm, whereas conical-shaped reflectors (angled 45–55°) produce broader foci and extend electronic steering range in depth. A proof-of-concept phased array applicator assembly was fabricated and characterized using hydrophone and radiation force balance measurements and demonstrated good agreement with simulation. The results of this study suggest that combining small diameter cylindrical phased arrays with expandable balloon reflectors can enhance minimally invasive ultrasound-based intervention by augmenting achievable focal gains and penetration depths with dynamic adjustment of treatment depth. (paper)