An Ultrasound-Guided Hemispherical Phased Array for Microbubble-Mediated Ultrasound Therapy.

Goal: To develop a low-cost magnetic resonance imaging (MRI)-free transcranial focused ultrasound (FUS) system for microbubble-mediated therapy. Methods: A 128-element 11 MHz array for skull localization was integrated within a 256-module multi-frequency (306/612/1224 kHz) dual-mode phased array. The systems transcranial transmit and receive performance was evaluated with ex-vivo human skullcaps using phase aberration corrections calculated from computed tomography (CT)-based simulations via ultrasound-based (USCT) and landmark-based (LMCT) registrations, and a gold-standard fixed source emitter (FSE)-based method. Results: Displacement and rotation registration errors of 1.4 0.4 mm and 2.1 0.2 were obtained using USCT, resulting in sub-millimeter transmit targeting errors driven at 306 kHz (0.9 0.2 mm) and 612 kHz (0.9 0.3 mm), and source localization errors of 1.0 0.3 mm and 0.6 0.2 mm at receive frequencies of 306 kHz and 612 kHz, respectively (mean SD). Similar errors were obtained using LMCT and no significant differences between these two approaches were found on either transmit (p = 0.64/0.99) or receive (p = 0.45/0.36) at 306 kHz/612kHz. During volumetric multi-point exposures, approximately 70% and 60% of the transmit frames in which microbubble activity was detected via FSE were recovered using USCT when imaging at the second-harmonic and half-harmonic, respectively, compared to 60% and 69% using LMCT. Conclusion: This low-cost ultrasound-guided transcranial FUS system affords USCT skull registration with accuracy comparable to LMCT methods. Significance: Such systems have great potential to advance the adoption of microbubble-mediated FUS brain therapy by improving access to the technology.