A Prototype Therapy System for Transcutaneous Application of Boiling Histotripsy

Abstract

Boiling histotripsy is a method of focused ultrasound surgery that noninvasively applies millisecond-length pulses with high-amplitude shock fronts to generate liquefied lesions in tissue. Such a technique requires unique outputs compared to a focused ultrasound thermal therapy apparatus, particularly to achieve high in situ pressure levels through intervening tissue. This article describes the design and characterization of a system capable of producing the necessary pressure to transcutaneously administer boiling histotripsy therapy through clinically relevant overlying tissue paths using pulses with duration up to 10 ms. A high-voltage electronic pulser was constructed to drive a 1-MHz focused ultrasound transducer to produce shock waves with amplitude capable of generating boiling within the pulse duration in tissue. The system output was characterized by numerical modeling with the 3D Westervelt equation using boundary conditions established by acoustic holography measurements of the source field. Such simulations were found to be in agreement with directly measured focal waveforms. An existing derating method for nonlinear therapeutic fields was used to estimate in situ pressure levels at different tissue depths. The system was tested in ex vivo bovine liver samples to create boiling histotripsy lesions at depths up to 7 cm. Lesions were also created through excised porcine body wall (skin, adipose, muscle) with 3–5 cm thickness. These results indicate that the system is capable of producing the necessary output for transcutaneous ablation with boiling histotripsy.

Dependence of inertial cavitation induced by high intensity focused ultrasound on transducer F-number and nonlinear waveform distortion

“…The transducers were powered by a custom-built class D amplifier that is capable of delivering up to 26 kW pulse average electrical power in pulses lasting up to 10 ms. The input waveform to the amplifier was generated by a computer-controlled field-programmable gate array (FPGA) board (Maxwell et al, 2017). The total acoustic output power for all three transducers was measured using an acoustic radiation force balance over the relevant power source voltage range (Maruvada et al, 2007).…”

HIFU Power Monitoring Using Combined Instantaneous Current and Voltage Measurement

“…This is because there is access to both voltage and current waveforms, so the technique inherently compensates or the direction of flow at all frequencies. Thus, the technique could be useful for class-D HIFU systems and histrotripsy sources [53]. However, since the latter is not a predominately thermal technique, acoustic power may be less useful than peak positive pressure is.…”

Characterizing the Acoustic Output of an Ultrasonic Propulsion Device for Urinary Stones

“…Since the characterization and first clinical trial of the system described here, the team has developed a technique for designing and fabricating transducers and amplifiers [30-32]. A new design incorporates a single element annular therapy array with a P4-2 imaging probe looking though a central opening [33, 34].…”