ABSTRACT
Histotripsy is a non-invasive ablation technique that focuses ultrasound pulses into the body to destroy tissues via cavitation. Heterogeneous acoustic paths through tissue introduce phase errors that distort and weaken the focus, requiring additional power output from the histotripsy transducer to perform therapy. This effect, termed phase aberration, limits the safety and efficacy of histotripsy ablation. It has been shown in vitro that the phase errors from aberration can be corrected by receiving the acoustic signals emitted by cavitation. For transabdominal histotripsy in vivo, however, cavitation-based aberration correction is complicated by acoustic signal clutter and respiratory motion. This study develops a method that enables robust, effective cavitation-based aberration correction in vivo and evaluates its efficacy in the swine liver. The method begins with a high-speed pulsing procedure to minimize the effects of respiratory motion. Then, an optimal phase correction is obtained in the presence of acoustic clutter by filtering with the singular value decomposition. This aberration correction method reduced the power required to generate cavitation in the liver by 26% on average (range: 0% to 52%) and required ~2 s for signal acquisition and processing per focus location. These results suggest that the cavitation-based method could enable fast and effective aberration correction for transabdominal histotripsy.
ABSTRACT
OBJECTIVE: The goal of the work described here was to develop the first neuronavigation-guided transcranial histotripsy (NaviTH) system and associated workflow for transcranial ablation. METHODS: The NaviTH system consists of a 360-element, 700 kHz transmitter-receiver-capable transcranial histotripsy array, a clinical neuronavigation system and associated equipment for patient-to-array co-registration and therapy planning and targeting software systems. A workflow for NaviTH treatments, including pre-treatment aberration correction, was developed. Targeting errors stemming from target registration errors (TREs) during the patient-to-array co-registration process, as well as focal shifts caused by skull-induced aberrations, were investigated and characterized. The NaviTH system was used in treatments of two <96 h post-mortem human cadavers and in experiments in two excised human skullcaps. RESULTS: The NaviTH was successfully used to create ablations in the cadaver brains as confirmed in post-treatment magnetic resonance imaging A total of three ablations were created in the cadaver brains, and targeting errors of 9, 3.4 and 4.4 mm were observed in corpus callosum, septum and thalamus targets, respectively. Errors were found to be caused primarily by TREs resulting from transducer tracking instrument design flaws and imperfections in the treatment workflow. Transducer tracking instrument design and workflow improvements reduced TREs to <2 mm, and skull-induced focal shifts, following pre-treatment aberration correction, were 0.3 mm. Total targeting errors of the NaviTH system following the noted improvements were 2.5 mm. CONCLUSIONS: The feasibility of using the first NaviTH system in a human cadaver model has been determined. Although accuracy still needs to be improved, the proposed system has the potential to allow for transcranial histotripsy therapies without requiring active magnetic resonance treatment guidance.
