Investigations of the Cavitation and Damage Thresholds of Histotripsy and Applications in Targeted Tissue Ablation.

Histotripsy is a noninvasive ultrasound therapy that controls acoustic cavitation to mechanically fractionate soft tissue. This dissertation investigates the physical thresholds to initiate cavitation and produce tissue damage in histotripsy and factors affecting these thresholds in order to develop novel strategies for targeted tissue ablation. In the first part of this dissertation, the effects of tissue properties on histotripsy cavitation thresholds and damage thresholds were investigated. Results demonstrated that the histotripsy shock scattering threshold using multi-cycle pulses increases in stiffer tissues, while the histotripsy intrinsic threshold using single-cycle pulses is independent of tissue stiffness. Further, the intrinsic threshold slightly decreases with lower frequencies and significantly decreases with increasing temperature. The effects of tissue properties on the susceptibility to histotripsy-induced tissue damage were also investigated, demonstrating that stiffer tissues are more resistant to histotripsy. In the second part of this dissertation, the feasibility of using histotripsy for targeted liver ablation was investigated in an intact in vivo porcine model, with results demonstrating that histotripsy was capable of non-invasively creating precise lesions throughout the entire liver. Additionally, a tissue selective ablation approach was developed, where histotripsy completely fractionated the liver tissue surrounding the major hepatic vessels and gallbladder while being self-limited at the boundaries of these critical structures. In the final part of this dissertation, a novel ablation method combining histotripsy with acoustically sensitive nanodroplets was developed for targeted cancer cell ablation, demonstrating the potential of using nanodroplet-mediated histotripsy (NMH) for targeted, multi-focal ablation. Studies demonstrated that lower frequency and higher boiling point perfluorocarbon droplets can improve NMH therapy. The role of positive and negative pressure on cavitation nucleation in NMH was also investigated, showing that NMH cavitation nucleation is caused directly from the peak negative pressure of the incident wave, similar to histotripsy bubbles generated above the intrinsic threshold. Overall, the results of this dissertation provide significant insight into the physical mechanisms underlying histotripsy tissue ablation and will help to guide the future development of histotripsy for clinical applications such as the treatment of liver cancer.PhDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113591/1/evlaisav_1.pd

Bubble Cloud Characteristics and Ablation Efficiency in Dual-Frequency Intrinsic Threshold Histotripsy

Histotripsy is a non-thermal focused ultrasound ablation method that destroys tissue through the generation and activity of acoustic cavitation. Intrinsic threshold histotripsy generates bubble clouds when the dominant negative pressure phase of a single-cycle pulse exceeds an intrinsic threshold of ~25-30 MPa. The ablation efficiency is dependent upon the size and density of bubbles within the bubble cloud. This work investigates the effects of dual-frequency pulsing schemes on the bubble cloud behavior and ablation efficiency in intrinsic threshold histotripsy. A modular histotripsy transducer applied dual-frequency histotripsy pulses to tissue phantoms with a 1:1 pressure ratio from 500 kHz and 3 MHz frequency elements and varying the 3 MHz pulse arrival relative to the arrival of the 500 kHz pulse (-100 ns, 0 ns, and +100 ns). High-speed optical imaging captured cavitation effects to characterize bubble cloud and individual bubble dynamics. Lesion formation and ablation efficiency were also investigated in red blood cell (RBC) phantoms. Results showed that the single bubble and bubble cloud size for dual-frequency cases were intermediate to published results for the component single frequencies of 500 kHz and 3 MHz. Bubble cloud size and dynamics were also shown to be altered by the arrival time of the 3 MHz pulse relative to the 500 kHz pulse, with more uniform cloud expansion and collapse observed for early (-100 ns) arrival. Finally, RBC phantom experiments showed that dual-frequency exposures were capable of generating precise lesions with smaller areas and higher ablation efficiencies than previously published results for 500 kHz or 3 MHz. Overall, results demonstrate dual-frequency histotripsy's ability to modulate bubble cloud size and dynamics can be leveraged to produce precise lesions at higher ablation efficiencies than previously observed for single-frequency pulsing.Comment: 22 pages, 10 figures, 2 table

First-in-man histotripsy of hepatic tumors: the THERESA trial, a feasibility study

Ablation; Hepatocellular carcinoma; HistotripsyAblación; Carcinoma hepatocelular; HistotriciaAblació; Carcinoma hepatocel·lular; HistotríciaRationale Current hepatic locoregional therapies are limited in terms of effectiveness and toxicities. Given promising pre-clinical results, a first in-human trial was designed to assess the technical effectiveness and safety profile of histotripsy, a noninvasive, non-thermal, non-ionizing focused ultrasound therapy that creates precise, predictable tissue destruction, in patients with primary and secondary liver tumors. Methods A multicenter phase I trial (Theresa Study) was performed in a single country with 8 weeks of planned follow-up. Eight of fourteen recruited patients were deemed eligible and enrolled in the study. Hepatic histotripsy, was performed with a prototype system (HistoSonics, Inc., Ann Arbor, MI). Eleven tumors were targeted in the 8 patients who all had unresectable end-stage multifocal liver tumors: colorectal liver metastases (CRLM) in 5 patients (7 tumors), breast cancer metastases in 1 (1 tumor), cholangiocarcinoma metastases in 1 (2 tumors), and hepatocellular carcinoma (HCC) in 1 (1 tumor). The primary endpoint was acute technical success, defined as creating a zone of tissue destruction per planned volume assessed by MRI 1-day post-procedure. Safety (device-related adverse events) through 2 months was a secondary endpoint. Results The 8 patients had a median age of 60.4 years with an average targeted tumor diameter of 1.4 cm. The primary endpoint was achieved in all procedures. The secondary safety profile endpoint identified no device-related adverse events. Two patients experienced a continuous decline in tumor markers during the eight weeks following the procedure. Conclusions This first-in-human trial demonstrates that hepatic histotripsy effectively destroys liver tissue in a predictable manner, correlating very well with the planned histotripsy volume, and has a high safety profile without any device-related adverse events. Based on these results, the need for more definitive clinical trials is warranted. Trial Registration: Study to Evaluate VORTX Rx (Theresa). NCT03741088. https://clinicaltrials.gov/ct2/show/NCT03741088This study was supported by the funding from Histosonics, Inc

Application of sub-micrometer vibrations to mitigate bacterial adhesion

As a prominent concern regarding implantable devices, eliminating the threat of opportunistic bacterial infection represents a significant benefit to both patient health and device function. Current treatment options focus on chemical approaches to negate bacterial adhesion, however, these methods are in some ways limited. The scope of this study was to assess the efficacy of a novel means of modulating bacterial adhesion through the application of vibrations using magnetoelastic materials. Magnetoelastic materials possess unique magnetostrictive property that can convert a magnetic field stimulus into a mechanical deformation. In vitro experiments demonstrated that vibrational loads generated by the magnetoelastic materials significantly reduced the number of adherent bacteria on samples exposed to Escherichia coli, Staphylococcus epidermidis and Staphylococcus aureus suspensions. These experiments demonstrate that vibrational loads from magnetoelastic materials can be used as a post-deployment activated means to deter bacterial adhesion and device infection

The role of positive and negative pressure on cavitation nucleation in nanodroplet-mediated histotripsy

WOS: 000369516600017PubMed ID: 26716568Nanodroplet-mediated histotripsy (NMH) is an ultrasound ablation technique combining histotripsy with acoustically sensitive perfluorocarbon (PFC) nanodroplets that can be selectively delivered to tumor cells for targeted tumor ablation. NMH takes advantage of the significantly reduced cavitation threshold of the nanodroplets, allowing for cavitation to be selectively generated only in regions containing nanodroplets. Understanding the physical mechanisms underlying the nanodroplet cavitation process is essential to the development of NMH. In this study, we hypothesize that cavitation nucleation is caused by the negative pressure (p-) exposed to the PFC, and the NMH cavitation threshold is therefore determined by the incident p- of the single-cycle pulses commonly used in NMH. This paper reports the first study that separately investigates the effects of negative and positive pressure on the NMH cavitation threshold using near half-cycle ultrasound pulses with dominant negative (negative-polarity pulses) or positive (positive-polarity pulses) pressure phases. Tissue phantoms containing perfluorohexane (PFH) nanodroplets were exposed to negative-polarity and positive-polarity pulses generated by a frequency compounding transducer recently developed in our lab, and the probability of generating cavitation was measured as a function of peak negative (p-) and peak positive (p+) pressure. The results showed close agreement in the p-cavitation threshold for PFH phantoms exposed to negative-polarity (11.4 +/- 0.1 MPa) and positive-polarity (11.7 +/- 0.2 MPa) pulses. The p+ at the cavitation threshold, in contrast, was measured to be significantly different for the negative-polarity (4.0 +/- 0.1 MPa) and positive-polarity (42.6 +/- 0.2 MPa) pulses. In the final part of this study, the experimental results were compared to the cavitation threshold predicted by classical nucleation theory (CNT), with results showing close agreement between simulations and experiments. Overall, the results support our hypothesis and provide significant insight into the physical mechanisms underlying NMH.National Science Foundation; Turkish Republic the Ministry of National Education Fellowship Program [1416]; United States Department of Defense [W81XWH-11-PCRP-ID]We would like to thank Sonja Capracotta, PhD (Technical Specialist, Nano Sight, School of Public Health, University of Michigan) for her help on NTA size and concentration measurements. This material is based upon work supported by a National Science Foundation Graduate Research Fellowship to Eli Vlaisavljevich. Omer Aydin acknowledges the support of the Turkish Republic the Ministry of National Education Fellowship Program (1416). This work was supported by a grant from the United States Department of Defense (W81XWH-11-PCRP-ID). Disclosure notice: Drs Zhen Xu, Brian Fowlkes, and Kuang-Wei Lin have financial interests and/or other relationship with HistoSonics Inc

Magnetoelastic Materials as Novel Bioactive Coatings for the Control of Cell Adhesion

Interfacial fibrosis is known to dramatically decrease the lifespan, stability, and function of biomedical implants and bone-anchored prosthetics. Bioactive coatings aimed at mitigating fibrous adhesions are one of the approaches to alleviate the problem. In this paper, we are developing a bioactive coating based upon a magnetoelastic (ME) material that vibrates in response to an ac magnetic field. In order to establish these coatings for this purpose, the ME material was first rendered bioactive through the sequential addition of polyurethane and chitosan thin films. Indirect live/dead assays were performed showing increased cell viability for polyurethane and chitosan-coated sensors compared to the uncoated controls. Direct adhesion experiments were performed to test the response of fibroblasts cultured on static and vibrated ME materials. Results showed cells adherent to static but not vibrated coatings. Detached cells showed no viability loss compared to controls. The finding that submicrometer ME vibrations can prevent cell adhesion in vitro without inducing cell death suggests the potential of these coatings to effectively control interfacial fibrosis. Future work will address the effect of vibrations on cell morphology and local gene expression in vitro, as well as fibrous tissue formation in vivo. © 2006 IEEE

Experimental and computational investigation of clustering behavior of cyclodextrin-perfluorocarbon inclusion complexes as effective histotripsy agents

Recently developed nanocones (NCs), which are inclusion complexes that are made up of cyclodextrins (CDs) and perfluorocarbons (PFCs), have shown promising results in nanoparticle-mediated histotripsy (NMH) applications due to stable inclusion complexation, PFC quantification, simple synthesis, and processing. FDA-approved βCD and its modified versions such as low-degree methylated βCD have been previously demonstrated as prime examples of structures capable of accommodating PFC molecules. However, the complex formation potential of different CDs with various cavity sizes in the presence of PFC molecules, and their consequent aggregation, needs to be explored. In the present study, the complexation and aggregation potential of some natural CDs and their respective derivatives either exposed to perfluoropentane (PFP) or perfluorohexane (PFH) were studied in the wet lab. Computational studies were also performed to account for the limitations faced in PFC quantification because of the low optical density of PFCs within the CD complex and to discover the best candidate for NMH applications. All results revealed that only βCD and γCD (except HMγCD) derivatives form an inclusion complex with PFCs and only LMβCD, βCD, and γCD form nanocone clusters (NCCs), which precipitate and can be collected for use. Furthermore, the data collectively show that βCD and PFCs have the best complexation due to stable complex formation, ease of production, and product recovery, especially with PFH as a more suitable candidate due to its high boiling point, which allows workability during synthesis. Although simulations suggest that highly stable inclusion complexes exist, such as HPβCD, the cluster formation resulting in precipitation is hindered due to the high solubility of CDs in water, resulting in intangible yields to work with even after employing general laboratory recovery methods. Conclusively, histotripsy cavitation experiments successfully showed a decreased cavitation threshold among optimal NCC candidates that were identified, supporting their use in NMH.United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Biomedical Imaging & Bioengineering (NIBIB

Focused ultrasound for the remote modulation of nitric oxide release from injectable PEG-fibrinogen hydrogels for tendon repair

Introduction: Tendon disorders such as tendinosis, the degradation of collagen in tendon, or tendonitis, inflammation of tendon tissue, contribute to 30% of musculoskeletal complaints. To address the limitations of currently available treatments for tendon repair, an injectable polyethylene glycol (PEG)-fibrinogen hydrogel encompassing nitric oxide (NO) releasing µ-particles was generated. The release of nitric oxide, a therapeutic molecule that modulates many wound healing processes, from the hydrogel can be modified with thermal and mechanical stimulus. To achieve remote control over NO release from hydrogels after deployment, focused ultrasound (FUS) was explored as it provides highly controlled thermal and mechanical stimulus non-invasively. Methods: In this work, the ability of FUS to remotely elicit on-demand NO generation from acoustically active composite hydrogels via thermal and/or mechanical stimulus was explored. Specifically, the temperature and time-dependent release of NO was simulated and characterized when applying FUS to composite hydrogels. Results: Results from acoustic simulations as well as thermocouple heating studies indicated that high spatial and temporal control over hydrogel warming could be achieved non-invasively with a 3.5 MHz FUS transducer. FUS was also able to remotely control NO release from hydrogels with various thermal magnitudes and durations. Additionally, no apparent changes in the mechanical properties of hydrogels were observed with FUS treatment. Discussion: Utilizing FUS thermal and mechanical stimulus provides a potential method of remotely controlling NO release from hydrogels at a wound site to aid in tendon repair