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Coalescence of residual histotripsy cavitation nuclei using low-gain regions of the therapy beam during electronic focal steering.

ABSTRACT: Following collapse of a histotripsy cloud, residual microbubbles may persist for seconds, distributed throughout the focus. Their presence can attenuate and scatter subsequent pulses, hindering treatment speed and homogeneity. Previous studies have demonstrated use of separate low-amplitude (~1?MPa) pulses interleaved with histotripsy pulses to drive bubble coalescence (BC), significantly improving treatment speed without sacrificing homogeneity. We propose that by using electronic focal steering (EFS) to direct the therapy focus throughout specially-designed EFS sequences, it is possible to use low-gain regions of the therapy beam to accomplish BC during EFS without any additional acoustic sequence. First, to establish proof of principle for an isolated focus, a 50-foci EFS sequence was constructed with the first position isolated near the geometric focus and remaining positions distributed post-focally. EFS sequences were evaluated in tissue-mimicking phantoms with gas concentrations of 20% and 100% with respect to saturation. Results using an isolated focus demonstrated that at 20% gas concentration, 49 EFS pulses were sufficient to achieve BC in all samples for pulse repetition frequency (PRF)?????800 Hz and 84.1%??±??3.0% of samples at 5?kHz PRF. For phantoms prepared with 100% gas concentration, BC was achieved by 49 EFS pulses in 39.2%??±??4.7% of samples at 50 Hz PRF and 63.4%??±??15.3% of samples at 5?kHz. To show feasibility of using the EFS-BC method to ablate a large volume quickly, a 1000-foci EFS sequence covering a volume of approximately 27?ml was tested. Results indicate that the BC effect was similarly present. A treatment rate of 27??±??6?ml min-1 was achieved, which is signficantly faster than standard histotripsy and ultrasound thermal ablation. This study demonstrates that histotripsy with EFS can achieve BC without employing a separate acoustic sequence which has the potential to accelerate large-volume ablation while minimizing energy deposition.

SUBMITTER: Lundt J

PROVIDER: S-EPMC7603413 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Coalescence of residual histotripsy cavitation nuclei using low-gain regions of the therapy beam during electronic focal steering.

Lundt Jonathan J Hall Timothy T Rao Akshay A Fowlkes J Brian JB Cain Charles C Lee Fred F Xu Zhen Z

Physics in medicine and biology 20181112 22

Following collapse of a histotripsy cloud, residual microbubbles may persist for seconds, distributed throughout the focus. Their presence can attenuate and scatter subsequent pulses, hindering treatment speed and homogeneity. Previous studies have demonstrated use of separate low-amplitude (~1 MPa) pulses interleaved with histotripsy pulses to drive bubble coalescence (BC), significantly improving treatment speed without sacrificing homogeneity. We propose that by using electronic focal steerin ...[more]

PMID: 30418936

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Project description:Histotripsy has been shown to be an effective treatment for model kidney stones, eroding their surface to tiny particulate debris via a cavitational bubble cloud. However, similar to shock wave lithotripsy, histotripsy stone treatments display a rate-dependent efficacy, with pulses applied at a low rate generating more efficient stone erosion in comparison with those applied at a high rate. This is hypothesized to be the result of residual cavitation bubble nuclei generated by bubble cloud collapse. Although the histotripsy bubble cloud only lasts on the order of 100 ?s, these microscopic remnant bubbles can persist on the order of 1 s, inducing direct attenuation of subsequent histotripsy pulses and influencing bubble cloud dynamics. In an effort to mitigate these effects, we have developed a novel strategy to actively remove residual cavitation nuclei from the field using low-amplitude ultrasound pulses. Previous work has demonstrated that with selection of the appropriate acoustic parameters these bubble removal pulses can stimulate the aggregation and subsequent coalescence of microscopic bubble nuclei, effectively deleting them from the target volume. Here, we incorporate bubble removal pulses in histotripsy treatment of model kidney stones. It was found that when histotripsy is applied at low rate (1 Hz), bubble removal does not produce a statistically significant change in erosion. At higher pulse rates of 10, 100, and 500 Hz, incorporating bubble removal results in 3.7-, 7.5-, and 2.7-fold increases in stone erosion, respectively. High-speed imaging indicates that the introduction of bubble removal pulses allows bubble cloud dynamics resulting from high pulse rates to more closely approximate those generated at the low rate of 1 Hz. These results corroborate previous work in the field of shock wave lithotripsy regarding the ill effects of residual bubble nuclei, and suggest that high treatment efficiency can be recovered at high pulse rates through appropriate manipulation of the cavitation environment surrounding the stone.

Dataset Information

Coalescence of residual histotripsy cavitation nuclei using low-gain regions of the therapy beam during electronic focal steering.

Publications

Coalescence of residual histotripsy cavitation nuclei using low-gain regions of the therapy beam during electronic focal steering.

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