The effects on thermal lesion shape and size from bubble clouds produced by acoustic droplet vaporization

Abstract

BackgroundBubbles formed by acoustic droplet vaporization (ADV) have proven to be an effective method for significant enlargement of the thermal lesions produced by high intensity focused ultrasound (HIFU). We investigated the influences of bubble cloud shape and droplet concentration on HIFU thermal lesions, as these relate to the ADV technique.MethodsUnlike previous studies where the droplets were simultaneously vaporized with the HIFU exposure for thermal lesion formation, droplets were vaporized by pulse wave (PW) ultrasound prior to continuous wave (CW) ultrasound heating in this experimental study. Under different experimental conditions, we recorded and quantified by the image processing methods the morphology and size of the bubble clouds created and the corresponding thermal lesions formed.ResultsThe results demonstrated that different ADV droplet concentrations produced a variety of thermal lesion shapes and sizes. The lesion volume could be increased using PW ultrasound followed by CW exposure, especially for higher droplet concentrations, e.g. 3.41 × 106/mL yielded a tenfold increase over that seen using CW alone.ConclusionThese findings could lead to optimization of HIFU therapy by selecting a bubble forming strategy and droplet concentrations, especially using lower ultrasound powers which is desirable in clinical applications.Electronic supplementary materialThe online version of this article (10.1186/s12938-018-0596-z) contains supplementary material, which is available to authorized users.

Review on Acoustic Droplet Vaporization in Ultrasound Diagnostics and Therapeutics

“…A current limitation is that this technique is limited to superficial tumors due to attenuation of ultrasound at higher depths. A novel method developed by Xin et al [96] utilizes LIFU and a pulse wave-continuous wave which formed larger bubble clouds than if only a continuous wave was used. Droplet concentration and vaporization pressure of the pulse wave also influenced the volume of the bubble cloud and enabled production of lesions of various sizes and shapes.…”

On-demand regulation and enhancement of the nucleation in acoustic droplet vaporization using dual-frequency focused ultrasound

“…This is a physical process termed acoustic droplet vaporization (ADV) [14] . The ADV bubbles have been proved effective in enhancing the acoustic thermal conversion efficiency [15] , enhancing inertial cavitation activity [16] and the mechanical bioeffects [17] , reducing the acoustic threshold of effective therapy [18] , accelerating the ultrasonic heating, shortening the treatment time [19] , expanding the injury area and reducing the possibility of complications. Moreover, the excellent ultrasound imaging characteristics of ADV bubble also give PFC nanodroplets a great potential for ultrasound theranostics [20] .…”

Comprehensive review on ultrasound-responsive theranostic nanomaterials: mechanisms, structures and medical applications

“…One possible solution is the use of targeted MBs to improve the efficiency of HIFU by decreasing the acoustic energy required to cause heating and lesion formation. Xin et al used pulsed-wave US and continuous-wave US heating to vaporize perfluoropentane (PFP) droplets for local thermal ablation [ 123 ]. They reported that different concentrations of ADV droplets could alter the shapes of the produced MBs from small dots to triangular bubbles, which in turn could affect the volume of the thermal lesion produced.…”

“…Therefore, a bubble-forming strategy may be useful in the clinical settings because the volume and morphology of the thermal ablation can be controlled by changes in both droplet concentration and acoustic pressure. This approach offers a new opportunity for the optimization of HIFU cancer therapy [ 123 ].…”

“…Therefore, a bubble-forming strategy may be useful in the clinical settings because the volume and morphology of the thermal ablation can be controlled by changes in both droplet concentration and acoustic pressure. This approach offers a new opportunity for the optimization of HIFU cancer therapy [123]. Furthermore, ADV-generated MBs can provide contrast-enhanced imaging and increase the temperature during HIFU therapy due to the cavitation produced when using ultrasound contrast agents [115].…”