In vitro parameter optimization for spatial control of focused ultrasound ablation when using low boiling point phase-change nanoemulsions

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  • Puett, Connor
    • Affiliation: School of Medicine, UNC/NCSU Joint Department of Biomedical Engineering
  • Phillips, Linsey C
    • Affiliation: School of Medicine, UNC/NCSU Joint Department of Biomedical Engineering
  • Sheeran, Paul S
    • Affiliation: School of Medicine, UNC/NCSU Joint Department of Biomedical Engineering
  • Dayton, Paul
    • Affiliation: School of Medicine, UNC/NCSU Joint Department of Biomedical Engineering
Abstract
  • Abstract Background Phase-shift nanoemulsions (PSNEs) provide cavitation sites when the perfluorocarbon (PFC) nanodroplets (ND) are vaporized to microbubbles by acoustic energy. Their presence lowers the power required to ablate tissue by high-intensity focused ultrasound (HIFU), potentially making it a safer option for a broader range of treatment sites. However, spatial control over the ablation region can be problematic when cavitation is used to enhance heating. This study explored relationships between vaporization, ablation, and the PSNE concentration in vitro to optimize the acoustic intensity and insonation time required for spatially controlled ablation enhancement using a PSNE that included a volatile PFC component. Methods HIFU (continuous wave at 1 MHz; insonation times of 5, 10, 15, and 20 s; cool-down times of 2, 4, and 6 s; peak negative pressures of 2, 3, and 4 MPa) was applied to albumin-acrylamide gels containing PFC agents (1:1 mix of volatile decafluorobutane and more stable dodecafluoropentane at 105 to 108 PFC ND per milliliter) or agent-free controls. Vaporization fields (microbubble clouds) were imaged by conventional ultrasound, and ablation lesions were measured directly by calipers. Controlled ablation was defined as the production of ‘cigar’-shaped lesions corresponding with the acoustic focal zone. This control was considered to be lost when ablation occurred in prefocal vaporization fields having a predominantly ‘tadpole’ or oblong shape. Results Changes in the vaporization field shape and location occurred on a continuum with increasing PSNE concentration and acoustic intensity. Working with the maximum concentration-intensity combinations resulting in controlled ablation demonstrated a dose-responsive relationship between insonation time and volumes of both the vaporization fields (approximately 20 to 240 mm3) and the ablation lesions (1 to 135 mm3) within them. Conclusions HIFU ablation was enhanced by this PSNE and could be achieved using intensities ≤650 W/cm2. Although the ablation lesions were located within much larger microbubble clouds, optimum insonation times and intensities could be selected to achieve an ablation lesion of desired size and location for a given PSNE concentration. This demonstration of controllable enhancement using a PSNE that contained a volatile PFC component is another step toward developing phase-shift nanotechnology as a potential clinical tool to improve HIFU.
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  • Article
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  • In Copyright
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  • Connor Puett et al.; licensee BioMed Central Ltd.
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Journal title
  • Journal of Therapeutic Ultrasound
Journal volume
  • 1
Journal issue
  • 1
Page start
  • 16
Language
  • English
Is the article or chapter peer-reviewed?
  • Yes
ISSN
  • 2050-5736
Bibliographic citation
  • Journal of Therapeutic Ultrasound. 2013 Sep 13;1(1):16
Publisher
  • BioMed Central Ltd
Access right
  • Open Access
Date uploaded
  • November 15, 2013

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