title: Acoustic droplet vaporization for enhancement of thermal ablation by high intensity focused ultrasound.
abstract: OBJECTIVE
  Acoustic droplet vaporization (ADV) shows promise for spatial control and acceleration of thermal lesion production. The investigators hypothesized that microbubbles generated by ADV could enhance high-intensity focused ultrasound (HIFU) thermal ablation by controlling and increasing local energy absorption.
  
  
  METHODS
  Thermal lesions were produced in tissue-mimicking phantoms using focused ultrasound (1.44 MHz) with a focal intensity of 4000 W · cm(-2) in degassed water at 37°C. The average lesion volume was measured by visible change in optical opacity and by T2-weighted magnetic resonance imaging. In addition, in vivo HIFU lesions were generated in a canine liver before and after an intravenous injection of droplets with a similar acoustic setup.
  
  
  RESULTS
  Thermal lesions were sevenfold larger in phantoms containing droplets (3 × 10(5) droplets/mL) compared to phantoms without droplets. The mean lesion volume with a 2-second HIFU exposure in droplet-containing phantoms was comparable to that made by a 5-second exposure in phantoms without droplets. In the in vivo study, the average lesion volumes without and with droplets were 0.017 ± 0.006 cm(3) (n = 4; 5-second exposure) and 0.265 ± 0.005 cm(3) (n = 3; 5-second exposure), respectively, a factor of 15 difference. The shape of ADV bubbles imaged with B-mode ultrasound was very similar to the actual lesion shape as measured optically and by magnetic resonance imaging.
  
  
  CONCLUSIONS
  ADV bubbles may facilitate clinical HIFU ablation by reducing treatment time or requisite in situ total acoustic power and provide ultrasonic imaging feedback of the thermal therapy.
authors.affiliation: Department of Radiology, University of Michigan Health System, Ann Arbor, 48109, USA. maggiez@umich.edu
authors.forename: Man
authors.initials: M
authors.lastname: Zhang
authors.forename: Mario L
authors.initials: ML
authors.lastname: Fabiilli
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Haworth
authors.forename: Frederic
authors.initials: F
authors.lastname: Padilla
authors.forename: Scott D
authors.initials: SD
authors.lastname: Swanson
authors.forename: Oliver D
authors.initials: OD
authors.lastname: Kripfgans
authors.forename: Paul L
authors.initials: PL
authors.lastname: Carson
authors.forename: Jeffrey Brian
authors.initials: JB
authors.lastname: Fowlkes
mesh_terms: D000162:Acoustics; D000818:Animals; D004285:Dogs; D005466:Fluorocarbons; D057086:High-Intensity Focused Ultrasound Ablation; D008099:Liver / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D045423:Microbubbles; D019047:Phantoms, Imaging; D014159:Transducers; D014463:Ultrasonography; D014835:Volatilization; D010420:Pentanes
chemical_list: D005466:Fluorocarbons; C008806:perfluoropentane; D010420:Pentanes