title: Direct methods for characterizing high-intensity focused ultrasound transducers using acoustic streaming.
abstract: Two techniques are presented for noninvasively determining the intensity field of high-intensity focused ultrasound transducers in a liquid medium. The techniques are based upon the streaming velocity induced in the liquid by the absorbed ultrasound beam. The approaches are similar to an iterative streaming method previously reported, but the present approaches are "direct:" The differential operations of the Navier-Stokes equations are performed directly upon the experimentally measured streaming velocity, rather than through an iterative approach that minimizes the difference between a theoretical estimate of the streaming velocity and the one measured experimentally. As such, the direct methods are much faster than the iterative technique. The price paid for the increase in speed is smaller spatial coverage; the direct techniques are applicable only where accurate streaming velocity is available. Comparisons performed in the range 100-1000 W/cm(2) focal intensity showed differences between the direct methods and the iterative streaming technique to be less than 20%. Similar differences were observed in low-power comparisons with hydrophone measurements.
authors.affiliation: Division of Solid and Fluid Mechanics, Center for Devices and Radiological Health, U. S. FDA, 10903 New Hampshire Avenue, Building 62, Room 2231, Silver Spring, Maryland 20993-0002, USA. matthew.myers@fda.hhs.gov
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Myers
authors.forename: Prasanna
authors.initials: P
authors.lastname: Hariharan
authors.forename: Rupak K
authors.initials: RK
authors.lastname: Banerjee
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D000465:Algorithms; D020342:Finite Element Analysis; D008962:Models, Theoretical; D009038:Motion; D016011:Normal Distribution; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013997:Time Factors; D014159:Transducers; D014465:Ultrasonics; D014783:Viscosity