Characterization of high intensity focused ultrasound transducers using acoustic streaming

Abstract

A new approach for characterizing high intensity focused ultrasound (HIFU) transducers is presented. The technique is based upon the acoustic streaming field generated by absorption of the HIFU beam in a liquid medium. The streaming field is quantified using digital particle image velocimetry, and a numerical algorithm is employed to compute the acoustic intensity field giving rise to the observed streaming field. The method as presented here is applicable to moderate intensity regimes, above the intensities which may be damaging to conventional hydrophones, but below the levels where nonlinear propagation effects are appreciable. Intensity fields and acoustic powers predicted using the streaming method were found to agree within 10% with measurements obtained using hydrophones and radiation force balances. Besides acoustic intensity fields, the streaming technique may be used to determine other important HIFU parameters, such as beam tilt angle or absorption of the propagation medium.

Direct methods for characterizing high-intensity focused ultrasound transducers using acoustic streaming

“…II, and discussed in more detail in Hariharan et al ͑2008͒, were performed using the three HIFU transducers featured in Table I. All experiments were performed in the 12 cP Natrosol medium, using the DPIV protocol described in Hariharan et al ͑2008͒. Intensity fields for the three transducers were derived from the streaming velocity fields using the GCF and FD direct methods.…”

“…͑2.6͒ are extracted from the finite-element calculations performed in the iterative method of Hariharan et al ͑2008͒, it can be seen that the second radial derivative possesses an approximately Gaussian shape as a function of radial position. We therefore assume a profile of the form…”

“…III the methods are applied to sets of experimental data for three different transducers. The experiments were performed using the DPIV method described in Hariharan et al ͑2008͒. Comparisons are made with the iterative approach and with experimental hydrophone measurements.…”

Localization of focused-ultrasound beams in a tissue phantom, using remote thermocouple arrays

“…Execution of the optimization algorithm required to attain the focal location required approximately 5 min using the exhaustive marching algorithm to search. Implementation of a more sophisticated optimization algorithm (e.g., Hariharan et al [11]) could reduce the localization time considerably, though care must be taken to ensure that the convergence properties are well understood.…”

“…although inverse methods have been applied outside ultrasound applications [9], [10], few studies have used inverse methods in conjunction with ultrasound phantoms. Hariharan et al [11] employed an inverse algorithm to back calculate the acoustic intensity on the basis of the ultrasound-induced streaming velocities measured in a liquid medium. o'neill et al [6] moved the focused ultrasound beam focus to 6 locations relative to a single thermocouple, and used a fitting procedure to predict the coordinates of the thermocouple relative to the beam locations.…”