![]() ![]() ![]() Although this approach is widely used in medical US, the challenge of directly measuring and modeling HIFU fields is worth revisiting since experimental tools and numerical models may improve over time, and no standard method, such as that for diagnostic US, 8 has yet been agreed upon for HIFU devices. Next, a method is used to relate the measurements in water to what is expected in tissue. First, measurements are performed in water. 2, 7 The high pressures and tight focusing of HIFU devices make accurate acoustic field measurements challenging.įor medical work, the characterization of acoustic output is often performed in two parts. Modern HIFU devices operate at very high focal intensity levels from 1000 W∕cm 2 to greater than 25 000 W∕cm 2 in situ and are highly focused to a millimeter or even a submillimeter sized focal spot. The acoustic characterization of HIFU fields is important both for the accurate prediction of US induced bioeffects in tissues and for the development of standards to ensure the safety and efficacy of treatments. In HIFU medical treatments, ultrasound (US) energy is focused into a small volume to heat and destroy the targeted tissue while ideally not damaging tissue outside the focal region. HIFU devices are currently under investigation for use as surgical tools, for example, to thermally ablate solid tumors of the prostate, 1 liver, 2 breast, 3 kidney, 4 and brain, 5 as well as for cauterizing internal bleeding. High intensity focused ultrasound (HIFU) is an evolving medical technology for noninvasive surgery and cancer therapy. It is shown that a combination of measurements and modeling is necessary to enable accurate characterization of HIFU fields. This underrepresentation was attributed mainly to the limited hydrophone bandwidth of 100 MHz. Numerical simulations and experimental measurements agreed well however, when steep shocks were present in the waveform at focal intensity levels higher than 6000 W∕cm 2, lower values of the peak positive pressure were observed in the measured waveforms. Strongly asymmetric waveforms with peak positive pressures up to 80 MPa and peak negative pressures up to 15 MPa were obtained both numerically and experimentally. ![]() The inputs to a Khokhlov–Zabolotskaya–Kuznetsov-type numerical model were determined based on experimental low amplitude beam plots. Measurements were performed with a fiber optic probe hydrophone at intensity levels up to 24 000 W∕cm 2. Nonlinear pressure waveforms were measured and modeled in water and in a tissue-mimicking gel phantom for a 2 MHz transducer with an aperture and focal length of 4.4 cm. In this paper, a method to determine HIFU field parameters at and around the focus is proposed. Acoustic characterization of high intensity focused ultrasound (HIFU) fields is important both for the accurate prediction of ultrasound induced bioeffects in tissues and for the development of regulatory standards for clinical HIFU devices. ![]()
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