Numerical modeling of ultrasound heating for the correction of viscous heating artifacts in soft tissue temperature measurements

Abstract

Measuring temperature during focused ultrasound (FUS) procedures is critical for characterization, calibration, and monitoring to ultimately ensure safety and efficacy. Despite the low cost and the high spatial and temporal resolutions of temperature measurements using thermocouples, the viscous heating (VH) artifact at the thermocouple-tissue interface requires reading corrections for correct thermometric analysis. In this study, a simulation pipeline is proposed to correct the VH artifact arising from temperature measurements using thermocouples in FUS fields. The numerical model consists of simulating a primary source of heating due to ultrasound absorption and a secondary source of heating from viscous forces generated by the thermocouple in the FUS field. Our numerical validation found that up to 90% of the measured temperature rise was due to VH effects. Experimental temperature measurements were performed using thermocouples embedded in fresh chicken breast samples. Temperature corrections were demonstrated for single high-intensity FUS pulses at 3.1 MHz and for multiple pulses (3.1 MHz, 100 Hz, and 500 Hz pulse repetition frequency). The VH accumulated during sonications and produced a temperature increase of 3.1 C and 15.3 C for the single and multiple pulse sequences, respectively. The methodology presented here enables the decoupling of the temperature increase generated by absorption and VH. Thus, more reliable temperature measurements can be extracted from thermocouple measurements by correcting for VH.

Iterative Curve Fitting of the Bioheat Transfer Equation for Thermocouple-Based Temperature Estimation $In~ Vitro$ and $In~ Vivo$

“…The artifact contribution decreased with the pressure amplitude and FUS beam location. These results corroborate previous studies that suggested placing the thermocouple tip slightly off the FUS focal spot to reduce the artifact [15], [19], [34]. This is a feasible approach, but a correction of the temperature decay with the beam profile is necessary to correctly retrieve the temperature estimation at the focal spot.…”

“…However, the method is limited for the analysis of the cooling time only. An analysis of the heating pattern would require simulations of heating due to both ultrasound absorption and viscous heating effect, as we presented in a recent work [19]. However, simulations require the estimation of the viscous heating contribution in different experimental conditions which, as we demonstrate here, is highly variable with acoustic parameters and thermocouple type.…”

“…transcranial ultrasound). Additionally, simulations could be used to estimate the increase in temperature due to viscous heating and correct the temperature readings [19]. However, similar issues with the estimation of tissue properties and heterogeneities can limit the application to a few experimental conditions.…”

Displacement Imaging for Focused Ultrasound Peripheral Nerve Neuromodulation

“…A sharp 3-dB temperature decrease occurred at 0.4 mm away from the center of the focus laterally and 1.6 mm in depth. The temperature returned to baseline within 2 seconds after 1 ms stimulations [37], [38].…”

Low-Loss Ultrasound Transmission Through Waveguide From Double Parabolic Reflectors (DPLUS) for Thermal Ablation

“…The simulation model is shown in Fig.5, with the tissue material properties listed in TABLEI. The only change is the acoustic absorption coefficient 𝛼 '6 which was measured by comparing the relative amplitude of ultrasound through transmission measurements in the tissue sample and in free water[26]. For this measurement, a 1 MHz transducer with a diameter of 20 mm was used as a transmitter and a hydrophone (HNR 0500, Onda Corporation, California, USA) was used as a receiver.…”