Assessment of Gold Nanoparticle-Mediated-Enhanced Hyperthermia Using MR-Guided High-Intensity Focused Ultrasound Ablation Procedure.

High-intensity focused ultrasound (HIFU) has gained increasing popularity as a noninvasive therapeutic procedure to treat solid tumors. However, collateral damage due to the use of high acoustic powers during HIFU procedures remains a challenge. The objective of this study is to assess the utility of using gold nanoparticles (gNPs) during HIFU procedures to locally enhance heating at low powers, thereby reducing the likelihood of collateral damage. Phantoms containing tissue-mimicking material (TMM) and physiologically relevant concentrations (0%, 0.0625%, and 0.125%) of gNPs were fabricated. Sonications at acoustic powers of 10, 15, and 20 W were performed for a duration of 16 s using an MR-HIFU system. Temperature rises and lesion volumes were calculated and compared for phantoms with and without gNPs. For an acoustic power of 10 W, the maximum temperature rise increased by 32% and 43% for gNPs concentrations of 0.0625% and 0.125%, respectively, when compared to the 0% gNPs concentration. For the power of 15 W, a lesion volume of 0, 44.5 ± 7, and 63.4 ± 32 mm3 was calculated for the gNPs concentration of 0%, 0.0625%, and 0.125%, respectively. For a power of 20 W, it was found that the lesion volume doubled and tripled for concentrations of 0.0625% and 0.125% gNPs, respectively, when compared to the concentration of 0% gNPs. We conclude that gNPs have the potential to locally enhance the heating and reduce damage to healthy tissue during tumor ablation using HIFU.

A theoretical assessment of a thermal technique to measure acoustic power radiated by ultrasound transducers.

The parameters affecting the temperature rise in an insonified absorber are studied computationally. Finite-element and analytical solutions are obtained for the transient energy equation in a cylindrical absorber. When the ultrasound beam radius is less than the radius of the absorber, the temperature field is seen to be considerably more complex than when the absorber cross section is uniformly heated. Circumstances in which power predictions based upon uniform heating would result in appreciable error are identified. The rise time required to achieve equilibrium is studied as a function of operational parameters, including absorber geometry and thermal properties as well as ultrasound beamwidth and frequency. The rise time is seen to increase approximately as the square of the absorber length, while optimized temperature rise increases linearly with absorber length, demonstrating a tradeoff in ultrasound power determination via equilibrium temperature measurements: longer lengths produce higher sensitivity, but also longer times before measurements can be made. A transient technique that may bypass this tradeoff is suggested.