Nonlinear acoustic properties of ex vivo bovine liver and the effects of temperature and denaturation.

Journal article

Thermal ablation by high intensity focused ultrasound (HIFU) has a great potential for the non-invasive treatment of solid tumours. Due to the high pressure amplitudes involved, nonlinear acoustic effects must be understood and the relevant medium property is the parameter of nonlinearity B/A. Here, B/A was measured in ex vivo bovine liver, over a heating/cooling cycle replicating temperatures reached during HIFU ablation, adapting a finite amplitude insertion technique, which also allowed for measurement of sound-speed and attenuation. The method measures the nonlinear progression of a plane wave through liver and B/A was chosen so that numerical simulations matched the measured waveforms. To create plane-wave conditions, sinusoidal bursts were transmitted by a 100 mm diameter 1.125 MHz unfocused transducer and measured using a 15 mm diameter 2.25 MHz broadband transducer in the near field. Attenuation and sound-speed were calculated using a reflected pulse from the smaller transducer using the larger transducer as the reflecting interface. Results showed that attenuation initially decreased with heating then increased after denaturation, the sound-speed initially increased with temperature and then decreased, and B/A showed an increase with temperature but no significant post-heating change. The B/A data disagree with other reports that show a significant change and we suggest that any nonlinear enhancement in the received ultrasound signal post-treatment is likely due to acoustic cavitation rather than changes in tissue nonlinearity.

Authors: Jackson, E; Coussios, C; Cleveland, R

• Publication status: Published
• Publisher: Institute of Physics Publishing
• Journal: Physics in medicine and biology
• Volume: 59
• Issue: 12
• Pages: 3223-3238
• Publication date: 2014-06-01
• DOI: 10.1088/0031-9155/59/12/3223
• EISSN: 1361-6560
• ISSN: 0031-9155
• Language: English
• Keywords: Animals; Transducers; Time Factors; Liver; Acoustics; Cattle; Nonlinear Dynamics; Temperature; High-Intensity Focused Ultrasound Ablation