Thermal properties and changes of acoustic parameters in an egg white phantom during heating and coagulation by high intensity focused ultrasound.

A polyacrylamide phantom containing egg white has been proposed previously as an adequate tissue-mimicking material for high intensity focused ultrasound (HIFU) application. In this work, we report on measurements of egg white phantom thermal conductivity and specific heat capacity. We measured changes in acoustical properties which occurred during the heating and the coagulation process. Using a thin thermocouple embedded in the phantom material, we recorded the temperature response in the focus of the ultrasound field during HIFU application and phantom coagulation. The measured values for the thermal conductivity (0.59 +/- 0.06 W/m/ degrees C) and the specific heat capacity (4270 +/- 365 J/kg/ degrees C) are similar to the values of water. The attenuation coefficient decreased in the temperature range between 26 degrees C and 50 degrees C and showed a nonlinear dependence on frequency with an exponent of 1.50 +/- 0.05 that was temperature-independent within the investigated temperature range. Below 65 degrees C, no irreversible changes in material absorption were observed. The coagulation process started at 67 degrees C and no adjacent rapid changes in temperature response were detected. In comparison with the noncoagulated phantom, the coagulated phantom material showed an enhanced absorption and a threefold higher attenuation coefficient at a frequency of 1 MHz.

[1]  Shahram Vaezy,et al.  Polyacrylamide gel as an acoustic coupling medium for focused ultrasound therapy. , 2003, Ultrasound in medicine & biology.

[2]  Z Petrovich,et al.  Utilization of a multilayer polyacrylamide phantom for evaluation of hyperthermia applicators. , 1992, International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group.

[3]  P. He,et al.  Experimental verification of models for determining dispersion from attenuation , 1999, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[4]  Xin-Gang Liang,et al.  The boundary induced error on the measurement of thermal conductivity by transient hot wire method , 1995 .

[5]  Y. Mine.  Recent advances in the understanding of egg white protein functionality , 1995 .

[6]  Yoichiro Matsumoto,et al.  Polyacrylamide gel containing egg white as new model for irradiation experiments using focused ultrasound. , 2004, Ultrasound in medicine & biology.

[7]  Roberto Olmi,et al.  The Polyacrylamide as a Phantom Material for Electromagnetic Hyperthermia Studies , 1984, IEEE Transactions on Biomedical Engineering.

[8]  C. Ma,et al.  Thermal analysis of foods , 1990 .

[9]  Y. Pao,et al.  On the determination of phase and group velocities of dispersive waves in solids , 1978 .

[10]  S. Davidson,et al.  Measurement of the thermal conductivity of polyacrylamide tissue-equivalent material , 2003, International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group.

[11]  Thomas Dreyer,et al.  Full wave modeling of therapeutic ultrasound: efficient time-domain implementation of the frequency power-law attenuation. , 2004, The Journal of the Acoustical Society of America.

[12]  G. ter Haar,et al.  Temperature rise recorded during lesion formation by high-intensity focused ultrasound. , 1997, Ultrasound in medicine & biology.

[13]  M J Bronskill,et al.  Magnetic resonance imaging of thermal coagulation effects in a phantom for calibrating thermal therapy devices. , 2000, Medical physics.

[14]  Vesna Zderic,et al.  Gel phantom for use in high-intensity focused ultrasound dosimetry. , 2005, Ultrasound in medicine & biology.

[15]  C R Hill,et al.  Review article: high intensity focused ultrasound--potential for cancer treatment. , 1995, The British journal of radiology.