By combining the magnetoacoustic tomography with magnetic induction (MAT-MI) with the ultrasound therapy, real-time temperature monitoring and treatment efficacy evaluation for the focal region in high-intensity focused ultrasound (HIFU) are investigated based on the impedance-temperature relationship of biological tissues. On the basis of the theories of the focused acoustic and temperature fields and the principles of magnetoacoustic excitation and radiation, the distributions of the acoustic, temperature and electrical conductivity in the focal region area are studied by solving the Helmholtz wave equation and the Pennes equation. The process of magnetoacoustic measurements during HIFU therapy is simulated based on the theory of MAT-MI. With the distributions of magnetoacoustic sources in the focal region, the transducer detected magnetoacoustic pressure and cluster are simulated. The dependences of the amplitude peak of the cluster and the corresponding derivative with respect to the treatment time during HIFU therapy are analyzed. It is proved that irreversible thermo-coagulations occur when the temperature in the focal region with the sizes of ±0.46 mm and ±2.2 mm in the radial and axial directions reaches 69℃. The maximum value of the derivative of the amplitude peak of the cluster provides a convenient and sensitive indicator for temperature monitoring, which might promote potential applications in real-time treatment efficacy evaluation and accurate dose control for HIFU therapy.

high-intensity focused ultrasound; magnetoacoustic measurements; impedance-temperature relationship; temperature monitoring; treatment efficacy evaluation