Abstract |
Nonlinear FDTD-Modeling of Ultrasound
Thermotherapy Including Temperature Dependent Tissue Parameters
M.Liebler, S.Ginter, T.Dreyer,
R.E.Riedlinger (Institut fuer Hoechstfrequenztechnik und Elektronik / Akustik,
University of Karlsruhe, Germany)
e-mail:
Marko.Liebler@etit.uni-karlsruhe.de
Ultrasound
thermotherapy (USTT) is used to induce thermal coagulation in human tissue by
high intensity focused ultrasound. In thermotherapy the absorbed ultrasound
energy mainly determines the temperature achieved. It strongly depends on the
counteracting processes of nonlinear ultrasound propagation and tissue
attenuation. The heating process leads to a change of tissue properties and
therefore influences the therapy itself. Here an USTT-model, implemented with a
FDTD-algorithm, is presented, combining nonlinear ultrasound propagation with a
broadband frequency-power-law attenuation. Special importance is attached to an
efficient numerical implementation of the frequency dependent attenuation in
the time domain method. Calculation of temperature distributions is done using
Pennes Bio-Heat-Transfer-Equation. The temperature dependence of tissue
parameters is taken into account for the complete model. Simulation results
show the influences of nonlinear effects on therapy. Furthermore it is
demonstrated that the temperature dependence of tissue parameters can not be
neglected for accurate predictions of the required heating time.
Section
: 5