Simulation of High-Intensity Focused Ultrasound (HIFU) thermal ablation in Mobile and Elastic Organs
Résumé
<b>Context</b>: Numerical modeling is performed to optimize therapies that use HIFU. In cardiac procedures, heart movements and deformations make the treatment particularly challenging. This study aims to demonstrate with a new numerical model of thermal ablations that accurate modeling of temperature and thermal dose in elastic and mobile organs requires considering deformations and motions. <b>Methods</b>: Ultrasound pressure field is calculated using the Rayleigh integral method and a point-by-point estimation of the attenuation in the tissues. Temperature map is obtained by the discretization with finite volume method of the Bio Heat Transfer Equation (BHTE) on a collocated, smooth and non-orthogonal tridimensional mesh with hexahedral cells. The equation is solved on a curvilinear coordinate system fitting the grid. Simulated HIFU beam is generated by a 3-cm<sup>2</sup> truncated spherical transducer with 40-mm natural focus and operating at 3 MHz. Tests are performed on two configurations with 6s-long sonication at an acoustic power of 32 W: 1) on a homogeneous matrix undergoing compression, dilatation, rotation or translation movements and 2) on the atrioventricular node (AVN) of a healthy beating heart model reconstructed from 4D CT-scan. <b>Results/Discussion</b>: In homogeneous volume (1), for static configuration, the maximum temperature reaches 69�C and the thermal lesion volume is 4.91 mm<sup>3</sup>. Depending on applied deformations, the maximum temperature varies from 55 to 70�C, and the lesion volume fluctuates from 0.05 to 5.51 mm<sup>3</sup>. In AVN (2), the maximum temperature reaches 83�C in static heart and the lesion volume is 18.74 mm<sup>3</sup>. Considering heart deformations and motions, temperature only reaches 46�C and no lesion is visible. Movements and deformations affect significantly simulation results in simple and more complex models. Neglecting heart movements and deformations induce overestimation of HIFU treatment efficacy. Thus, considering deformations and movements in modeling studies is required to provide accurate treatment strategies.