Parametric Study of a Conical Applicator for 4 MHz HIFU Transducer for its Possible Application in Bone Tumour Ablation Therapy

In thermal ablation therapy, high intensity focused ultrasound is used to concentrate the acoustic beams in a specific region. This ultrasonic energy concentration causes a rapid temperature increase in a short time. In some clinical applications, a truncated cone coupled to the transducer contains a propagation medium to allow the delivery of the therapy; besides, its shape points in the target direction. This paper presents a parametric study of a conical applicator for a 4 MHz HIFU transducer with 100 mm focal length for the evaluation of its use in bone tumors. The conical applicator was varied in radius and thickness from 4 -7.5 mm and 1 to 2 mm, respectively, in order to achieve similar acoustic distribution to the HIFU transducer without cone. Three different materials compatible with 3D printing were studied: polylactic acid, acrylonitrile butadiene styrene and low density polyethylene. Simulations were realized in COMSOL Multiphysics
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for Finite Element Method. A convergence study was realized for mesh values of λ/6, λ/8 and λ/10. The best results were achieved with a cone aperture radiuses larger than 5 mm and a cone tip thickness of 2 mm. The best mesh size was λ/8.