Th e Correction of Focal Point Displacement Caused by the Refraction of the Beams in High-Intensity Focused Ultrasound

Mohammad Rezaei, Karim Khoshgard, Mehdi Mousavi


Nowadays, high-intensity focused ultrasound (HIFU) as nonionizing radiation is used for cancertreatment. Basically, the function of HIFU is similar to conventional ultrasound. Ultrasound beamsare perverted when crossing the border of different environments. This decreases the beam’s focuswithin the tumor and may induce damage to the normal tissues. In this study, we aim to developappropriate algorithms for correcting the focal point displacement duced by the beam’s refraction. First,the level of displacement due to difference in two specific tissues was calculated for one element of thetransducer and, then, it extended to all of the elements. Finally, a new focal point was calculated, which isconsidered as a desired focal point of the transducer in which the maximum temperature occurs.Designed algorithms were implemented in MATLAB software. A HIFU simulator (by the Food andDrug Administration of US) was used to simulate HIFU therapy. The proposed algorithm was tested onfour models with two layers of tissue. Results illustrated the use of proposed algorithm results for 78%correction in the focal point displacement. In addition, it was noted that a part of this displacement wascaused by the absorption of the beam in the tissues. The proposed algorithm can significantly correct thefocal point displacement in HIFU therapy and consequently prevent damage to the normal tissues.

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