Focused ultrasound (FUS) is a promising non-invasive technology for tumor treatment. Yet, its clinical adoption for upper abdominal organs faces challenges due to the presence of rib bone and structures. This affects the safety and efficacy of the FUS procedures in the upper abdominal anatomical locations. To better understand the effect of the ribs obstructing the acoustic beam path and the subsequent shear stresses produced, we created a finite element model (FEM) simulating acoustic waves focused inside segments 6,7, and 8 forming the right lobe or dome of the liver. Our FEM model incorporated anatomy with hyperelastic constitutive behavior for tissues assessed by two commercially available FUS transducers operating at fundamental (0.5MHz) and third harmonic (1.5MHz) frequencies, with surface pressure mimicking acoustic power. The model showed a focal pressure reduction by up to $24 %$ with rib bone inclusion and significant reflections marked at -4 ~dB in periosteum layers due to bone inclusion. Additionally, diffraction and scattering of FUS waves were observed, particularly at the third harmonic, causing a focus splitting effect with secondary focus exceeding -3 ~dB level at 16 ~mm above the focal point. Furthermore, the study quantified shear stresses induced in the focal region by acoustic waves, revealing an inverse quadratic relationship between shear stresses and focal pressures. These findings offer insights for planning abdominal FUS procedures.
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Sabale et al. (2024) studied this question.