Simulation of focused shear wave penetration to the deep liver through the human body wall

Ultrasound-Based tests for liver fibrosis such as transient elastography (TE) are attractive due to high accessibility and low cost, but suffer from nondiagnostic test rates of up to 20% in patients with coexisting obesity due to limited penetration to deep livers. Focused shear wave elastography (fSWE), in which a concave vibration source generates converging shear waves for increased signal at the needed depths, was recently introduced to overcome this limitation. In clinical application the focused shear wave must penetrate through the viscous body wall, past the rib cage, and into the liver stiffness measurement (LSM) region. Here, custom simulations are employed to investigate penetration to the LSM region in fSWE. The body wall and liver are modeled as viscoelastic and ribs as perfectly absorbing obstacles, each with stiffness and size based on measurements from a cohort of MASLD patients with obesity. Correlation of fSWE penetration with liver stiffness, liver depth, and intercostal space width is moderately negative, moderately-strongly negative, and strong, respectively. Unfocused shear waves (based on Fibroscan XL) show similar correlations, but with 3.5× lower signal amplitude in the LSM region. Results suggest that liver depth and stiffness do not significantly adversely affect fSWE compared to conventional TE, while intercostal space width may. The custom simulation can be used for optimization of fSWE for clinical application.