Radiation Characteristics of Cranial Leaky Lamb Waves

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 68; no. 6; pp. 2129 - 2140
• Main Authors: Mazzotti, Matteo, Kohtanen, Eetu, Erturk, Alper, Ruzzene, Massimo
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.06.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Angles (geometry); Bones; Computed tomography; Cranial; Dispersion; Finite element method; Geometry; Lamb waves; Mathematical models; Mechanical properties; Medical signal and image processing; medical tissue characterization; Phantoms; Radiation; Skull; Sound propagation; Ultrasonic imaging; underwater ultrasound; Wave propagation; Waveguides
• ISSN: 0885-3010; 1525-8955; 1525-8955
• DOI: 10.1109/TUFFC.2021.3057309

We numerically and experimentally investigate the dispersion properties of leaky Lamb waves in the cranial bone. Cranial Lamb waves leak energy from the skull into the brain when propagating at speeds higher than the speed of sound in the surrounding fluid. The understanding of their radiation mechanism is significantly complicated by the geometric and mechanical characteristics of the cortical tables and the trabecular bone (diploë). Toward such understanding, we here analyze the sub-1.0 MHz radiation angle dispersion spectrum of porous bone phantoms and parietal bone geometries obtained from <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula>CT scans. Our numerical results show that, when diploic pores are physically modeled, leakage angles computed from time transient finite-element analyses correspond to those predicted by an equivalent three-layered fluid-loaded waveguide model. For the bone geometries analyzed, two main leaky branches are observed in the near-field dispersion spectrum: a fast wave radiated at small angles, which is related to the fastest fundamental Lamb mode supported by the cranial bone, and a slower wave radiated at larger angles. This observation is also confirmed by experimental tests carried out on an immersed parietal bone.