Sound Transmission in a Lung Phantom Model

Alterations in the structure and function of the pulmonary system that occur in disease or injury often give rise to measurable changes in lung sound production and transmission. A better understanding of sound transmission and how it is altered by injury and disease might improve interpretation of lung sound measurements, including new lung imaging modalities that are based on an array measurement of the acoustic field on the torso surface via contact sensors or are based on a 3-dimensional measurement of the acoustic field throughout the lungs and torso using magnetic resonance elastography. It is beneficial to develop a computational acoustic model that would accurately simulate generation, transmission and noninvasive measurement of sound and vibration within the pulmonary system and torso caused by both internal and external sources. In the present study, sound transmission in the airway tree and coupling to and transmission through the surrounding lung parenchymal tissue were investigated on a mechanical lung phantom with a built-in bifurcating airway tree through airway insonification. Sound transmission in the airway tree was studied by applying the Horsfield self-consistent model of asymmetric dichotomy for the bronchial tree. The acoustics of the bifurcating airway segments and lung phantom surface motion were measured by microphones and scanning laser Doppler vibrometty respectively. Finite element simulations of sound transmission in the lung phantom were performed. Good agreement was achieved between experiments and finite element simulations. This study validates the computational approach for sound transmission and provides insights for simulations on real lungs.