Porcine Lung Acoustics: Simulating Airway Insonification and Magnetic Resonance Elastography

Pulmonary diseases are one of the main causes leading to death worldwide. Due to various reasons, however, the detection of lung related diseases in early stages is still an issue. Magnetic Resonance Elastography (MRE) was found to be a non invasive diagnostic tool that can assess tissue properties and potentially give fundamental information on their variation, hence on the discovery and progression of the disease. Sound propagation, also, may be used as vibratory source to perform MRE: the insonification of pig lungs is thus performed in order to evaluate its acoustic properties and the basics of a MRE setup are described. After the generation of a 3D model of the airways starting from CT images and the algorithmic generation of the smallest branches, a 1Pa acoustic pressure sound is propagated inside the lungs and their acoustic properties are assessed for three different conditions (health, fibrosis and bronchoconstriction). The main requirements for lung MRE are then described: a hyperpolarized gas such as 129Xe and a loudspeaker for sound generation are needed. The insonification in the overall tree, the mid-trachea and the terminal segments shows various results for the acoustic pressure and wall radial velocity, according to the considered condition; also, the soft tissue resonance peak clearly appears. The analysis of the wall radial displacements suggests MRE feasibility in the mid-trachea, where they are in the range of 10^-6m, but that does not apply to the terminal branches area (10^-11m or lower displacements). Further studies are needed in order to develop a better and more specific MRE setup and to effectively verify the possibility to apply MRE to the lungs.