A noninvasive ultrasound elastography technique for measuring surface waves on the lung

The purpose of this work was to demonstrate an ultrasound based surface wave elastography (SWE) technique for generating and detecting surface waves on the lung. The motivation was to develop a noninvasive technique for assessing superficial lung tissue disease including interstitial lung disease (ILD). ILD comprises a number of lung disorders in which the lung tissue is stiffened and damaged due to fibrosis of the lung tissue. Currently, chest radiographs and computed tomography (CT) are the most common clinical methods for evaluating lung disease, but they are associated with radiation and cannot measure lung mechanical properties. The novelty of SWE is to develop a noninvasive and nonionizing technique to measure the elastic properties of superficial lung tissue. We propose to generate waves on the lung surface through wave propagation from a local harmonic vibration excitation on the chest through an intercostal space. The resulting surface wave propagation on the lung is detected using an ultrasound probe through the intercostal space. To demonstrate that surface waves can be generated on the lung, an ex vivo muscle-lung model was developed to evaluate lung surface wave generation and detection. In this model, swine muscle was laid atop a swine lung. A vibration excitation of 0.1 s 100 Hz wave was generated on the muscle surface and the surface waves on the lung were detected using a linear array ultrasound probe at 5 MHz. To test its feasibility for patient use, SWE was used to measure both lungs of an ILD patient through eight intercostal spaces. The mean wave speed was 1.71 ± 0.20 m/s (±SD) at the functional residual capacity, while the mean wave speed was 2.36 ± 0.33 m/s at the total lung capacity. These studies support the feasibility of SWE for noninvasive measurement of elastic properties of lung and demonstrate potential for assessment of ILD.