Lung Ultrasound Surface Wave Elastography: A Pilot Clinical Study

Abstract

A lung ultrasound surface wave elastography (LUSWE) technique is developed to measure superficial lung tissue elastic properties. The purpose of this paper was to translate LUSWE into clinical studies for assessing patients with interstitial lung disease (ILD) and present the pilot data from lung measurements on 10 healthy subjects and 10 patients with ILD. ILD includes multiple lung disorders in which the lung tissue is distorted and stiffened by tissue fibrosis. Chest radiography and computed tomography are the most commonly used techniques for assessing lung disease, but they are associated with radiation and cannot directly measure lung elastic properties. LUSWE provides a noninvasive and nonionizing technique to measure the elastic properties of superficial lung tissue. LUSWE was used to measure regions of both lungs through six intercostal spaces for patients and healthy subjects. The data are presented as wave speed at 100, 150, and 200 Hz at the six intercostal spaces. As an example, the surface wave speeds are, respectively, 1.88 ± 0.11 m/s at 100 Hz, 2.74 ± 0.26 m/s at 150 Hz, and 3.62 ± 0.13 m/s at 200 Hz for a healthy subject in the upper right lung; this is in comparison to measurements from an ILD patient of 3.3 ± 0.37 m/s at 100 Hz, 4.38 ± 0.33 m/s at 150 Hz, and 5.24 ± 0.44 m/s at 200 Hz in the same lung space. Significant differences in wave speed between healthy subjects and ILD patients were found. LUSWE is a safe and noninvasive technique which may be useful for assessing ILD.

Figures

Fig. 1

CT images for two patients with mild and moderate lung fibrosis. (a) mild bibasilar, mainly peripheral, ground glass abnormality; (b) moderate bibasilar fibrosis with mainly peripheral distribution.

Fig. 2

Representative B-mode images of lung for a healthy control (a) and for a patient (b). The lung surface of a healthy subject is typically smooth while a patient’s lung surface is relatively rough. Eight locations over a length of approximately 6 mm on the lung surface were used to measure the lung surface motion using ultrasound tracking beams.

Fig. 3

The wave phase delay of the remaining locations, relative to the first location, is used to measure the surface wave speed. Representative examples of wave speed at 150 Hz for a patient (a) and a healthy subject (b).

Fig. 4

Comparison of wave speeds between 10 healthy subjects and 10 patients through six intercostal spaces. Surface wave speed at (a) 100 Hz, (b) 150 Hz, (c) 200 Hz.