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 study 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 (CT) 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 Hz, 150 Hz, 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.

Effect of a Thin Fluid Layer on Surface Wave Speed Measurements: A Lung Phantom Study

“…As shown in the figure, the surface wave speeds of both sponges increased with the shaker frequency. This trend was observed in our patient study, which further validates the use of these sponges as lung phantoms. We performed t tests at P < .05 between measurements done at different frequencies to test the significance of the increase.…”

“…The above measurement and speed analysis were repeated 3 times for each shaker frequency. The averaged results are summarized and shown in Figure along with our previously reported patient study data . (The human study here was approved by the Mayo Clinic Institutional Review Board.…”

“…The averaged results are summarized and shown in Figure 4 along with our previously reported patient study data. 10 (The human study here was approved by the Mayo Clinic Institutional Review Board.) 10 The surface wave speeds for the sponge without the thin gel layer are in blue; the gel-covered ones are in yellow; and the statistical average for 10 patients is in green.…”

“…4 High-resolution computed tomography is the clinical standard for the diagnosis, 5 but the ionizing radiation from high-resolution computed tomography 6 may increase the risk of cancer. 7 In search of a noninvasive alternative, we have invented lung ultrasound (US) surface wave elastography (SWE), [8][9][10][11] which assesses pulmonary fibrosis by measuring the surface wave speed of superficial lung tissue.…”

“…The movement of the locations in the 0.1 second was Fourier transformed onto the inversed space, where the phase shift was calculated from cross-spectra and used to determine the sponge surface wave speeds. [8][9][10][11] The surface wave speeds for sponges with and without a thin layer of gel were compared to model the effect of the plural fluid layer on lung surface wave measurements in lung US SWE.…”