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

Abstract

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 second 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.

Noninvasive measurement of wave speed of porcine cornea in ex vivo porcine eyes for various intraocular pressures

“…The tissue motion at a location was measured by analyzing the ultrasound tracking beam through that location [22]. The wave speed was analyzed by the change in wave phase with distance.…”

“…The quality of the measurement of wave speed was assured by the sum of squares of linear regression residuals (R 2 ) being ≥ 0.8 [22]. R 2 is the coefficient of determinant ranging from 0 to 1, a statistical measure of how close the data fit the regression line.…”

Lung Ultrasound Surface Wave Elastography: A Pilot Clinical Study

“…With the goal of developing a noninvasive technique for measuring lung elastic property, we have developed an ultrasound-based LUSWE technique capable of measuring superficial lung tissue stiffness safely and quickly [12, 13]. In LUSWE, a harmonic vibration at a given low frequency is generated by the indenter of a handheld vibrator on the chest wall of a subject.…”

A surface wave elastography technique for measuring tissue viscoelastic properties

“…SWE has been used to measure different tissues. The wave speed ranges were typically between 1.5 m/s and 3 m/s for the skin on the forearms and lung tissue [19–21]. The wave speeds were between 3 m/s and 5 m/s for arterial tissues depending on the intravascular pressure [16].…”

“…SWE may also be used to study tissue decay over time. SWE is also applicable to internal tissues, such as the lung, where the surface wave on the lung is measured using ultrasound [21]. SWE may be used to investigate nonlinear or hyperelastic properties of skin if strong and large ranges of excitation are applied.…”