Background/Purpose: Surface wave elastography is an ultrasound based noninvasive technique to measure tissue viscoelasticity (“stiffness”). Preliminary studies in assessing scleroderma associated skin thickening have been promising. Ultrasonography is not widely used in clinic for lung assessment. Lung tissue is normally filled with air, and the difference in acoustic impedance between air and tissue is large. Most of the energy of an ultrasound wave is reflected from the lung surface and ultrasound cannot image deep lung tissue. In this abstract, we present a novel technique, lung ultrasound surface wave elastography, for measuring the elastic properties of superficial lung tissue. The lung changes in many interstitial lung diseases (ILD), including scleroderma associated ILD, are peripheral/superficial and have fibrosis-related “stiffening.”

Methods: A handheld vibrator was used to generate a small, local, and 0.1 second harmonic vibration on the chest of a subject. A Versonics ultrasound probe (L11-4/central frequency of 6.4 MHz) was used to measure the resulting surface wave speed on the lung. In a large clinical study of ILD patients, we measure both lungs through six intercostal spaces for patients and controls. Patients were selected from the Adult Pulmonary and Rheumatology outpatient clinics. Clinical and CT diagnosis of interstitial lung disease, either idiopathic or associated with a connective tissue disease/autoimmune inflammatory arthritis. Controls were never-smoking, asymptomatic adults with no history of cardiorespiratory disease. We compared 91 ILD patients to 30 normal controls. The 91 ILD patients’ diagnoses included: Scleroderma (39), rheumatoid arthritis (12), overlap CTD (10), idiopathic ILD (10), antisynthetase (7), myositis (7), Sjögren’s (5), and SLE (1).

Results: The surface wave speed was measured at 100 Hz, 150 Hz, and 200 Hz. The surface wave speeds at 100 Hz, were 2.26 ± 0.4 m/s and 2.87 ± 0.53 m/s, respectively, for 30 healthy subjects and 91 patients with ILD at the lower right lungs The surface wave speeds were significantly higher in ILD patients than that in healthy subjects (p<0.001) at each intercostal space and at each frequency.

Conclusion: Lung ultrasound surface wave elastography may prove to be a useful noninvasive and nonionizing technique to measure the elastic properties of superficial lung tissue. Significant differences of wave speed between healthy subjects and patients with peripherally distributed interstitial fibrosis were found. Lung ultrasound surface wave elastography has potential utility in assessing ILDs.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-non-invasive-ultrasound-surface-wave-elastography-technique-for-assessing-interstitial-lung-disease/