Assessment of interstitial lung disease using lung ultrasound surface wave elastography

We have developed a noninvasive lung ultrasound surface wave elastography (LUSWE) technique for measuring superficial lung tissue stiffness. The purpose of this paper was to demonstrate the clinical use of LUSWE for assessing patients with interstitial lung disease (ILD). In LUSWE, a local 0.1s harmonic vibration is generated on the chest wall of a subject using a handheld vibrator. An ultrasound probe is aligned with the indenter of vibrator in the same intercostal space to measure the generated surface wave propagation on the lung. The Verasonics ultrasound system with an L11-4 ultrasound probe with a central frequency of 6.4 MHz is used. Subjects are examined in a sitting position. The lung testing is performed with full inspiration breath hold. The surface wave speeds of lung were measured at 100 Hz, 150 Hz, and 200 Hz. In a prospective clinical study, we measured both lungs through six intercostal spaces for patients and controls. Significant differences in wave speed between healthy subjects and ILD patients were found. For example, the surface wave speeds of the lung were 1.98 ± 0.07 m/s at 100 Hz, 2.63 ± 0.46 m/s at 150 Hz, and 3.18 ± 0.58 m/s at 200 Hz for a healthy subject, and the surface wave speeds of the lung were 3.30 ± 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 for an age matched ILD patient in the same intercostal space. LUSWE is a safe and noninvasive technique for generating and measuring surface wave propagation on the lung.