A focused air-pulse system for optical-coherence-tomography-based measurements of tissue elasticity

Abstract

Accurate non-invasive assessment of tissue elasticity in vivo is required for early diagnostics of many tissue abnormalities. We have developed a focused air-pulse system that produces a low-pressure and short-duration air stream, which can be used to excite transient surface waves (SWs) in soft tissues. System characteristics were studied using a high-resolution analog pressure transducer to describe the excitation pressure. Results indicate that the excitation pressure provided by the air-pulse system can be easily controlled by the air source pressure, the angle of delivery, and the distance between the tissue surface and the port of the air-pulse system. Furthermore, we integrated this focused air-pulse system with phase-sensitive optical coherence tomography (PhS-OCT) to make non-contact measurements of tissue elasticity. The PhS-OCT system is used to assess the group velocity of SW propagation, which can be used to determine Young’s modulus. Pilot experiments were performed on gelatin phantoms with different concentrations (10%, 12% and 14% w/w). The results demonstrate the feasibility of using this focused air-pulse system combined with PhS-OCT to estimate tissue elasticity. This easily controlled non-contact technique is potentially useful to study the biomechanical properties of ocular and other tissues in vivo.

Assessing mechanical properties of tissue phantoms with non-contact optical coherence elastography and Michelson interferometric vibrometry

“…A home-built focused air-pulse delivery system [14] induced elastic waves in tissue-mimicking agar phantoms of various concentrations (1%, 1.5%, 2%, w/w, n=3 for each concentration) The elastic waves were then detected by the LMIV and PhS-SSOCE systems, separately. The air-pulse delivery system employed an air gate and a control unit to provide a short duration (~800 µs) focused air-pulse to the sample surface, and the control unit enabled synchronization of the air-pulse with the OCE and LMIV systems.…”

“…All of these methods combine an imaging technique with external loading, such as mechanical compression [11], acoustic radiation force [12], pulsed laser [13], or focused air-pulse [14]. The imaging modalities measure the tissue response to the excitation, and these measurements can then characterize the biomechanical properties of tissue through the use of appropriate mechanical models.…”

Noncontact depth-resolved micro-scale optical coherence elastography of the cornea

“…The custom-designed focused air-puff system [53] relies on an air gate and a control unit to provide a short-duration air stream with ~0.8 ms FWHM (Gaussian shape). The delivery of the air puff is through a port with flat tip and ~0.15 mm inner diameter.…”

Noncontact quantitative biomechanical characterization of cardiac muscle using shear wave imaging optical coherence tomography

“…1(a). The home-built air-puff device provides a short-duration (Gaussian shape, 0.8 ms FWHM), low-pressure air stream on the sample surface with an excitation pressure that can be controlled and estimated based on the loading parameters [38]. The phase-sensitive OCT system employs a Titanium:Sapphire laser source (Micra-5, Coherent, Inc.) with the central wavelength of ~808 nm and the bandwidth of ~110 nm.…”