Real-time, non-contact, non-invasive imaging of elasticity properties in soft tissues using the combination of light and air-coupled ultrasound

Abstract

A new non-contact method for efficient, non-invasive imaging of elasticity in soft media is presented. It uses transient mechanical waves excited in the object under study from air (i.e., non-contact) using either ultra-violet (UV) pulsed laser radiation (photoacoustic) or air-coupled focused ultrasound (US) and resultant displacements detected a high frame rate, phase-sensitive (PhS)-OCT system. UV laser radiation is absorbed in a thin subsurface region of the tissue creating transient mechanical waves due to thermal expansion, whereas the air-coupled focused US beam reflected from the air/medium interface provides acoustic radiation force (ARF) to the medium surface, launching a transient mechanical wave in the transverse (lateral) direction. Real time tracking/imaging of resultant mechanical wave propagation can be used to reconstruct tissue elastic properties. Tissue mimicking phantoms, porcine eyes, and skin were used in ex-vivoexperiments to prove the concept. Results of these experiments strongly suggest that simple, non-contact excitation holds great promise for non-invasive characterization of soft media, in general, and for elasticity measurements in delicate soft tissues and organs (e.g., in the eye), in particular.