Spatial resolution in dynamic optical coherence elastography

Abstract

Dynamic optical coherence elastography (OCE) tracks elastic wave propagation speed within tissue, enabling quantitative three-dimensional imaging of the elastic modulus. We show that propagating mechanical waves are mode converted at interfaces, creating a finite region on the order of an acoustic wavelength where there is not a simple one-to-one correspondence between wave speed and elastic modulus. Depending on the details of a boundary's geometry and elasticity contrast, highly complex propagating fields produced near the boundary can substantially affect both the spatial resolution and contrast of the elasticity image. We demonstrate boundary effects on Rayleigh waves incident on a vertical boundary between media of different shear moduli. Lateral resolution is defined by the width of the transition zone between two media and is the limit at which a physical inclusion can be detected with full contrast. We experimentally demonstrate results using a spectraldomain OCT system on tissue-mimicking phantoms, which are replicated using numerical simulations. It is shown that the spatial resolution in dynamic OCE is determined by the temporal and spatial characteristics (i.e., bandwidth and spatial pulse width) of the propagating mechanical wave. Thus, mechanical resolution in dynamic OCE inherently differs from the optical resolution of the OCT imaging system.

Nearly-incompressible transverse isotropy (NITI) of cornea elasticity: model and experiments with acoustic micro-tapping OCE

“…In the phantom experiment, the spatial push width was approximately 600 µm due to its tilt angle relative to the sample 22 . Due to corneal geometry, the axial focus in the porcine experiment was closer to the theoretically measured axial width of 420 µm 53 .…”

“…The axial particle vibration velocity of propagating mechanical waves was detected using a phase-sensitive frequency-domain OCT (PhS-OCT) system, which has been described in a previous study 53 , 67 – 69 . The M-B mode PhS-OCT system includes a broadband super-luminescent diode with a 1,310 nm center wavelength and 86 nm spectral BW (Denselight Ltd., Singapore), a 90/10 beam splitter, a stationary reference arm, a sample arm integrated with a set of galvo-scanners, and a high-speed spectrometer.…”

Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus

“…A train of 8 cycles of an 800 Hz sinusoidal signal was output by a function generator (DG4062; Rigol Technologies, Beijing, China), amplified by a miniature piezo amplifier (PDu100B; PiezoDrive), and delivered to the piezoelectric transducer for the generation of mechanical waves in the tissue. An excitation frequency of 800 Hz was chosen to achieve enough mechanical resolution to distinguish elasticity gradients along the surface of the sample according to Kirby et al 13 The mechanical resolution in this study refers to the accuracy of the imaging method in detecting speed changes along space. Even though higher frequencies are desired to improve the mechanical resolution, 13 they produced stronger wave attenuation impeding the elastography of the complete cornea-limbus-sclera section.…”

“…Optical coherence elastography (OCE) is an established field that allows for quantitative viscoelastic characterization of tissues with the micrometer-scale resolution. 13 – 16 In particular, wave-based OCE, which leverages the propagation of mechanical waves for imaging mechanical contrast of soft tissues, has proven to be a useful technique for noninvasive elastography of the eye in a wide variety of applications. 17 However, OCE of the eye has been mostly concentrated on the central cornea.…”

Detection of disbonds in adhesively bonded aluminum plates using laser-generated shear acoustic waves

“…was used to fit the amplitude profiles [ 36 ]. The resolution was obtained using the full width at half amplitude of the derived C(x) profile, as illustrated in Fig.…”