Abstract
.Dynamic elastography is an attractive method to evaluate tissue biomechanical properties. Recently, it was extended from US- and MR-based modalities to optical ones, such as optical coherence tomography for three-dimensional (3-D) imaging of propagating mechanical waves in subsurface regions of soft tissues, such as the eye. The measured group velocity is often used to convert wave speed maps into 3-D images of the elastic modulus distribution based on the assumption of bulk shear waves. However, the specific geometry of OCE measurements in bounded materials such as the cornea and skin calls into question elasticity reconstruction assuming a simple relationship between group velocity and shear modulus. We show that in layered media the bulk shear wave assumption results in highly underestimated shear modulus reconstructions and significant structural artifacts in modulus images. We urge the OCE community to be careful in using the group velocity to evaluate tissue elasticity and to focus on developing robust reconstruction methods to accurately reconstruct images of the shear elastic modulus in bounded media.
Highlights
Mapping tissue mechanical properties, or elastography, has become an important medical imaging modality
Both load types can provide valuable information on tissue mechanical properties, dynamic elastography has a distinct advantage because quantitative elastic modulus maps can be obtained from local mechanical wave speed estimates for a wide range of practical operating conditions.[5,6]
We first explore the effects of intrinsic and extrinsic parameters on group/phase velocity measurements and their relation to elasticity maps
Summary
Elastography, has become an important medical imaging modality. High-resolution optical coherence tomography (OCT) systems have been used for elastography with both static[4] and dynamic[5,6] loads. Both load types can provide valuable information on tissue mechanical properties, dynamic elastography has a distinct advantage because quantitative elastic modulus maps can be obtained from local mechanical wave speed estimates for a wide range of practical operating conditions.[5,6] Due to the very high line rates of spectral-domain (tens of kHz5–9) and swept-source OCT (a few MHz10–13), dynamic elastography can operate at sub-mm spatial resolution using pulsed, temporally compact mechanical waves. Dynamic optical coherence elastography (OCE) can acquire snapshots of shear wave temporal profiles in soft tissues propagating with speed many times smaller (a few m/s typically) than the speed of sound
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