The elasticity mapping of individual layers in the cornea using non-destructive elastography techniques advances diagnosis and monitoring of ocular diseases and treatments in ophthalmology. However, transient Lamb waves, currently used in most dynamic optical coherence and ultrasound elastography techniques, diminish the translation of wave speed into shear/Young’s modulus. Here, we present reverberant 3D optical coherence elastography (Rev3D-OCE), a novel approach leveraging the physical properties of diffuse fields in detecting elasticity gradients not only in the lateral direction, but also along the depth axis of the cornea. A Monte Carlo analysis, finite element simulations, and experiments in layered phantoms are conducted to validate the technique and to characterize the axial elastography resolution. Experiments in ex vivo porcine cornea at different intraocular pressures reveal that Rev3D-OCE enables the elastic characterization of single layers that matches the anatomical description of corneal layers with unprecedented contrast in the dynamic OCE field.

We study the properties of pulsed solutions to the scalar and vector wave equations composed of plane-waves with equal longitudinal spatial frequency. This condition guarantees that, at all times, the field profile is invariant in the longitudinal direction. Particular emphasis is placed on solutions with rotational symmetry. For these solutions, the wave concentrates strongly near the axis at a given time. We provide closed-form expressions for some of these fields, and show that their wavefronts are approximately spherical. Solutions carrying orbital and spin angular momenta are also considered.

From the development of x-ray imaging in the late 19th century, the field of medical imaging developed an impressive array of modalities. These can measure and image a variety of physical parameters from absorption coefficients to spin–spin relaxations. However, throughout most of the 20th century, the intrinsic biomechanical properties of tissues remained hidden from conventional radiology. This changed around 1990 when it was demonstrated that medical ultrasound systems with their fast pulse repetition rate and high sensitivity to motion could create images related to the stiffness of tissues and their shear wave properties. From there, vigorous development efforts towards imaging the elastic properties of tissues were launched across different modalities. These progressed from the research phase, through implementation on clinical scanners, through extensive clinical trials of selected diagnostic tasks, to government approvals, payer approvals, international standards statements, and into routine clinical practice around the globe. This review covers highlights of some major topics of the technical and clinical developments over the last 30 years with brief pointers to some of the remaining issues for the next decade of development.

A rising wave of technologies and instruments are enabling more labs and clinics to make a variety of measurements related to tissue viscoelastic properties. These instruments include elastography imaging scanners, rheological shear viscometers, and a variety of calibrated stress–strain analyzers. From these many sources of disparate data, a common step in analyzing results is to fit the measurements of tissue response to some viscoelastic model. In the best scenario, this places the measurements within a theoretical framework and enables meaningful comparisons of the parameters against other types of tissues. However, there is a large set of established rheological models, even within the class of linear, causal, viscoelastic solid models, so which of these should be chosen? Is it simply a matter of best fit to a minimum mean squared error of the model to several data points? We argue that the long history of biomechanics, including the concept of the extended relaxation spectrum, along with data collected from viscoelastic soft tissues over an extended range of times and frequencies, and the theoretical framework of multiple relaxation models which model the multi-scale nature of physical tissues, all lead to the conclusion that fractional derivative models represent the most succinct and meaningful models of soft tissue viscoelastic behavior. These arguments are presented with the goal of clarifying some distinctions between, and consequences of, some of the most commonly used models, and with the longer term goal of reaching a consensus among different sub-fields in acoustics, biomechanics, and elastography that have common interests in comparing tissue measurements.