Optical coherence elastography (OCE), as the use of OCT to perform elastography has come to be known, began in 1998, around ten years after the rest of the field of elastography – the use of imaging to deduce mechanical properties of tissues. After a slow start, the maturation of OCT technology in the early to mid 2000s has underpinned a recent acceleration in the field. With more than 20 papers published in 2015, and more than 25 in 2016, OCE is growing fast, but still small compared to the companion fields of cell mechanics research methods, and medical elastography. In this review, we describe the early developments in OCE, and the factors that led to the current acceleration. Much of our attention is on the key recent advances, with a strong emphasis on future prospects, which are exceptionally bright.

Optical coherence elastography – OCT at work in tissue biomechanics [Invited]

This tutorial-review introduces the fundamentals of polarized light interaction with biological tissues and presents some of the recent key polarization optical methods that have made possible the quantitative studies essential for biomedical diagnostics. Tissue structures and the corresponding models showing linear and circular birefringence, dichroism, and chirality are analyzed. As the basis for a quantitative description of the interaction of polarized light with tissues, the theory of polarization transfer in a random medium is used. This theory employs the modified transfer equation for Stokes parameters to predict the polarization properties of single- and multiple-scattered optical fields. The near-order of scatterers in tissues is accounted for to provide an adequate description of tissue polarization properties. Biomedical diagnostic techniques based on polarized light detection, including polarization imaging and spectroscopy, amplitude and intensity light scattering matrix measurements, and polarization-sensitive optical coherence tomography are described. Examples of biomedical applications of these techniques for early diagnostics of cataracts, detection of precancer, and prediction of skin disease are presented. The substantial reduction of light scattering multiplicity at tissue optical clearing that leads to a lesser influence of scattering on the measured intrinsic polarization properties of the tissue and allows for more precise quantification of these properties is demonstrated.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-21/issue-7/071114/Polarized-light-interaction-with-tissues/10.1117/1.JBO.21.7.071114.pdf

Polarized light interaction with tissues

Optical elastography, the use of optics to characterize and map the mechanical properties of biological tissue, involves measuring the deformation of tissue in response to a load. Such measurements may be used to form an image of a mechanical property, often elastic modulus, with the resulting mechanical contrast complementary to the more familiar optical contrast. Optical elastography is experiencing new impetus in response to developments in the closely related fields of cell mechanics and medical imaging, aided by advances in photonics technology, and through probing the microscale between that of cells and whole tissues. Two techniques — optical coherence elastography and Brillouin microscopy — have recently shown particular promise for medical applications, such as in ophthalmology and oncology, and as new techniques in cell mechanics.

The emergence of optical elastography in biomedicine

Cell-matrix Mechanical Interaction in Electrospun Polymeric Scaffolds for Tissue Engineering: Implications for Scaffold Design and Performance

Quantitative mapping of deformation and elasticity in optical coherence tomography has attracted much attention of researchers during the last two decades. However, despite intense effort it took ~15 years to demonstrate optical coherence elastography (OCE) as a practically useful technique. Similarly to medical ultrasound, where elastography was first realized using the quasi-static compression principle and later shear-wave-based systems were developed, in OCE these two approaches also developed in parallel. However, although the compression OCE (C-OCE) was proposed historically earlier in the seminal paper by J. Schmitt in 1998, breakthroughs in quantitative mapping of genuine local strains and the Young's modulus in C-OCE have been reported only recently and have not yet obtained sufficient attention in reviews. In this overview, we focus on underlying principles of C-OCE; discuss various practical challenges in its realization and present examples of biomedical applications of C-OCE. The figure demonstrates OCE-visualization of complex transient strains in a corneal sample heated by an infrared laser beam.

Strain and elasticity imaging in compression optical coherence elastography: The two‐decade perspective and recent advances

Visualizing stiffness within the local tissue environment at the cellular and subcellular level promises to provide insight into the genesis and progression of disease. In this Letter, we propose ultrahigh-resolution optical coherence elastography (UHROCE), and demonstrate 3D imaging of local axial strain of tissues undergoing compressive loading. We combine optical coherence microscopy (OCM) and phase-sensitive detection of local tissue displacement to produce strain elastograms with resolution (x,y,z) of 2×2×15  μm. We demonstrate this performance on a freshly excised mouse aorta and reveal the mechanical heterogeneity of vascular smooth muscle cells and elastin sheets, otherwise unresolved in a typical, lower resolution optical coherence elastography (OCE) system.

/pdf/ultrahigh-resolution-optical-coherence-elastography-1fuu1r1vb2.pdf

Ultrahigh-resolution optical coherence elastography

Visualizing stiffness within the local tissue environment at the cellular and sub-cellular level promises to provide insight
into the genesis and progression of disease. In this paper, we propose ultrahigh-resolution optical coherence
elastography, and demonstrate three-dimensional imaging of local axial strain of tissues undergoing compressive
loading. The technique employs a dual-arm extended focus optical coherence microscope to measure tissue displacement
under compression. The system uses a broad bandwidth supercontinuum source for ultrahigh axial resolution, Bessel
beam illumination and Gaussian beam detection, maintaining sub-2 μm transverse resolution over nearly 100 μm depth
of field, and spectral-domain detection allowing high displacement sensitivity. The system produces strain elastograms
with a record resolution (x,y,z) of 2×2×15 μm. We benchmark the advances in terms of resolution and strain sensitivity
by imaging a suitable inclusion phantom. We also demonstrate this performance on freshly excised mouse aorta and
reveal the mechanical heterogeneity of vascular smooth muscle cells and elastin sheets, otherwise unresolved in a
typical, lower resolution optical coherence elastography system.

Alexander Fritz

Papers

Ultrahigh-resolution optical coherence elastography

Ultrahigh resolution optical coherence elastography using a Bessel beam for extended depth of field