From supersonic shear wave imaging to full-field optical coherence shear wave elastography

Abstract

Elasticity maps of tissue have proved to be particularly useful in providing complementary contrast to ultrasonic imaging, e.g., for cancer diagnosis at the millimeter scale. Optical coherence tomography (OCT) offers an endogenous contrast based on singly backscattered optical waves. Adding complementary contrast to OCT images by recording elasticity maps could also be valuable in improving OCT-based diagnosis at the microscopic scale. Static elastography has been successfully coupled with full-field OCT (FF-OCT) in order to realize both micrometer-scale sectioning and elasticity maps. Nevertheless, static elastography presents a number of drawbacks, mainly when stiffness quantification is required. Here, we describe the combination of two methods: transient elastography, based on speed measurements of shear waves induced by ultrasonic radiation forces, and FF-OCT, an en face OCT approach using an incoherent light source. The use of an ultrafast ultrasonic scanner and an ultrafast camera working at 10,000 to 30,000 images/s made it possible to follow shear wave propagation with both modalities. As expected, FF-OCT is found to be much more sensitive than ultrafast ultrasound to tiny shear vibrations (a few nanometers and micrometers, respectively). Stiffness assessed in gel phantoms and an ex vivo rat brain by FF-OCT is found to be in good agreement with ultrasound shear wave elastography.

Non-contact single shot elastography using line field low coherence holography

“…However, there was an intrinsic trade-off between the temporal and transverse spatial resolutions, which constrained the dynamic range of the elasticity measurements. Nahas et al proposed a full-field OCT system free of transverse mechanical scanning to monitor acoustically generated Scholte wave propagation on the surface of an ex vivo rat brain [13]. However, the limited field of view of a few hundred microns and the slow readout time of the two-dimensional camera limited the maximum detectable elastic wave speed.…”

Optical coherence tomography today: speed, contrast, and multimodality

“…3). OCT contrast enhancement (prerequisite 3) has been accomplished by introducing polarization-sensitive OCT, [24][25][26][27][28] phasesensitive OCT, [29][30][31][32][33] optical coherence elastography, [34][35][36][37][38][39] spectroscopic low coherence interferometry, [40][41][42][43] elastic scattering spectroscopy, 31,[44][45][46] and nonlinear interferometric vibrational imaging (NIVI), as well as employing endogenous or exogenous contrast. [47][48][49][50][51][52] In this paper, a recently developed contrast improvement for OCT, named label-free optical angiography, is reviewed (cf.…”

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

“…Whilst the transverse spatial resolution can be increased to 10s of μm via postprocessing of multiple temporal scans acquired at different spatial locations with multiple mechanical stimulations [103,180], it intrinsically increases the acquisition time to several seconds or longer. Improving both the temporal and the transverse spatial resolutions are absolutely required in future clinically oriented OCE developments, which is a fast evolving area of research [182][183][184][185]. We note in passing that axial (depth) resolution of shear wavebased OCE methods is limited, in theory, to the OCT axial resolution (typically on the order of 7-15 μm), but the practical limits have yet to be comprehensively investigated.…”