High resolution imaged laser speckle strain gauge for vascular applications

Abstract

An imaged laser speckle strain gauge that yields strain rates directly is described for vascular applications. The strain gauge does not rely upon cross correlations between a reference image and subsequent strain-modulated images as most current speckle interferometric methods do. Instead, it relies upon a two-dimensional frequency transform of "stacked speckle histories" which are time series of one-dimensional views of the speckle patterns arranged into a spatio-temporal array such that space is along the abscissa and time is along the ordinate. The tilt of the stacked speckle histories is related to the time rate of speckle pattern shift. The strain gauge is sensitive only to in-plane strains. Strain rates of 30.1 +/- 3.2 and 24.83 +/- 2.1 mu epsilon/s were evaluated in vitro on a fresh human tibial artery and rat inferior vena cava, respectively. The total strains measured were 21.6 and 19.86 mu epsilon, respectively. This is at least one order of magnitude more sensitive than other current soft-tissue strain measurement techniques.

OCT-based elastography for large and small deformations

“…From this real time velocity map, the instantaneous displacement, strain rate and strain maps were obtained according to Eq. (14) and Eq. (16), respectively.…”

“…Optical elastography employs optical frequency radiation to detect and image the strain response of a tissue subjected to mechanical or acoustic forces. Various implementations of optical elastography have been used to evaluate the mechanical behavior of ex vivo cortical bone [12], chicken skin [13], human and rat arteries [14], elastin [15], and porcine skin [16]. Elastographic methods have also been combined with optical coherence tomography (OCT).…”

Performance analysis of a maximum-likelihood speckle motion estimator

“…The simulated speckle patterns used herein represent data that are acquired using a laser speckle strain gauge [2,7,[8][9][10]. For this speckle strain gauge, the test specimen is sequentially illuminated through two equal, but opposite illumination angles, ±θ s , by a coherent optical source.…”

Characterization of Atherosclerotic Plaques by Laser Speckle Imaging

“…35,36 An optical method, laser strain gauge, has been described that evaluates laser speckle shifts to compute strains in arterial tissue resulting from an extrinsic applied load. 37 These techniques provide important information in that they afford the measurement of arterial response to a dynamic external loading environment, thus aiding the investigation of features contributing to plaque instability. However, measurement of plaque biomechanical properties with these approaches requires a priori knowledge of the microscopic plaque morphology and loading conditions to solve the inverse problem.…”