Performance evaluation of different implementations of the Lagrangian speckle model estimator for non-invasive vascular ultrasound elastography.

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Bibliographic Details
Title:	Performance evaluation of different implementations of the Lagrangian speckle model estimator for non-invasive vascular ultrasound elastography.
Authors:	Mercure, Elizabeth¹, Cloutier, Guy², Schmitt, Cédric³, Maurice, Roch L.²
Source:	Medical Physics. Jul2008, Vol. 35 Issue 7, p3116-3126. 11p. 1 Color Photograph, 1 Diagram, 1 Chart, 3 Graphs.
Subjects:	Medical imaging systems, Arteries, Blood vessels, Preventive medicine, Medical sciences
Abstract:	Non-invasive vascular ultrasound elastography (NIVE) was recently introduced to characterize mechanical properties of carotid arteries for stroke prevention. Using the Lagrangian speckle model estimator (LSME), the four components of the 2D deformation matrix (Δ), which are the axial strain (Δyy) and shear (Δyx) and the lateral strain (Δxx) and shear (Δxy), can be computed. This paper overviews four different implementations of the LSME and addresses their reliability. These implementations include two unconstrained (L&M and L&M+) and one constrained (ITERc) iterative algorithms, and one optical flow-based (OF-based) algorithm. The theoretical frameworks were supported by biomechanical simulations of a pathology-free vessel wall and by one single layer vessel-mimicking phantom study. Regarding simulations, the four LSME implementations provided similar biases on axial motion parameters, except the L&M that outperformed other methods with a minimum strain bias of -3%. LSME axial motion estimates showed good consistence with theory, namely the OF-based algorithm that in a specific instance estimated Δyy with no relative error on the standard deviation. With regards to lateral motion parameters, ITERc exhibited a minimum strain bias of -8.5% when ultrasound beam and motion mostly run parallel, whereas L&M performs strain and shear estimates with less than 23% bias independently of orientations. The in vitro vessel phantom data showed LSME Δyy and Δyx maps that were qualitatively equivalent to theory, and noisy Δxx and Δxy elastograms. In summary, the authors propose to promote the OF-based LSME as an optimal choice for further applications of NIVE, because of its reliability to compute both axial strain and shear motion parameters and because it outperformed the other implementations by a factor of 30 or more in terms of processing time. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	Non-invasive vascular ultrasound elastography (NIVE) was recently introduced to characterize mechanical properties of carotid arteries for stroke prevention. Using the Lagrangian speckle model estimator (LSME), the four components of the 2D deformation matrix (Δ), which are the axial strain (Δyy) and shear (Δyx) and the lateral strain (Δxx) and shear (Δxy), can be computed. This paper overviews four different implementations of the LSME and addresses their reliability. These implementations include two unconstrained (L&M and L&M+) and one constrained (ITERc) iterative algorithms, and one optical flow-based (OF-based) algorithm. The theoretical frameworks were supported by biomechanical simulations of a pathology-free vessel wall and by one single layer vessel-mimicking phantom study. Regarding simulations, the four LSME implementations provided similar biases on axial motion parameters, except the L&M that outperformed other methods with a minimum strain bias of -3%. LSME axial motion estimates showed good consistence with theory, namely the OF-based algorithm that in a specific instance estimated Δyy with no relative error on the standard deviation. With regards to lateral motion parameters, ITERc exhibited a minimum strain bias of -8.5% when ultrasound beam and motion mostly run parallel, whereas L&M performs strain and shear estimates with less than 23% bias independently of orientations. The in vitro vessel phantom data showed LSME Δyy and Δyx maps that were qualitatively equivalent to theory, and noisy Δxx and Δxy elastograms. In summary, the authors propose to promote the OF-based LSME as an optimal choice for further applications of NIVE, because of its reliability to compute both axial strain and shear motion parameters and because it outperformed the other implementations by a factor of 30 or more in terms of processing time. [ABSTRACT FROM AUTHOR]
ISSN:	00942405
DOI:	10.1118/1.2936771