Shear Wave Induced Resonance Elastography of Venous Thrombi: A Proof-of-Concept

Shear wave induced resonance elastography (SWIRE) is proposed for deep venous thrombosis (DVT) elasticity assessment. This new imaging technique takes advantage of properly polarized shear waves to induce resonance of a confined mechanical heterogeneity. Realistic phantoms
$(n = 9)$
of DVT total and partial clot occlusions with elasticities from 406 to 3561 Pa were built for in vitro experiments. An ex vivo study was also performed to evaluate the elasticity of two fresh porcine venous thrombi in a pig model. Transient shear waves at 45–205 Hz were generated by the vibration of a rigid plate (plane wavefront) or by a needle to simulate a radiation pressure on a line segment (cylindrical wavefront). Induced propagation of shear waves was imaged with an ultrafast ultrasound scanner and a finite element method was developed to simulate tested experimental conditions. An inverse problem was then formulated considering the first resonance frequency of the DVT inclusion. Elasticity agreements between SWIRE and a reference spectroscopy instrument (RheoSpectris) were found in vitro for total clots either in plane
$({\rm r}^{2} = 0.989)$
or cylindrical
$({\rm r}^{2} = 0.986)$
wavefront configurations. For total and partial clots, elasticity estimation errors were
$9.0 \pm 4.6\%$
and
$9.3 \pm 11.3\%$
, respectively. Ex vivo, the blood clot elasticity was
$498 \pm 58~{\rm Pa}$
within the inferior vena cava and
$436 \pm 45~{\rm Pa}$
in the right common iliac vein
$(p = 0.22)$
. To conclude, the SWIRE technique seems feasible to quantitatively assess blood clot elasticity in the context of DVT ultrasound imaging.