2012 Proceedings - International Tissue Elasticity Conference

038 DYNAMIC SHEAR ELASTICITY PROPERTIES OF BLOOD COAGULATION ASSESSED BY
SHEAR WAVE IMAGING AND CLASSIC RHEOLOGY.
Miguel Bernal 1 , Jean–Luc Gennisson 1 , Mathias Fink 1 , Patrice Flaud 2 , Mickael Tanter 1 .
1 Institut Langevin – Ondes et Images, ESPCI ParisTech, CNRS UMR7587, INSERM U979, 1 rue
Jussieu, 75005 Paris, FRANCE; 2 Matière et Systèmes Complexes, CNRS UMR7057, Université
Paris VII Denis Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, FRANCE.
Background: Millions of people worldwide are affected by deep venous thrombosis (DVT) every year.
Pulmonary embolism, a dangerous complication, affects about 30 to 50% of these patients [1]. This
happens when the thrombus breaks off from veins and blocks the pulmonary arteries. The diagnosis and
treatment of DVT usually depends on the risk of breakage and stability of the clots. The stability has been
related to the age and elasticity of the blood clots [2,3].
Aims: This work describes the use of the Supersonic shear wave imaging (SSI) technique in the study of
dynamic shear elasticity properties of blood coagulation. We compared the results from this technique
with classical rheology studies.
Methods: Blood was collected from pigs and anticoagulated using ethylenediaminetetraacetic acid
(EDTA). Coagulation was initiated using calcium ions. Ultrasound radiation force was used to
generate shear waves with 100μs tone bursts of 8MHz at 3 different locations in the lateral direction.
The shear wave displacements were measured by ultrafast imaging at a repetition rate of 2kHz. Using
a time–of–flight algorithm, shear wave speed (Vs) was recovered giving access to the shear elasticity (μ)
according to μ=ρVs2. Using a Haake Mars II classical rheology (between 0.2 and 25Hz) was done
simultaneously on the same blood sample. Three different types of experiments were done: dual systems
(70 minutes), ultrasound alone (2 hours) and a multi–day experiment (ultrasound alone).
Results: SSI allowed the visualization of two dimensional (2D) maps of elasticity at every time point. The
spatial shear elasticity of aregion of interest (ROI) in the sample varied with time, from a minimum of
67.4±8.7Pa at coagulation (about 5 minutes) to a maximum of 2168.4±326.8 at 91 minutes. It decreased
to 753.5±138.8Pa after 18 hours, 763.1±107.1 after 24 hours and to 708.3±117.41 after 96 hours. In the
dual experiments, using G’ (conservation modulus) and G” (loss modulus) values from the rheology
experiments, we calculated the phase velocities at 25Hz. The values at coagulation and minute 70 were
0.54±0.02m/s and 0.63±0.01m/s, respectively. While the values from the SSI experiments for the
mean phase velocities (50–350Hz) increased from 0.46±0.12m/s at coagulation to 0.76±0.01m/s at
the same time points. Syneresis phenomenon (expulsion of free water from the clot) was visible in the
2 hour B–mode experiment at the bottom of the sample. This affected the shear elasticity and created two
regions in the blood clot. The mean phase velocity values were similar for the two regions at coagulation,
0.56±0.01 and 0.54±0.1m/s, respectively, but differed with time. At minute 15 (beginning of syneresis
viewed by B–mode), the velocities were 0.85±0.04 for the syneresis region and 0.90±0.01m/s for no
syneresis. At minute 120, they were 0.83±0.09 and 1.06±0.06m/s, respectively. The spatial median shear
values for two ROI’s in the two regions of the 2D maps at minute 120 were 748.5±145.1 and
1477.9±465.7Pa.
Conclusions: The phase velocity values obtained with the SSI technique showed good agreement with
those calculated from the classical rheology experiments. SSI proved to be useful mapping the elasticity of
clots in 2D at multiple time points. It allowed the quantification of the mechanical properties of the thrombi
and their heterogeneities, illustrated by the dynamic mapping of syneresis region appearance showing that
this technique has potential use in predicting thrombi breakage. Future studies include in vivo experiments
in small animals and quantifying the viscosity in order to try to estimate thrombus age.
References:
[1] J. Hirsh and J. Hoak: Management of Deep Vein Thrombosis and Pulmonary Embolism. A Statement for
Healthcare Professionals. Council on Thrombosis (in consultation with the Council on Cardiovascular Radiology),
American Heart Association. Circulation, Vol. 93, No. 12, pp. 2212–45, Jun 1996.
[2] S. Y. Emelianov et al.: Triplex Ultrasound: Elasticity Imaging to Age Deep Venous Thrombosis. Ultrasound in
Medicine and Biology, Vol. 28, No. 6, pp. 757–767, 2002.
[3] H. Xie et al.: Correspondence of Ultrasound Elasticity Imaging to Direct Mechanical Measurement in Aging DVT
in Rats. Ultrasound in Medicine and Biology, Vol. 31, No. 10, pp. 1351–9, Oct 2005.
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