2012 Proceedings - International Tissue Elasticity Conference

016 HYPER–FREQUENCY VISCOELASTIC SPECTROSCOPY OF A VASCULAR–MIMICKING
PHANTOM AND A PORCINE AORTA WITH THE RHEOSPECTRIS INSTRUMENT.
Cédric Schmitt 1 , Anis Hadj Henni 1 , Simon LeFloc’h 2 , Jacques Ohayon 2 , Jonathan Vappou 3 , Guy Cloutier 4 .
1 Rheolution Inc., Montréal, Québec, CANADA; 2 Laboratory TIMC–IMAG/DyCTiM, Université
Joseph Fourier, Grenoble, FRANCE; 3 IMFS (FRE3240) / LSIIT (UMR 7005) CNRS – University of
Strasbourg, Strasbourg, FRANCE; 4 Laboratory of Biorheology and Medical Ultrasonics, University
of Montréal Hospital Research Center (CRCHUM), Montréal, Québec, CANADA.
Background: Vascular elastography based on dynamic stress of arterial walls at frequencies typically up
to 1500Hz is increasingly developed to monitor the mechanical properties of healthy and pathological
vessels. However, available mechanical testing instruments can only measure viscoelastic properties up
to 200Hz. Recently, a new instrument, RheoSpectrisTM (Rheolution Inc., Canada), has been introduced to
perform viscoelastic spectroscopy of biomaterials between 10 and 1000Hz [1]. Thus, there is a great
interest for using such an instrument to characterize vascular phantoms and tissues.
Aims: The first objective was to measure the Young’s storage (E’) and loss (E’’) moduli of a vascular
phantom material and a porcine aorta from 10 to 1000Hz with the hyper–frequency viscoelastic
spectroscope RheoSpectrisTM C400 using a new beam geometry. The second objective was to compare, on
phantom material, the viscoelasticity measurements with those obtained with DMA instruments.
Methods: A standard silicone rubber (Platsil 71–10 silicone, Polytek Development Corp., USA) was first
characterized using RheoSpectrisTM between 10 and 1000Hz with the bending modality (beam samples).
For comparison, cylinders and plates made from the same material were tested using two DMA
instruments: the Electroforce 3200 (Bose Corp, USA) using the compression modality and the Eplexor
25N (GABO, Germany) using the compression and tensile modalities. Finally, beam–shaped samples
(n=4) of a healthy porcine abdominal aorta were explanted and tested with RheoSpectrisTM .
Results: Both E’ and E’’ obtained with the DMA instruments and RheoSpectrisTM (Figure 1a ) between 10
and 100Hz and the corresponding coefficients of variation (Table 1) are within the same order of
magnitude. E’ and E” evolutions at high frequencies indicate a continuous increase of E’’ up to 1000Hz.
The low elastic dispersion of the silicone material is also noticeable even at high frequencies. The
viscoelastic spectroscopy of fresh beam–shaped specimens (Figures 1b and c) shows a frequency
dependence of E’ (20% increase between 50–800Hz) and of less importance, of E’’. This behavior is
important for developments in elastography to avoid biased estimations of mechanical parameters.
E’ and E’’ variability
E’ (%) E’’ (%)
GABO Comp. 5.7 6.6
GABO Tensile 6.2 43.5
Electroforce 3.7 3.6
Rheospectris 12.6 23.6
Table 1: Mean measurement
variability of the silicone
sample between
10–100Hz of E’ and E’’
for the GABO, the
Electroforce and
RheoSpectris TM.
Figure 1: (a) Mean storage (E’) and loss (E’’) moduli of a silicone material
measured by two DMA instruments (Gabo and Electroforce) between
10 and 100Hz, and by the RheoSpectris TM C400 spectroscope between
10 and 1000Hz. (b) Pictures of a fresh porcine aorta specimen used to
prepare samples tested by RheoSpectris TM C400. (c) Mean E’ and E’’ of
the aorta wall samples obtained by RheoSpectris TM C400 between 50
and 780Hz. The mean variabilities are equal to 12.9% and 48.3% for
E’ and E’’, respectively.
Conclusions: The use of beam geometry with the RheoSpectrisTM instrument has been validated by
comparing measurements with those of classical DMA instruments. The same geometry served to
successfully characterize the viscoelastic behavior of an artery at high frequencies. These results exhibit
an important viscoelastic dispersive effect that may impact in vivo quantitative elastographic scanning of
arteries with classical methods measuring group velocities over a given frequency bandwidth.
Acknowledgment: Funding was provided by a strategic grant of the Natural Sciences and Engineering Research
Council of Canada (#STPGP–381136–09).
References:
[1] Hadj Henni, A., et al.: Hyper–Frequency Viscoelastic Spectroscopy of Biomaterials. J. Mech. Behav. Biom. Mater.,
Vol. 4, pp. 1115–1122, 2011.
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