deletions | additions       diff --git a/Material_methods.tex b/Material_methods.tex  index 02cc301..c40376e 100644  --- a/Material_methods.tex  +++ b/Material_methods.tex 
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Main tested sample was a 4x8x8 cm$^3$ water-based tissue-mimicking phantom made with 5\% polyvinyl alcohol (PVA), 0.1\% graphite powder and 5\% NaCl, giving a theoretical electrical conductivity of 7.5 S.m$^{-1}$. Three freezing/thawing cycles were applied to stiffen the material \cite{fromageau2007estimation}. The graphite powder (\#282863 product, Sigma-Aldrich, Saint-Louis, MO, USA) was made of submillimeter particles, which presented a speckle pattern on ultrasound images. The sample was placed in a rigid plastic box of 2 mm thick layers with an opening on a side to introduce the ultrasound probe. The rigid box simulated a solid interface such as a skull and ensure also that any observed movement was not due to surrounding displacement of air. Alternatively, we used a similar phantom made of 5\% PVA, 0.1\% graphite powder and 2\% NaCl, giving a theoretical electrical conductivity of 3.5 S.m$^{-1}$. A biological tissue sample was also tested. This tissue was a chicken breast sample bought in local grocery of approximately 3x5x5 cm$^3$. It was degassed in a 20$^o$C saline water (0.9\% NaCl) during two hours prior to the experiment.  Each sample was observed with a 5 MHz ultrasonic probe made of 128 elements (ATL L7-4, Philips, Amsterdam, Netherlands) coupled to a Verasonics scanner (Verasonics V-1, Redmond, WA, USA). The probe was in contact with the sample with an ultrasound coupling gel but was fixed on a third independent support. It was used in ultrafast mode \cite{bercoff2004supersonic}, to acquire 1000 frames per second using plane waves and Stolt's fk migration algorithm \cite{garcia2013stolt}. The Z component of the displacement in the sample was observed by performing cross-correlations between radiofrequency images with a speckle-tracking technique technique, using 64x3 pixels$^2$ cross-correlation windows  \cite{montagnon2012real}. Noise was partly reduced using a low-pass frequency filter. Time $t$ = 0 ms was defined as the electrical burst emission. Great care was taken to ensure that the three supports were not in contact and fixed separately. It could ensure that any vibration of one of the element could not be transmitted to the medium.