deletions | additions       diff --git a/Discussions.tex b/Discussions.tex  index 01b7f91..ab04826 100644  --- a/Discussions.tex  +++ b/Discussions.tex 
...
For elastography measurements, Muthupillai et al. assumed that a displacement of a few hundreds of nanometers should be sufficient to perform shear wave elastography \cite{7569924}. However, displacements of the order of the micrometer is usually required, which is higher than the displacement observed at 10 mJ (thermoelastic regime) and about the same order of magnitude at 200 mJ (ablative regime). The minimum energy of our laser (532 nm, 10 ns, 10 mJ, 5 mm diameter) used in our experiments to get a shear wave is still 2.5 times above the maximum exposure permissible as given by the current American National Standard Institute (Z136.1-2000) for skin \cite{ANSIZ1361}, a value which is also used in typical photoacoustic imaging experiments with 532 nm Q-switch Nd:YAG lasers \cite{Ku_2005}. This value is also a few hundred times lower than the typical energy used for skin tatoo removal, which use same type of lasers \cite{8352621}.  Generation of shear waves by laser also has the advantage of being non-contact and totally remote. For example, Li et al. have proposed to induce surface acoustic waves by laser to measure elastic properties of biological thin layers like skin or cornea \cite{li2011elastic}, \cite{li2014laser}. Moreover, a laser probe can be made extremely small (smaller than 100 $\mu$m diameter if required), especially if optical fibres are employed, for example for insertion in small vessels. Additionally, the shear wave source emits very weak electromagnetic noise (apart from the laser device itself), so it can be quite convenient for magnetic resonance elastography measurements, which are currently using external drivers or non-magnetic ultrasound probes. Moreover, the laser probe could help to shape precisely the shear wave shape, with focusing capabilities for example (see for example \cite{noroy1993laser}).  In summary, this study presented observation of elastic shear waves generated in soft tissues using a laser beam. The involved phenomenons were investigated and we distinguished thermoelastic and ablative regimes. Experiments in chicken breast sample showed the feasibility of the elastography method using a laser beam as a shear wave source.  The authors would like to thank Damien Garcia for lending the laser device and Simon Bernard for his help in Matlab coding. Pol Grasland-Mongrain received a CRSNG post-doctoral grant. The authors declare no conflict of interest in the work presented here.