Pol Grasland-Mongrain edited The_sample_was_then.tex  over 8 years ago

Commit id: 2f4ff1c0e6a150b8f13ec4bfe1b404c3d0b60eab

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The sample was then replace replaced  by another phantom. This phantom was a  similar phantom  except that graphite cellulose  particles were replaced by cellulose particles, in order to maintain a comparable speckle pattern with used instead of graphite particles: thus, the phantom presented  a weak optical absorption. absorption but a comparable speckle pattern.  A black disk of variable diameter was painted on a surface of the phantom at the laser beam impact location, to control the absorption area. The amplitude of the induced shear waves versus black disk diameter in the second phantom is illustrated in Fig. \ref{Figure4}-(B). We observe a linear relationship between shear wave amplitude and black disk diameter, with a correlation coefficient of 0.9281.% The resulting shear waves have same propagation pattern as in the first phantom, meaning that most of the energy was absorbed in the first hundreds of micrometers (thickness of the black paint) in both cases. Two other parameters have been investigated, and showed no correlation: (1) correlation coefficient between shear wave wavelength and diameter of the black paint is 0.27, and between shear wave speed and diameter is 0.089. These results were expected, as shear wave wavelength depends primarily on thermal conductivity value of the medium, and shear wave speed on shear modulus of the medium, which were constant parameters in these experiments.  These results indicate that the main occurring phenomenon using a 532 nm, 10 ns, 200 mJ pulse laser on a black soft solid is mostly the ablative regime, without formation of plasma.  The potential application of these results on a biological tissue was finally studied. The medium phantom  was replaced by a chicken breast sample bought in the local grocery. Due to the absence of absorbing material like melanin or haemoglobin, the laser was diffused in a large area with a very small increase of temperature to and couldn't  induce shear elastic  waves. A Accordingly, a  5 mm diameter black disk was painted on the surface of the sample at the laser beam impact location. Displacement amplitude maps along Y axis and Z axis 5, 6, 7, 8 and 9 ms after laser emission in the biological tissue are illustrated in Figure \ref{Figure5}. Shear waves propagated at a velocity of 4$\pm$1 m.s$^{-1}$. It corresponds to a shear modulus of 16$\pm$8 kPa, which is a typical value for a relaxed muscle tissue (typically between 1 and 100 kPa). kPa \cite{10385964}).  The pattern is moreover very similar to the one presented in Figure \ref{Figure2}, suggesting that involved phenomena are probably similar.