The mechanical properties of biological tissues are increasingly recognized as crucial parts of signaling cascades involved in developmental and pathological processes. Most existing mechanical measurement techniques require either highly invasive sample preparations and destruction of the tissue for access, such as atomic force microscope, or provide insufficient spatial resolution, such as sonoelastography and magnetic resonance elastography. The optical elastography is an emerging field in biomedicine, which allows to capture an image of the elasticity module with subcellular resolution. We present as a promising method a quantitative micro-elastography based on Brillouin scattering, which is the inelastic scattering of photons by acoustic phonons with gigahertz frequency. Using a virtually imaged phased array (VIPA) based spectrometer and a confocal microscope a label-free, three-dimensional, non-intrusive micro-elastography with the absence of extrinsic mechanical loading is provided. In this paper, we present a systematic application of Brillouin micro-elastography to quantify physical properties of native larval zebrafish tissues in vivo. We detected a transiently decreasing Brillouin frequency shift after spinal cord injury. The presented work constitutes the first step towards an in vivo assessment of spinal cord tissue mechanics during regeneration, provides a basis to identify key determinants of mechanical tissue properties and allows to test their importance in combination with biochemical and genetic factors.
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