Large-field-of-view optical elastography using digital image correlation for biological soft tissue investigation

Nonlinear microscopy using impulsive stimulated Brillouin scattering for high-speed elastography

The impulsive stimulated Brillouin microscopy promises fast, non-contact measurements of the elastic properties of biological samples. The used pump-probe approach employs an ultra-short pulse laser and a cw laser to generate Brillouin signals. Modeling of the microscopy technique has already been carried out partially, but not for biomedical applications. The nonlinear relationship between pulse energy and Brillouin signal amplitude is proven with both simulations and experiments. Tayloring of the excitation parameters on the biologically relevant polyacrylamide hydrogels outline sub-ms temporal resolutions at a relative precision of <1%. Brillouin microscopy using the impulsive stimulated scattering therefore exhibits high potential for the measurements of viscoelastic properties of cells and tissues.

Diffraction-grating-based in situ displacement, tilt, and strain measurements on high-speed composite rotors

Polymer composite rotors offer promising perspectives in high-speed applications such as turbomachinery. However, failure modeling is a challenge due to the material's anisotropy and heterogeneity, which makes high-speed in situ deformation measurements necessary. The challenge is to maintain precision and accuracy in the environment of fast rigid-body movement. A diffraction-grating-based sensor is used for spatio-temporally resolved displacement, tilt, and strain measurements at surface velocities up to 260 m/s with statistical strain uncertainties down to $16\,\,\unicode{x00B5}{\epsilon}$. As a line camera is used, vibrations in the kHz range are measurable in principle. Due to sensor calibration and the use of a novel scan-correlation analysis approach, the rigid-body-movement-induced uncertainties are reduced significantly. The measurement of strain fluctuations on a rotating composite disc show that the crack propagation can be tracked spatially resolved and as a function of the rotational speed, which makes an in situ quantification of the damage state of the rotor possible.

Impulsive stimulated Brillouin microscopy for non-contact, fast mechanical investigations of hydrogels

The mechanical properties of tissues and cells are increasingly recognized as an important feature for the understanding of pathological processes and as a diagnostic tool in biomedicine. Impulsive stimulated Brillouin scattering (ISBS) is promising to overcome shortcomings of other measurement methods such as invasiveness, low spatial resolution and long acquisition time. In this paper, we present for the first time ISBS measurements of hydrogels, which are model materials for biological samples. We demonstrate ISBS measurements discriminating hydrogels of different stiffness. ISBS measurements with lateral resolution close to cellular level are presented. These results underline that ISBS microscopy has a high potential for biomedical applications.

Soft tissue elastography via shearing interferometry

Early detection of cancer can significantly increase the survival chances of patients. Palpation is a traditional method in order to detect cancer; however, in minimally invasive surgery the surgeon is deprived of the sense of touch. We demonstrate how shearing elastography can recover elastic parameters and furthermore can be used to localize stiffness imhomogenities even if hidden underneath the surface. Furthermore, the influence of size and depth of the stiffness imhomogenities on the detection accuracy and localization is investigated.