Rapid imaging of tissue mechanical properties

Mechanical properties, such as stiffness, promise to provide new biomarkers and diagnostic indicators for underlying disease of biological organisms, from cells to organs. However, existing technology is invasive and/or too slow to provide mechanical information of large samples at high resolution. A new optical configuration that speeds up the acquisition by ~100 times is described below.

HFSP Young Investigator Grant holder Giuliano Scarcelli and colleagues
authored on Mon, 05 December 2016

Researchers have realized the crucial role of mechanical properties on the functioning of biological organisms for a long time, but research in this field has been hampered by the lack of measurement methods. Specifically, most technologies to probe material mechanical properties need physical contact with the sample under test so they are usually invasive, only measure the sample surface, and generally provide an average estimation of the bulk mechanical properties, without spatial resolution.

In the past decade, an all-optical technique named Brillouin microscopy was developed to overcome these limitations via non-contact and non-invasive light-scattering measurements. Brillouin scattering arises from the interaction of light and sound waves within a medium, and thus depends upon the elastic properties of the medium. Therefore, by measuring the frequency shift caused by the scattering, Brillouin spectroscopy can quantify the longitudinal modulus of the material. The technique has been recently demonstrated to be very powerful: at tissue level, it is in clinical trials for monitoring ocular tissue mechanics, at the cell level, it can map intracellular and extracellular mechanical properties in 3D. However, traditional Brillouin microscopy can measure only one point of the sample at a time. This results in long acquisition times for mechanical imaging of large areas.

To speed up the acquisition of Brillouin microscopy, a research group led by Scarcelli from the University of Maryland at College Park, USA devised a novel configuration that can measure hundreds of points in a sample simultaneously using line-scanning parallel detection of scattering spectra. With this setup, they pushed forward the equivalent acquisition time of less than 1 ms per sample point, two orders of magnitude shorter than any previous protocols of Brillouin microscopy. As a demonstration, this novel configuration effectively shortens the acquisition time of two-dimensional Brillouin imaging of a 1.1mm-by-1.5mm sample from hours to 30 seconds, thus making it a powerful technology for label-free mechanical characterization of biological samples.

Reference

Line-scanning Brillouin microscopy for rapid non-invasive mechanical imaging, J. Zhang, A. Fiore, S.-H. Yun, H. Kim and G. Scarcelli. Sci. Rep. 6, 35398 (2016). doi: 10.1038/srep35398.

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