Image analysis applied to Brillouin images of tissue-mimicking collagen gelatins.

Noemi Correa,Francesca Palombo,Michelle Bailey,Sophie Brasselet,Simon Harding

doi:10.1364/boe.10.001329

Abstract

Brillouin spectroscopy is an emerging analytical tool in biomedical and biophysical sciences. It probes viscoelasticity through the propagation of thermally induced acoustic waves at gigahertz frequencies. Brillouin light scattering (BLS) measurements have traditionally been performed using multipass Fabry-Pérot interferometers, which have high contrast and resolution, however, as they are scanning spectrometers they often require long acquisition times in poorly scattering media. In the last decade, a new concept of Brillouin spectrometer has emerged, making use of highly angle-dispersive virtually imaged phase array (VIPA) etalons, which enable fast acquisition times for minimally turbid materials, when high contrast is not imperative. The ability to acquire Brillouin spectra rapidly, together with long term system stability, make this system a viable candidate for use in biomedical applications, especially to probe live cells and tissues. While various methods are being developed to improve system contrast and speed, little work has been published discussing the details of imaging data analysis and spectral processing. Here we present a method that we developed for the automated retrieval of Brillouin line shape parameters from imaging data sets acquired with a dual-stage VIPA Brillouin microscope. We applied this method for the first time to BLS measurements of collagen gelatin hydrogels at different hydration levels and cross-linker concentrations. This work demonstrates that it is possible to obtain the relevant information from Brillouin spectra using software for real-time high-accuracy analysis.

Highlights

Brillouin light scattering (BLS) spectroscopy is an emerging technique in biomedical sciences, biophysics and biophotonics
The method that we present here for the first time is capable of automatically analysing Brillouin images, to identify peaks and to apply fit analysis to extract the relevant parameters for viscoelastic characterization
In summary, new software was developed for virtually imaged phase array (VIPA) Brillouin image analysis to improve visualization and extraction of spectral data in real time

Summary

Introduction

Brillouin light scattering (BLS) spectroscopy is an emerging technique in biomedical sciences, biophysics and biophotonics. The actual frequency shift depends on the stiffness and the linewidth on the attenuation of the acoustic waves in the material [1,2,3] Viscoelastic materials such as biopolymers and biomaterials in general exhibit frequency-dependent mechanical responses, and their elastic moduli differ based on the spatial and temporal scale of the technique employed. In these materials, Brillouin measurements giving access to microscale mechanics yield longitudinal elastic moduli of the order of GPa [4,5], whilst traditional quasistatic mechanical testing give Young’s moduli in the MPa range [6]. Whilst this indicates that the techniques probe different forms of elastic modulus, it is apparent that measurements and molecular dynamics simulations on a nanometre scale provide Young’s moduli in the GPa range [7]

Methods

Results

Conclusion