Hyperspectral imaging

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Hyperspectral imaging in biophysics and energy physics

Scattering effects have been considered as a major obstacle for the interpretation and further use of the infrared spectra and hyperspectral infrared images of cells and tissues. A major problem in the infrared spectroscopy and hyperspectral infrared spectroscopy of cells is so-called Mie type scattering. Mie scattering is strong when the wavelength of the infrared light is in the same range as the sizes of the cells, i.e. in the infrared range. Mie scattering leads to strong and broad oscillations in the complete infrared range. In addition, when passing absorption bands, fluctuations of the real refractive index lead to additions dispersion effects. The broad oscillations and the dispersion effects near absorption bands are described by the Mie theory. The research of the ISP project has contributed to resolve several questions related to the understanding, modelling and correction of Mie type scattering in infrared spectroscopy of single cells. 

Hyperspectral imaging

Research Council of Norway

NFR ISPNATTEK
Project No: 216687
Period covered - start date: 01/10/2012
Period covered - end date: 05/01/2016
Project Administrator: Achim Kohler

The project group has developed a theory that describes analytically the Mie scattering for infrared microscopes with high numerical apertures as used in the infrared microspectroscopy of cells and tissues. The obtained analytical understanding of the problem has been used to develop a method for correcting Mie type scattering in infrared spectroscopy of single cells. The correction of Mie type scattering in spectra of single cells is an important prerequisite for the interpretation of the chemical absorbance bands in the spectra.

When modelling Mie scattering in infrared spectra of cells, the refractive index of the biological material is an unknown parameter. The group has developed two approaches for estimating the refractive index of the biological material: The primary approach is used for the modelling of Mie-type scattering described above and gives a very rough estimate. The second approach is based on so-called ripples that appear primarily in the higher frequency range of the infrared region in the scattering of light at spherical particles with sizes of some microns. The ripples are directly related to electric and magnetic modes and allow a high-precision estimation of the refractive index. This is an important finding, since it allows to estimate the refractive index in the infrared for all materials that can be investigated as microspheres by infrared spectroscopy. For most materials, the refractive index in the infrared is unknown.

A scattering phenome that appears frequently in infrared spectroscopy and hyperspectral imaging of tissues are the so-called fringes. Fringes are interference effects that appear due to internal reflections in the material. They are present in many applications of infrared spectroscopy and hyperspectral imaging such as infrared microspectroscopy of biological tissues or life cell imaging. During the project, the group developed a method based on extended multiplicative signal correction for the correction of fringes in tissue spectra and images. 

 

Literature:

Konevskikh T., Lukacs R., Kohler A. 
An improved algorithm for fast resonant Mie scatter correction of infrared spectra of cells and tissues
Journal of Biophotonics 11 (2018) DOI: 10.1002/jbio.201600307

Published 10. June 2016 - 15:12 - Updated 28. May 2019 - 13:52