Application of infrared spectroscopic imaging in specular reflection mode for determination of distribution of chemical components in urinary stones

Distribution of chemical components in the mixed oxalatic, phosphatic and uratic urinary stones was analysed by means of infrared microspectroscopy. The specular reflection from the surface of the cross-sectioned stones was used for the infrared spectroscopic imaging. It was found that the reflection spectra consist from specular and diffuse reflection components and the former one exhibit Reststrahlen bands which resemble first derivative of the spectral bands in the absorption spectrum. In order to use the measured spectra for the chemical imaging they were corrected for asymmetry by subtracting the diffuse reflection component and applying Kramers–Kronig transform to the specular reflection component. The Kramers–Kronig transformed spectrum was then combined with the diffuse reflection component. Spectra corrected in this manner were used to create false-colour images of the stones. It was found that the images obtained after applying the correction procedure to the spectra differ substantially from the ones obtained from the raw spectra. They are in good agreement with the stones’ images obtained from the FT-Raman spectra.

► For the first time, chemical images of urinary stones from corrected infrared reflection spectra were formed.
► For the correction, modified procedure of Kramers–Kronig transform was performed.
► Spectral evidences of domain structure of multi-component urinary stones are presented.