Abstract :
[en] Background: The structure of kidney stones might provide clinical useful information in addition to the stone composition. The Raman chemical imaging (RCI) is a new technology used for the production of two-dimensions maps of the constituents' distribution in samples. We aimed at determining the use of RCI in urinary stone analysis.
Methods: Twelve calculi were analyzed by RCI using a confocal Raman microspectrophotometer. They were selected according to their heterogeneous composition and morphology. Prior to the analysis, samples were sliced and milled in order to detect the nucleus of the stones and having a smooth surface. RCI was performed on the whole section of stones. Once acquired, the data were baseline corrected and analyzed by MCR-ALS. Results were then compared to the spectra obtained by Fourier Transform Infrared spectroscopy, the gold standard method for the determination of urolithiasis composition.
Results: RCI succeeded in identifying all the chemical components contained in each sample, including monohydrate and dihydrate calcium oxalate, anhydrous and dihydrate uric acid, apatite, struvite, brushite, whitlockite and ammonium urate. However, proteins couldn't be detected because of the huge autofluorescence background and the small concentration of these poor Raman scatterers. Carbapatite and calcium oxalate were correctly detected even
when they represented less than 5 percent of the whole stones, allowing the detection of very small structures like Randall's plaques. Moreover, RCI provided the distribution of components within the stones. The nuclei were accurately identified, as well as thin layers of other components. Conversion of dihydrate to monohydrate calcium oxalate was correctly observed in the center of one sample.
Conclusion: RCI showed a good accuracy in comparison with infrared spectroscopy in identifying components of kidney stones. In addition, RCI is nondestructive enabling the storage of samples. This analysis was also useful in determining the organization of components within stones, which help locating constituents in low quantity, such as nuclei. However, this analysis is time-consuming, which makes it more suitable for research studies rather than routine analysis.
