Abstract
Background and objectivesThe kidney stone’s structure might provide clinical information in addition to the stone composition. The Raman chemical imaging is a technology used for the production of two-dimension maps of the constituents' distribution in samples. We aimed at determining the use of Raman chemical imaging in urinary stone analysis.Material and methodsFourteen calculi were analyzed by Raman chemical imaging using a confocal Raman microspectrophotometer. They were selected according to their heterogeneous composition and morphology. Raman chemical imaging 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.ResultsRaman chemical imaging succeeded in identifying almost all the chemical components of each sample, including monohydrate and dihydrate calcium oxalate, anhydrous and dihydrate uric acid, apatite, struvite, brushite, and rare chemicals like whitlockite, ammonium urate and drugs. 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. Moreover, Raman chemical imaging provided the distribution of components within the stones: nuclei were accurately identified, as well as thin layers of other components. Conversion of dihydrate to monohydrate calcium oxalate was correctly observed in the centre of one sample. The calcium oxalate monohydrate had different Raman spectra according to its localization.ConclusionRaman chemical imaging showed a good accuracy in comparison with infrared spectroscopy in identifying components of kidney stones. 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, making it more suitable for research studies rather than routine analysis.
Highlights
Urolithiasis is a spreading condition in developed countries, with an increasing prevalence from 5% to 8% between 1994 and 2010 [1,2]
Raman chemical imaging provided the distribution of components within the stones: nuclei were accurately identified, as well as thin layers of other components
The calcium oxalate monohydrate had different Raman spectra according to its localization
Summary
Urolithiasis is a spreading condition in developed countries, with an increasing prevalence from 5% to 8% between 1994 and 2010 [1,2]. Complications and highly active genetic urolithiasis can lead to chronic kidney disease [6]. Overall, acquired factors like diet, pathologies or even medication, together with inherited factors as sex, age, urologic malformation and genetics, have been associated to different stone compositions [8,9]. In some specific and acute nephrolithiasis like cystinuria and adenine phosphoribosyltransferase deficiency, stone analysis is often the fastest and most reliable way to diagnosis [10,11]. This is why stone analysis is mandatory for every recurrent stone-formers [12,13]. We aimed at determining the use of Raman chemical imaging in urinary stone analysis
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