Analysis of urinary calculi using an infrared microspectroscopic surface reXectance imaging technique

This investigation highlights the use of infrared microspectroscopy for the morphological analysis of urinary stones. The research presented here has utilized the reXectance mode of an infrared microscope for use in creating chemically speciWc maps of cross-sectioned renal calculi surfaces, precisely showing the placement of renal stone components in a calculus sample. The method has been applied to renal stones of both single and multiple components consisting primarily of hydroxyapatite, calcium oxalate monohydrate and calcium oxalate dihydrate. Factors discussed include the photometric accuracy of the spectra obtained, a comparison of the surface reXectance method with existing methods such as diVuse reXectance infrared Fourier transform spectroscopy (DRIFTS) and attenuated total internal reXection (ATR) analysis, and the inXuence of specular reXectance between polished and unpolished sample spectra. Full spectral maps of cross-sectioned renal stones provided positive localization of components using qualitatively accurate spectra similar in appearance to DRIFTS spectra. Unlike ATR and DRIFTS spectra, surface reXectance spectra lack photometric accuracy and are therefore not quantiWable; at present, however, spectra are suitable for qualitative analysis. It was found that specular reXectance increases minimally with a highly polished stone cross-section surface, though qualitative data is not aVected. Surface reXectance imaging of sections of renal stones is useful for determining the identity of stone components while simultaneously providing precise locations of mineral components within the stone using presently available