Automated analysis of urinary stone composition using Raman spectroscopy: pilot study for the development of a...

We evaluate a compact portable system for immediate automated postoperative ex vivo analysis of urinary stone composition using Raman spectroscopy. Analysis of urinary stone composition provides essential information for the treatment and metaphylaxis of urolithiasis. Currently infrared spectroscopy and x-ray diffraction are used for urinary stone analysis. However, these methods may require complex sample preparation and costly laboratory equipment. In contrast, Raman spectrometers could be a simple and quick strategy for immediate stone analysis.

Pure samples of 9 stone components and 159 human urinary calculi were analyzed by Raman spectroscopy using a microscope coupled system at 2 excitation wavelengths. Signal-to-noise ratio, peak positions and the distinctness of the acquired Raman spectra were analyzed and compared. Background fluorescence was removed mathematically. Corrected Raman spectra were used as a reference library for automated classification of native human urinary stones (50). The results were then compared to standard infrared spectroscopy.

Signal-to-noise ratio was superior at an excitation wavelength of 532 nm. An automated, computer based classifier was capable of matching spectra from patient samples with those of pure stone components. Consecutive analysis of 50 human stones demonstrated 100% sensitivity and specificity compared to infrared spectroscopy (for components with more than 25% of total composition).

Our pilot study indicates that Raman spectroscopy is a valid and reliable technique for determining urinary stone composition. Thus, we propose that the development of a compact and portable system based on Raman spectroscopy for immediate, postoperative stone analysis could represent an invaluable tool for the metaphylaxis of urolithiasis.