Microstructure of urinary stones as studied by means of multimodal nonlinear optical imaging

Tracing aetiology and pathogenesis of urinary stone disease is of great importance in order to prescribe appropriate treatment and prevent recurrences. For this purpose, morphological examination combined with determination of chemical composition of urinary stones is fundamental. In this work, we have evaluated the potential of multimodal nonlinear optical imaging for investigation of (micro)structure and chemical composition of human urinary stones. The method provides high-resolution multimodal images of the cross-sectioned stones without any labelling or some other pretreatment of the samples. We have shown that various constituents of urinary stones can be well discriminated in the multimodal images according to their optical signals. In addition, small structures (1–5 µm in size) were observed in the cross-sections of urinary stones of various types. These structures were identified as crystallites of uric acid. They could either act as an active element during formation of urinary stones or, more probably, be accidentally incorporated into their structure, as it is suggested by random distribution of the crystallites. The results of this work show that multimodal nonlinear optical imaging can provide relevant information about growth processes of urinary stones and deliver useful insights in aetiology and pathogenesis of urolithiasis.