Experimental evaluation of human kidney stone spectra for intraoperative stone-tissue-instrument analysis using autofluorescence

Objectives Precision and safety of laser lithotripsy in the upper urinary tract is solely controlled by the surgeon. Laser systems with integrated real-time analysis of target tissues are not available. An intelligent laser system with automated target differentiation and laser feedback control would provide tremendous improvement in patient safety and surgical precision. This study evaluated technical, medical and physical conditions for real-time analysis using fluorescence for future development of a new laser for lithotripsy. Material & Methods Fluorescence spectra of native human calculi (n=82) covering the 8 most relevant subtypes were collected in comparison to spectra of endoscope components, organic porcine urinary tract, and pure samples of urinary stone compositions. Data analysis was performed in terms of the samples' differences in signal intensity and emission wavelengths. Results All native stones showed a significant fluorescence signal compared to porcine urinary tract tissue or endoscope components. The amplitude of the fluorescence signal varied by factor 75, the weakest signal of stone material (0,038 +/- 0,043 arb. u.) was 3,6-fold larger than the strongest signal of pig kidney tissue (0,00058 +/- 0,00058 arb. u.). No fluorescence signal was observed for endoscope components. Fluorescence amplitude and spectral curve form was found to be unrelated to the stone type. Conclusions Our study provides essential information on the spectral differentiation of tissue, urinary stones, and relevant endoscope components. The measurements indicate that differentiation using fluorescence is possible for all relevant stone types.