Experimental Evaluation of Human Kidney Stone Spectra for Intraoperative Stone-Tissue-Instrument Analysis Using Autofluorescence.

The precision and safety of laser lithotripsy in the upper urinary tract is solely controlled by the surgeon. To our knowledge 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. We evaluated the technical, medical and physical conditions for real-time analysis using fluorescence for future development of a new laser for lithotripsy. We collected data on the fluorescence spectra of 82 native human calculi covering the 8 most relevant subtypes compared to the spectra of endoscope components, the organic porcine urinary tract and pure samples of urinary stone compositions. Data analysis was performed to determine differences in sample signal intensities and emission wavelengths. 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 a factor of 75. The weakest signal of stone material was 3.6-fold larger than the strongest signal of pig kidney tissue (mean ± SD 0.038 ± 0.043 vs 0.00058 ± 0.00058 arbitrary units). No fluorescence signal was observed for endoscope components. Fluorescence amplitude and spectral curve form were found to be unrelated to stone type. Our study provides essential information on the spectral differentiation of tissue, urinary stones and relevant endoscope components. The measurements indicate that differentiation by fluorescence is possible for all relevant stone types.