Autofluorescence of Renal Tissue and Its Impact on Fluorescence-Guided Lithotripsy

When illuminated with green light, tissue shows negligible autofluorescence in comparison to urinary stones. In automatically controlled lithotripsy, this property is utilized to prevent the laser from being triggered if the fiber is mispositioned: the fluorescence signal is compared to a set threshold before each pulse. However, previous studies have shown that tissue damage cannot be completely ruled out. We are investigating this phenomenon and its impact on fluorescence guidance. An experiment with porcine calyx (with the automatic control switched off) shows that single Ho:YAG laser pulses are sufficient to coagulate tissue, resulting in an increase in autofluorescence. During lithotripsy of fluorescent artificial stones embedded in renal cortex, thermal damage occurs despite automatic laser control. Maximum fluorescence values measured on those tissue places were above the control's set threshold for laser emission. Therefore, an increase in autofluorescence in the event of denaturation must be considered when using automatically controlled lithotripsy.