Improved urethral fluorescence during low rectal surgery: a new dye and a new method.

BACKGROUND: The aim of this study was to demonstrate highlighting of the urethra during surgery through the use of two different methods: a new near-infrared fluorophore IRDye800BK, and indocyanine green (ICG) mixed with silicone. METHODS: Male cadavers from the department of anatomy at the University of Oxford were used to visualise the urethra during near-infrared fluorescence excitation. To assess IRDye800BK, a perineal incision was utilised after infiltrating the urethra directly with an IRDye800BK solution mixed with Instillagel. ICG-silicone was assessed when the urethra was purposely exposed as part of a simulated transanal total mesorectal dissection. ICG was previously mixed with ethanol and silicone and left to set in a Foley catheter. Fluorescence was visualised using an in-house manufactured fluorescence-enabled laparoscopic system. RESULTS: IRDye800BK demonstrated excellent penetration and visualisation of the urethra under fluorescence at an estimated tissue depth of 2 cm. An ICG-silicone catheter demonstrated excellent fluorescence without leaving any residual solution behind in the urethra after its removal. CONCLUSIONS: The newly described ICG-silicone method opens up the possibility of new technologies in this area of fluorescence guided surgery. IRDye800BK is a promising alternative to ICG in visualising the urethra using fluorescence imaging. Its greater depth of penetration may allow earlier detection of the urethra during surgery and prevent wrong plane surgery sooner.