Real-time, near-infrared, fluorescence-guided identification of the ureters using methylene blue

Background The aim of this study was to determine whether the invisible near-infrared (NIR) fluorescence properties of methylene blue (MB), a dye already approved by the U.S. Food and Drug Administration for other indications, could be exploited for real-time, intra-operative identification of the ureters. Methods The optical properties of MB were quantified in vitro. Open surgery and laparoscopic NIR fluorescence imaging systems were employed. Yorkshire pigs were injected intravenously with 0.1-mg/kg MB ( n = 8), 10-mg furosemide followed by 0.1-mg/kg MB ( n = 6), or 0.5-mg/kg MB ( n = 6). The contrast-to-background ratio (CBR) of the kidney and ureters, and the MB concentration in the urine, were quantified. Results Peak MB absorbance, emission, and intensity in urine occurred at 668 nm, 688 nm, and 20 μmol/L, respectively. After intravenous injection, doses as low as 0.1-mg/kg MB provided prolonged imaging of the ureters, and a dose of 0.5 mg/kg provided statistically significant improvement of CBR. The preinjection of furosemide increased urine volume but did not improve CBR. Laparoscopic identification of the ureter using MB NIR fluorescence was demonstrated. Conclusion Ureteral imaging using MB NIR fluorescence provides sensitive, real-time, intra-operative identification of the ureters during open and laparoscopic surgeries.