Intraoperative Near Infrared Fluorescence Guided Identification of the Ureters Using Low Dose Methylene Blue: A First in Human Experience

Purpose: Near infrared fluorescence imaging is a promising technique that offers real-time visual information during surgery. In this study we report the first clinical results to our knowledge of ureteral imaging using near infrared fluorescence after a simple peripheral infusion of methylene blue. Furthermore, we assessed the optimal timing and dose of methylene blue. Materials and Methods: A total of 12 patients who underwent lower abdominal surgery were included in this prospective feasibility study. Near infrared fluorescence imaging was performed using the Mini-FLARE T imaging system. To determine optimal timing and dose, methylene blue was injected intravenously at doses of 0.25, 0.5 or 1 mg/kg after exposure of the ureters. Imaging was performed for up to 60 minutes after injection. Results: In all patients both ureters could be clearly visualized within 10 minutes after infusion of methylene blue. The signal lasted at least up to 60 minutes after injection. The mean signal-to-background ratio of the ureter was 2.27 +/- 1.22 (4), 2.61 +/- 1.88 (4) and 3.58 +/- 3.36 (4) for the 0.25, 0.5 and 1 mg/kg groups, respectively. A mixed model analysis was used to compare signal-to-background ratios among dose groups and times, and to assess the relationship between dose and time. A significant difference among time points (p < 0.001) was found. However, no difference was observed among dose groups (p = 0.811). Conclusions: This study demonstrates the first successful use of near infrared fluorescence using low dose methylene blue for the identification of the ureters during lower abdominal surgery.