Advances in surgical techniques, combined with a greater knowledge of prostate anatomy, have enabled improved cancer control and functional outcomes . During radical prostatectomy, lack of identification of anatomical landmarks may potentially have an adverse impact on oncologic results and result in a higher risk of erectile dysfunction (ED). For example, identification of the artery in the neurovascular bundle (NVB) is important for nerve-sparing .
To enhance real-time visualisation of structures during surgery, the new technique of optical imaging using near-infrared (700–900 nm) fluorescence (NIRF) was developed. Advantages of NIRF include high tissue penetration (depth of millimetres to centimetres) and low autofluorescence, thereby providing a good contrast . The da Vinci Xi® Surgical System (Intuitive Surgical, Sunnydale, CA, USA) has a built-in NIRF visualisation system (Firefly®, Novadaq Technologies, Missisauga, ON, Canada) that can detect indocyanine green (ICG) dye in real-time. This fluorescent molecule binds rapidly and almost completely to serum proteins  and is carried by albumin in blood. Protein binding reduces aggregation, increases brightness (i.e. quantum yield) by over threefold, and increases the effective hydrodynamic diameter to that of the bound proteins [4, 5]. ICG is associated with favourable characteristics such as confinement to the vascular compartment by binding to plasma proteins, fast and almost exclusive excretion into the bile, and very low toxicity [4, 6]. Intravenously-delivered ICG may be used to identify vessel perfusion and differentiate tissue density [7, 8]. In plasma, ICG has an absorption peak around 807 nm and an emission peak around 822 nm, which is within the NIRF window. Incident infrared (IR) light at a wavelength of 780 nm provokes detectable photon emission at 820–830 nm . The IR laser from the illuminator causes the ICG to fluoresce, which is picked up by the endoscope signal detector (IR camera) and relayed to the console, where the surgeon visualises vessels containing the albumin-bound ICG as green, fluorescent structures. After intravenous administration, ICG has a short blood half-life (150–180 s) and is cleared exclusively by the liver . The safety profile of ICG is favourable when used at the standard dose for diagnostic procedures (between 0.1 and 0.5 mg/kg). Above 0.5 mg/kg, the incidence of immediate allergic reactions increases . The adverse event rate reported with ICG is 0.34%, including nausea, vomiting, and rarely shock (1 in 300,000 patients) .
The use of ICG with an NIRF imaging system (Akorn, Lake Forest, IL) has been described as an adjunct during robot-assisted partial nephrectomy, to help identify the renal artery and parenchymal perfusion ; this has become a consolidated technology to visualise edge lesions in laparoscopic, robot-assisted, nephron-sparing surgery . Moreover, ICG-NIRF is used for endoscopic marking of colorectal tumours and intraoperative identification of certain solid tumours after intravenous injection [14, 15]. It may also be used during prostatectomy to visualise sentinel prostatic drainage because of the ability of ICG to mark the target prostate tissue with limited diffusion, acting as a lymphangiography agent .
We aimed to assess the value of ICG-NIRF in identifying the NVB, visualising vascularisation and haemostasis, and improving the preservation of ED in laparoscopic robot-assisted radical prostatectomy (RARP). Our primary outcome was the safety and feasibility of ICG-NIRF, while secondary outcomes included functional erectile dysfunction over 9 months, the proportion of bilateral NVBs identified, and ICG-related complications.