This study demonstrates the successful translation of NIR angiography with the FLARE™ imaging system for use in microsurgical perforator-flap breast reconstruction. The design of our optical imaging system incorporated the ergonomic needs for use by surgeons in the operating room environment. The system is portable and completely self-contained; it can easily be transferred into the operating room and deployed rapidly. The ability to visualize the operative field simultaneously with NIR fluorescence is particularly advantageous. As the reconstructive surgeon is able to recall stored video and images, the findings can be correlated with surgical findings without any distortion.
NIR fluorescence imaging has the potential to find widespread use in plastic and reconstructive surgery, as well as general and oncologic surgery. It provides real-time guidance for tumor resection,19
, rapid identification of sentinel lymph nodes,9
real-time avoidance of critical structures, such as nerves and blood vessels,20
and quantitation of tissue metrics.15
By altering the intravenous dose of the fluorophore ICG we determined that 4 mg of ICG per injection had the highest observed CBR for clinical NIR angiography, although a larger study with more statistical power will be needed to better define the optimal dose. In addition, at a time interval of ≈ 20 min between injections, 4 mg resulted in significantly less residual background fluorescence intensity compared to 6 mg. Use of a higher dose would require a longer time interval, i.e., a longer clearance period, between doses to avoid dose stacking. It should be noted that even with repeat dosing at 6 mg, the total dose (24 mg) was below the standard package size (25 mg).
The use of a real-time, intraoperative imaging system is particularly advantageous in microsurgical perforator flap reconstruction in order to provide a dynamic assessment of flap perfusion. In this study, we performed four assessments: both sides of the abdominal flap prior to elevation, the selected abdominal flap after isolation on the perforators prior to transfer, and the same flap after microsurgery. This permitted a comparison of perforator vessel selection and identification, analysis of flap perfusion after isolation on the perforating vessels, and differences after flap harvest and microsurgical transfer. Flap physiology changes with vessel isolation, harvest, and transfer, so that obtaining real-time NIR imaging at multiple points becomes a dynamic process. This is in contrast to preoperative imaging modalities such as duplex ultrasound, CT, or MRI, where identification of the dominant perforator is a static one-time assessment. In the future, we plan to use NIR imaging to assist directly in vessel selection and isolation, as well as to apply quantitative metrics previously validated in large animal model systems,15
to determine arterial or venous insufficiency.
In two cases, the dominant perforator identified by NIR imaging was not the perforator selected by the operating surgeon. This occurred as the surgeon was blinded to the results of the FLARE™ system. Of note, the CBR at the dominant perforator decreased after ligation, and the CBR at the selected perforator increased to the previous level of the dominant perforator (). This further demonstrates that flap physiology is often altered during surgery and the results will differ from preoperative imaging. The changes in flap physiology from perforator vessel isolation can only be seen with a real-time, intraoperative system.
The early clinical use of NIR imaging has been described previously.21-29
The imaging systems used in these studies were limited to a handheld camcorder device. These systems provide subjective, qualitative results with low resolution. In addition, the outputs from previous generation devices were single grayscale images. As these systems used laser-induced fluorescence, the ICG dose was also higher at 0.5 mg/kg,29
so that an average 70-kg patient would require a 35-mg dose.
Newer commercially available NIR imaging systems, such as the SPY system (Novadaq Technologies Inc., Toronto, Canada), have been used recently in reconstructive surgery.30,31
These early clinical experiences mirror the results seen in our study. There are major differences between the two imaging systems, however. The SPY system is laser-based while the FLARE™ system is LED-based; this may pose differences in eye safety in the operating room. More importantly, the FLARE™ imaging system acquires color video and NIR fluorescence images simultaneously and is capable of real-time overlay of the invisible NIR light images onto the color video images. This provides the surgeon with unambiguous surgical landmarks for image-guided surgery. The FLARE™ system also has the ability to quantify perforator perfusion metrics, as previously shown by our laboratory.14,15,32
The cost of parts in quantity 1 for the FLARE™ imaging system is ≈ $120,000 USD. A miniaturized version of FLARE™, termed Mini-FLARE™, costs ≈ $40,000 USD (Troyan et al., in review).
Although this is the first successful clinical pilot study with the FLARE™ system in reconstructive surgery, there are many areas that will need to be evaluated. Larger-scale studies need to be performed to assess clinical benefits. Each NIR angiography evaluation takes only two minutes, and a more effective decision-making process for perforator selection could potentially decrease overall operative times. Other benefits include the potential ability to prevent complications associated with poor perfusion. The costs associated with the additional use of this type of technology also need to be assessed. One limitation of the FLARE™ system is its 15-cm field of view: it is possible that flaps larger than this size would not be completely captured. For example, imaging was performed on each side of the abdomen, as the entire abdominal flap could not be captured with one scan. Finally, the surgeons in this study were blinded to the results of NIR imaging; in future studies we plan to have the surgeons directly apply the imaging results in perforator choice and flap design.