Due to the improvement of health awareness and the increasing number of spiral chest CT examinations, the detection rate of intrapulmonary subcentimeter nodules is continuously increasing . However, the wide use of thoracoscopic surgery leads to increasing difficulties in localizing pulmonary nodules by the conventional method of tactile sense. With the development of minimally invasive concepts, uniportal thoracoscopic surgery represents a new frontier for minimally invasive thoracic surgery [7, 8]. Given this basis, the new generation of thoracic surgeons are eager to further reduce surgical time and trauma, thereby providing better healthcare for patients. Thus, a more precise and effective localization method for uniportal endoscopic surgery is urgently needed . Over time, different localization techniques, including the hookwire and microcoil methods, have been proposed, inevitably leading to complications such as dislodgement, systemic air embolism, pulmonary hemorrhage, and pain [10, 11, 12]. Colored dyes, including methylene blue, can easily contaminate operative areas and affect surgical exposure, and because of their small molecular weight, these dyes can easily diffuse, leading to incorrect intraoperative identification or excessive resection of nodules [13, 14].
The near-infrared dye ICG has been widely used in many fields. The Chinese Experts’ Consensus of Preoperative-assisted Localization of Pulmonary Nodules (2019 version) recommends localization methods using liquid materials, including ICG, as a 2A-level technique . Rho J et al  found that an optimal emulsion of 10% ICG and 90% lipiodol mixed through 90 passages exhibited an even distribution and the highest signal intensity under fluorescence microscopy and that all emulsion types injected were well localized around the target nodules without any side effects or procedure-related complications. Chao Zhan et al  performed preoperative ICG localization for lung lobectomy in 11 patients, and the localization failed in 2 patients due to unclear fluorescent signals. They also found that for segmentectomy, ICG fluorescence was visible at 14 seconds after peripheral intravenous administration. They concluded that ICG fluorescence imaging could facilitate a precise segmentectomy and reduce the surgical time and trauma. Further studies demonstrated that near-infrared fluorescence imaging could safely identify lung tumors after systemic injection of ICG; in addition, low-dose ICG was adequate for near-infrared fluorescence imaging of lung tumors. However, as passive accumulation of ICG cannot be used to distinguish between tumors and inflammation, targeted fluorescent agents should be developed to address this problem .
This study showed that the optimal imaging effect was obtained when 0.4–0.5 ml of ICG (25 mg/ml) was administered at a needle depth of 1 cm. If the dose was too large or the needle depth was too shallow, ICG overflow could occur. An injection volume of less than 3 ml may not be sufficient for localization. If the injection is performed too quickly, ICG overflow may occur. In this study, 2 cases of ICG overflow were separately caused by an excessive dose and rapid injection. One case of localization failure was caused by an inadequate dose (no ICG reached the lung). The surgical time in the cases with localization failure was obviously prolonged. No patients had allergic reactions. Three patients reported pain after puncture. Complications such as pneumothorax and hemothorax did not occur.
We conclude that ICG imaging is a safe and effective technique for pulmonary nodule localization. Because of the short study time, small sample size, and lack of controls in this study, further observations and randomized controlled clinical trials should be conducted in the future. With the widespread application of near-infrared imaging devices, fluorescent imaging localization will become more widely used in thoracic surgery. Due to the continuous development of uniportal thoracoscopic surgical techniques, the combination of these two methods is expected to provide greater benefits for patients.