Despite remarkable advances in surgical techniques over the last few decades, regional imbalances have grown dramatically, particularly in developing countries and remote rural areas. The implementation of surgical telementoring is critical and imperative to meet the increasing demand for surgery in these areas and to provide safe, timely, and affordable surgical opportunities for the region’s residents. According to the different display methods, the current remote surgical navigation instruments can be generally divided into monitor display and augmented reality display. Although the former has the advantages of convenience and low cost, it requires the surgeon to constantly switch the focus of vision between the surgical area and the monitor, which is distracting and time-consuming and may also result in surgical errors due to position matching errors. Although the latter can reduce surgical technical errors and shifts in visual focus, the weight, field of view, ergonomic design, and battery life must still be improved. Furthermore, the target surgical area is prone to large soft tissue deformation in most surgeries, and accurate integration of the virtual scene with the surgical display scene requires real-time 3D reconstruction of the complex surgical environment, which significantly reduces the reliability of augmented reality guidance. To overcome the limitations of current surgical telementoring devices in terms of display intuitiveness, interactive efficiency, and resistance of guidance marks to tissue deformation and displacement, we developed a coaxial vision photochromic marking system and a biocompatible photochromic film to retain remote surgical guidance marks directly on the patient’s skin.
In this study, we used solvent volatilization to create a photochromic film from spiropyran, a biocompatible photochromic material, and poly(lactic-co-glycolic acid), an FDA-approved film-forming material. When the film was exposed to ultraviolet (UV) light at 200-400 nm, the spiropyran molecule isomerized and transformd into the highly colored merocyanine. Taking advantage of this photochromic property, we proposed a technique for visualizing surgical guidance, that is, producing photochromic marks by precisely controlling the UV laser to scan the mark on the film. So, we created a surgical telementoring system (the CV-PM system) based on coaxial visual photochromic marking, which includes a 360 nm continuous UV laser, a color complementary metal-oxide semiconductor camera, and a two-dimensional laser galvanometer, and a beam splitter. We designed the coaxial optical path to match the camera field of view with the scanning area of the laser galvanometer. The remote specialist could view the surgical scene captured by the local CV-PM system, draw surgical guide marks, and drive the CV-PM system to complete the photochromic mark scan. The local trainee could perform the surgery while directly observing the guidance marks. We designed experiments to test the film’s extreme discoloration performance, determined the system’s laser parameters, and verified the fading performance of the photochromic marks. We devised a skin phantom experiment to quantify and compare the benefits of using this system to draw surgical guide marks versus viewing a display. Finally, we designed a nevus excision surgery on ex-vivo pig skin to validate the CV-PM system’s feasibility.
The performance experiment shows that the CV-PM system can scan 160 mm long marks in 7 s if the maximum permissible exposure requirements are met. Furthermore, within 20 min, all lengths of marks can retain the visible color difference that can be seen with the naked eye (Fig. 5). The skin phantom experiment demonstrates that using the CV-PM system has obvious advantages over viewing a display to draw surgical guide marks in terms of marking accuracy [intersection over union (IoU)], operation time, and the number of sight switches. Additionally, the mean value of IoU between the marks scanned by the CV-PM system and the expert drawn marks in this experiment is up to 0.93±0.02, and the mean value of operating time is 5.4 s±0.9 s (Fig. 6). The surgery of nevus excision on porcine skin ex-vivo tissue provides strong support for the system’s application to surgical telementoring (Fig. 7).
This surgical telementoring visualization technology provides an efficient, accurate, safe, and intuitive telemedicine display solution, addressing many of the shortcomings of current screen-displayed telementoring devices, such as poor intuitiveness, limited interaction, low efficiency, and poor timeliness of guidance information due to tissue deformation and displacement. The design of the CV-PM system and the preparation of the photochromic film have fully considered the biosafety requirements, which makes this technology have the prospect of being widely used in clinical applications. Furthermore, the system is appropriate for emergency rescue and surgical teaching seminars, and it is extremely important in promoting the development of telemedicine, realizing the sharing of high-quality medical resources, and resolving the problem of unbalanced medical resources.
