FGS (also called “Fluorescence Guided Surgery”) is a medical imaging technique for detecting fluorescence labeled structures during surgery. It helps to provide guidance and advance imaging in real time during operation. Nowadays, FGS is widely used in minimally invasive surgery and open surgery， such as tumor imaging, lymph node mapping, liver and lung segment detection, perfusion assessment, etc. Meanwhile, FGS is more and more popular with surgeons as an innovative method of visualization, a safe and reliable method of intraoperative imaging, and an effective method of improving the surgical outcomes.
In 1852, George Gabriel Stokes discovered that Fluorite would emit blue light after exposure to ultraviolet light, he called this phenomenon “Fluorescence”, which is very common in nature. It can be owed to the active delocalized electrons in aromatic ring structures. Once light energy is absorbed by the fluorochrome’s organic molecules, the delocalized electrons would go from a ground state to a higher energy level. Upon return from excited singlet state to ground state, its energy would be emitted in the form of photons reaching the observer’s eye as fluorescence.
Since the 1960s, the feature of these substances to emit fluorescent light has been used for real-time fluorescence imaging in life sciences and medicine. One of the main methods is Indocyanine green (ICG) and Near Infrared Light (NIR) that have been used for various types of clinical applications. The inherent feature is after injection ICG would bind to the plasma proteins and lipoproteins forming ICG protein complexes, then ICG protein complexes will have a fluorescence light emission (emission peak λEM=835nm) when they are exposed to NIR excitation light (excitation peak λEX=805nm) and the penetration depth for tissue detection is around 10mm.
Meanwhile, as the research continues, people have a clear idea of metabolic pathway of ICG. When ICG is injected into bloodstream, it binds to the plasma protein immediately and runs over the whole body in 20 seconds, then it is efficiently taken up and almost completely cleared by hepatocyte (Liver) in 20 minutes, after clearance it goes with bile into bile duct system and intestinal system, finally excrete from human body. If ICG is injected into submucosa, ICG would be distributed in lymph where it binds to lipoproteins, and would be drained via lymphatic pathways and nodes gradually for several hours.
Nowadays, rely on the inherent feature of ICG to emit fluorescence light in NIR spectral range and its metabolic pathways in human tissue, the ICG and NIR fluorescence imaging via fluorescence imaging camera system have been widely used in surgical procedure that help the surgeons to have an innovative visualization, a safe and reliable method, and significant improvement of surgical outcomes.
A fluorescent dye that was used since 1959. And it’s also the first and only FDA approved NIR dye that has been used to angiographies in ophthalmology and hepatology, measure hepatic and cardiac function, nerve imaging in neurosurgical procedures.
The section of electromagnetic radiation wavelengths (760nm ~ 1500nm) is nearest to the normal visible range but it’s not visible to human eye. And it’s safe for the eyes and human body. safe for the eyes and human body.
4 CMOS ：RGB +N light channels lead to color and surgical
precision
4 CMOS Design is the innovative design in OptoMedic FloNavi Series Imaging System that can capture the Red, Green, Blue and NIR light at the same time for further processing and visualization. 4 CMOS can not only realize the true color reproduction but also produce the high contrast and adjustable sensitivity fluorescence imaging. It’s recognized as the best technology application of camera in the minimally invasive surgery and open surgery.
As we all know, the camera system is designed according to the bionics principle of human eyes, but they are not exactly the same. The differences between camera system and human eyes are on the quantity of color and the kinds of light what they can see or capture. Human can see the visible light for around 10 million colors, and the camera system can capture both the visible and invisible light, but it can’t capture so many colors.
So, when we capture the NIR light for fluorescence imaging by camera, we have to consider how to achieve the true color reproduction to get high quality image. And the answer is 4 CMOS.
Dual Camera: Dual imaging processing for higher contrast and adjustable
sensitivity
Dual Camera design is another innovative and important technology in OptoMedic FloNavi Series Imaging System that can separate the white-light (RGB) and fluorescence (NIR) signals into two groups for independent imaging processing instead of interference, losing frame rate and quality.
Sometimes, we can see the fluorescence in nature, a kind of soft glow, but only in the evening as the fluorescence is weaker than the sunlight. It’s very difficult to recognize while they are mixed.
It’s similar situation in the fluorescence guided surgery. So, the most challenge and valuable thing is to produce a clear image with both white-light and fluorescence. This means it has to separate the fluorescence and white-light signal in order to get the complete and excellent signals for both. Thus, with dual camera design and unique imaging algorithm of visualization, the surgeons will get a higher contrast and adjustable sensitivity fluorescence imaging depending on their need.
Fluorescence Visualization: Unique Imaging Algorithm for various
application
Standard FL Mode is a kind of fluorescence overlay on the white-light imaging, also it’s the most common and important image for the surgeons. So, both white-light image and fluorescence image must be brilliant and fluency in anytime.
Color Scale FL Mode is also a kind of fluorescence overlay on the white-light image, but the fluorescence image is with a color scale from yellow, green to blue which means it could show up different colors upon different concentration of ICG. It will help the surgeons to know the location of lymph nodes and blood perfusion during the surgeries.
Imaging Enhancement: More brilliant Imaging, More Accurate Surgery
With D+ Enhancement, the details of blood capillary and tissue will be more clear, the imaging will be with higher contrast, less smoke and more depth of the surgical field.
With C+ Enhancement, the color of blood capillary and tissue will be brighter, it improves the color contrast and clarity of the image. It helps surgeons to have a better image during the surgeries.
With W+ Enhancement, the dark field of the image will be improved, so it could provide more details and reduce the potential risk for surgeons.
The main application of FGS in Gynecology department is sentinel lymph node (SLN) mapping for biopsy to know whether it’s cancerous or not. It helps surgeons for making decision of lymph node dissection. With evolving technology, further innovative research on the new applications of fluorescence visualization in cancer surgery may help to establish these techniques as standards of high-quality surgery in gynecology.
Indocyanine green (ICG) is a fluorescent dye that has been widely used for fluorescence imaging during hepatobiliary surgery. ICG is injected intravenously, selectively taken up by the liver, and then secreted into the bile. The catabolism and fluorescence feature of ICG provides a wide range of visualization methods in hepatobiliary surgery. The applications of ICG during hepatobiliary surgery includes: 1) cholangiography, 2) primary hepatic carcinoma imaging, and 3) hepatic segment detection. Intra-operative ICG fluorescence imaging is a safe, simple, and feasible method that improves the visualization of hepatobiliary anatomy and liver tumors.
Thoracic surgeons perform a wide variety of cancer operations, which are often associated with high morbidity and mortality. Fluorescence imaging technology (FIT), involving the implementation of fluorescent dyes and imaging systems, is currently used as assitant method for general thoracic surgery in many situations, such as pulmonary intersegmental plane identification, pulmonary nodule identification, evaluation of the anastomotic perfusion after tracheal surgery, etc. This technology enhances the surgeon’s ability to perform operations, and has specific advantages.
Real-time fluorescence-guided surgery (FGS) has spread worldwide, mainly because of its usefulness during the intraoperative decision-making processes. FGS allows to evaluate the blood perfusion at the gastrointestinal stumps after colorectal or esophageal resections. Therefore, a reduction on the anastomotic leak rates has been postulated as one of the foreseeable benefits of FGS in these procedures.
