State-of-the-art technology is often used in cutting-edge surgical tools, but this can limit their overall accessibility. For example, several near-infrared fluorescence-guided surgical systems have been approved for various medical uses, but they are hindered by two significant drawbacks: size and cost. These systems often have a large footprint in the operating room (OR), and some require additional assistance from another user to operate, which disrupts the surgeon's workflow. Moreover, the high price of these devices makes them unaffordable for many clinical centers, which can impact patient outcomes. To address these challenges, a research team is developing a compact fluorescence-guided surgery system made from cost-effective, off-the-shelf components, which could drastically reduce costs compared to current commercially available models.

In fluorescence-guided surgery for cancer, the first step involves administering a contrast agent that specifically targets the tumor. This agent, known as a fluorophore, emits light when exposed to certain wavelengths, allowing the surgeon to see the tumor’s boundaries and ensure the complete removal of cancerous tissue while preserving healthy tissue. It also helps detect any malignant tissue left behind during the procedure. Various fluorophores are under investigation, with some activated by visible light, making them detectable to the naked eye. However, like the glow of a firefly, the fluorescence is most visible in the dark, and turning off the lights in the operating room is not a feasible solution. To overcome this issue, researchers are exploring fluorophores that respond to near-infrared light.

Near-infrared light, which is just beyond the visible spectrum, can penetrate tissues more effectively, allowing surgeons to detect tumors deeper within the body. However, human eyes cannot see near-infrared light without a special camera that is sensitive to these wavelengths. Additionally, the signal must be projected in a way that the surgeon can view it. In existing systems, this signal is typically displayed on a nearby screen. Researchers at the University of Texas Southwestern Medical Center (Dallas, TX, USA) have been working on a low-cost, fluorescence-guided surgical system that uses goggles to view the fluorescent signal. Instead of watching the tumor’s fluorescence on a screen, this augmented reality system projects the near-infrared signal directly onto an eyepiece, allowing the surgeon to see the illuminated tumor overlaid on their field of view. Building on previous research, the team introduced their latest model, made entirely from off-the-shelf components and simple 3D-printed parts. The system consists of visible and near-infrared light sources (similar to laser pointers), a minimal camera system and processor, and commercial augmented reality glasses.

These components are connected using 3D-printed mounts, and the entire unit sits on the user's head. Along with the processor, a battery pack that powers the system is placed on the user’s waist, making the system portable and hands-free. The total cost of the individual components is around USD 1,000, and the researchers aim to make a commercial version of the system much more affordable than current models. Initially, the researchers tested the simplest camera system to see if it could detect the near-infrared signal, and to their surprise, it outperformed their earlier designs. With some adjustments, they were able to fine-tune the system to filter out background signals, providing the essential functionality for fluorescence-guided surgery.

An important advancement in their design was the placement of the cameras. Many technologies that overlay one image over another—like the fluorescence signal on the surgeon’s field of view—often suffer from the parallax effect, where the overlay is not perfectly aligned with the real image. To solve this, the team used a beamsplitter, a device that divides incoming light into two paths. The beamsplitter was placed in front of the augmented reality glasses, and the camera was positioned just above the user's eye in line with the light reflected off the beamsplitter. This setup ensures that light either passes through the beamsplitter into the eye or reflects off the beamsplitter into the camera, significantly improving the optical alignment of the system.

The team benchmarked their device against more than 10 existing fluorescence-guided systems, comparing specifications such as fluorescence sensitivity, resolution, and irradiance (brightness). Despite the smaller size and lower cost of their design, the researchers found that their goggles had comparable specifications to the more expensive systems on the market. In their study published in Nature Scientific Reports, the researchers also tested the real-world utility of their system in a mouse model, performing surgery on mice with breast tumors.

“With our system, we can see the tumors, remove them, and if there is any residual tumor left, we can see it in real time,” said senior study author Samuel Achilefu, Ph.D., professor and chair in the Department of Biomedical Engineering at UT Southwestern Medical Center. With a cost-effective approach, our team aims to make an accessible real-time fluorescence system that highlights tumors in a similar fashion across all hospitals, no matter their location or budget.” 

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