Physical Sciences Inc helps surgeons identify nerves during surgery

Fluorescence techniques are valuable sources of visual data for clinicians carrying out investigations or surgical procedures, but the viewing conditions in an operating room (OR) are less than ideal.

One such technique is fluorescence-guided surgery (FGS) based on nerve-labeling agents, designed to be employed during orthopedic, craniofacial and otolaryngological surgeries, where identifying the nerves at the site of surgery is a critical consideration.

A team from Physical Sciences Inc (PSI) research center and Dartmouth College has now developed a fluorescence imaging platform intended for use in the OR and able to suppress interference from the strong overhead lights in those locations. The results were published in Journal of Biomedical Optics.

In 2024 a Dartmouth College project helped investigate FGS methods for cancer resection and nerve sparing using a two-color approach, whereby different markers with different fluorescence behavior are targeted at the tumor cells and the nerve tissues. The new project takes a different approach to the imaging of nerves under OR lighting.

"A major challenge in FGS is the adverse impact of strong ambient light, which interferes with weak fluorescence signals, especially at visible wavelengths," wrote the project in its paper.

"Currently this issue is mitigated by dimming or turning off the OR lights during the fluorescence imaging procedure. However, this causes substantial disruption to the surgical workflow and reduces the potential for clinical adoption of FGS technologies."

One solution would be an effective way to separate fluorescence emitted by labeled nerves from the much stronger background illumination, so that the nerves could be visualized under standard lighting. The project aimed to achieve this via a line-scan-based spatio-temporal modulation (STM) fluorescence imager.

Tackling a basic hurdle in fluorescence-guided surgeries

"The STM approach is conceptually related to spatial frequency domain imaging, as both techniques employ spatially modulated excitation and demodulation to separate an encoded imaging signal from the background," said the team.

An STM fluorescence platform can use a conventional scientific CMOS camera operated in line-readout mode without requiring a custom CMOS sensor, while a short line-detection window reduces the integration of ambient light at each spatial location. A line-scanning imaging scheme produces a quasi-confocal effect, commented researchers, suppressing out-of-focus and multiply scattered fluorescence, while improving image contrast under strong ambient lighting.

In trials on animal models, ex vivo human nerve specimens and human nerves from an amputated limb, the STM imager successfully acquired high-contrast nerve-specific images from the specimens via dual-wavelength fluorescence imaging under standard OR lighting.

A spatial and temporal modulation approach in the STM platform will be a significant factor in clinical translation of the nerve-imaging technology, commented the project group. Further clinical evaluation to determine how the technique performs during human surgical procedures will now follow. 

Since the detection of weak, tissue-specific optical signals in brighter and visually demanding clinical environments is a basic hurdle in fluorescence-guided surgeries and imaging procedures, the STM findings may also have implications for other, broader clinical scenarios.

"This innovative imaging technology represents a significant step toward practical clinical implementation of FGS for enhanced nerve identification," wrote the group.