Megahertz OCT improves view of tumor margins and brain anatomy

08 Oct 2024

University of Lübeck integrates faster OCT into commercial neurosurgical microscope.

A project at the University of Lübeck has demonstrated a fast MHz-rate OCT system integrated into a standard neurosurgical microscope.

Described in Biomedical Optics Express, the device represents an important step toward developing an OCT instrument that could be used to identify tumor margins during brain surgery, according to the team.

"The MHz-OCT system we developed is very fast, about 20 times faster than most other OCT systems," said Wolfgang Draxinger from the University of Lübeck's Institute of Biomedical Optics.

"This allows it to create 3D images that reach below the brain's surface. These could be processed, for example with AI, to find and show parts that are not healthy and need treatment yet would remain hidden with other imaging methods."

Applying OCT to ex vivo brain tumor biopsy samples has shown that the technique could be valuable in assessing the extent of a malignancy, while the nature of tumorous growths may allow light to propagate deeper than healthy tissue and with less scattering. But to date the bulk of research has been into deploying OCT in supplementary probing devices.

The Lübeck project investigated whether the imaging modality could instead be integrated into the microscopes already used in surgeries, potentially avoiding excision of biopsy samples or the need to switch between instruments. Previous attempts at OCT integration have shown limited scan rates of less than 50 kHz.

"The past decade saw tremendous advances in OCT technology, driven by the development of rapidly tunable, continuously sweeping light sources and high speed detector and signal acquisition systems, the combination of which increased depth scan speeds by well over two orders of magnitude achieving MHz depth scan rates," said the team in its published paper.

"With the technology of these MHz speed imaging system now being mature, an in vivo clinical study of such a system integrated into a surgical microscope continues this line of research."

A tool in every neurosurgery setting

OCT integration involved a number of challenges, including the design of suitable scanner optics and a beam delivery system overcoming constraints posed by the mechanical and optical parameters of the microscope, plus the development of bespoke image acquisition software.

Once these were tackled, the project began a clinical study investigating the application of MHz-OCT to brain tumor resection neurosurgery in 30 patients.

"We found that our system integrates well with the regular workflow in the operating room, with no major technological issues," commented Wolfgang Draxinger. "The quality of the images acquired surpassed our expectations, which were set low due to the system being a retrofit."

The project is now preparing to investigate whether the new system can indicate the exact locations of brain activity, for example due to an external stimulus during neurosurgery. This could enhance the precise implantation of neuroprosthetic electrodes, allowing more accurate control of prosthetic devices by tapping into the brain's electrical signals.

"We see our microscope-integrated MHz-OCT system being used not just in brain tumor surgeries, but as a tool in every neurosurgery setting, since it can acquire high contrast pictures of anatomy such as blood vessels through the thick membrane that surrounds the brain," said Draxinger.