OCT system integrated into neurosurgical microscope

German researchers have successfully integrated a megahertz-speed optical coherence tomography (MHz-OCT) system into a commercially available neurosurgical microscope and demonstrated its clinical usefulness. This advancement, published in the journal Biomedical Optics Express, represents an important step toward developing an OCT instrument that could be used to identify tumour margins during brain surgery.

“The MHz-OCT system we developed is very fast — about 20 times faster than most other OCT systems,” said first author Wolfgang Draxinger, from the University of Lübeck. “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 further need treatment yet would remain hidden with other imaging methods.”

The researchers have been working for some time to speed up OCT technology by improving the light sources and sensors used and developing software to process the large amount of data generated. This resulted in the development of a MHz-OCT system that can achieve over a million depth scans per second.

The megahertz speed makes it possible to acquire over a million depth scans in just one second. This imaging speed is possible because the system incorporates a Fourier domain mode locking laser, first conceived in 2005 by Robert Huber during his doctoral thesis research at MIT under OCT co-inventor James G Fujimoto. In addition, the development of graphics processing unit (GPU) technology over the past 15 years led to the computational capabilities required for processing the raw OCT signal into readable visuals without a bulky computer.

To find out if the MHz-OCT instrument they developed could be used to view brain tumour margins, the researchers integrated it with a special type of microscope that surgeons use to get a better view of the brain. After building the integrated system, they tested it with calibration targets and tissue analog phantoms. Once satisfied with these results, they proceeded through patient safety testing and began a clinical study investigating its application in brain tumour resection neurosurgery in 30 patients.

The researchers showed that the system can be used during a surgical procedure to acquire high-quality volumetric OCT cross-sectional scans within seconds, with the images immediately available for post-processing. The researchers acquired about 10 TB of OCT imaging data, along with matched pathological histology information.

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

“We see our microscope-integrated MHz-OCT system being used not just in brain tumour 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,” Draxinger added. “This could significantly improve outcomes for procedures requiring detailed information about anatomical structures beneath the brain’s surface, such as deep brain stimulation for Parkinson’s disease.”

The researchers acknowledge that they are still in the very early stages of understanding the data the new system is producing and developing AI methods for classifying the tissue, so it will likely be years before this technology could be widely used to support brain tumour resection neurosurgery. They are now preparing a new study in which the system will be used to demonstrate the exact location of brain activity in reaction to an external stimulus during neurosurgery, which could hold promise for enhancing the precision of implantation of neuroprosthetic electrodes.

Image credit: iStock.com/Jacob Wackerhausen