The researchers integrated their megahertz-speed optical coherence tomography (MHz-OCT) system into a commercially available neurosurgical microscope. The top left image shows a typical surgical microscope view of a tumor located beneath the surface of the brain, illuminated by white light. The only visible sign of the tumor is a peculiar growth of new blood vessels. With a fluorescent agent and viewed under blue-violet light, parts of the tumor become faintly visible (bottom left). The new MHz-OCT system built into the microscope, however, can look beneath the surface to reveal structure at depth, as seen in the upper left image, which shows the slice indicated by the blue line. When projected into a top view, as shown in the lower left image, the tumor becomes clearly visible. Credit: Universität zu Lübeck, Medizinisches Laserzentrum Lübeck GmbH & Universitätsklinikum Schleswig-Holstein
Researchers successfully integrated a megahertz-speed optical coherence tomography (MHz-OCT) system into a commercially available neurosurgical microscope and demonstrated its clinical utility. This advance represents an important step toward the development of an OCT instrument that could be used to identify tumor margins during brain surgery.
OCT is a non-invasive imaging technique that provides high-resolution cross-sectional images of tissue allowing visualization of subsurface structures. Although this imaging approach is widely used in ophthalmology and cardiology, most commercial OCT systems can only acquire approximately 30 2D images per second.
“The MHz-OCT system we developed is very fast, around 20 times faster than most other OCT systems,” said Wolfgang Draxinger from the Universität zu Lübeck. “This allows it to create 3D images that reach beneath the surface of the brain. These could be processed, for example with AI, to find and show parts that are unhealthy and require further processing, but which would remain hidden with other imaging methods.”
In the magazine Express Biomedical Opticsresearchers led by Robert Huber describe the results of a clinical study of the microscope-integrated MHz-OCT system. The article is titled “Microscope-integrated MHz optical coherence tomography system for neurosurgery: development and in vivo clinical imaging.”
They show that the system can be used during surgery to acquire high-quality volumetric OCT cross-sectional scans in seconds, with images immediately available for post-processing.
“We see our microscope-integrated MHz-OCT system used not only in brain tumor surgeries, but as a tool in all neurosurgery settings, as it can acquire high-contrast images of anatomy, such as blood vessels. blood, through the thick membrane that surrounds the brain,” said Draxinger, first author of the new paper.
“This could significantly improve the outcomes of procedures requiring detailed information about anatomical structures beneath the surface of the brain, such as deep brain stimulation for Parkinson’s disease.”
Accelerate OCT
Researchers have been working for some time to accelerate 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 capable of performing over a million in-depth scans per second.
The megahertz speed allows more than a million depth scans to be acquired in just one second. This imaging speed is possible because the system incorporates a Fourier domain mode-locked laser, first designed in 2005 by Huber during his doctoral dissertation at MIT under the direction of James G. Fujimoto, who along with Eric Swanson and David Huang, invented OCT.
Additionally, the development of graphics processing unit (GPU) technology over the past 15 years has led to the computational capabilities required to process the raw OCT signal into readable visuals without a bulky computer.
To find out whether the MHz-OCT instrument they developed could be used to visualize the margins of brain tumors, the researchers integrated it with a special type of microscope that surgeons use to get a better view of the brain.
Take him to the operating room
After building the integrated system, they tested it with calibration targets and tissue analog phantoms. Once satisfied with these results, they conducted patient safety testing and then began a clinical study examining its application in brain tumor resection neurosurgery in 30 patients.
“We found that our system integrates well with regular operating room workflow, without major technological issues,” Draxinger said. “The quality of the images acquired exceeded our expectations, which were low due to the fact that the system was a retrofit.”
During the clinical study, researchers acquired approximately 10 TB of OCT imaging data along with corresponding histological pathological information. They note that they are still in the very early stages of understanding the data and images produced by the new system and developing AI methods to classify tissues. It will therefore likely be years before this technology can be widely used to support brain tumor resection neurosurgery.
They are also preparing a study in which the new system will be used to demonstrate the exact localization of brain activity in response, for example, to an external stimulus, during neurosurgery. This could be promising for improving the precision of neuroprosthetic electrode implantation, thereby enabling more precise control of prosthetic devices by exploiting electrical signals from the brain.
More information:
Wolfgang Draxinger et al, Microscope-integrated MHz optical coherence tomography system for neurosurgery: development and in vivo clinical imaging, Express Biomedical Optics (2024). DOI: 10.1364/BOE.530976
Quote: Researchers integrate a fast optical coherence tomography system into a neurosurgical microscope (October 1, 2024) retrieved October 1, 2024 from
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