A new collaborative project ‘BetterView’ is working on a special surgical microscope to detect cholesteatomas - an aggressive form of chronic otitis media that triggers inflammation of the middle ear - and bacterial biofilms and to remove them safely. The special surgical microscope uses short-wave infrared light to illuminate blood, bacterial biofilms, cartilage, and soft tissue; display them spatially; and make them distinguishable from each other.

The so-called SWIR microscope system is being developed under the collaborative project by a research network that includes Bielefeld University (Bielefeld, Germany) and is coordinated by Munich Surgical Imaging (MSI, Munich, Germany) with the aim of fighting bacterial contamination. SWIR stands for Short-Wave InfraRed. Minimally invasive surgery works with the smallest of skin incisions—so that there is hardly any injury to tissue during operations. Optical microscopes help surgeons to examine the area they will be operating on. They illuminate the surgical field and transfer a high-resolution image to a screen. Until now, however, surgical microscopy has worked almost exclusively with light from the visible spectral range. Currently available microscopes reach their limits when a surface is covered by bleeding or contaminated by bacteria. To give surgeons a clear view in such situations, the ‘BetterView’ project is developing the new SWIR surgical microscope.

The team is constructing and using high-resolution microscopes while also developing the software for image processing. Microscopes with sensors such as the SWIR surgical microscope first have to analyze and process the recorded image signal automatically. So that the surgical microscope can display the short-wave infrared signals, the team is developing its own software that filters out light outside the short-wave infrared spectrum and calculates a three-dimensional view of the image. The software has to display the video image in real time so that surgeons in the operating theatre can work precisely and face no delay in seeing what their intervention is doing to the surgical field.

In order to test the SWIR surgical microscope in practice, the project will initially use it to treat cholesteatoma—a chronic pus-producing inflammation of the middle ear. In later stages, the inflammation can also lead to facial palsy, meningitis, and intracranial abscesses. Cholesteatoma, generally accompanied by severe bone destruction, can be caused by a middle ear infection or by the tympanic membrane retractions extending into the middle ear. Surgical microscopes, which work only with the light range visible to humans, are normally used for diagnosis, surgery, and follow-up care. If a cholesteatoma becomes inflamed by bacteria, it will grow faster and damage the adjacent bones more severely. However, the extent to which bacterial colonization has spread is often not visible with standard microscopes because, for example, bleeding that obscures the biofilm.

In addition to microscopy, specialists also use computer tomography (CT) and magnetic resonance imaging (MRI) to diagnose cholesteatoma. However, this cannot distinguish possible fluid in the middle ear from a cholesteatoma. Magnetic resonance imaging is also used to prepare for surgery. Although it provides a higher resolution than CT, the disadvantage is that it cannot show the details of the ossicles precisely enough. The project team expects a number of advantages from the new SWIR microscope. Its ability to see through blood and distinguish bacterially infested tissue, bone, nerves, and soft tissue is particularly important.

MSI is providing a surgical microscope that is already used in surgery and provides high-resolution images. The new project is building on this development. Compared to conventional microscopes, the future SWIR microscope will also be able to see through soft tissue. This will make it possible to examine optically hidden areas as well. Then, surgeons will be able to see whether bone material in the inner ear has been colonized or damaged by bacteria. In addition, the microscope should increase patient safety. If surgeons can see and distinguish the inner ear precisely, there is less risk of damaging sensitive structures such as the facial nerve or the labyrinths of the inner ear.

“An advanced generation of image sensors now makes it possible to equip surgical microscopes with a new function: to process and display images in the short-wave infrared light spectrum in real time,” said Professor Dr Thomas Huser from the Faculty of Physics at Bielefeld University.

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