When a surgeon operates on a brain tumor, it can be medically challenging to tell whether or not they’ve managed to remove all of the necessary tissue. Correctly identifying the margins of the tumor can be further complicated if there is damage from previous surgery or other anti-cancer therapies, and even the best of eyes will fail to detect a few microscopic cells left behind. That is, of course, where the pathologist comes in. Identifying the presence of remaining tumor tissue is a crucial element of the treatment process, but it’s a step that generally takes place once surgery is complete, which is often not ideal.
Clearly, a solution that supports the identification of tumor tissue during surgery would help avoid unnecessary further treatment and distress to the patient, and would save time and presumably costs. That’s what researchers from the Vrije Universiteit Amsterdam thought when they devised a near-real-time, label-free method of detecting tumor tissue in the brain (1). Third harmonic generation microscopy (THG) involves firing photons of a given wavelength into tissue; when three photons simultaneously interact with the tissue, the reaction produces a single photon at one-third the wavelength (and triple the frequency), which is picked up by a detector to generate an image of the tissue (see Figure 1). Because the technique is so clear – allowing visualization of subcellular features – and so fast – ranging from under one second to five minutes, depending on image size and detail – it’s possible to apply it during surgery, allowing neurosurgeons to assess tumor boundaries while there’s still time to act. “The special thing about our images is that we showed they contain so much information,” said principal investigator Marloes Groot (2). “When I showed these images to the pathologists that we work with, they were amazed.” Although THG isn’t a new technique, this is the first time it has been used on human brain tumor samples – and the outlook is promising. What’s next for Groot and her colleagues? Now that they’ve established that THG works on tumor samples, they’d like to construct a tabletop THG device for placement in an operating room, so that it can provide immediate feedback to surgeons during complicated operations. They’re also working on a new device to overcome one of THG’s current limitations: the fact that its laser pulses can only penetrate about 100 μm into a given tissue. They hope to develop a THG-based bioptic needle to deliver photons below the tissue surface for greater reach, potentially expanding the technique’s usefulness. Such a device might even be able to yield diagnostic information prior to or instead of surgery – not just in brain tumors, but for a wide variety of histopathological applications.
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References
- NV Kuzmin et al., “Third harmonic generation imaging for fast, label-free pathology of human brain tumors”, Biomed Opt Express, 7, 1889–1904 (2016). MedicalXpress, “New method allows surgeons to identify brain tumors in real time”, (2016). Available at: http://bit.ly/1R3BFAe. Accessed May 16, 2016.
