Authors: Alice Weatherston
In brain tumor surgery, establishing the boundaries between healthy tissue and tumor cells is key. Typically, pathologists utilize staining methods to identify the location of brain tumors. Chemicals such as hematoxylin and eosin are used to turn different tissue components blue and red, revealing its structure and whether or not there are any tumor cells.
However, a definitive diagnosis using this procedure can take up to 24 hr, meaning that neurosurgeons may perform surgery without full knowledge of the cancerous tissue that is present. This incomplete prognosis may mean that a second operation is required, increasing the risk to the patient.
Researchers from VU University Amsterdam (Netherlands), have spent time developing an alternative technique that can detect the presence of tumor cells in tissues at a speed that results in quick feedback to the neurosurgeon performing the operation.
Short, 200-femtosecond-long laser pulses are fired into the tissue and when three photons converge at the same time and place the photons then interact with the nonlinear optical properties of the tissue. Through well-known phenomena in optics, termed second and third harmonic generation, these interactions produce a single photon.
The incoming and outgoing photons during this process have different wavelengths; the incoming photons are at 1200 nanometers (nm), which is long enough to penetrate deep into the tissue. The single photon that is produced during these interactions, however, is at 600 or 400 nm, depending on if it’s second or third harmonic generation. Because this single photon is a shorter wavelength it can scatter in the tissue and thus contains information about the whole tissue. When it reaches a detector (in this case a high-sensitivity GaAsP photomultiplier tube), it reveals what the structure of the tissue.
“The special thing about our images is that we showed they contain so much information,” commented lead author Marloes Groot of VU University Amsterdam. “When I showed these images to the pathologists that we work with, they were amazed.”
This technique has been exploited before for other applications, such as imaging images of insects and fish embryos, but this is the first time anyone has utlized it to analyze glial brain tumor samples from humans. Most images were generated in under a minute, with smaller images taking less than a second.
The next step for Groot and her team is to develop a handheld device that a surgeon can utilize during operations to determine the tumor’s border. Currently the incoming laser pulses can only reach a depth of about 100 micrometers into the tissue; in order to reach further Groot proposes attaching a needle that can pierce the tissue and deliver these photons deeper.
Groot concluded: “With our technique it’s potentially possible to diagnose not only during an operation but possibly before surgery.”