In an important step toward endoscopic diagnosis of cancer, researchers have developed a handheld fiber-optic probe that can be used to perform multiple nonlinear imaging techniques without the need for tissue staining. The new multimodal imaging probe uses an ultrafast laser to create nonlinear optical effects in tissue that can reveal cancer and other diseases.

Cancer is typically diagnosed by removing a bit of tissue with a biopsy and then sending that tissue to a specially trained pathologist who stains the tissue and uses a microscope to look for cancerous cells. The ability for doctors to skip the biopsy and use a multimodal imaging endoscope to diagnose cancer on the spot would save valuable time and could also allow surgeons to differentiate more easily between cancerous and healthy tissue during surgery.

With the new probe, imaging techniques that previously required bulky table-top instruments can be performed with a handheld device measuring only 8 millimeters in diameter, about the same diameter as a ballpoint pen. If miniaturized further, the probe could easily be integrated into an endoscope for nonlinear multimodal imaging inside the body.

"We hope that, one day, multimodal endoscopic imaging techniques could help doctors make quick decisions during surgery, without the need for taking biopsies, using staining treatments or performing complex histopathological procedures," said Jürgen Popp from the Leibniz Institute of Photonic Technology in Jena, Germany.

The researchers detail their new handheld probe in the Optical Society's journal for high impact research. It is the first miniaturized probe for multimodal biological imaging to incorporate a multicore imaging fiber, a type of optical fiber consisting of several thousand light-guiding elements. This special imaging fiber allowed the researchers to keep all moving parts and electric power outside of the probe head, making the probe easy and safe to use in the body.

The researchers have tested the probe with many types of tissue samples, but because it is currently designed for forward view mode, the primary applications of the probe would likely include skin, brain or head, and neck surgery. They are working on implementing a side view mode that could be used to investigate hollow organs and arteries such as the colon, bladder, or aorta.

"The new probe serves as a miniaturized microscope that uses near-infrared lasers to investigate tissue," said Popp. "Different components of biological tissue react differently to the excitation lasers, and their unique response gives us information about the molecular composition and morphology within the tissue."

The handheld multimodal imaging probe can simultaneously acquire several types of images: coherent anti-stokes Raman scattering, second harmonic generation, and two-photon excited auto-fluorescence. These nonlinear imaging techniques have been shown to be useful for clinical diagnostics, including identifying cancerous cells, but it has been difficult to miniaturize the required instrumentation for use inside the body. The probe's reduced size comes from its use of gradient index, or GRIN, lenses to focus the laser light. Compared to traditional spherical lenses that use complicated shaped surfaces to focus light, GRIN lenses can be made very small because they focus light through continuous refractive index changes within the lens material.