NEUROSURGERY/MID-INFRARED LASERS: European team unveils super-precise prototype brain surgery laser

An interdisciplinary team of European researchers have created a tabletop solid-state laser system that claims to cut brain tissue with unprecedented precision. The project responsible, called mid-infrared solid-state laser systems for minimally invasive surgery (MIRSURG; www.mirsurg.eu), has secured nearly €2.8 million in funding under the 'Information and communications' (ICT) Theme of the European Union's Seventh Framework Programme (FP7).

The project was inspired by the 1999 success of scientists at Vanderbilt University (TN), who removed a brain tumor from a patient using a free-electron laser in the mid-infrared (IR) wavelength of 6.45 μm. The mid-IR spectral region had been recognized in a number of early experiments with soft tissues as being the one most suitable for such operations. But the technology has not transitioned to operating rooms for a few key reasons: Free-electron lasers are huge, and accelerator-based facilities are both expensive and generally not suitable for routine use in clinical conditions.

In 2008, MIRSURG launched to develop a laser source that would emit near 6.45 μm and provide high single-pulse energy and average power to enable minimally invasive neurosurgery. The project partners believed such an achievement would close the gap for diode-pumped solid-state lasers in the mid-IR spectral range around 6.45 μm. "There were so far no compact and reliable solid-state lasers emitting at the desired mid-infrared wavelength," said Valentin Petrov of the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI), which headed the project.

At a recent meeting in Saint-Louis, France, the MIRSURG team presented their tabletop device, which generates the desired 6.45 μm by way of frequency conversion (nonlinear optical crystals convert a laser beam around 2.0 μm to mid-IR).

The new laser emits short pulses exactly at 6.45 μm with a repetition rate of 100–200 Hz, ensuring the targeted average power of over 1.0 W. The greatly reduced collateral damage at this wavelength is due to the combined absorption of water and resonant laser heating of non-aqueous components (proteins). The penetration depth is on the order of several microns, which is comparable to the cell size, and is therefore close to the optimum value—and what's more, not achievable by any other state-of-the-art lasers, according to the researchers.

The MIRSURG partners plan to further optimize the new tabletop laser, assess its tissue ablation capabilities and, possibly with a follow-up project, demonstrate real solid-state laser surgery at 6.45 μm.