Tabletop Laser Precisely Cuts Brain Tissue

A new tabletop solid-state laser system that produces 6.45 µm of short pulses to precisely cut brain tissue was developed as part of an interdisciplinary European Union project that involved partners from seven European countries.

The idea dates back to a 1999 study from Vanderbilt University in Nashville, Tenn., in which scientists removed a brain tumor using a free-electron laser operating at a wavelength of 6.45 µm, which is ideal for surgery. However, because free-electron lasers are enormous and require an expensive accelerator, they are not suitable for clinical use. In laser surgery, wavelengths of about 2, 2.8 and 10.6 µm have been in use, but no solid-state laser operating at the mid-infrared has been available.

“There were so far no compact and reliable solid-state lasers emitting at the desired mid-infrared wavelength,” said Dr. Valentin Petrov of the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI).

Tissue ablation with the novel all-solid-state light source at 6.45 µm based on frequency conversion is compared to ablation with two clinical lasers: a 2.79-µm erbium solid-state laser and a 10.6-µm carbon dioxide gas laser. (Image: UMC)

Until now, that is. The new laser developed at MBI emits 6.45-µm pulses with a repetition rate of 100 to 200 Hz, ensuring a targeted average power of more than 1 W. Collateral damage during surgery is greatly reduced at this wavelength because of the combined absorption of water and resonant laser heating of non-aqueous components, or proteins. The penetration depth is several microns at this wavelength — nearly cell size — almost reaching the optimum value.

The EU-funded project MIRSURG, launched in 2008, focused on closing the gap in diode-pumped solid-state lasers in the mid-infrared spectral range. During its final meeting in spring 2012, the MIRSURG team demonstrated a compact all-solid-state prototype that can fit on a tabletop. Frequency conversion generated the desired optical wavelength of 6.45 µm. Nonlinear optical crystals were used to convert the approximately 2-µm laser beam wavelength to the mid-infrared.

The challenge for the researchers was to simultaneously achieve all of the technically feasible parameters for soft tissue ablation. They achieved a high single pulse energy of more than 5 mJ with the desired wavelength as well as good focusing capability and short pulse duration of about 30 ns. The long-term stability, repetition rate and reliability of the entire laser system are suitable for practical surgical applications.

Partner members of MIRSURG will further optimize the new tabletop laser and assess its tissue ablation capabilities; they hope to demonstrate real solid-state laser surgery at 6.45 µm.

“I hope that in the near future, such a laser could become a practical surgical tool in every specialized operating room,” Petrov said.

For more information, visit: www.mirsurg.eu