Lasers, Spectroscopy, and OCT Cut Bone Safely

Researchers at the University of Basel have developed a system that increases the safety and precision of lasers used to cut bone in surgical settings. The system is able to cut bone, control the cutting depth, and differentiate between tissues, using a cutting laser, imaging system, and spectroscopy.

The functions are carried out by three lasers aligned to focus on the same spot. One serves as a tissue sensor in that it scans the surroundings of the site where the bone is to be cut. Pulses are sent with this laser to the surface at regular intervals, vaporizing a tiny bit of tissue each time.

The composition of the vaporized tissue is analyzed with a spectrometer. An algorithm processes this data and creates a map showing where the bones are located and where the soft tissue is.

Lead author Arsham Hamidi (left) and Ferda Canbaz worked to develop a laser system capable of distinguishing soft tissue from bone to enable safer cuts with controlled depth. Courtesy of Reinhard Wendler/Universität Basel.

Once this is completed, the second laser, which cuts bone, activates, but only if it is in a position where it can cut bone, free from soft tissue. At the same time, the third laser, part of an optical coherence tomography (OCT) system, measures the depth of the cut and checks that the cutting laser is not penetrating deeper than planned. During the cutting phase, the tissue sensor continuously monitors whether the correct tissue is being cut.

“The special thing about our system is that it controls itself — without human interference,” said laser physicist Ferda Canbaz.

The researchers have so far been testing their system on pigs’ femur bones and tissue acquired from a local butcher. They were able to prove that their system works accurately down to fractions of a millimeter. The speed of the combined laser also approaches that of a conventional surgical procedure.

The researchers are currently working to make the system smaller. They already have it down to the size of a matchbox when combining the optical system and the cutting laser alone. Once they have added the tissue sensor and managed to miniaturize the entire system further, they should be able to fit it into the tip of an endoscope to carry out minimally invasive operations.

“Making more use of lasers in surgery is a worthy ambition for a number of reasons,” said Arsham Hamidi, lead author of the study. Contact-free cutting somewhat reduces the risk of infections, he noted. “Smaller and more precise incisions also mean that the tissue heals more rapidly, and that scarring is reduced.”

Cutting in a controlled manner using lasers also permits new cutting shapes to be applied, so that, for instance, a bone implant could be physically interlocked with the existing bone.

“One day we might be able to do without bone cement completely,” Canbaz said.

The setup may also be useful in surgical settings such as tumor removal, where it could distinguish tumors from the surrounding healthy tissue and enable safer cuts.

The research was published in Lasers in Surgery and Medicine (www.doi.org/10.1002/lsm.23732).