Laser Beam Replaces Mechanical Cranial Trephine

A novel high-energy femtosecond laser could lower the risk of brain damage resulting from a release craniotomy.

Developed by researchers at the Fraunhofer Institute for Photonic Microsystems (IPMS; Dresden, Germany), the Fraunhofer Institute for Laser Technology (ILT; Aachen, Germany), and the Fraunhofer Institute for Integrated Circuits (IIS; Erlangen, Germany), the novel laser beam system is based on an articulated mirror arm that consists of two new types of micromirrors that direct the beam through a handpiece.


The first makes the cranial vault incision; it directs the laser beam dynamically across the cranial bones, while the second adjusts any malpositioning. The components are miniaturized, but can tolerate up to 20 watts of laser output, which is about two hundred times more than conventional micromirrors that reach their limits at 100 milliwatts, depending on the specific design. In addition, the micromirrors measure 5x7 mm or 6x8 mm, thus guiding large diameter laser beams; for comparison, conventional micromirrors measure from 1 to 3 millimeters.

And while the silicon panel in conventional micromirrors is mirrored by an aluminum layer measuring a hundred nanometers thick, the new micromirrors have highly reflective electric layers lined to the silicon substrate. As a result, in the visible spectral range, the mirror reflects not merely 90% of the laser beam, as in typical components, but 99.9%. This means that much less of the high-energy radiation penetrates into the substrate, resulting in a mirror that tolerates markedly greater power generated by the femtosecond laser.

“If the brain starts to swell after a stroke, surgery is often the only treatment option—one in which the physicians open the patient’s cranial vault. Up to now, they would reach for the drill and the saw,” said Thilo Sander, PhD, group manager at IPMS. “Our colleagues at ILT have engineered a device that allows the surgeon to guide the laser beam and cut the cranial bone.”

A release craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often a critical operation performed on patients suffering from brain lesions or traumatic brain injury (TBI), and can also allow doctors to implant deep brain stimulators for the treatment of Parkinson's disease, epilepsy, and cerebellar tremor. The procedure is also widely used in neuroscience for extracellular recording, brain imaging, and for neurological manipulations such as electrical stimulation and chemical titration.

Related Links:
Fraunhofer Institute for Photonic Microsystems
Fraunhofer Institute for Laser Technology
Fraunhofer Institute for Integrated Circuits