Brain injuries and strokes can sometime require surgeons to relieve pressure on the brain by drilling burr holes through the skull using a trephine. The device is straight out of the good old days of medicine when surgical tools and torture implements were made by the same manufacturers. Yet, while even dentistry has moved on, performing burr hole craniotomies is still very much a manual cranking operation prone to causing injury and even leading to meningitis.
Researchers at Fraunhofer Institutes for Photonic Microsystems, Laser Technology, and Integrated Circuits have developed a new laser system that may soon replace the trusty trephine with a safer, more consistent option. The system uses advanced new mirrors and a femto-second laser to allow the surgeon to guide the cutting beam and penetrate the skull without causing injury.
Some details from Fraunhofer:
The laser beam is fed into the hand piece through an articulated mirror arm. Its core consists of two new types of micro-mirrors that the researchers at IPMS developed. The first makes the cranial vault incision; it directs the laser beam dynamically across the cranial bones. The second adjusts any malpositioning. The special thing: The components are miniaturized, but can tolerate up to 20 watts of laser output – which is about two hundred times more than conventional micro-mirrors. These can already reach their limits at 100 milliwatts, depending on their specific design. In addition, at 5 x 7 or 6 x 8 millimeters, they are very large and thus, can also guide large diameter laser beams. By comparison: Conventional micro-mirrors measure from 1 to 3 millimeters.
How did the researchers achieve this? “Whereas the silicon panel in conventional micro-mirrors is mirrored by an aluminum layer measuring a hundred nanometers thick, we applied highly-reflective electric layers to the silicon substrate,” explains Sander. Therefore, in the visible spectral range, the mirror reflects not merely 90 percent of the laser beam, like typical components, but 99.9 percent instead. Much less of the high-energy radiation penetrates into the substrate. That means the mirror “discerns” less of the laser beam and tolerates markedly greater power. The challenge for the researchers primarily lay in capturing this high power coating onto the silicon substrate, just a few micrometers thin, that is commonplace in microsystems technology. Because the researchers must apply several different layers – altogether a few micrometers thick – in order to achieve the desired reflective properties. However, a certain mechanical stress prevails in each of these layers; in addition, all layers expand at different intensities at high temperature. As a result, the substrate becomes deformed – it arches. “This arching diminishes the optical quality of the mirror. We counterbalance this by applying this same coating on the reverse side of the substrate,” reveals Sander.
Press announcement: Laser instead of drill…
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