Dr. Stefan HambückerDr. Stefan Hambücker is a managing partner at Ingeneric, a leading manufacturer of micro-optical systems and aspherical lenses. TRUMPF has been the parent company of Ingeneric since 2014.
Lasers already perform many useful functions in the field of medicine, acting as optical scalpels for surgeons and providing tools for correcting defective vision and treating skin conditions. Dentists use them too, for example to pinpoint and remove tooth decay and clean periodontal pockets. In all these cases, the laser light is decoupled outside the body, so the only safety precaution required is some form of protection against burns and eye damage.
“But it’s always been too risky to use a laser once you get under the skin,” says Stefan Hambücker. Part of the fiber that guides the light waves in minimally invasive procedures runs inside the patient’s body – and that’s exactly what makes it so dangerous. If the fiber were to fail due to breakage or overheating, the burning fiber or ‘fiber fuse’ could lead to an embolism. In the worst case scenario, the patient could die. “That’s why it was always too tricky to perform those kinds of procedures in the past – but now we’ve found the solution!“ says Hambücker.
Hambücker is a managing partner at Ingeneric GmbH, a company located in Aachen, Germany, which produces ultra-high-precision micro-optical systems. “There’s no way of eliminating the structural risk of fiber fuse or failure. So we decided to look for a kind of early warning system which would deactivate the laser within a matter of milliseconds if it detected any sign of imminent failure.” The clearest warning of fiber fuse or failure actually comes from the laser light itself.
There is always a certain amount of back reflection within a fiber, but when a fiber starts to fail, the emission spectrum of the light changes. This change is minimal, but measurable, so the engineers decided to develop a highly sensitive and spectrally selective sensor as the centerpiece of their solution. The result was a small black box with two connection ports which, at first glance, does not look particularly remarkable. “The sensor is positioned between what is known as the proximal fiber – in other words the supply fiber to the body – and the distal fiber, the connection to the light source.”
It measures both the incident light from the beam source and the outgoing light in the proximal fiber and continuously transmits the results to the control software. This software also works continuously to check these measurements against the back reflections. If it detects a deviation, it switches the laser off within 3 milliseconds.
Telltale back reflection
The most frequent time for a fiber to fail is when it is switched on and a tiny, existing area of damage suddenly gives way as the laser light passes through the fiber, Hambücker explains. “That’s why we added an additional safeguard in the form of a green pilot beam which the control system sends through the fiber first. This beam is too weak to cause fiber failure, but strong enough to generate a telltale back reflection if an area is damaged or if the fiber is not properly connected and to prevent activation of the working laser.”
„There’s no way of eliminating the structural risk of fiber fuse or failure. So we decided to look for a kind of early warning system.
Dr. Stefan Hambücker, managing partner at Ingeneric GmbH
In principle this kind of safeguard could be incorporated into any medical laser system. To ensure perfectly reliable control of the process, however, Ingeneric has also developed the complete laser system for these kinds of applications, based on the principle that the greater the developers’ understanding and control of the beam source and light path – including its respective parameters – the more accurately they can calibrate the safety system. One example of a suitable beam source is a thermoelectrically cooled high-power diode laser.
To ensure the laser beam doesn’t damage the catheter fiber, the power is increased slowly until it reaches its working level. Combined with the sensor, the system is also suitable for use in other medical applications. It can cater to a range of wavelengths, so there is no risk even when using polymer-clad fibers. As Hambücker puts it so succinctly: “The door to minimally invasive laser therapy is finally open!”
Dr. Stefan Hambücker,
phone: +49 (0) 241 963 – 1341