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Trend Report: Photonic Applications Offer Glimmer of Light

By Klaus Jopp
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Medtech laser

Lasers have become a universal tool in medicine.

With its use in endoscopy, laser surgery, lab-on-a-chip systems, and biomedical optical sensors, light has played an indispensible role in medicine for some time. In certain applications, lasers can provide much greater precision than a scalpel; they are also capable of fusing tissue together. This focused beam of light is the tool of choice for blasting kidney stones from outside the body (laser lithotripsy). In addition, lasers are considered by some to be superior to other technologies (i.e., electrosurgery and sound-wave techniques) when it comes to cutting and removing soft tissue.

In the field of medicine, there is great interest in having the ability to see directly into a cell. The process involves understanding and verifying biological processes at a cellular or molecular level, with the objective of detecting a disease at an early stage as well as provide more specific treatment. A fluorescence microscope developed by Max Planck Institute researcher Stefan Hell from Göttingen, Germany provides resolution so high that individual molecules are visible. Last year Hell received the Nobel Prize for Chemistry, along  with his American colleagues Eric Betzig and William Moerner, for this innovation.

This year’s COMPAMED and MEDICA event will occur November 16-19 in Dusseldorf, Germany. At the COMPAMED Spring Convention earlier this year, Thorsten Jürgens, coordinator of technology development at Olympus Surgical Technologies Europe, commented on new imaging procedures that improve the possibilities in microsurgery. “With Narrow Band Imaging (NBI), it is, for example, possible to identify fine structures and capillary patterns on the surface of mucous membranes,” said Jürgens. Human tissue absorbs light used here at shorter wavelengths very good. NBI successfully makes use of this characteristic, thus providing additional information that cannot retrieved by means of normal endoscopic images. A filter creates two 60-nm-wide spectrums within the wavelength range of 415 nm (blue light) and 540 nm (green light). The absorbing characteristics of hemoglobin improve the contrast of blood vessels. Due to the various penetration depths of the blue and green light, the anatomical layer where a blood vessel is running can be identified.”

Photodynamic diagnosis (PDD) is also very promising. Currently being used in dermatology and urology, the method provides in-vivo data that can identify specific tumors. A photo sensitizer is applied and accumulates in or on tumor cells. Upon exposure to light, the dyes fluoresce. Broadband Xenon light sources are used, and a filter focuses on the required wavelengths from their spectrum. In recent years, new and specific dyes have been developed. “NBI and PDD are already being regularly used in the field of clinical care. In the future, alternative dyes and coloring agents will make the precise demarcation of risk structures and disease possible,” said Jürgens.

The Austrian Institute of Technology in Vienna (AIT) has developed several photonic platforms. The institute created simple-to-use, functionalized core-shell nanorods. “Readings can already be taken from a patient’s saliva in an ambulance, ” stated Dr. Giorgio C. Mutinati from AIT. The procedure is based on optical changes in the rotational dynamics of magnetic rods that have a magnetic core and a stainless-steel shell. Special molecules from the sample bind to the nanoparticles and by means of this process alter their physical characteristics, which can be measured. Only small sample quantities are need and no preparation is involved..

Nanorods

In the realm of optical microsensors, noninvasive in-ear sensor that takes pulse and blood oxygen saturation readings, transmitting the data to a recording device has been developed by CiS, a non-profit research institute for microsensor technology. The system consists of a miniaturized light source and laser-Doppler sensors. “The measurement principle is based on detecting a frequency shift when laser light is scattered by the components of blood due to the Doppler effect, with the frequency shift being reliant on the flow rate and direction,” said Dr. Hans-Georg Ortlepp from CiS. By superimposing this on the original wave, interference effects within the measurable range of frequency occur at the detector. Further work is being conducted to establish a measurement point at the entrance of the ear canal, with the sensor integrated into the ear mold so that the unit can be worn like a hearing aid.

Hearing with Light

Seeing thanks to light is normal, hearing by means of light is a new approach that the CSEM center (Centre Suisse d’Electronique et de Microtechnique) is exploring. Cochlea implants have traditionally used electrical simulation, but this is limited due to poor spatial resolution and so-called crosstalk. Using optical acoustical stimulation, CSEM is participating an EU project called ACTION (ACTive Implant for Optoacoustic Natural sound enhancement). “The project should strengthen the level of hearing of severely hearing-impaired patients by eliminating constraints of spatial and temporal stimulation of cochlea implants that are based on electrical stimulation,” said Dr. Stefan Mohrdiek from CSEM. ACTION builds on the discovery that pulsed infrared laser light can triggering auditor activity in hair cells. The optical microsystem includes lasers that provide optical stimulation (semiconductor laser diodes are preferred), response electrodes, can printed electronic circuits. Challenges to overcome include miniaturization, integration of vertical-cavity surface-emitting lasers for long wavelengths, biocompatibility, the creating micro-lenses on a wafer, and the ability for low-volume manufacturing,

Real-time Control in Laser Surgery

At the COMPAMED Spring Convention, Dr. Alexander Krüger from the Laser Center in Hannover (Germany) discussed the potential of laser surgery under real-time control via optical coherence tomography (OCT). The laser for cutting tissue can be linked directly to the optical access for imaging. The fully integrated solution jointly uses lasers, scanners and an objective. There are also modularly integrated (joint scanners) and extensively separated versions. Today, femtosecond and excimer lasers are used in ophthalmic surgery. Using these technologies, vitreous bodies in the eye can be specifically changed without injuring the retina or nerves. By means of ultra-rapid lasers, innovative cataract, age-related hyperopia and retina treatments are possible, whereby OCT serves for direct examination. In the future, we can anticipate that laser therapy supported by imaging will innovate in other areas, including for use in tumor removal, endoscopic brain laser surgery, cutting bones and larynx laser operations.

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