FEATURE

Photonics gets under the skin

Nick Morris takes the pulse of the medical photonics sector

Photonics and electro-optical products are being used for an ever-increasing variety of applications in the medical sector, from cutting-edge cancer research to cosmetic and beauty treatment. Laser materials processing techniques are bringing greater precision and hygiene levels to the manufacture of sterile medical equipment.

Optical cancer scanning

Many people will develop a form of cancer at some point in their lives. Luckily, most cancers can be successfully treated if they are detected early enough. However, many forms of testing currently used, such as tissue biopsy, involve minor surgery. Samples taken must be sent for accurate testing. The time taken for this process can be mean a distressing wait for the patient, and also adds to the cost of diagnosis.

A new method of cancer detection, called the CancerScannerT, developed by the bioscience division of the US Department of Energy and further developed by SpectraPath Technologies, is currently undergoing clinical trials. The system uses a spectroscopy system from Ocean Optics to detect changes from normal to pre-cancerous and cancerous cells. The scanner has already been successful in discovering malignant cells in both animal and human trials.

The system uses a USB2000 spectrometer to analyse light scattered elastically from cellular nuclei. The altered nuclei of malignant cells generate different scattered light spectra when compared to normal cells. The CancerScannerT can recognise the altered scattered spectra, allowing quick, easy, and relatively cheap detection of potential tumours, when compared to the alternative of time-consuming biopsies and related minor invasive surgery, giving patients a better chance for survival.

Precise neural stimulation

In order to understand neurological conditions, like Parkinson's disease and epilepsy, and other nerve damage such as spinal cord injuries, doctors and researchers need to understand how nerves and neurons react with each other. Direct stimulation of the neural system lies at the basis of the field of neural interfaces. Until recently electric probe stimulators were used in applications such as locating and treating peripheral nerves, brain mapping, and nerve conduction studies. However, electrical pulse treatment is not a precise art. It can even result in nerve and tissue damage in the targeted area.

Optical neural stimulation can overcome the problems associated with electrical stimulation. American firm Aculight, in association with Vanderbilt University, has recently been granted an award from the US National Institutes of Health to develop a suitable device. Aculight's system uses a pulsed, mid-infrared laser coupled with an optical fibre probe.

Jim Webb, senior scientist at Aculight, says: 'Optical stimulation is more spatially precise and highly controlled, so you can activate individual nerves. It also avoids the collateral tissue or nerve damage that can result from electrical pulses'.

Laser bone imaging

Until recently, the only way doctors could measure bone strength was by using traditional X-ray imaging. A new laser imaging technique, which can more fully measure the strength of bones, has now been developed. Scientists hope this new method will help in the prediction of whether young women will be likely to develop osteoporosis at some point in their lives.

When checking for osteoporosis, X-ray imaging is used to measure the density of the mineral content of bones. However, the strength of bones is derived not only from the mineral density, but also from the collagen density. Adding mineral crystals to collagen makes bones. Collagen is the protein that quite literally holds bones together. The new laser-based spectroscopic technique can measure the density of collagen in bone tissue, giving doctors a much clearer picture of the strength of bones, hence any problems or possible risk of developing osteoporosis can be highlighted earlier and more accurately. Steps can then be taken to counteract the development of this crippling condition.

Dr Edward Draper, of Imperial College London, and the Royal Veterinary College, says: 'We hope we can further develop this technique, and use it as part of a screening programme that, hopefully, could be done in any doctor's surgery. By identifying the risk of any problems developing early enough, this could not only make an enormous difference to the health of individuals, but could help health services by negating the need for more extreme and costly interventions later'.

Drug testing

An optical testing instrument from new company VariDose, based in Loughborough, UK, could dramatically reduce the time taken for pulmonary drug delivery analysis in the pharmaceutical industry.

Rather than using traditional measurement systems, such as flow impingers and cascade impactors, the VariDose system uses a series of optoelectronic sensors to measure the size and flow of particles in the drug cloud released from an inhaler. Specifically, sensors monitor the drug cloud as it passes through planes of red, blue, and infrared light. In less than a minute, the device measures the structure of the drug cloud as it evolves, in terms of particle size distribution, fine particle fraction, and cloud turbulence. Other measuring devices and inhalation simulators can be added to enhance the system. Detailed analysis of experimental data can be carried out on a standard lab computer.

Researches can use the data, obtained quickly and easily from VariDose, to enhance drug delivery from inhalers, making both research, and the treatment itself, more efficient.

Laser eye surgery

Laser eye surgery can offer many people who are severely long or shortsighted dramatic improvement in their vision and, in some cases, can even give people near-perfect sight. However, there are risks associated with current techniques. The procedure involves cutting a 'flap' into the cornea, the surface of the eye, then using a laser to reshape the cornea or lens within the eye. But in cutting open the protective surface of the eye, this procedure can lead to scaring, infection, or other related problems, all of which may have a detrimental effect on the functioning of the eye.

A new technique developed by a team at the Fraunhofer Institute for Biomedical Engineering aims to overcome these potential problems by using femtosecond pulse lasers. This sort of laser can be focused through the outer tissue and focused directly onto the target area, reducing surgical time and helping the healing process. The team, led by Karsten König, is currently working to reduce the effect of radiation transmitted beyond the target sight onto the retina of the eye, where it can cause adverse effects (similar to the current method). 'We are attempting to remove tissue constituents gently and very precisely, using extremely low pulse energies of just a few nanojoules,' says König.

This process can be extended to other forms of microsurgery. For example, the research team at the Fraunhofer Institute has succeeded in making the world's smallest artificial incision in living tissue, by cutting a hole with a width of just 70nm. Exploiting this high-precision cutting technique may lead to precision gene splicing or drug delivery. 'In this way we can introduce pharmaceutical agents or genes into individual cells,' explains König.

Aesthetic treatment

Spectrographic systems are now being used for both medical and cosmetic analysis. Systems such as the Moritex Facial Stage DM-3 use fluorescent and ultraviolet lighting, digital cameras, and computer imaging analysis, to help skin specialists identify potential problems such as pores blocked with dirt or oil, and other blemishes that may not be visible to the naked eye. Other products, such as Moritex's Clarity image management system, allow users to compare captured images with a database of illustrative images of many typical skin conditions, allowing quick and accurate diagnosis.

Microscopy

Microscopy is one of the oldest practices of medical research. New imaging methods, which use advanced photonic systems, allow medical researchers to better understand biological processes, and therefore develop better treatments.

Modern medical microscopy systems use a variety of imaging methods, such as laser reflection, transmission, and fluorescence, to acquire data about biological systems and processes. Many photonics companies, such as Laser Components, offer dedicated microscopy equipment, such as individual filters and filter sets, for dye-specific fluorescent protein imaging.

Other companies offer complete microscopy systems. For example, Andor's Revolution XD confocal spinning disk microscope allows researchers to capture multi-dimensional, high-resolution images of fast dynamic biological activity. The Revolution uses high speed multi-point confocal scanning with a sensitive EMCCD camera, in conjunction with a solid-state laser combiner to generate images of biological samples.

Such technology is particularly useful in cases where fluorescent dye concentrations or fluorescent protein labelling needs to be kept to a minimum to avoid disrupting the physiological events or the natural functions of proteins that are being investigated. The revolution also minimises specimen exposure, thereby reducing photo bleaching and photo toxicity.

Take, for example, the case of cell signalling, where researchers wish to study discrete releases of calcium in biological samples. Lower dye concentration minimises the risk that calcium in the cell will be 'buffered' by the dye, and the calcium wave can travel the full length of the cell being investigated. Less time is wasted observing artefacts of the dying process, so more time can be spent on relevant biological phenomena.

Non-invasive temperature taking

Thermal imaging finds many uses in the medical and medical research fields. Body temperature is a major issue in many diagnoses, such as pneumonia, studies of wound healing, and blood flow through transplanted tissue.

For medical applications, accurate calibration is critical. For example, a temperature difference of two degrees can mean the difference between a common cold and a life endangering fever. Uncertainties in calibration data repeatability and sensitivity mean that many thermal imaging cameras have an accuracy of only +/- 2ºC. This is clearly undesirable in a medical camera.

On its FTI MV camera system, Land Instruments overcomes this problem by combining the infrared detector array with two high-stability, P100i blackbody sources for temperature reference. This means the system is calibrated continuously, thereby providing reliable temperature measurement, accurate to +/-0.5ºC, improving to +/-0.2ºC with repeated measurements. The imager does not need to be returned to the manufacturer for recalibration, reducing instrument downtime, increasing its potential use for medical diagnosis.

Laser processing of medical devices

One of the prime concerns for makers of medical apparatus is hygiene. This is particularly true for equipment that comes into contact with, or is designed for operation within, the human body. Foreign bodies can lead to infection and surgical complication.

One of the major attractions for using laser-welding and cutting systems, such as the StarWeld Performance, from Rofin-Baasel, for the production of medical instruments is that laser welding is hygienic. Laser welding is a non-contact process, so it does not produce metal burrs. Neither does it use any consumables, such as glue or solder. This means there is less risk of contamination when laser-welded devices are used for surgery. This benefit is equally relevant for devices designed to operate inside the body, such as pacemakers. In the construction of such systems the hermetic properties of laser welds are particularly useful.

The high precision achievable with laser cutting and welding (the StarWeld has a standard range of spot sizes from 0.3 to 2mm) means that small, intricate medical devices, such as fine wires and foils, can be produced with relative ease. Medical grade materials, such as titanium, which is usually difficult to join, can also be welded easily using lasers.

As we have seen, optics products are used for many varied applications in the medical sector. Photonics equipment is helping accelerate the pace of medical research, increase the accuracy of diagnosis, and provide better treatments for many ailments.

Medical lighting

Good lighting is essential in the operating theatre. For surgeons to operate safely, the operating table must be illuminated brightly and evenly. Modern surgical lamps call for the integration of multiple high-quality optical components. For companies that supply the medical market, the simulation and optimisation of the systems by using state-of-the-art optics simulation tools guarantee the development of sophisticated surgical lamps within a short time.

Due to the importance of illumination geometry and spectral characteristics, lamp manufacturers, such as Opsira, cannot simply aim to optimise the maximum brightness of the lamp, but must carefully design all the parts to ensure a good combination of illumination characteristics.

Surgical lamps contain more components than just a light source. The emitted light must be controlled and directed, using components such as reflectors and lens coatings. It is the job of these components to ensure even lighting across the illuminated area. To this end, Opsira lamp lenses are developed and tested with small reflective facets, and indentations, called lamellae, built into the transmitting surface, designed to diffuse the light evenly. The lens may also be coated with a filter to suppress or enhance certain frequencies in the emitted spectrum. Besides the spectral characteristics, the filters are particularly responsible for the elimination of long-wave thermal radiation, which causes an undesirable heating of the surgical field.

Good lamp design requires good computer simulation. Good simulation requires accurate component modelling. This is particularly true in the case of the light source itself, especially as new sources, such as gas discharge lamps and LEDs, become more common. Opsira uses a goniometer to study the luminance of various lamp designs. This device measures and records the three-dimensional near-field intensity and spectral characteristics of the light source being measured. This information can be fed back into the design system creating a feedback that serves to enhance the design process constantly.