Special Report
FIBRE-OPTIC SYSTEMS OPEN UP NEW FRONTIERS
From ultrathin fibres for minimally invasive surgery to photodynamic therapy,
medical OEMs and suppliers are finding opportunities in a growing market.
Leslie Laine
For decades, manufacturers have experienced a rapidly increasing demand for medical fibre-optic systems that can be used for illumination, imaging, and delivery of tissue-cutting laser light. For high-precision surgical procedures such as ophthalmic surgery and for the imaging of areas that are deep within the body, lasers and fibre optics have replaced earlier tools. Today, the market for these medical fibre optics is strong, and new applications for these systems are being discovered and developed all the time.
For medical OEMs, these new specialty applications have created opportunities, as well as a need to find suppliers who can produce components that solve very specific manufacturing challenges.
In response to this need, suppliers are expanding their capabilities. Fibres can now be made with more control than ever before, allowing a wider variety of performance characteristics to be determined. Suppliers have introduced new processes, such as coating fibres with fluorescent dyes to enable them to transmit weak signals or signals that must travel convoluted paths within complex devices. Lasers are not only more precise than before, but they can also be much less costly.
These types of improvements in component manufacturing have been an essential part of the advances in medical fibre-optic devices over the past few years. In some cases, innovations in component performance have been driven by device manufacturers. For example, when Diametrics Medical Ltd. (High Wycombe, Bucks, UK) developed and began producing a continuous optical blood-gas sensor, the firm needed to source a supplier who could mass produce suitable materials for the clinical environment.
The sensor monitors the pH, pCO2, and pO2 content in arterial blood and allows the results to be displayed in real time. The sensor operates by using indicator dyes to measure the amount of fluorescent light that is absorbed. Because the sensor resides in a patient's artery, its outer package must be no larger than 0.5 mm diam. This space constraint limits the size of the optical fibre within the device to 0.178 mm diam maximum.
According to Michael Irvine, R&D manager at Diametrics, the suppliers of the optical fibres and other critical materials had to expand their production capabilities to support the sensor construction, as well as conduct very sophisticated testing to ensure that the materials would be reliable.
Photodynamic Therapy Lasers
Together, medical device and pharmaceutical companies are furthering the use of light-activated drugs. Unlike drug developer PDT Inc. (Santa Barbara, CA, USA), which has the ability to produce peripheral devices in-house, most pharmaceutical firms rely upon an external supplier for devices that make the drugs work.
One of the most promising new applications for medical fibre optics is photodynamic therapy (PDT), and developing cost-effective PDT lasers is an area of opportunity for suppliers. In PDT, a patient receives a drug that is activated by only a specific wavelength of light. The light is then focused on the area of the body where the drug is needed.
The potential of PDT technology is just beginning to be realized. The first PDT application was approved for use about five years ago. This application was Photofrin, a photosensitive drug approved by Canada in 1993 for the treatment of bladder cancer. Since then, Photofrin, which is developed and marketed by QLT PhotoTherapeutics Inc. (Vancouver, BC, Canada), has also been approved by the United States, France, Japan, and the Netherlands for the treatment of esophageal cancer.
When Photofrin is injected at the cancer site, it attaches to the proteins that accumulate in tumors, creating a concentration of the drug in the abnormal tissue rather than in healthy tissue. A fibre-optic tube is then introduced to the tumor to activate the drug, which releases toxins that kill cancerous cells.
PDT may offer an answer to many medical conditions. In addition to the treatment of cancers, the therapy has proven to be efficacious in treating inflammatory ailments such as arthritis. PDT may also be able to treat bacteria and viruses, or even to decontaminate blood for transfusions.
The therapy also offers a challenge for laser manufacturers. PDT requires lasers that can produce very specific wavelengths. For example, Photofrin requires light at exactly 632 nm for activation. Until very recently, only gas lasers that can cost hundreds of thousands of dollars have been available for PDT. In the United States, these expensive lasers are still the only ones that are approved for this therapy.
However, one German supplier has developed and is marketing a cost-effective diode laser for PDT. CeramOptec GmbH (Bonn), a manufacturer of a wide variety of cutting-edge and experimental medical fibre optics and lasers, has developed diode lasers that are capable of delivering the wavelengths required by PDT drugs. The diode lasers, which can cost as little as a few thousand dollars, weigh only about 9 kg and measure 16 x 22 x 34 cm. They can operate with standard 110- or 220-V input and produce 2-W output.
Inexpensive diode lasers have not been widely used for PDT in the past because structural limitations have prevented them from accurately producing the wavelengths needed for PDT, and from precisely focusing on the affected body area.
But CeramOptec has developed proprietary fluorescent fibres that eliminate these design problems, and the company offers diode lasers in wavelengths of 630, 632, and 635 nm, which is sufficient for most PDT applications.
The lasers are CE marked and available for sale in Europe, but US FDA approval is pending.
Complex Signal Paths
The problem of routing data through complex paths within certain medical devices has also led to innovations in fibre production.
For example, computed tomography (CT) systems are made up of a rotating scanner and a stationary base unit. In these systems, optical fibres have typically had to be incorporated into the rotating axis to enable data transmission from the scanner to the base.
Schleifring und Apparatebau GmbH (Fürstenfeldbruck, Germany) has developed a contactless optical rotary joint for CT systems. With this new joint, data are converted into an optical signal, the light is coupled laterally by reflection into a fibre doped with fluorescent dyes, and the signal is carried to the fibre's end, where it is converted back into an electrical signal. This contactless transmission of light allows for a free bore on the CT scanner from 50 mm to 5 m, produces no friction, and enables a data transmission rate of 150 Mbaud.
Minimally Invasive Fibres
With the current emphasis on minimally invasive surgery and diagnostics, the need for ever smaller and more efficient optical fibres is another area in which suppliers are making rapid improvements.
Schölly Fiberoptic GmbH (Denzlingen, Germany) produces tiny optics for illumination and image transmission. The company's sales manager, Daniel Lacher, has observed the trend toward miniaturization in fibre optics. A decade ago, says Lacher, typical medical fibres measured 10 mm diam, but today fibres of 1 mm or less are preferred because they lessen patient trauma during surgery or diagnostics.
Schölly produces disposable endoscopes as small as 0.034 mm diam and autoclavable endoscopes as small as 1 mm. Over the years, the company has expanded its capabilities to anticipate the need for ever smaller fibres, and it has sometimes actually found itself waiting for new developments in medicine to create a demand for the fibres it can produce. "The technology is progressing faster than applications for it," Lacher says. "We have problem solutions just sitting in the drawer waiting for applications."
Continuing Progress
Inexpensive lasers for PDT, fibre miniaturization, and complex data paths are just a few examples of the numerous innovations developed by suppliers in recent years.
One announcement for a technical conference on specialty fibre optics and lasers at the recent International Biomedical Optics Symposium (BiOS '98) boldly predicts that "we are at the threshold of a new generation of medical devices involving specialty optical fibre and lasers."
Sponsored by the International Society for Optical Engineering (SPIE), BiOS '98 was held on 2430 January in San Jose, CA, USA. The conference has been in existence for 14 years. Its growth from 19 technical papers in 1985 to about 750 in 1998 reflects the expansion of the medical fibre-optic industry as a whole.
The pace of invention and discovery in this area of manufacturing continues to be rapid. As fast as medical researchers point out new ways to use fibre optics, manufacturers and suppliers continue to find new methods to produce them.
