Optoelectronics takes medical devices into uncharted territories

While the past year has seen a slowdown in the introduction of "traditional" medical-laser products, improvements in optoelectronic components are enabling the development of some clever new medical devices, most notably for diagnostic and monitoring applications.

Flexible fibers, smart sensors, miniaturized optics and ultracompact lasers are simplifying patient monitoring diagnostic procedures.

Wearables into washables

Two commercial startups, Sensatex/Lifelink (Dallas, TX) and Lifeshirt.com (Ojai, CA), have found unique ways to integrate wearable computers with wireless patient-monitoring products. While mobile vital-sign-monitoring devices are not new, lightweight, form-fitting monitors that are comfortable and unobtrusive offer some advantages.

Using technology licensed from Georgia Institute of Technology (Atlanta, GA), Sensatex/Lifelink has designed a wireless platform that facilitates moving information from the wearer's body to any point on a network. A textile developed at Georgia Tech that integrates sensors, optical fibers, and other components into the fabric eliminates the attachments characteristic of other monitoring systems. The company's first product to incorporate this platform is the Smart Shirt.

The Smart Shirt enables data collection from the wearer's body to an outside network or wireless device and data transmission from networks or devices to the wearer's body. Live video and audio also can be run through the shirt. "There are really no practical limits to the capacity of the shirt," says Jeff Wolf, CEO of Sensatex/Lifelink. "It is only constrained by network bandwidth capacities."

Sensatex also is developing an application programming interface (API) to facilitate the development of other applications using the Smart Shirt platform. The API will support standards-based wireless networking protocols such as Bluetooth and IEEE 802.11. The Smart Shirt and the API are in beta testing and should be commercially available on an OEM basis next year, according to the company.

LifeShirt.com is focusing on monitoring applications by defining the vital signs that its product, the LifeShirt, can track. The system consists of a tanktop-style shirt with embedded sensors, a personal-digital-assistant (PDA) module, and related monitoring software called RespiEvents that received US Food and Drug Administration 510(k) clearance last August. The RespiEvents software turns raw data into waveforms so that a researcher or physician can read the data, according to Andrew Behar, COO of LifeShirt.com.

The shirt's embedded sensors gather data continuously on more than 40 vital signs, and this information is loaded into the PDA. The module encrypts the data and sends the information to the LifeShirt.com data center for processing and analysis. The data are sent via modem or by hotsyncing the PDA to a computer or the Internet.

The current prototype is in beta testing; a commercial version should be available in early 2001 at a cost of $100 for the shirt, $150 for the Palm OS-based PDA module, and $30 a day for the monitoring service.

Advances in CMOS imagers, white-light LEDs, and mixed-signal application-specific integrated circuits have enabled Given Imaging (Yokneam, Israel) to develop a miniature video system that literally fits inside a pill. The tetherless device includes illumination, camera, a radio transmitter, and a battery, all within a package just 3 cm long and 11 mm in diameter. Patients swallow the device and wear a belt-pack-sized radio receiver and video recorder while going about their normal activities. The goal is to improve upon existing endoscopic viewing methods, which can be difficult, uncomfortable, and, in some cases, risky.

One end of the device contains a fisheye-lens optical dome designed to allow LED light from within to illuminate the tissue and light reflected from the tissue to enter and be captured by the imaging chip. The image is transmitted via UHF signals from the capsule to the antenna array attached to the patient. In current clinical trials, the disposable system moves through the gastrointestinal (GI) tract, recording images every few minutes for more than five hours. Once it has finished traveling through the GI tract, the pill is expelled. The physician can then view the recording from the belt-pack. "We believe use of the device will prove to be completely painless," says Dr. Paul Swain of the Royal London Hospital, who is lead investigator for the London-based clinical trials. US trials are taking place at Mount Sinai School of Medicine (New York, NY).

Smart scalpel, smarter surgery

Researchers at Sandia National Laboratories (Albuquerque, NM) are developing a unique vertical-cavity surface-emitting laser (VCSEL) designed to be embedded in a scalpel to provide surgeons with real-time data about the tissue they are cutting. Paul Gourley and colleagues have built a prototype and performed some in vitro testing to demonstrate how their "smart scalpel" can detect the presence of cancer cells as a surgeon cuts away a tumor.

In essence, the scalpel functions as a portable flow-cell cytometer. The underlying technology combines a VCSEL with a tiny pump built onto a single chip. The chip combines microfluidic technology with the VCSEL; the micropump pushes cells through tiny channels cut into the glass surface of the device chip, and the channels pass through the laser cavity. In the absence of cells, the VCSEL emits only spontaneous emission. The presence of cells triggers lasing.

The GaAlAs/GaAs laser operates in a single longitudinal mode but in multiple lateral modes. By examining the lateral modes and how the laser peak shifts around 850 nm, the researchers have been able to glean information about the biochemistry of the cells. In this section of the near-infrared, cells refract but do not absorb light. Subtle differences in the index of refraction provide clues about the biochemistry, size, and even shape of the cells.

Further development is required before the smart scalpel will be ready for clinical applications.