New optical sensors monitor patients during MRIs

September 25, 2008--European researchers have developed a system of wearable textiles incorporating optical sensors to monitor breathing, heart rate, and blood oxygen levels during magnetic resonance imaging procedures, which is especially useful in eliminating the need for anesthesia in children.

September 25, 2008--Magnetic resonance scans will be safer for children and other patients needing anesthesia, thanks to new kinds of optical sensors developed by a team of European researchers with the "Optical Fiber Sensing Embedded in Textiles for Healthcare" (OFSETH) project.

Magnetic resonance imaging (MRI) is a powerful, non-invasive way of obtaining detailed internal images of the human body. Unlike X-rays, MRI does not use ionizing radiation but probes the inside of the body with strong magnetic fields. It has become an indispensable aid to diagnosis and treatment. But for some people, the experience of MRI can be upsetting. The patient must lie motionless for as much as an hour or more within the tunnel of the MRI machine. Children, especially, can find the experience frightening and the solution is to calm them with sedative or anesthetic drugs.

"Anesthesia for MRI examination uses the same drugs as anesthesia for any surgical procedure," says Mathieu Jeanne of the Centre Hospitalier Régional Universitaire de Lille, one of the partners in the OFSETH project. "Even if spontaneous respiration can be preserved most of the time during anesthesia, it is constantly at risk of being impaired by anesthetic drugs or by upper airway obstruction."

As the anesthetist cannot accompany the patient, it is essential that the patient be monitored remotely from the neighboring control room. Unfortunately, the magnetic fields can interfere with electrical equipment, meaning that conventional electronic sensors cannot be used while patients are having their scan. There is also a risk of burns from electric currents induced in metal components by the strong magnetic field.

Optical solution
According to an article in ICT Results, the EU-funded OFSETH project is pursuing a solution using optical sensors and optical fibers. With no metal parts, optical sensors transmit information in the form of light pulses and are unaffected by magnetic fields. The OFSETH project is developing wearable textiles that incorporate optical monitoring systems. The partners are concentrating on systems suitable for children between 1 and 5 years old that will monitor breathing, heart rate, and blood oxygen levels.

"The light-guiding properties of an optical fiber can change depending on its surrounding environment," explains François Narbonneau of Multitel, an independent research center based in Mons, Belgium, which is coordinating the project. "By measuring the constraints applied to an optical fiber or by analyzing modifications of the signal properties transmitted in an optical fiber, it is possible to measure a lot of parameters."

To monitor breathing, the researchers wove a plastic optical fiber into an elastic bandage to be placed around the chest or abdomen. The bandage expands and contracts as the patient breathes and two types of sensors detect the strains in the fiber to monitor the breathing rate.

The team has also designed a non-invasive blood-oxygen sensor that compares the absorption of red and infrared light to gauge how much oxygen is present in the blood. The sensor fits on a finger-tip and detects reflected light from the skin. It measures pulse rate as well. Although other non-electronic devices can be used to measure vital functions, they can be cumbersome and expensive. And while optical technology is already in use for MRI monitoring, the patient often needs to be switched between two or three different systems as they are moved between different parts of the hospital.

Woven into textiles
The system developed by OFSETH avoids the need for such changes by incorporating the sensors into a garment worn by the patient. Plastic optical fibers are particularly suitable for such applications as they can be woven into the fabric.

"The main innovation is to use optical fiber sensors embedded into textile during the fabrication process for medical applications," says Narbonneau. "The key idea is to provide a garment which allows monitoring of the patient from arrival at the hospital until departure without changing or disconnecting the monitoring system."

All the hardware components are now ready and the next phase is to integrate them into a prototype garment which will then be tested in clinical trials. The project is due to finish in August 2009.

The ten partners contributed their expertise on health care, optical sensing and textile technology to make the project a reality. The lessons learned can be applied to a much wider range of applications. For example, the team is already planning to use the same sensors to create baby clothes that can be used at home to guard against sudden 'cot deaths'.

OFSETH is part of SFIT, a cluster of projects to develop 'smart' textiles supported by the EU's Sixth Framework Programme for research.

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