30 Jan 2003
OPTO delegates hear that high-brightness white LEDs are making an impact in Japanese medicine.
Nichia's white LEDs are beginning to find medical applications in Japan, according to two presentations from Wednesday's OPTO conference:
• Junichi Shimada from Kyoto University of Medicine in Japan told a packed conference session about an LED-based lighting system for surgeons. In early December, Shimada's "lighting goggles" were put to their first test during an operation to remove a tumor in a patient's chest.
The head-mounted light source makes use of an array of Nichia's indium gallium nitride (InGaN) high brightness white LEDs to illuminate the patient during an operation. The goggles are portable, lightweight and power-efficient.
They ensure that illumination is always aligned with the surgeon's line of sight and can reach deep inside the body. This is in contrast to conventional overhead lighting, which is often obscured by the surgeon bending over the patient, resulting in troublesome shadows.
Shimada and his colleagues from Kyoto University's electrical engineering department have developed a series of prototypes. The most recent uses 16 white LED chips from Nichia, each emitting 23 lumens at an operating current of 350 mA. The LEDs, located in two equal arrays on the side of the goggles, are mounted on an aluminium nitride plate to help dissipate heat.
Although initial results are promising there are still some problems to be overcome. Currently, the goggles can only be worn for a maximum of 15 minutes before they become too hot. They also suffer from poor color rendering so that muscles appear to have a bluish tint. Shimada hopes to improve the situation by using InGaN LEDs doped with Eu3+.
• In another Japanese study, Katsuya Kobashi from Yamaguchi University and colleagues have developed an electronic endoscope that uses a white LED and a CCD camera. The system, which has a color-rendering index of 93, has produced clear images of an animal's abdominal cavity. Kobashi has tested several different types of white LED and says that those using an orange-yellow-green-blue (OYGB) phosphor gave images with the most natural colors.
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.