Safety assessment of near infrared light emitting diodes for diffuse optical measurements

Bozkurt Alper, Onaral, Onaral Banu

Description

Near infrared (NIR) light has been used widely to monitor important hemodynamic parameters in tissue non-invasively. Pulse oximetry, near infrared spectroscopy, and diffuse optical tomography are examples of such NIR light-based applications. These and other similar applications employ either lasers or light emitting diodes (LED) as the source of the NIR light. Although the hazards of laser sources have been addressed in regulations, the risk of LED sources in such applications is still unknown. Methods Temperature increase of the human skin caused by near infrared LED has been measured by means of in-vivo and in-vitro experiments. Effects of the conducted and radiated heat in the temperature increase have been analyzed separately. Results Elevations in skin temperature up to 10°C have been observed. The effect of radiated heat due to NIR absorption is low – less than 0.5°C – since emitted light power is comparable to the NIR part of sunlight. The conducted heat due to semiconductor junction of the LED can cause temperature increases up to 9°C. It has been shown that adjusting operational parameters by amplitude modulating or time multiplexing the LED decreases the temperature increase of the skin significantly. Conclusion In this study, we demonstrate that the major risk source of the LED in direct contact with skin is the conducted heat of the LED semiconductor junction, which may cause serious skin burns. Adjusting operational parameters by amplitude modulating or time multiplexing the LED can keep the LED within safe temperature ranges.

Informations

• Publié par: biomed
• Publié le: 01 janvier 2004
• Nombre de lectures: 0
• Langue: English

Extrait

BioMedical Engineering OnLine

BioMedCentral

Open Access Research Safety assessment of near infrared light emitting diodes for diffuse optical measurements Alper Bozkurt* and Banu Onaral

Address: School of Biomedical Engineering, Science and Health Systems, Drexel University, 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, USA Email: Alper Bozkurt*  [e-mail]; Banu Onaral  [e-mail] * Corresponding author

Published: 22 March 2004Received: 30 January 2004 Accepted: 22 March 2004 BioMedical Engineering OnLine2004,3:9 This article is available from: http://www.biomedical-engineering-online.com/content/3/1/9 © 2004 Bozkurt and Onaral; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.

Abstract Background:Near infrared (NIR) light has been used widely to monitor important hemodynamic parameters in tissue non-invasively. Pulse oximetry, near infrared spectroscopy, and diffuse optical tomography are examples of such NIR light-based applications. These and other similar applications employ either lasers or light emitting diodes (LED) as the source of the NIR light. Although the hazards of laser sources have been addressed in regulations, the risk of LED sources in such applications is still unknown. Methods:Temperature increase of the human skin caused by near infrared LED has been measured by means of in-vivo and in-vitro experiments. Effects of the conducted and radiated heat in the temperature increase have been analyzed separately. Results:Elevations in skin temperature up to 10°C have been observed. The effect of radiated heat due to NIR absorption is low – less than 0.5°C – since emitted light power is comparable to the NIR part of sunlight. The conducted heat due to semiconductor junction of the LED can cause temperature increases up to 9°C. It has been shown that adjusting operational parameters by amplitude modulating or time multiplexing the LED decreases the temperature increase of the skin significantly. Conclusion:In this study, we demonstrate that the major risk source of the LED in direct contact with skin is the conducted heat of the LED semiconductor junction, which may cause serious skin burns. Adjusting operational parameters by amplitude modulating or time multiplexing the LED can keep the LED within safe temperature ranges.

Background New medical applications using optical measurement techniques are emerging rapidly. These methods are used to study the content of biological pigments and tissue structures by analyzing the absorption and scattering of the induced light. When visible or near infrared light at specific wavelengths in the window of 600 to 950 nm (fig. 1) is shone through the tissue, information about the

amount of blood chromophores such as oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) can be obtained. This constitutes an important measure of the hemody namic state of the tissue [1], and is the principle upon which pulse oximetry is based.

The hazard potential of the nearinfrared light should be considered from two perspectives: eye hazards and skin

Page 1 of 10 (page number not for citation purposes)