Abstract
BackgroundNear 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.MethodsTemperature 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.ResultsElevations 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.ConclusionIn 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.
Highlights
Near infrared (NIR) light has been used widely to monitor important hemodynamic parameters in tissue non-invasively
We concentrate on effects of NIR light on skin, since the light source is attached to the skin during diffuse optical measurements
A typical temperature increase due to the combined effect of conducted and radiated heats of the light emitting diodes (LED) is plotted in figure 4
Summary
Near infrared (NIR) light has been used widely to monitor important hemodynamic parameters in tissue non-invasively. 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. 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. 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 hemodynamic state of the tissue [1], and is the principle upon which pulse oximetry is based. We concentrate on effects of NIR light on skin, since the light source is attached to the skin during diffuse optical measurements
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