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Amrish Walke
Posted on Monday, January 05, 2004 - 3:59 pm:   

Is it possible to use NIRS to measure the temperature of blood that is say 3 cms deep within the body? I am assuming that there are no blood vessels before that depth. I read a few articles about this and they dont really talk about the accuracy of the temperature measurement at that depth.
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hlmark
Posted on Monday, January 05, 2004 - 4:33 pm:   

Amrish - I think your assumption is a bad one. If I cut my skin anywhere on my body, I will bleed at much smaller depths than 3 cm. (say, even 0.5 mm), so there are certainly blood vessels closer to the surface than that depth.

Even that notwithstanding, I don't think you can use NIR to measure the temperature at depth without that measurement being interfered with by the body tissue at smaller depths, whether they have blood or not. The principle of NIR temperature measurement is emission of electromagnetic radiation, which occurs for all materials that are above zero degrees Kelvin (absolute zero). The total emission increases as the fourth power of the radiation, so sometimes it is possible to measure a hot object that is behind a colder object, since most of the radiation will come from the hot object. Since the human body is mostly at a pretty uniform temeprature, though, you will not be able to avoid including radiation from the layers of tissue closer to the surface of the skin in your measurement.

In addition, in the body, the radiation does not simply emerge when it is generated. The nature of tissue is to scatter radiation, so that radiation arising from one given layer does not emerge only from that layer, but will scatter from all layers in between the source layer and the skin surface.

Overall, I think the answer to your question is "no".

Howard

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