Skin project

Hello all,

I was hoping you could help me with a project of mine. I'm an engineering student trying to solve the problem of pressure ulcers on the human skin.
Normally, when you press down on your skin, it blanches (changes colour). In patients where a pressure ulcer is beginning its onset, the reigon where the ulcer is developing is red and does not blanch. This is hard to detect in people with tans and dark-coloured skin, so I was trying to develop a device that could detect changes in the colour of the skin quickly and efficiently for nurses and caretakers.

I wanted to use a device with electronics which I've been reading about, namely phototransistors and photodiodes. I was thinking I could incorporate them with a LED of some sort on a clear plate that could be pushed on the skin to elicit a blanching response, which could then be detected by the photo-sensor.

My questions about this are:

1. Is this idea feasable?
if not, could someone give me ideas on hat to look for if I wanted to make a compact skin surface temperature detector that was accurate to 0.1 degrees centigrade?

2. What is the better choice for a project like this? Phototransistors or diodes?

3. Finally, I understand that that light striking the base of these photo-sensors generates a voltage or current, but how could something like be incorporated with an LED? How do they go together in function? Also, how would this fit together in a device that would be placed on a clear plate of some sort that would be placed on the skin?


Thank you in advance!

If I understand you correctly, you are talking about venous skin ulcers which result from a lack of blood flow to certain tissues of a body, most notably the legs.

I am not certain how deep light would penetrate the skin for such a device. I do know they can measure heart rate with a device on your finger. Intruiging idea I think, not sure what the pitfalls are. Currently ultrasound is used to detect poor bloodflow.

Infra-red will penetrate. IR sensors are used to monitor pulse rate, IR film will show veins through skin. The sensors are cheap and easy to get, might be worth experimenting with to see if they will get through the melannin to the capilaries.

Take a look at how a pulse-oximeter works and you may find what you need. It's more or less the same thing as you are doing but for a different reason. Just do a quick google on pulse oximeter and you'll see what I mean.

That uses infra-red and red, and works through the non-pigmented skin on the bottom of the hand. Real question is if it will work on pigmented skin where you could have a pressure ulcer. (is that like a bed sore?) Qaiserms is probably going to have to do some experimenting to find out.

qaiserms said:

2. What is the better choice for a project like this? Phototransistors or diodes?

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I dont' know anything about the medical end of your project. However, I can apply some common sense. I believe that skin pigments (melanin) would block visible and ultraviolet light very effectively, since its function is to protect the skin from too much sunlight. Any hope to accomplish your goals would need to come from the infrared region, as mentioned by others.

However, you may want to look into devices used in the fiber optics communications field. There, they use wavelengths of 1300 nm and 1550 nm which may work better than the more familiar 700-1000 nm devices. You may also want to consider using optical fiber to deliver and receive the laser/LED radiation.

Note that a standard silicon photodetector will not work at these wavelenths, but germanium, or InGaAsP based photodiodes work well in this region. Note that diode lasers, LEDs, photodiodes and optical fiber for either 1300 nm or 1550 nm operation are reasonably priced lately, due to the widespread use of optical fiber communication technology.

That's a good idea, maybe longer wavelength IR would help.

Kinda looks like a familiar 900nm device MIGHT work - here's some absorption spectra:
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But then the reflectance goes up and up...
Melanoma - skin cancer reviewed :: Skin reflectance spectra :: March :: 2006

Maybe plain old red light would be the most effective.

duffy said:

But then the reflectance goes up and up...

Maybe plain old red light would be the most effective.

Click to expand...

Wow, that's a good point. It's amazing how reflective the skin is at longer wavelengths.