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Veins in NIR

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#21 Andy Perrin

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Posted 30 December 2020 - 17:10

View PostBernard Foot, on 30 December 2020 - 09:16, said:

Looks like this is not just for IR:

https://www.ebay.co....P4AAOSwmo5Zm61~
I know I sound like a broken record, but look at the graph I posted up top. Any contrast ratio greater than 1 will show the veins. Definitely that includes the 650-700nm range shown in the graph, and probably a bit lower than 650 too. Human vision doesn't work so well at the longer wavelengths, though, so even though the contrast ratio would go up for a camera as you go towards the peak at 875nm, your vision would not be sensitive there. So there is probably a different "unaided eye" peak where the contrast ratio goes up but it's balanced by the decline of your eyesight. My guess is that the device you linked is set for that peak.

Edited by Andy Perrin, 30 December 2020 - 17:12.


#22 dabateman

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Posted 30 December 2020 - 23:45

Bernard's linked device is 625nm.
I am surprised by that as not a common led. I would have expected 650nm or 635nm which were used in dvd players or burners.


#23 Andy Perrin

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Posted 31 December 2020 - 04:40

I would have thought 650 also, but who knows what the consideration was? Maybe someone made them a great offer on 625nm LEDs? ("We can't get rid of these things!")

#24 Stefano

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Posted 31 December 2020 - 07:09

I don't think they are that rare. I have one rated at 620-625 nm, but I don't know where it actually peaks.

Edited by Stefano, 31 December 2020 - 08:00.


#25 Bernard Foot

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Posted 03 January 2021 - 10:59

With IR you can also see veins near the skin using reflected IR. The following is a slide I used in a presentation: the hand at the left is mine, the stuff on the right was borrowed from the internet. I guess with the backlight method you can detect veins which are deeper down.

Attached Image: Black Light.jpg
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#26 Bernard Foot

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Posted 27 January 2021 - 13:57

The BBC published an item "Covid: How a £20 gadget could save lives" (see https://www.bbc.co.u...health-55733527 ).

So I thought I'd be at the head of the stampede to get one before they disappeared from the market like toilet paper at the start of a lockdown, and got one of these: https://www.ebay.co....872.m2749.l2649

The reason I mention it here is that it uses the same principle that started this thread - the device uses a red or IR (depending on model) emitter below the finger tip and a detector above the finger nail, and obviously is looking at variations in IR transmision as blood is pumped through the veins.

Anyway, the device has confirmed that I'm still alive. The brand name is Yonkers, so at first I thought great - it's made in New York. But no, it comes from Xuzhou Yongkang Electronic Science Technology Co. (At least it wasn't the Xuzhou Yongkang Novelty and Toy Co.)
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#27 Andy Perrin

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Posted 27 January 2021 - 15:44

I have a pulse oximeter, they are widely available in every US drugstore. NYtimes published a similar article not long ago.

The principle is actually a bit different than what started this thread. Instead of using the single wavelength of maximum contrast to image the veins, they use TWO other important NIR wavelengths — the peak absorptions of oxygenated and unoxygenated blood (I’m sure I have the terms wrong but I’m typing on my phone so hard to google). By looking at the ratio of the transmissions over time, they can calculate the percentage of oxygen. It might be interesting to try this with images also and see the colors fluctuate as the blood flows around in your hand.

Edited by Andy Perrin, 27 January 2021 - 15:50.


#28 dabateman

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Posted 28 January 2021 - 05:07

A Samsung Galaxy smart watch will currently do that. They have leds to monitor your oxygen and heart rate.

The rumor is that the newest Samsung watch and iPhone watches due out this year will have a new Raman monitor and will be able to monitor your blood glucose. No more finger picking needed. But I haven't seen any submissions and don't have access, as this will be a medical device it would need approvals.