Posted by
Benjamin Smith on
URL: http://confocal-microscopy-list.275.s1.nabble.com/thermal-imaging-through-microscope-tp7588813p7588820.html
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One thing no one has brought up yet is the emissivity problem. Thermal
imaging works only if the object has high emissivity (i.e. black in the IR
spectrum). For example, put a piece of black electrical tape on a piece of
aluminum foil and heat the foil up to 100°C (use a thermocouple to confirm
the temperature). If you point an IR thermometer at the electrical tape,
you will get a reading of 100°C, but if you point the IR thermometer at the
aluminum, you will get a temperature of 22°C. This is because aluminum is
highly reflective, meaning that it will emit very little IR when heated (it
has 1/25th the emissivity of the electrical tape). As such, the faint IR
emitted from the foil is swamped out by the much brighter IR being emitted
from nearby objects with higher emissivity, which them reflects off of the
aluminum foil, giving you the reading of 22°C (or whatever the ambient
temperature is). The point is that the amount of IR something emits does
not correlate to its temperature, due to different objects having different
emissivities. Along these lines, if someone wrapped themselves in a space
blanket, they would become effectively invisible to an IR camera. Here is
a nice article explaining the emissivity problem with images:
https://crimsoniv.co.uk/thermography-tips-n-tricks-1-emissivity-estimate/That said, water has a relatively high emissivity, but here in lies the
problem. The water around the nematode will be emitting almost exactly the
same amount of IR as the nematode itself, and even in the same spectrum (as
the temperatures are effectively identical). This is like trying to image
a FITC stained sample that is immersed in a concentrated fluorescein
solution. Conversely, if you removed all of the surrounding water and
placed the nematode on a piece of aluminum foil, you would have a
reasonable shot at using IR to measure the temperature of the nematode, but
I doubt they would survive very long. The only way I could begin to think
of how to make this work would be to have a reflective optics microscope
(as mentioned by Craig) and place the nematodes on a polished aluminum
block with a thin film of water on top, such that there is minimal water
above and below the nematode.
A few practical/economical solutions that come to mind:
1) Place a fine guage thermocouple adjacent to the nematode:
http://www.twire.co.jp/english/Thermocouple2-en.html2) To enhance the signal in #1, place the nematode in a micro-scale
calorimeter.
3) Use the proteins mentioned by Tobias.
Ideally, I would use all three ideas, and a bit of computational modelling
and calibration, such that you can get independent verification of the
result.
Hope this helps,
Ben Smith
P.S.
With all this talk of putting on aluminum foil to avoid IR cameras, a
certain Al Yankovic song comes to mind:
https://www.youtube.com/watch?v=urglg3WimHA&feature=youtu.be&t=109On Fri, Oct 12, 2018 at 9:49 PM Karel Zuzak <
[hidden email]> wrote:
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>
> Dear Kathy,
>
> I am not aware of any commercially available thermal microscope but that
> doesn’t mean it doesn’t exist.
>
> While at NIH In the late 90s our lab was exploring various military
> technologies for medical application and thermal imaging was one.
>
> As you might imagine there have been great advances in thermal imaging as
> well as NIR based night vision. The advantage of thermal is that it is
> passive. Meaning one does not need a source. Your subject is the source.
> Unlike fluorescence or NIR where one must expose the subject to an
> excitation wavelength or NIR illumination.
>
> So thermal is great but we found a lot of subject to subject variability
> in temperature which may have been from the ambient surrounding or one of
> the many physiologic factors influencing temperature.
>
> The other difficulty with thermal was the need for expensive custom
> optics.
>
> So please know once you get a thermal system working you may encounter a
> lot of variability from your experiments that will require a lot of control
> to separate the potentially different sources to metabolism.
>
> Regarding the optics it’s a question of your budget. Back in the 1990s a
> system could easily cost over 100k for the camera alone and needed constant
> liquid nitrogen. The reason being thermal emission occurs around 7 to 14
> um. Assuming I’m remembering correctly. A standard ccd or cmos detector
> won’t detect these wavelengths and standard glass optics won’t transmit
> those wavelengths sufficiently. So one must use specialized focal plane
> arrays and optics along with imaging methods using long integration or
> exposure times or co-adds etc. Then if you need greater magnification and
> need microscope optics then you need to be sure all the optics in that
> microscope light path will transmit the thermal wavelengths.
>
> That said great advances have been made in the thermal field. One can pick
> up a point/shoot IR thermometer at the hardware store. As an example the
> cost of consumer thermal imaging scopes for hunting applications are down
> to 5k where previously they could cost up around 80k. I have seen some as
> low as 700 but the image resolution and thermal variability reflect that
> price.
>
> So if you are set on doing this I would suggest knowing your continuum;
> the thermal/temperature and imaging sensitivity and resolution. Then I
> would start with a call to FLIR. They make a variety of thermal and NIR
> cameras and can possibly help you out. Another place you might like to call
> are microscope companies such as Zeiss, Nikon, Olympus etc and see what
> they have to offer.
>
> If after all this you are still interested and have the budget. I’m happy
> to work with you toward finding/developing a custom solution.
>
> Warm Regards
> Karel Zuzak
>
[hidden email]
>
[hidden email]
>
> 🤠
>
>
> On Oct 12, 2018, at 3:05 PM, Craig Brideau <
[hidden email]>
> wrote:
>
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>
> BK7 optical glass, which is pretty common in microscope optics, drops off
> fairly sharply in transmission by 2 to 2.5um, so that will be a problem.
> The last time I heard about a lab attempting thermal imaging they had a
> custom gold-coated reflective objective constructed for the purpose, and
> designed all their other optics with IR glass like zinc selenide or
> similar. It seems unlikely this would work at all through a conventional
> microscope. I can point you to some additional resources if you are
> interested.
>
> Craig
>
> On Fri, Oct 12, 2018 at 12:17 PM Kathryn Spencer <
[hidden email]>
> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> >
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy> > Post images on
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> posting.
> > *****
> >
> > Hi;
> > I'm looking for suggestions and equipment to do thermal
> > imaging through a microscope. We want to image C. elegans to look at
> their
> > body temperature under different metabolic conditions. While I know they
> > are poikilotherms, we believe they will show a difference to their local
> > background under these conditions. Can you recommend a decent camera for
> > thermal imaging? Are there IR cutoff filters or optics that will not
> > transmit IR wavelengths in a basic fluorescence-type microscope (needed
> for
> > worm-sized resolution ~10x mag)?
> > Thanks in advance.
> > Kathy Spencer
> >
> > The Scripps Research Institute
> > Dept of Molecular and Cellular Neuroscience
> > 10550 N. Torrey Pines Road
> > DNC 216
> > La Jolla, Ca 92037
> >
>
--
Benjamin E. Smith, Ph. D.
Imaging Specialist, Vision Science
University of California, Berkeley
195 Life Sciences Addition
Berkeley, CA 94720-3200
Tel (510) 642-9712
Fax (510) 643-6791
e-mail:
[hidden email]
http://vision.berkeley.edu/?page_id=5635 <
http://vision.berkeley.edu/>