Do surface temperatures measure core temperature? No.

Working from home during the COVID19 pandemic has proven a challenge for many of us. Our students are not allowed to pursue their research, and yet most of us are working as hard from home as we would be on campus.

Anyhow, at the beginning of the lockdown, I gathered what equipment I could from the lab and set up to research at home. Hardly a serious pursuit, but I was designing some training material for an overseas student and needed the equipment at home anyway.

What kind of research can you do on yourself on lockdown you might ask? A little bit of thermal imaging!

Since COVID19 is/was on everyone’s mind, I knew it was only a matter of time before the fever scanning would start up again (remembering SARS 2003 and all the thermal cameras in airports).

But thermoregulatory physiologists know that surface temperature rarely, if ever, is equal to core temperature so then, how do we reconcile this with the return to use of superficial fever scanning?

Maybe it is because imaging is appealing to people and it is compelling that a region of the face or head close to the eye always appears warm, so naturally people assume it might represent or correlate to core measurements of body temperature. Indeed, even in animal thermal biology, this is one of more common questions people ask me: “Can eye temperature be an estimate of core temperature?”. To which I quip, “No”, with caveats.

I am not aware of systematic studies demonstrating that these warm eye/head surface temperatures are really good at estimating core temperature, but we previously measured core and surface temperatures in a previous study of ours in ducklings across different times of day and during a period of fasting:

Duckling thermal images – captures at two air temperatures and under different conditions.

Core temperature rises and falls quite substantially (ranging from ~39 to ~42C) across these different states and time periods:

Core (crop) temperature in ducklings measured over a course of 12 days, including a fasting period between days 5-8.

But the correlation between core temperature and the maximum eye region temperature is not that great. Indeed, you would expect the values to fall along or at least be parallel to the dotted line of equality below, but in the case of low air temperatures, the relationship is quite poor and the surface temperatures are much cooler than core.

Maximum eye region temperature correlates with core temperature, but not very strongly and is quite heavily dependent on surrounding air temperature.

So, it is easy to conclude that max eye temperature is not always a reliable indicator of core temperature in these ducks. Maybe we could derive an empirical calibration curve, taking into account air temperature, but the point is that this requires accurate temperature data and stable environmental conditions rarely present in the field.

So, what about the lockdown research mentioned earlier?

Having plenty of time to myself, I set up a thermal camera to capture a thermal image of my face at various times throughout the day to capture the natural variation in body temperature (no fever, per se, but my daily oral temperature measurements range from 35.6 to 36.9C). Here is a sample image, outlining the typical regions of skin surface measured:

Red arrow (inner canthus of the eye, typical hottest part of the face, ~35.2C here). Blue arrow (tongue, equivalent to measurement with oral thermomemeter, ~36.7C here). Green question mark (forehead, location of scanners seen on a lot of websites, ~32.4C here).

It got too scary the longer I was in lockdown as my hair grew too long and disheveled, so I ceased the experiment after only a short period.

But the results (next 3 graphs) below show how poorly forehead assesses normal oral temperature, and even how maximum eye temperature is ~1C cooler than oral temperature and influenced by nearby ambient conditions (my garage was cold back in April so I set up there for a few measurements).

Conclusions: Ignoring the N=1 subject (due to the pandemic this seems justified), forehead is a poor measure of oral temperature (3.85C too low), maximum eye temperature a bit better (but still 1C too low and affected by air temperature), while simply pointing the camera in your mouth and getting maximum temperature yields a temperature ~0.5C higher than an oral thermometer.

So, why if you look at any images of companies and airports doing fever scanning they point devices at people’s foreheads or relying on a single pixel value from possibly the eye region?

The simple answer is that it is easy to do, but from a target accuracy perspective, it is terrible, especially if low accuracy devices are being employed inappropriately. In the one image above, the device is pointing at someone’s hair, which shields the skin and thus produces a cooler value. Cooler values will not trigger a fever detection even if it is there!

So, wherefore is the future of fever scanning? Intuitively, it seems it should work, but are we measuring the wrong thing? Why don’t we measure inside the mouth where normal oral thermometers do? At least this is better than crappy forehead measurements. Is this a privacy issue? Is it feasible to do in rapid scanning processes? Will it be feasible if we are all wearing masks?

I am not the first to write on this. This blog project was mostly a distraction in the early days of lockdown to keep my mind off the situation. I attach a few key articles and opinion pieces on the subject below that have commented more clearly on the connection (or lack) between fever and infection and why fever screening is not a panacea.

Links to further reading:

Scientific studies demonstrating reasonable predictive power for fever scanning:

Other articles discussing why using fever scanning does not equate to infection and misses asymptomatic cases of COVID19:

WHO Recommendations on temperature screening:

Idea for a Review Paper Anyone?

I think this situation really needs another look by the physiology community. My anecdote here is simply based on self reflection/measurement but also based on years of experience with thermal imaging.

The first rule of thermal imaging in biological systems: “Surface Temperature is not equal to Core Temperature.” We can’t forget that. If you want to use surface temperature, you have to do a lot of calibration checks or have very good control over your subject.

In case a grad student locked down at home wants a writing project, here are a few key points that I know should impact the predictive power of max surface temperature measurements in the context of rapid fever scanning in public places:

  • Air temperature near skin
  • Air flow (convective heat exchange) over skin
  • Blood flow relationship with the skin surface
  • Camera user skills and training
  • Quality and accuracy of the thermal scanner (some scanners I see people using have accuracies of +-2 to 4C).
  • Pre-symptomatic people lack fever
  • Masking of fever with antipyretic drugs undetected by scanning
  • What is the precise correspondence of eye canthus temperature with core temperature measurement?

Unreasonable requests…

A letter I wrote explaining why I declined to review a manuscript for PLOS One:

Dear PLOS One,

I am sorry, but 10 days is an unreasonable turn around time to request a peer reviewer. I prefer to focus my peer review activities toward journals that outwardly promote work-life balance and value the peer reviewers’ busy schedules. I realise PLOS one is a large journal so I would ask that these comments not be taken personally, but perhaps be passed along to someone who might be able to effect change. Let PLOS One set an example by returning to the halcyon days of a 3 week turn around request time for reviews and providing reviewers with compensation for their time! I know that won’t happen, but if reviewers don’t explain their reasons for declining to review, how will journals change their practises. As a fee based journal, this is something that could potentially be structured into the publication costs.

_____

This evoked an immediate and sympathetic response from the editor, and as a result I think it only fair that I agree to review the manuscript now.  I guess I cannot really be unreasonable to the scientific editor or the authors.  Now if we can only convince the journals to stop obsessing over rapid turnaround times, and recognise that volunteers are what keep their machines running.

 

 

Thoughts on Crowd-Sourcing of Basic Scientific Research?

crowdsourced1

I meant to post this a month or two ago, but have been busy with teaching and grant reviews!

Recently, I participated in a crowd-sourcing initiative (Can thermal imaging detect torpor in Hummingbirds?) that many of my friends and colleagues no doubt saw me posting a lot about.  I cannot take credit for the efforts behind this; the initiative was started by an organised and enthusiastic group from Loyola Marymount University in California.  They were kind enough to invite/allow me to participate in the process, partly to lend expertise and support.  I also wanted to see how crowd-sourced research funding works from the inside, so participating allowed me to see.   Here are thoughts on the experience so far, Pro vs. Con (my comments below should not be construed to reflect those of the team, they are simply my reflections on seeking funding):

Pros

  • Access to a new funding source (ok, that’s a no-brainer).
  • Encourages scientists to take on riskier, but interesting research.  There could be a niche here for research that the public likes, but scientists might not actually initially consider to be novel or relevant.  I am accustomed to hearing the oft coined criticism of ivory-tower types pursuing esoteric research….at least the crowd-sourcing provides the public direct input via donations!
  • Students get to be involved in the research funding stages.  I think this is actually an excellent learning experience for graduate students, as they learn to write their proposal in language understandable by all and are allowed to be responsible for their research question.
  • You can engage the general public in science at the planning stages and throughout the research.  Experiment.com actually asks you to keep the public up to date on their website.  Ultimately, this enhances outreach and demonstrates our shared passion for science.

Cons

  • There is a general feeling that you are being overly sales pitchy about your science; I would think most scientists are comfortable with arguing from facts, rather than coercion or emotions.  Prepare to work outside your comfort zone.
  • Families and friends become rapidly tapped out so you might only get one shot at raising enough funds!  Thank your family and friends, since they will likely be the ones that support the research.
  • The crowd-source organisers do not appear to actively promote any particular campaign, other than hosting the project online.  This surprised me.  Maybe they were doing more behind the scenes we did not notice.
  • The levels of funds are usually only sufficient for small projects that likely do require some nominal attachment to already funded research, so the point above requires careful planning.
  • If asked to update the public website with research progress, there is chance of running into conflict when trying to publish the work at a later date.
  • Working with animals or doing field studies poses challenges from the perspective of ethical oversight.  Usually, in Canada, ethical approval for research comes after the funding, but crowd-source websites expect the research to be approval in principal before seeking funds.  This could effectively disqualify many from applying.

 

I know my Cons appear to outweigh the Pros….that should not dissuade people from looking into this, but I did not consider many of these aspects until we were well into the fund raising part of the project, and I think it would be helpful for others to know how to plan ahead if they speak to others who have used scientific crowd-funding websites.

 

Two final thoughts

Should research labs that are already funded really be asking for more money?  In our case, this was a novel project and association of new collaborators who would not be doing the research in the first place, wishing to pursue something new.  But what about researchers using crowd-sourcing to supplement their already funded research?

A final (but distant) concern I have is that this approach might be suggested as a free-market replacement for research council funding.  I hope this is never the case.  No scientists have the time to spend marketing their research, nor the resources to do it in a manner that would really raise enough money.  These are not money making ventures, they are knowledge generation for the most part.  A free-market approach would have the perverse effect of highlighting “popular” research, but not necessarily scientific research (think Reality TV).  My own experience suggests that the crowd-sourcing efforts was like an elaborate bake sale for raising money, where you convince your friends, family, and neighbours to fund your research!  Presumably after one round of this, chances of asking for future funding risks turning people off of science, and the sustainability in the long term would be limited.