Building Diagnostics Using Infrared Camera
7. 2. 2020
Why thermal camera Workswell Medicas – How to measure body temperature accurately and avoid false alarms
20. 3. 2020Non-Contact Temperature Measurement via Thermal Camera
Body temperature measurement via both non-contact and contact thermometers, as well as thermal cameras, is possible at several locations on the human body. However, in order to achieve an exact body temperature reading, the body’s natural circadian rhythm must be taken into account. In a normal circadian rhythm, the lowest body temperature occurs between 3 and 4 o’clock in the morning, and the highest between 4 and 5 in the afternoon. In women, body temperature also varies depending on the phase of the menstrual cycle.
- Contact methods of body temperature measurement:
These are standard body temperature measurement methods in which the sensor measuring is in direct contact with the skin. The results of contact measurements are relatively accurate because the thermometer is placed around large blood vessels, which best reflect the temperature of the core of the body.
The most familiar places for contact measurements are the axilla region (armpit), rectum (anus) and oral cavity (mouth). A sufficiently long contact of the thermometer with the measured individual is a necessary condition for an accurate measurement. However, such measurement is quite time-consuming, as it can take several minutes, and it is done in direct contact with the patient or the examined person. Indeed, another necessary condition for accurate measurement via traditional methods is solid contact with the measured surface – human skin.
- Non-contact methods of body temperature measurement:
Non-contact body temperature measurement methods work by quantifying the intensity of infrared radiation. What makes this approach attractive in the case of infectious disease is that the measured object does not have to touch the sensor, which is a thermal camera.
The forehead and temporal bone areas are the most common locations for non-contact measurement in healthcare institutions, since a superficial temporal artery is located in these regions. The basic requirement for accuracy here is that professionals set correct values for emissivity and reflected apparent temperature, as described in the following sections.
Non-contact body temperature measurement is becoming increasingly popular, especially at healthcare institutions, due to its rapid and safe provision of accurate results. This method can be decisive in delivering an accurate temperature reading for a range of applications, including paediatric care, as it can be very difficult to accurately measure a child’s body temperature. After all, both oral and rectal thermometers are invasive and can present a stress factor for children. On the other hand, axillar thermometers require the thermometer to be held in one place for 30 seconds, which can prove very difficult with an anxious child.
This is where non-contact temperature measurement with infrared thermometers comes in handy. This method is typically used to quickly and hygienically identify fever in the forehead, and it has become a key part of epidemiologic measures. Since it is very quick, it is possible to repeat several measurements over a short period of time and calculate the average of all measured values, resulting in high measurement accuracy (Wang, 2014).
Body Temperature Table with Evaluation
Temperature measured on the forehead is slightly different from the temperature values measured under the arm or in the mouth (the difference is usually approx. 0.1°C). Therefore, it is necessary to follow the table below when reading the values measured by a thermal camera.
| Temperature status | Ear / Forehead | Armpit / Mouth |
| Low body temperature | 35.7 and less | 35.8 and less |
| Normal body temperature | 35.8 – 36.9 | 35.9 – 37.0 |
| Increased body temperature | 37.0 – 37.5 | 37.1 – 37.5 |
| Low-grade fever | 37.6 – 38.0 | 37.6 – 38.0 |
| Moderate fever | 38.1 – 38.5 | 38.1 – 38.5 |
| High fever | 38.6 – 39.4 | 38.6 – 39.4 |
| Very high fever | 39.5 – 42.0 | 39.5 – 42.0 |
The emissivity value of human skin is approximately 0.96. When measuring with a thermal camera, we recommend deflecting from the surface of the forehead (to be more exact, from the normal incline of the measured surface) by approximately 5°. The reflected apparent temperature should be set either to the value equal to the surrounding air temperature, or it can be defined exactly as per the ČSN ISO 18434-1 standard. However, due to the very high emissivity of the human skin, the exact reflected apparent temperature is not of major importance.
Ideal Conditions for Accurate Measurement Include:
- Body temperature is measured no less than 30 minutes after the completion of the most recent physical exertion.
- Body temperature is measured at room temperature.
- Skin on the head is not covered by hair nor cosmetics.
- Skin is dry, without sweat nor dirt.
- The person whose temperature is being measured is acclimatized in the room.
Body temperature is usually the lowest in the morning, around 4 a.m., and it is usually the highest in the late afternoon, around 6 p.m.
Coronavirus (COVID-19) and Temperature Measurement for Screening
Coronavirus screening requires a standard non-contact temperature measurement, one in accord with the conditions described above. There are only a handful of additional steps to take, which have to do with the fact that measurements may take place on a large number of persons at the same time (e.g. in the lobby), and that device operation should result in the reporting of persons with increased temperatures.
KEYWORDS
Measuring temperature, thermal imaging, body temperature, infrared camera, thermal camera, coronavirus, covid-19, thermal vision, thermography, measuring temperature with thermal camera
SOURCES
- Erickson, R. S. (1999). The continuing question of how best to measure body temperature. Critical care medicine, 27(10), 2307-2310.
- Childs, C., Zu, M., Wai, A., Tsai, Y., Wu, S., Li, W. (2012). Infra-red Thermal Imaging of the Inner Canthus: Correlates with the Temperature of the Injured Human Brain. Engineering, 4(10), 53-56. doi: 4236/eng.2012.410B014.
- Bridges, E., Thomas, K. (2017). Noninvasive Measurement of Body Temperature in Critically Ill Patients. Critical Care Nurse. Available at: https://pdfs.semanticscholar.org/8ab1/c49afdd409045c6c7228b3891852f95ec964.pdf
- CARR, E., A., WILMOTH, M., L., ELIADES, A., B., BAKER, P., J., SHELESTAK, D., HEISROTH, K., L., STONER, K., H. (2011). Comparison of temporal artery to rectal temperature measurements in children up to 24 months. ELSEVIER, vol. 26, p. 179-185. Available at: http://www.sciencedirect.com/science/article/pii/S0882596309004126
- BETTA, V., CASCETTA, F., SEPE, D. (1997). An assessment of infrared tympanic thermometers for body temperature measurement, [online], IOPscience, vol. 18, p. 215-225, available at: http://iopscience.iop.org/0967-3334/18/3/006
- Teunissen, L. P. & Daanen, H. A. (2011) Infrared thermal imaging of the inner canthus of the eye as an estimator of body core temperature. Journal of Medical Engineering & Technology, 35(3-4), 134-138. doi: 10.3109/03091902.2011.554595
- Osio, C. E., Carnelli, V. (2007) Comparative study of body temperature measured with a non-contact infrared thermometer versus conventional devices. The first Italian study on 90 paediatric patients. Minerva Pediatr. 59(4): 327–336. Available at: https://www.ncbi.nlm.nih.gov/pubmed/17947839
- Wang, K., Gill, P., Wolstenholme, J., Price, CH. P., C., Thompson, M., Plüddemann, A. (2014). Non-contact infrared thermometers for measuring temperature in children: primary care diagnostic technology update. British Journal of General Practice. 64 (627): e681-e683. DOI: https://doi.org/10.3399/bjgp14X682045