Laser Doppler imaging (LDI) has been considered the gold standard for assessing wound depth in patients with burn injuries. By analyzing the blood flow in a burn wound, Moor LDI can predict healing time and has been shown to have 97% accuracy. However, the Moor LDI is a large, cumbersome machine that is difficult to move between rooms, requires patients to remain still (especially difficult with children), and is cost prohibitive. In contrast, FLIR ONE— a smartphone-attached, thermal imaging camera that uses infrared technology to determine the temperature of a burn wound—is a low-cost, portable alternative to Moor LDI that takes instant images via a point-and-shoot feature.
For a paper published in Scars, Burns & Healing, our study team aimed to demonstrate the usefulness of the FLIR ONE’s thermal imaging capabilities in assessing burn injuries by comparing its use in clinical practice with the Moor LDI. Forty-five patients who sustained burn injuries within the previous 5 days were imaged using both the FLIR ONE and LDI. Images taken with the FLIR ONE were imported into the FLIR Tools mobile application and analyzed using the temperature measurement feature.
The average temperature of the burn injury was compared with the temperature of the surrounding skin. If the burn injury was less than 1.1˚C cooler than normal skin, it was categorized as a deep dermal injury and used as a surrogate marker for a healing time of greater than 21 days. This was compared with the Moor LDI prediction for healing time for the same burn injuries.
Correlation Between Skin Temperatures and Healing Time
The FLIR ONE achieved a sensitivity of 66.67% (95% CI, 52.71-89.86) and specificity of 76.67% (95% CI, 12.52-85.51) when predicting a burn injury would heal within 21 days. The research also indicated with statistical significance that the FLIR ONE shows that burns healing in less than 21 days have a mean temperature difference (when compared to normal skin) of approximately 1˚C compared with burns healing in more than 21 days. This mean temperature difference for burns healing in less than 21 days compared with burns healing in more than 21 days reflects what we found in previous literature. Pearson’s test showed a significant correlation between the difference in burn wound and normal skin temperature with healing times. The warmer the burn injury compared with normal skin, the shorter the healing time, which is to be expected, as one would predict a shorter healing time the closer the burn wound temperature is to that of normal skin (Figure).
Evaporative Cooling Can Affect Readings
The FLIR ONE, however, is not without its own limitations. Several of the images taken with the FLIR ONE were affected by evaporative cooling. Water vapor released from the burn injury can make it appear cooler on thermal imaging compared with its actual temperature. In these cases, thermography can overpredict healing time and, therefore, influence management, as a predicted healing time of more than 21 days was a relative threshold for surgical intervention in our burn center.
My colleagues and I would like to see future research focus on additional thermal imaging cameras with improved thermographic accuracy. The issue of evaporative cooling has been widely documented in thermography research and needs to be addressed if thermography’s role is to be expanded in this field. Although the FLIR ONE is unlikely to rival the Moor LDI as the gold standard, there is potential for its use in centers where the LDI’s costs and size act as barriers.
