# Optimization of Image Capture Distance for Facial Thermograms in Dentistry
## 4 Discussion  
The current study was undertaken to standardize and optimize the shooting distances when capturing facial thermographic images for screening oral health problems. For this purpose, normal adult volunteers who were considered generally healthy were recruited and facial thermograms were taken in three profile views (front, left, and right) with three shooting distances (15 cm, 30 cm, and 50 cm) for each view. The findings of this study revealed that there was a decrease in the temperature measured as the distances were increased, which was highly significant (\(p\) < 0.001). This trend was observed in both the evaluated temperatures (i.e., in the mean overall temperature of the entire image as well as in mean temperature in the selected ROI). Therefore, the primary null hypothesis, that there is no effect of different shooting distances on the mean overall temperature and the mean temperature at the ROI in the extraoral thermographic images of the face when the image capturing views are kept constant, is thus rejected. Furthermore, this study further confirmed that the mean overall temperature and the mean temperature at the ROI were influenced by demographic and other external factors. Therefore, the secondary hypothesis was also rejected. This trend for the temperature to vary at different shooting distances was consistent with the findings observed in previously published studies where an acceptable temperature difference of 0.2 \({}^{\circ}\)C was seen when the measurements were performed at 0.2 m and 2.5 m distances from the ROI [64; 65; 66]. However, the magnitude of the measured differences in this study, in comparison to the previously published studies, varied. The temperature differences observed in the ROI for these three distances ranged between 0.00 and 0.26 \({}^{\circ}\)C for the left profile; a difference of 0.21 and 0.71 \({}^{\circ}\)C was calculated for the right view, respectively. The temperature differences for the various shooting distances for the front view were between 0.45 and \(-\)1.14 \({}^{\circ}\)C. In the present study, the distances chosen were between 15 cm (0.15 m), which was the camera's minimum focusing, and two other convenient distances of 30 cm (0.3 m) and 50 cm (0.5 m). These were selected to remain within realistic clinical norms, as distances beyond these may not be practically possible in a normal dental clinic setting because of a lack of space. Furthermore, a large distance would involve the inclusion of various elements in the clinic environment within the frame, which may causeinterferences in the thermal imaging. To avoid these influences, the shooting distances were kept small but at the same time viable. Currently, there exists no consensus for a recommended shooting distance for taking facial thermograms. In dental applications, for monitoring post-surgical healing and inflammatory sites, the camera distance used was limited to 0.9 \(\pm\) 0.1 m [59]. However, it has been reported that measurement distances between 0.2 m and 2.5 m produced small differences in temperature variations (0.2 \({}^{\circ}\)C), however, this recommendation was for the thermography of musculoskeletal imaging of the lower extremities [64]. In bench experiments, an image capture distance between 0.7 m and 1.5 m produced the highest inter-camera reproducibility, and shorter capture distances and cameras with superior hardware were preferable [67]. In the current study, the temperature difference observed for the different distances for the left view was in an acceptable range of less than 0.2 \({}^{\circ}\)C, thus indicating that perhaps all three chosen distances for the facial thermograms were acceptable.