Curvature effect quantification for in-vivo IR thermography

Medical Infrared (IR) Imaging has become an important diagnostic tool over recent years. However, one underlying problem in medical diagnostics is associated with accurate quantification of body surface temperatures. This problem is caused by the artifacts induced by the curvature of objects, which leads to inaccurate temperature mapping and biased diagnostic results. Therefore, in our study, an experiment-based analysis is conducted to address the curvature effects toward the 3D temperature reconstruction of the IR thermography image. For quantification purposes, an isothermal copper plate with flat surface, and a cylindrical metal container filled with water are imaged. For the flat surface, the tilting angle measured from camera axis was varied incrementally from 0̊ to 60 ̊, such that the effects of surface viewing angle and travel distance on the measured temperature can be explored. On the cylindrical curved surface, the points viewed from 0̊ to 90̊ with respect to the camera axis are simultaneously imaged at different temperature levels. The experimental data obtained for the flat surface indicate that both viewing angle and distance effects become noticeable for angles over 40 ̊. The travel distance contributes a minor change when compared with viewing angle. The experimental results from the curved surface indicate that the curvature effect becomes pronounced when the viewing angle is larger than 60 ̊. The measurement error on the curved surface is compared with the simulation using the non-dielectric model, and the normalized temperature difference relative to 0̊ viewing angle was analyzed at six temperature levels. These results indicate that the linear formula associated with directional emissivity is a reasonable approximation for the measurement error, and the normalized error curves change consistently with viewing angle at various temperatures. Therefore, the analysis in this study implies that the directional emissivity based on the non-dielectric model can be applied for the calibration of measurement error. The normalized error curve serves as a consistent basis to correct the measurement error due to curvature artifacts.