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Thermal Imager Fundamentals
Published in James Stewart Campbell, M. Nathaniel Mead, Human Medical Thermography, 2023
James Stewart Campbell, M. Nathaniel Mead
As uncooled infrared detectors, microbolometer sensors provide a resistance proportional to the received thermal radiance. The focal plane array (FPA) chip in a thermal imager consists of tiny bolometer sensors that measure the energy of incoming mid-infrared rays. The FPA-integrated circuit contains 307,200 active pixels for a 640 × 480 array. Each pixel is a microbolometer leaflet measuring as small as 10 μm × 10 μm × 0.5 μm thick, or a little bigger than a human red blood cell. As leaflets become smaller, they become less effective antennas for thermal radiation, resulting in a relative increase in electronic noise (NETD). This cutoff limits the minimum pixel dimensions.
Basic Approaches of Artificial Intelligence and Machine Learning in Thermal Image Processing
Published in U. Snekhalatha, K. Palani Thanaraj, Kurt Ammer, Artificial Intelligence-Based Infrared Thermal Image Processing and Its Applications, 2023
U. Snekhalatha, K. Palani Thanaraj, Kurt Ammer
Thermal imaging involves capturing infrared radiations emanating from the source by an array of IR sensors. These sensors are made up of photosensitive materials that convert the incident radiations into electrical signals. Then, these electrical signals are sampled and quantized to produce a thermal image. Advanced thermal imagers consist of thermal detectors called microbolometers which convert the radiant IR energy to a change in resistance which in turn is converted to a change in the electrical signal. An array of microbolometers forms the thermal imaging sensor (Focal plane array IR sensor) with each unit size varying from 0.9 to 14 μm, thus leading to IR resolution ranging from 640 × 512 to 320 × 240, respectively, based on the thermal imager type. As the number of pixels increases, the resolution of the camera also increases, producing high spatial resolution images. For example, a 640 × 512 pixel array thermal camera consists of 327680 measurement points for acquiring the temperature data of the object under focus. Similarly, a 320 × 240 pixel resolution thermal camera provides 76800 temperature measurement points of the scene (Vollmer and Möllmann, n.d.).
Infrared Thermal Imagers
Published in Kurt Ammer, Francis Ring, The Thermal Human Body, 2019
There are now a wide range of electronic sensors, and thermal cameras built around uncooled bolometers can be effective for medical use. Imaging with uncooled detectors is now well established, and microbolometer arrays are the most used technology. Present state-of-the-art microbolometers are based on polycrystalline or amorphous materials, usually vanadium oxide (Vox) or amorphous silicon (a-Si).
Non-contact infrared assessment of human body temperature: The journal Temperature toolbox
Published in Temperature, 2021
Josh Foster, Alex Bruce Lloyd, George Havenith
Assuming a camera resolution of 640 by 480 pixels, a thermogram like that in Figure 1, with a field of view estimated at 300 mm wide, roughly has a size of 0.5 mm per pixel (2 pixels/mm). This meets the criteria set in IEC 80601-2-59 (2019) which suggests that for optimal analysis there should be at least 1 pixel per mm. This implies that several pixels will cover the inner(medial) canthus, as required, providing a reliable measurement for this area. However, when considering situations observed, e.g., at airports, cameras are often aimed at a stream of people rather than an individual’s face and cover a field of view with a width of several meters. Taking an example of 3 meters with the same camera and lens, each pixel covers around 4.5 mm (0.22 pixels/mm). Thus, no individual pixel will be representing only the inner eye-canthus, making the measurement more error prone. Budzan and Wyzgolik [23] observed a reduction of 1.6°C in their assessment of inner canthus temperature going from 1 to 3 meters distance (384 × 288-pixel uncooled FPA microbolometer camera). Lens angle is not provided, but field of view is estimated at 70 cm at 1 m (0.55 pixels/mm) to 140 cm at 2 m (0.28 pixels/mm). Note that neither of the conditions in this experiment meets the IEC advised resolution.
Noninvasive intratumoral thermal dose determination during in vivo magnetic nanoparticle hyperthermia: combining surface temperature measurements and computer simulations
Published in International Journal of Hyperthermia, 2020
Gustavo Capistrano, Harley F. Rodrigues, Nicholas Zufelato, Cristhiane Gonçalves, Clever G. Cardoso, Elisangela P. Silveira-Lacerda, Andris F. Bakuzis
The IR Cam spectral bandwidth of acquisition is in the long-wave infrared range (7.5–13 μm), with a temperature measurement ranging from –40 °C to 500 °C and uncertainty of ±2% (an uncooled vanadium oxide-based microbolometer detector). Noise-equivalent temperature difference is less than 40 mK at 30 °C. The objective lens has a focal length equal to 19.31 mm and when IR Cam is placed at a distance d = 50 cm and a resolution of 640 2: a horizontal size of 410 mm and a vertical size of 310 mm, since each pixel has the physical squared dimension of (0.65 2. The commercial software used for IR imaging analysis was the FLIR ResearchIR® (version 1.2.10173.1002). During the MNH treatment, the objective lens of the IR Cam is maintained parallel to the normal direction of the animals tumor to avoid curved object error effects on the surface temperature determination. The temperature error with IR Cam in the in vivo MNH studies is estimated to be 27].