Modern operating microscopes offer high power illumination to ensure optimal visualization, but can also cause thermal damage. The aim of our study is to quantify the thermal effects in vivo and discuss conditions for safe use. In a pilot study on volunteers, we measured the temperature at the skin surface during microscope illumination, including the influence of anaesthesia and the effects of staining, draping, or moistening of the skin. Irradiation within the limit given by safety regulations (200 mW/cm(2)) results in skin surface temperature of 43 degrees C. Higher intensities (forearm 335 mW/cm(2), back 250 mW/cm(2)) are tolerated, resulting in reversible hyperaemia. At a very high illumination intensity (750 mW/cm(2)), pain occurs within 30 s at temperatures of 46 degrees C+/-1 degrees C (hand and forearm), and 43 degrees C+/-2 degrees C (back), respectively. Anaesthesia has no distinct effect on the temperature, whereas staining and drapes result in much higher temperatures (>100 degrees C). Moistening at practicable flow rates can reduce temperature efficiently when combined with a light absorbing and water absorbent drape. In conclusion, surgeons must be aware that surgical microscope illumination without protective means can cause skin temperatures to rise much above pain threshold, which in our study serves as a (conservative) benchmark for potential damage.
Photothermal radiometry is being used e.g. for characterization of changes in the microstructure of metals. It is non-destructive, non-contact and much faster than a metallographic analysis. However, this method uses only one detector element, therefore the inspection of areas requires time-consuming scanning. In this paper, we will show that infrared cameras can be used for detection as well. With an exact synchronization between the excitation laser and the IR image grabbing, reproducible phase contrast values can be obtained, thus converting photothermal radiometry into an imaging method. This is demonstrated on samples with different case hardening depths and grinding burn respectively.
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