Non-contact multi-spectral imaging combined with thermography to determine physiological changes in perfusion during clinical interventions

Abstract

Reflectance spectroscopy and thermography are used as non-invasive, non-contact imaging method to study the physiology of skin processes or pathophysiology of skin diseases. In this proceeding the development of a multispectral imaging system based on a tunable LED light source is described. The system is validated under laboratory conditions on volunteers. Different algorithms to calculate the O2Hb and HHb changes in the tissue are being developed and the results are presented for different sets of selected wavelengths. Simultaneously thermal images were recorded to image the temperature changes caused by perfusion changes. The first clinical studies have been started. IntroductionBoth reflectance spectroscopy and thermography can be used as a non-invasive, non-contact imaging method to study the physiology of skin processes or pathophysiology of skin diseases. Near infrared (NIR) light has been used for more than 3 decades to study blood and tissue oxygenation changes in animal studies, clinical intervention studies and in oxygen supply and consumption in the brain and muscles [2;5;9;10;12]. Thermography for measuring absolute surface temperatures is recently rediscovered because the new generation thermal cameras have become more practical in use and they are easy to calibrate. Both these techniques can be used to study localized differences in tissue characteristics (e.g. tumor) and dynamic changes in the tissue (e.g. perfusion, oxygenation and temperature changes). In this paper the response of the skin after provocation is described by monitoring changes in temperature and oxygenation induced by tissue perfusion changes. A LED Multi-spectral imaging system has been developed and has been validated. Algorithms are being developed [11] to calculate oxygenation changes in the superficial skin or tissue layer (~1 mm depth). In this paper, reflective spectroscopy and thermography are applied to studying the oxygenation and temperature changes in the skin. First proof of principle is shown in laboratory experiments, hereafter the imaging methods are being applied in clinical studies. Physiology of tissue perfusionThe microcirculation is defined as that part of the vascular tree with vessels smaller than 100 μm: arterioles, capillaries and venules. All those vessels expand to many small branches for optimal oxygen exchange to the surrounding tissue cells. The delivery of oxygen to the tissue depends on the red blood cell content en flow (regulation) in the microcirculation [8;13]. The flow can be regulated by variation in arteriolar resistance (vascular smooth muscles) and the number of open and closed capillaries. In muscles and tissue a large number of capillaries are closed due to contraction of the pre-capillary sphincter, this is a reserve capacity that can be opened when local conditions change (e.g. fall in pO2) and extra oxygen is needed. Figure 1 shows a schematic drawing of the blood vessels in the human skin and a table with average depths where the blood vessels are located. The skin is a comp...

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