Page 17 - Effects of radiotherapy and hyperbaric oxygen therapy on oral microcirculation Renee Helmers

General introduction and outline of the thesis
DEVELOPMENT OF BEDSIDE MICROCIRCULATION MONITORING 1 TECHNIQUES
It is an ongoing challenge to develop suitable techniques to monitor and quantify the microcirculation at the patient-side. Several techniques exist and over the years they have assisted and facilitated clinicians and researchers with the ability to examine and investigate different aspects of the microcirculation. These established techniques range from routine static evaluation of microvascular tissue based on histology,4 estimation of tissue microvascular flow (e.g., laser Doppler flowmetry, laser speckle contrast imaging),15,40 tissue oxygenation (e.g., near-infrared spectroscopy)21 and direct microvascular visualization (e.g., intravital microscopy, optical coherence tomography, spectroscopy-based hand-held vital microscopy (e.g., orthogonal polarization spectral imaging, sidestream dark-field imaging, incident dark-field illumination imaging)).8,10,30 Bedside application and the potential to assess different microcirculatory parameters are essential for clinical evaluation of microvascular tissue overtime. HVM techniques evolved rapidly in the last 3 decades to meet clinical and diagnostic requirements associated with different medical specialties.
After introduction of incident dark-field (IDF) illumination for intravital microscopy in 1971, which provided a deeper field of illumination and visualization of erythrocytes below the surface,35 devices to improve clinical applicability and image quality followed. Groner et al. developed the orthogonal polarization spectral (OPS) imaging technique (CytoscanTM, Cytometrics, Philadelphia, PA, USA).14 OPS has been validated against intravital microscopy in different settings showing significant correlation between parameters like red blood cell (RBC) velocity, vessel diameter and functional capillary density.5 Following OPS imaging an upgrade in the form of the sidestream dark-field (SDF) imaging device (MicroScan Video Microscope System, MicroVision Medical, Amsterdam, The Netherlands) was developed in 2007 by Goedhart et al. and again was validated against the OPS. The results of Goedhart et al. showed good comparative values for parameters like capillary diameters and RBC velocities between the two imaging devices with SDF imaging presenting a higher image quality in sublingual microcirculation versus OPS.13 SDF imaging used a new way of illumination by positioning LEDs at the tip and around the central light guide which prevents light reflections from tissue surface and improved contrasting. The illuminating outer core causes scattering which resulted in the illumination
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