Improvement of Sidestream Dark Field Imaging with an Image Acquisition Stabilizer

Background: In the present study we developed, evaluated in volunteers, and clinically validated an image acquisition stabilizer (IAS) for Sidestream Dark Field (SDF) imaging.Methods: The IAS is a stainless steel sterilizable ring which fits around the SDF probe tip. The IAS creates adhesion to the imaged tissue by application of negative pressure. The effects of the IAS on the sublingual microcirculatory flow velocities, the force required to induce pressure artifacts (PA), the time to acquire a stable image, and the duration of stable imaging were assessed in healthy volunteers. To demonstrate the clinical applicability of the SDF setup in combination with the IAS, simultaneous bilateral sublingual imaging of the microcirculation were performed during a lung recruitment maneuver (LRM) in mechanically ventilated critically ill patients. One SDF device was operated handheld; the second was fitted with the IAS and held in position by a mechanic arm. Lateral drift, number of losses of image stability and duration of stable imaging of the two methods were compared.Results: Five healthy volunteers were studied. The IAS did not affect microcirculatory flow velocities. A significantly greater force had to applied onto the tissue to induced PA with compared to without IAS (0.25 ± 0.15 N without vs. 0.62 ± 0.05 N with the IAS, p < 0.001). The IAS ensured an increased duration of a stable image sequence (8 ± 2 s without vs. 42 ± 8 s with the IAS, p < 0.001). The time required to obtain a stable image sequence was similar with and without the IAS. In eight mechanically ventilated patients undergoing a LRM the use of the IAS resulted in a significantly reduced image drifting and enabled the acquisition of significantly longer stable image sequences (24 ± 5 s without vs. 67 ± 14 s with the IAS, p = 0.006).Conclusions: The present study has validated the use of an IAS for improvement of SDF imaging by demonstrating that the IAS did not affect microcirculatory perfusion in the microscopic field of view. The IAS improved both axial and lateral SDF image stability and thereby increased the critical force required to induce pressure artifacts. The IAS ensured a significantly increased duration of maintaining a stable image sequence

Measuring blood flow in the skeletal muscle microcirculation using laser speckle flowmetry

The presence of a native collateral circulation, which serves as a natural bypass for blood flow around an occlusion, improves prognosis for patients with ischemic diseases, such as peripheral arterial occlusive disease (PAOD). However, not all patients have a native collateral circulation, and animal models suggest a genetic basis for this variability. In mice, such as the BALB/c, that lack native arteriolar collaterals, neocollateral formation from capillaries that connect two arterial trees can occur after arterial occlusion, resulting in reperfusion of the ischemic watershed. Immature arterialized collateral capillaries (ACCs) at 7 days post arterial occlusion do not vasodilate in response to physiological stimuli and are therefore unable to match blood flow with metabolic demand, but mature ACCs at 21 days exhibit normal vascular reactivity. Therefore we wanted to determine if vasodilation of ACCs at 21 days post arterial occlusion is capable of increasing flow throughout the ischemic arteriolar tree, because the ACCs are small-caliber vessels feeding progressively larger arterioles. One aspect of blood flow, vessel diameter, is measured routinely in our lab using bright field intravital microscopy; however blood velocity is more challenging to measure in the spinotrapezius microvasculature. In particular, we wanted to assess vasculature-wide changes in blood flow, which cannot be accomplished using laser Doppler flowmetry due to its small field of view or particle image velocimetry due to the curvature of the spinotrapezius. Therefore, we adapted a laser speckle flowmetry (LSF) protocol to measure blood velocity in the spinotrapezius microvasculature. In LSF, the scattering of laser light incident on the muscle produces a characteristic speckle. This speckle changes over time as erythrocytes flow through the vasculature of the muscle. If captured over the finite exposure time of a detector, the speckle is blurred, and the degree of blurring is related to the speed at which the erythrocytes are flowing through the vasculature. LSF yields velocity information across the entire field of view, and multiple fields of view can be stitched together to create a velocity map of the spinotrapezius vasculature. Using LSF, in conjunction with bright field intravital microscopy, we measured blood velocity and blood vessel diameter in vivo to quantify changes in blood flow. We found that vasodilation of mature ACCs (i.e. at day-21) increases blood flow (288 ± 72%) in the ischemic tree, which is comparable to the contralateral, control arterial tree (168 ± 76%), while vasodilation of immature ACCs (i.e. at day-7) does not increase blood flow (17 ± 27%) in the ischemic tree. The ability of mature ACCs to increase flow in the ischemic tree supports their potential as a therapeutic target for patients with PAOD who lack native collateral vessels. Future work will include the use of a contrast agent to provide more detailed vessel analysis (e.g. branch order effects), and similar analyses on mice with relevant comorbidities such as diabetes mellitus and hypercholesterolemia to study any potential impairment in arterialization and outward remodeling

An automated method for analysis of microcirculation videos for accurate assessment of tissue perfusion

Abstract Background Imaging of the human microcirculation in real-time has the potential to detect injuries and illnesses that disturb the microcirculation at earlier stages and may improve the efficacy of resuscitation. Despite advanced imaging techniques to monitor the microcirculation, there are currently no tools for the near real-time analysis of the videos produced by these imaging systems. An automated system tool that can extract microvasculature information and monitor changes in tissue perfusion quantitatively might be invaluable as a diagnostic and therapeutic endpoint for resuscitation. Methods The experimental algorithm automatically extracts microvascular network and quantitatively measures changes in the microcirculation. There are two main parts in the algorithm: video processing and vessel segmentation. Microcirculatory videos are first stabilized in a video processing step to remove motion artifacts. In the vessel segmentation process, the microvascular network is extracted using multiple level thresholding and pixel verification techniques. Threshold levels are selected using histogram information of a set of training video recordings. Pixel-by-pixel differences are calculated throughout the frames to identify active blood vessels and capillaries with flow. Results Sublingual microcirculatory videos are recorded from anesthetized swine at baseline and during hemorrhage using a hand-held Side-stream Dark Field (SDF) imaging device to track changes in the microvasculature during hemorrhage. Automatically segmented vessels in the recordings are analyzed visually and the functional capillary density (FCD) values calculated by the algorithm are compared for both health baseline and hemorrhagic conditions. These results were compared to independently made FCD measurements using a well-known semi-automated method. Results of the fully automated algorithm demonstrated a significant decrease of FCD values. Similar, but more variable FCD values were calculated using a commercially available software program requiring manual editing. Conclusions An entirely automated system for analyzing microcirculation videos to reduce human interaction and computation time is developed. The algorithm successfully stabilizes video recordings, segments blood vessels, identifies vessels without flow and calculates FCD in a fully automated process. The automated process provides an equal or better separation between healthy and hemorrhagic FCD values compared to currently available semi-automatic techniques. The proposed method shows promise for the quantitative measurement of changes occurring in microcirculation during injury.http://deepblue.lib.umich.edu/bitstream/2027.42/112336/1/12880_2011_Article_161.pd

The microcirculation of the critically ill pediatric patient

textabstractNote: This article is one of eleven reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2011 (Springer Verlag) and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/annual. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/890