Three‐dimensional microvascular network reconstruction from in vivo images with adaptation of the regional inhomogeneity in the signal‐to‐noise ratio

Abstract

Objective: Quantification of angiographic images with two-photon laser scanning fluorescence microscopy (2PLSM) relies on proper segmentation of the vascular images. However, the images contain inhomogeneities in the signal-to-noise ratio (SNR) arising from regional effects of light scattering and absorption. The present study developed a semiautomated quantification method for volume images of 2PLSM angiography by adjusting the binarization threshold according to local SNR along the vessel centerlines.Methods: A phantom model made with fluorescent microbeads was used to incorporate a region-dependent binarization threshold. Results:The recommended SNR for imaging was found to be 4.2-10.6 that provide the true size of imaged objects if the binarization threshold was fixed at 50% of SNR.However, angiographic images in the mouse cortex showed variable SNR up to 45 over the depths. To minimize the errors caused by variable SNR and a spatial extent of the imaged objects in an axial direction, the microvascular networks were threedimensionally reconstructed based on the cross-sectional diameters measured along the vessel centerline from the XY-plane images with adapted binarization threshold.The arterial volume was relatively constant over depths of 0-500 µm, and the capillary volume (1.7% relative to the scanned volume) showed the larger volumes than the artery (0.8%) and vein (0.6%). Conclusions:The present methods allow consistent segmentation of microvasculature by adapting the local inhomogeneity in the SNR, which will be useful for quantitative comparison of the microvascular networks, such as under disease conditions where SNR in the 2PLSM images varies over space and time.

Capillary responses to functional and pathological activations rely on the capillary states at rest

“…The methods are based on a full visualization of blood plasma labelled with SR101, so the imaging field was limited to the upper cortical layers due to signal-to-noise ratio issues in our two-photon microscopic angiography. 9 Thus, the observed results on probability distribution and other capillary parameters could be specific to the cortical regions measured in this study. For example, the most prominent changes in blood volume occur in cortical layer IV during neural activation.…”

“…28,29 However, substantial heterogeneity is present through capillary networks and even in single capillaries. 30 Therefore, in this study, the lumen diameter was measured along the centreline of the vessel in the 3D reconstructed images, 9 allowing us to determine the spatiotemporal heterogeneity in the diameter distributions. The observed variability in the capillary lumen structure could represent an anatomical variation of the capillaries, such as variable coverage by pericytes, 31 phenotypic variations in vascular endothelial cells, 32 and/or variable thickness of glycocalyx layers 33 or variable noises in the image.…”

“…Our previous study on the living mouse cortex showed that more than 50% of parenchymal vessels are composed of microvessels, including capillaries with diameters smaller than the size of the red blood cells. 9 In response to increased neural activity, nearby capillaries dilate and recruit fresh arterial blood from upstream to active sites. 10 Accumulating evidence indicates that capillaries are an active part of neurovascular coupling.…”

Automated capillary flow segmentation and mapping for nailfold video capillaroscopy

“…The length and diameter of each segment were measured (Figure 1C). The diameter was measured at the minimum distance between the two sides of the vessel walls along the centerline 21 . In addition, the radius of curvature was measured for curved segments, and the interval between two straight segments (i.e., between the vessel centerlines) was measured within each capillary loop for straight segments (Figure 1C).…”

Spatiotemporal analysis of blood plasma and blood cell flow fluctuations of cerebral microcirculation in anesthetized rats

“…Capillaries (e.g., vessel less than 8 lm in diameter) constitute more than 50% of the parenchymal microvasculature and thus significant compartments determining cerebral blood flow (CBF) in the parenchyma. 19,20 Capillary flow spontaneously varies at low frequency ($0.1 Hz) and responds to the neuronal activity evoked. 21,22 Recent studies have shown that capillaries are involved in functional hyperemia in neurovascular coupling (for reviews [23][24][25] ).…”