Abstract
Vascular targeted photodynamic therapy (V-PDT) has been successfully utilized for various vascular-related diseases. To optimize the PDT dose and treatment protocols for clinical treatments and to elucidate the biological mechanisms for V-PDT, blood vessels in the dorsal skin-fold window chamber (DSWC) of nude mice are often chosen to perform in vivo studies. In this study, a new automatic protocol to quantify the vasoconstriction of blood vessels in the DSWC model is proposed, which focused on tracking the pixels of blood vessels in pre- V-PDT images that disappear after V-PDT. The disappearing pixels indicate that the blood vessels were constricted, and thus, the vasoconstriction image for pixel distribution can be constructed. For this, the image of the circular region of interest was automatically extracted using the Hough transform. In addition, the U-Net model is employed to segment the image, and the Speeded-Up Robust Features algorithm to automatically register the segmented pre- and post- V-PDT images. The vasoconstriction of blood vessels in the DSWC model after V-PDT is directly quantified, which can avoid by the potential of generating new capillaries. The accuracy, sensitivity and specificity of the U-Net model for image segmentation are 90.64%, 80.12% and 92.83%, respectively. A significant difference in vasoconstriction between a control and a V-PDT group was observed. This new automatic protocol is well suitable for quantifying vasoconstriction in blood vessel image, which holds the potential application in V-PDT studies.
Highlights
Photodynamic therapy (PDT) is based on light activation of photosensitizer localized in target tissue to produce reactive oxygen species (ROS) which selectively eradicate target cells though direct cytotoxicity, vascular shutdown and indirect activation of an immune response
For vascular targeted PDT (V-PDT), a photosensitizer is site-directly delivered to vasculature, and the highly toxic ROS are produced in the vascular lumen upon irradiation with a laser at a particular wavelength, leading to irreversible vessel constriction resulting in damages of the target lesion [1,2]
Given that there are a number of both technical and conceptual reasons why measuring the blood vessel vasoconstriction may fail in the complex and heterogeneous milieu of solid tumors and port-wine stain (PWS) model, blood vessels in the dorsal skin-fold window chamber (DSWC) [11,12] of nude mice and the chorioallantoic membrane (CAM) [13,14] in chicken eggs are widely selected to perform in vivo studies, to optimize the dose and protocol for clinical V-PDT and to further elucidate the biological mechanisms
Summary
Photodynamic therapy (PDT) is based on light activation of photosensitizer localized in target tissue to produce reactive oxygen species (ROS) which selectively eradicate target cells though direct cytotoxicity, vascular shutdown and indirect activation of an immune response. The accuracy in describing the V-PDT response by determining the diameter of a single selected blood vessel is insufficient To overcome this limitation, the vessel density was proposed as an index in optical coherence angiography (OCA) images to predict V-PDT outcome. The changes in vascular density were only analyzed, while the changes in their vascular location were neglected To overcome this limitation, Buzzá et al used the vessel area of the CAM model to analyze the V-PDT response through the calculation of the total pixels in the images for both pre- and post-PDT [14]. The increased number of pixels by appearing thin vessels resulted in a vasoconstriction decrease, suggesting greater errors in the analysis
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