Abstract
Pressure myography studies have played a crucial role in our understanding of vascular physiology and pathophysiology. Such studies depend upon the reliable measurement of changes in the diameter of isolated vessel segments over time. Although several software packages are available to carry out such measurements on small arteries and veins, no such software exists to study smaller vessels (<50 µm in diameter). We provide here a new, freely available open-source algorithm, MyoTracker, to measure and track changes in the diameter of small isolated retinal arterioles. The program has been developed as an ImageJ plug-in and uses a combination of cost analysis and edge enhancement to detect the vessel walls. In tests performed on a dataset of 102 images, automatic measurements were found to be comparable to those of manual ones. The program was also able to track both fast and slow constrictions and dilations during intraluminal pressure changes and following application of several drugs. Variability in automated measurements during analysis of videos and processing times were also investigated and are reported. MyoTracker is a new software to assist during pressure myography experiments on small isolated retinal arterioles. It provides fast and accurate measurements with low levels of noise and works with both individual images and videos. Although the program was developed to work with small arterioles, it is also capable of tracking the walls of other types of microvessels, including venules and capillaries. It also works well with larger arteries, and therefore may provide an alternative to other packages developed for larger vessels when its features are considered advantageous.
Highlights
Pressure myography is widely used to monitor the responses of small arteries and veins to physical and chemical stimuli
Pressure myography has been instrumental in our current understanding of the myogenic response and in characterising the pharmacological actions of drugs and other vasoactive compounds on the vascular system [1], [2]
Small vessels (,50 mm in diameter) are unsuitable for use with commercially available pressure myography systems, we have recently developed methods to carry out myography studies on isolated arterioles from the rat retina [25]
Summary
Pressure myography is widely used to monitor the responses of small arteries and veins to physical and chemical stimuli. The SoftEdge Myocyte Cell Length Acquisition Module [13], [14], [15], [16] detects and tracks vessel walls within a couple of user-defined windows after a threshold value and a ‘crossing condition’ have been set. Another algorithm, developed by Kim et al [17], involves the user defining a line perpendicular to the vessel and extending beyond the outer walls for intensity analysis at a high-contrast region of the vessel before carrying out Otsu’s thresholding. All of these programs rely on the use of thresholding methods which are well-suited to the analysis of arteries and veins where there is normally a high level of contrast between the vessel wall and other areas of the image
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