A Simplified Implementation of Edge Detection in MATLAB is Faster and More Sensitive than Fast Fourier Transform for Actin Fiber Alignment Quantification

Abstract

Fiber alignment plays a critical role in the structure and function of cells and tissues. While fiber alignment quantification is important to experimental analysis and several different methods for quantifying fiber alignment exist, many studies focus on qualitative rather than quantitative analysis perhaps due to the complexity of current fiber alignment methods. Speed and sensitivity were compared in edge detection and fast Fourier transform (FFT) for measuring actin fiber alignment in cells exposed to shear stress. While edge detection using matrix multiplication was consistently more sensitive than FFT, image processing time was significantly longer. However, when MATLAB functions were used to implement edge detection, MATLAB's efficient element-by-element calculations and fast filtering techniques reduced computation cost 100 times compared to the matrix multiplication edge detection method. The new computation time was comparable to the FFT method, and MATLAB edge detection produced well-distributed fiber angle distributions that statistically distinguished aligned and unaligned fibers in half as many sample images. When the FFT sensitivity was improved by dividing images into smaller subsections, processing time grew larger than the time required for MATLAB edge detection. Implementation of edge detection in MATLAB is simpler, faster, and more sensitive than FFT for fiber alignment quantification.

Glycated collagen alters endothelial cell actin alignment and nitric oxide release in response to fluid shear stress

“…Actin fiber alignment was analyzed using a custom edge detection Matlab program (Kemeny and Clyne, 2011). Edge detection uses image intensity changes to find fiber edges, and then determines the direction of maximum intensity gradient to calculate the fiber orientation angle.…”

Glycated Collagen Decreased Endothelial Cell Fibronectin Alignment in Response to Cyclic Stretch Via Interruption of Actin Alignment

“…Images were taken at four loca tions in the central region, which was previously validated to experience uniform strain [31]. Fibronectin fiber alignment was quantified using an edge detection method developed in our labo ratory [35]. Edge detection uses image pixel intensity changes to find fiber edges.…”

“…Rhodamine phalloidin (0.165/tM, Invitrogen) and bis-benzimide (0.2/ig/ml, Invitrogen) were used to label actin fibers and cell nuclei, respectively. Actin fiber alignment was quantified using edge detection as previously described [35].…”

Glycated Collagen Impairs Endothelial Cell Response to Cyclic Stretch

“…Actin fiber alignment was quantified using edge detection as per a previously published technique. 39 Actin angles (0-90°) were sorted into 10°bins, and actin fibers in the 80-90°bin were defined as being aligned.…”

“…Whereas cells and actin stress fibers aligned perpendicular to the strain direction on native collagen, alignment was not observed in cells on glycated collagen. (b) When actin stress fiber alignment was quantified by edge detection,39 actin alignment (# fibers between 80 and 90°) increased significantly only on native collagen (d) after 6 and 12 h of cyclic strain (*p < 0.001 compared to cells on glycated collagen (m)).…”