Rapid, Accurate Single Particle Tracking Based on Radial Symmetry Center Determination

Abstract

Accurately tracking particles in images is a crucial task in areas as diverse as super-resolution microscopy, membrane biophysics, and soft-matter microrheology. Tracking errors can easily propagate into flawed conclusions about mechanisms underlying particle dynamics. The commonly used method of locating the center of a particle by direct fitting of a two-dimensional Gaussian function to a measured intensity profile is very accurate, but is computationally intensive and not generalizable to non-point-like particles. Its slowness is a necessary consequence of iteratively, numerically searching through a large fitting parameter space. I introduce a new approach to sub-pixel particle tracking based on exploiting the radial symmetry of particle images, valid for any radially symmetric intensity profile. I provide an algorithm that employs an analytic, non-iterative calculation of the best-fit symmetry center to determine the particle location. Over a wide range of signal-to-noise ratios, this approach yields tracking accuracies nearly identical to those of Gaussian fitting with execution times over two orders of magnitude faster and with greater robustness in the presence of nearby particles. The performance of this algorithm is tested on simulated images as well as experimental data from several fields.