Rapid, accurate single particle tracking based on radial symmetry center determination

Accurately tracking particles in images is a crucial task for applications as diverse as super-resolution microscopy, membrane biophysics, and 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 a 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 numerically searching a large parameter space. I introduce a new approach to sub-pixel particle tracking based on exploiting radial symmetry, valid for any radially symmetric particle intensity profile. I provide an algorithm that analytically, non-iteratively calculates the best-fit symmetry center to determine the particle location. Over a wide range of signal-to-noise ratios, this approach yields 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. This algorithm is tested on simulated data as well as real images from several experimental systems, including colloidal assemblies and single fluorescent proteins.