Evaluation of sted super-resolution image quality by image correlation spectroscopy (QuICS)

Quantifying the imaging performances in an unbiased way is of outmost importance in super-resolution microscopy. Here, we describe an algorithm based on image correlation spectroscopy (ICS) that can be used to assess the quality of super-resolution images. The algorithm is based on the calculation of an autocorrelation function and provides three different parameters: the width of the autocorrelation function, related to the spatial resolution; the brightness, related to the image contrast; the relative noise variance, related to the signal-to-noise ratio of the image. We use this algorithm to evaluate the quality of stimulated emission depletion (STED) images of DNA replication foci in U937 cells acquired under different imaging conditions. Increasing the STED depletion power improves the resolution but may reduce the image contrast. Increasing the number of line averages improves the signal-to-noise ratio but facilitates the onset of photobleaching and subsequent reduction of the image contrast. Finally, we evaluate the performances of two different separation of photons by lifetime tuning (SPLIT) approaches: the method of tunable STED depletion power and the commercially available Leica Tau-STED. We find that SPLIT provides an efficient way to improve the resolution and contrast in STED microscopy.

Automated summary

Quantifying imaging performances in an unbiased way is crucial in super-resolution microscopy. An algorithm based on image correlation spectroscopy is described to assess super-resolution image quality by calculating autocorrelation function parameters related to resolution, brightness, and noise variance. Evaluating STED images shows that increasing depletion power improves resolution but may reduce contrast, while increasing line averages improves signal-to-noise ratio but may lead to photobleaching. SPLIT approaches, such as tunable STED depletion power and Leica Tau-STED, efficiently improve resolution and contrast in STED microscopy.