Figure 3: Image correlation spectroscopy. A: Several frames of time image series of Figure 2B. B: Spatial ICS to obtain the point spread function of LSM (see text). For example, the raw spatial autocorrelation function of the 1st frame of the image series is denoted by the colored surface, and the fitted 2D Gaussian function is denoted by the grey mesh. The point spread function, i.e., beam radius of LSM, is obtained by the fitting. C: Intensity at a pixel fluctuates with number of frames separated 10 s interval. D: Temporal ICS to obtain the diffusion time in which mtDNAs transverse the beam radius. A temporal image autocorrelation function (open circles) was derived from the time image series same as A. The temporal autocorrelation function was fitted to a simple one component 2D model (solid line) which can be derived from the diffusion equation. The residuals are denoted in the bottom. Finally, diffusion constant was calculated from the beam radius and diffusion time as shown in Table 1.