  Image based diagnostics are interpreted in the context of spatial resolution.
The same is true for tomographic image reconstruction. Current empirically
driven approaches to quantify spatial resolution rely on a deterministic
formulation based on point-spread functions which neglect the statistical prior
information, that is integral to rank-deficient tomography. We propose a
statistical spatial resolution measure based on the covariance of the
reconstruction (point estimate) and show that the prior information acts as a
lower limit for the spatial resolution. Furthermore, the spatial resolution
measure can be employed for designing tomographic systems under consideration
of spatial inhomogeneity of spatial resolution.
