Irregular sampling and the Radon transform
  In image reconstruction there are techniques that use analytical formulae for the Radon transform to recover an image from a continuum of data. In practice, however, one has only discrete data available. Thus one often resorts to sampling and interpolation methods. This article presents an approach to the inversion of the Radon transform that uses a discrete set of samples which need not be completely regular. 
Isaac Pesenson, Eric Grinberg
math.FA