X-ray computed tomography in the presence of arbitrary symmetrical focal spot intensity distributions.

A loss of resolution in tomographic images is due to the well-known bimodal spatial variations in photon emission across the x-ray focal spot combined with the finite width of the x-ray detector. Such departures from the ideal infinitely narrow beams which are usually considered can be taken into account by replacing the customary line integrals by suitably chosen integrals over strips. The image degradation resulting from using those strip integrals as ingredients in conventional reconstruction formulas is expressible as a complicated point spread function, which can always be computed in any given situation. Restoring the reconstructed image to provide higher resolution is a nontrivial operation, which however greatly benefits from experience already gained in dealing with optical imagery degraded by the aberrations of astigmatism and curvature of field. Typical point spread functions are shown for a simple bimodal source intensity distribution of primordial importance.