Experimental determination of CT point spread function anisotropy and shift-variance

The authors propose an experimental method to quantitatively assess the shift-variance and anisotropy of commercial CT scanners. A custom phantom consisting of 89 wires arranged in concentric circles was built for this purpose. A separable Gaussian model, expressed in a polar coordinate system, is proposed along with the corresponding estimation method. The estimated model parameters provide the quantitative information sought. The authors conclude that the scanner presents a rotating blur, i.e., that the PSF is independent of angular position when expressed in a polar coordinate system, and that the PSF shape broadens more quickly in the tangential direction than along the radial axis. Both of these observations agree with theoretical studies.