The relation between interpolating functions and reconstructed image quality in fan-beam-CT system

On the interpolating treatment required for the reconstruction operation for the tomographic images of so-called third generation CT system which obtains projection data by using fan beam X-ray, nearest neighbor substitution method, linear interpolation method, Lagrange's interpolation method and the method by spline approximation were taken up, and the relation of these interpolating methods to the quality of reconstructed images was examined by computer simulation. As the result, the spatial resolution of reconstructed images depended upon the frequency transmission characteristics of the interpolating functions used, and the interpolation by the nearest neighbor substitution showed the best critical resolution, but the deterioration of images due to artifacts was remarkable. As to the Lagrange's interpolation, third to fifth order was suitable, and even if that of too high order was used, the effect of image quality improvement was small. In the interpolation by spline approximation, the cutoff characteristics above Nyquist's frequency were excellent for a small number of the operation, but artifacts tended to increase. (Kako, I.)