Modified Filtered Back Projection 

Filtered back projection was modified with interpolation. Projections (logarithm of intensity ratio of incident and outcoming beam) which have abnormaly high values are truncated and linearly interpolated with values of neighbouring projections. Adjacent values must be carefuly selected so that only projections which pass an implant are truncated. That may not necessarily be achieved because it is possible that projection which passes many cells representing a bone might have higher value than a projection which passes some cells representing a metal implant but mostly passing through cells representing water or air.

Comparison of head geometry (up left), image reconstructed with filtered back projection (up right), image reconstructed with modified filtered back projection (down left) and a compound image: an implant was reconstructed with FBP and other parts were reconstructed with MFBP.

Comparison of sinograms of head geometry with implant (left), without implant (middle) and a sinogram of interpolated projections of geometry with implant.

Comparison of prostate geometry (first), image reconstructed with filtered back projection (second), image reconstructed with modified filtered back projection (third) and a compound image (fourth): an implant was reconstructed with FBP and other parts were reconstructed with MFBP. (Click on image to view real size images)