complete helical cone - beam scanning and non - redundant data acquisition are obtained for three - dimensional tomographic imaging of arbitrary long objects . the minimum sized two - dimensional detector window is bounded by two consecutive turns of the helix . the ray source exposes all object points during a rotation of exactly 180 degrees when seen from the points themselves . only one - dimensional filtering is employed in the reconstruction . rebinning to parallel beams , as seen along the axis of rotation , allows for especially simple procedures without any need for pre - weighting or magnification factors . as a special case , the invention is applicable to helical fan - beam scanning with one - dimensional detector arrays .