Computer tomography apparatus for conducting a spiral scan of an examination subject

A computer tomography apparatus comprising:

• examination means, including a radiation source and a radiation detector, for conducting a spiral scan of an examination subject by rotating said radiation source and said radiation detector around a longitudinal axis through a plurality of projections, each projection generating output signals at said radiation detector corresponding to radiation incident on said detector attenuated by said examination subject, all of said output signals for a single slice of said examination subject comprising a data set;
• computer means for calculating a new image I.sub.lr+1 (x), using only a data set from a single slice, from an initial image I.sub.lr (x) in the plane of a referenced projection l.sub.r at a defined location along said longitudinal axis from an auxiliary image I.sup.d.sub.lr+1 (x) at a distance d/N.sub.2.pi. from said initial image I.sub.lr (x) according to the equation:
• I.sub.lr+1 (x)=I.sub.lr (x)-I.sup.d.sub.lr+1 (x)
• and means for calculating said auxiliary image I.sup.d.sub.lr+1 (x) from its predecessor I.sub.lr (x), wherein d is the slice thickness and N.sub.2.pi. is the number of projections on the circumferential angle;
• and
• means for displaying said image.