[Spiral CT. Better resolution by increased pitch?].

The longitudinal resolution of spiral CT has been investigated in dependence on table increment and beam collimation by use of a phantom. The results show clearly that the pitch (ratio of table increment per tube rotation to beam collimation) alone does not allow one to draw any conclusions about the resolution. Thus, a large pitch can yield a better resolution than the pitch of 1. The individual parameters table increment and beam collimation are more relevant with regard to the resolution than the rate of pitch. An alteration of the pitch can be achieved in two different ways. An increase of the pitch by a decreased beam collimation improves the resolution. In contrast, an increase of the pitch by an increased table increment decreases the resolution. A good spatial resolution of objects with high contrast (bone, lung, enhanced vessels) needs a narrow beam collimation, even if a pitch as high as 2 is necessary for a given scanning coverage. A large pitch does not cause gaps in the data set. Moreover, the patient's radiation dose decreases.