[Slice thickness of spiral CT images as function of pitch]

This report comments on several measures of effective slice thickness. In particular, the full width at half maximum FWHM of the slice sensitivity profile is discussed. An analytical approximation between FWHM and the pitch p is established. Values of FWHM are compared as a function of pitch from the approximate formula, from an empirical formula, from an exact calculation and from measurements. In addition, the approximation for the full width at tenth maximum is also given and is compared with exact calculations. The main results of this investigation is that the analytical formulae, although approximate, are sufficiently precise and easy to use.