Rotational positron computed tomographs

A description and analysis are presented of positron-emission computed tomographs which utilize the continuous rotation scan of a ring detector array. The detectors are arranged in a particular irregularity determined by a computer. The aim of the rotation scan is to exceed the sampling requirement to recover intrinsic detector resolution with high sampling redundancy. It has already been shown that fine and uniform sampling can be achieved with continuous multiple rotation. To obtain an angularly invariant sampling with limited angle (<3600) rotation, the angle of rotation must be 3600/n where n is an odd integer (>=3), and the detector array should be composed of n identical subarrays arranged in every 3600/n. The detectors must also be arranged on a non-circular ring to avoid concentration of sampling points. An example of a detector array for 1200 rotation (n=3) shows excellent sampling characteristics. The effect of linear and angular sampling on spatial resolution is discussed taking into account the smoothing effect of data binning. It is shown that the smoothing effect is not appreciable if the Nyquist frequencies for sampling are properly chosen. A rotary positron tomograph, Positologica, which has been developed for brain study, has a circular array of 64 BGO crystals. The spatial resolution is 5.8 mm FWHM at the centre and less than 9 mm FWHM in the field of view. The point spread functions well reflect the results of theoretical analysis. (author)