Sampling properties of stationary and half-rotation rings in positron emission tomography

The aim in positron emission tomography is to provide quantitative information about the uptake, localization, and turnover of labeled molecules in the human body. Instruments designed for this purpose are based on the coincidence detection of the emitted annihilation photons. In this paper, we examine those instruments that use a ring of detectors. We investigate such instruments with respect to their sampling properties in the stationary and half-rotation modes. It is shown that, although the half-rotation motion provides an improvement if the data are treated as a set of parallel projections, there is no improvement when divergent projections are assumed by the reconstruction procedure. The effects on reconstruction quality of the radial and the angular sampling in ring collected data are discussed and illustrated.