A phantom to assess quantitative recovery of positron tomographs.

A simple phantom has been employed to investigate the image linearity for a wide range of activity distributions and count rates. The phantom is composed of two activity regions, one contains a short-lived isotope and the other a long-lived isotope. Specifically, the phantom consists of a 20 cm flood phantom containing 68Ga (half-life 1.14 h) into which a 6 cm diameter cylinder containing 64Cu (half-life 12.7 h) is placed in an off-centre position. The copper region is initially a cold spot but, after many gallium half-lives, becomes a hot spot. Successive data sets from the phantom are taken over a long period and the reconstructed images analysed to establish the linearity within each region and hence the stability against "cross-talk" from neighbouring regions.