The authors characterize the effects of crystal penetration by annihilation photons in circular ring positron tomographs. A mathematical correction of emission data is performed using a two-dimensional spatially variant deconvolution of the emission data in sinogram format. Examples for the Donner 600 crystal positron tomograph are presented, and the amplification of statistical errors resulting from the correction procedure is discussed. The proposed compensation method appears to amplify statistical noise a great deal in order to gain a modest improvement in radial resolution. The statistical correlations in the corrected projections are so high that images resulting from statistically poor data are expected to have a high degree of correlated noise. Preliminary tests indicate that the method causes artifacts for data generated from point sources, because the assumptions made when the blurring transition probabilities were calculated are not met. >
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