Physical criteria for the performance of tomographic imaging systems Paper entitled 'Physical criteria for the performance of tomographic imaging systems' by H.G.Gemmell, P.P.Dendy, W.R.Pitt, N.T.S.Evans and J.R.Mallard, Department of Bio-Medical Physics and Bio-Engineering, University of Aberdeen. This paper was presented at the Third World Congress of Nuclear Medicine and Biology, Paris, 29 August - 2 September 1982 and at the Thirteenth World Congress on Medical Physics and Biomedical Engineering, Hamburg, 5-11 September 1982. This copy is a photocopy. 1982