Clinical imaging with a single chain Fv anti-CEA, potential for application to antibody directed enzyme prodrug therapy : R.H.J. Begent, K.A. Chester, M.N. Napier, J.L. Casey, M. Green, L.D. Hope-Stone, P.A. Keep, C.J. Johnson, A.J.W. Hilson, L. Robson, CRC Targeting and Imaging Group, Royal Free Hospital School of Medicine, London NW3, UK