1. Biomedical Radiation Sciences, Box 535, Uppsala University, S-751 21 Uppsala, Sweden, Department of Diagnostic Radiology, Uppsala University and Uppsala University PET-Centre, Uppsala University Hospital, S-751 85 Uppsala, Sweden, Pharmacia Biotech AB, S-751 82 Uppsala, Sweden, and Centre of Surface Biotechnology, Uppsala Biomedical Centre, Box 577,S- 751 23 Uppsala, Sweden