Published by CLB,Plesmanlaan 125,

1066 CX Amsterdam,

The Netherlands.

CLB, 1996

Text:Drs A.J. Meulenbroek Dr. W.P. Zeijlemaker

ISBN 90-5267-011-0

The authors are grateful to Dr. A.J. van Houte,Medical Centre Alkmaar, for his expert advice. Thanks are due to their colleagues at CLB: Dr.A.Vlug,Ing.E.J. Nieuwenhuys,Dr.T.A. Out, Prof. Dr.R.C. Aalberse and Drs R.Vis for their valuable support.