private IActiveAssociation OpenAssociation()
 {
     IAssociation association = _associationFactory.NewRequestor(_hostName, _port);
     IPdu assocAC = association.Connect(_aAssociateRequest, ASSOCIATE_TIME_OUT);
     var associateRj = assocAC as AAssociateRJ;
     if (associateRj != null)
     {
         throw new DcmServiceException(associateRj.Reason(), associateRj.ReasonAsString());
     }
     _activeAssociation = _associationFactory.NewActiveAssociation(association, null);
     _activeAssociation.Timeout = ASSOCIATE_TIME_OUT;
     _activeAssociation.Start();
     return _activeAssociation;
 }