Icon on a radWindow programatically

[Iheb]

I want to put an icon on the top left of a radWindow programatically

my code is like this

RadWindow radWindow = new RadWindow();
radWindow.Header = "The header";
radWindow.Icon = new Image()
   {
   Source = new BitmapImage(new Uri("../ressources/enregistrer.png", UriKind.Relative))
   };
radWindow.Show();

but the icon dont show up

Pls help me :)