Button with images (newb)

Ruby
1

Hey guys,
i just want to add a png file to a button, but the image is not
visibile…
im doing this

imgOk = Gtk::Image.new(“run.png”)

ok = Gtk::Button.new “Calcular”
ok.set_size_request 70, 30
ok.image = imgOk

whats the problem?
thanks