def remove_structure(instance_or_number)
      raise ArgumentError, "Invalid argument 'instance_or_number'. Expected a ROI Instance or an Integer (ROI Number). Got #{instance_or_number.class}." unless [ROI, Integer].include?(instance_or_number.class)
      s_instance = instance_or_number
      if instance_or_number.is_a?(Integer)
        s_instance = structure(instance_or_number)
      end
      index = @structures.index(s_instance)
      if index
        @structures.delete_at(index)
        s_instance.remove_references
      end
    end
def remove_structure(instance_or_number)
      raise ArgumentError, "Invalid argument 'instance_or_number'. Expected a ROI Instance or an Integer (ROI Number). Got #{instance_or_number.class}." unless [ROI, Integer].include?(instance_or_number.class)
      s_instance = instance_or_number
      if instance_or_number.is_a?(Integer)
        s_instance = structure(instance_or_number)
      end
      index = @structures.index(s_instance)
      if index
        @structures.delete_at(index)
        s_instance.remove_references
      end
    end
Removes a ROI or POI from the structure set.

 @param [ROI, POI, Integer] instance_or_number the ROI/POI instance or its identifying number