def structures
      frame_rois = Array.new
      structs.each do |struct|
        frame_rois << struct.structures_in_frame(@frame.uid)
      end
      return frame_rois.flatten
    end
def structures
      frame_rois = Array.new
      structs.each do |struct|
        frame_rois << struct.structures_in_frame(@frame.uid)
      end
      return frame_rois.flatten
    end
Gives all structures having the same Frame of Reference as this image
 series from the structure set(s) belonging to this series.

 @return [Array<ROI, POI>] the ROIs & POIs associated with this image series