def add_struct(struct)
      raise ArgumentError, "Invalid argument 'struct'. Expected StructureSet, got #{struct.class}." unless struct.is_a?(StructureSet)
      # Do not add it again if the struct already belongs to this instance:
      @structs << struct unless @associated_structs[struct.uid]
      @associated_structs[struct.uid] = struct
    end
def add_struct(struct)
      raise ArgumentError, "Invalid argument 'struct'. Expected StructureSet, got #{struct.class}." unless struct.is_a?(StructureSet)
      # Do not add it again if the struct already belongs to this instance:
      @structs << struct unless @associated_structs[struct.uid]
      @associated_structs[struct.uid] = struct
    end
Adds a StructureSet to this ImageSeries.

 @param [Image] struct a structure set instance to be associated with this image series