def add_slice(slice)
      raise ArgumentError, "Invalid argument 'slice'. Expected Slice, got #{slice.class}." unless slice.is_a?(Slice)
      @slices << slice unless @associated_instance_uids[slice.uid]
      @associated_instance_uids[slice.uid] = slice
    end
def add_slice(slice)
      raise ArgumentError, "Invalid argument 'slice'. Expected Slice, got #{slice.class}." unless slice.is_a?(Slice)
      @slices << slice unless @associated_instance_uids[slice.uid]
      @associated_instance_uids[slice.uid] = slice
    end
Adds a Slice instance to this ROI.

 @param [Slice] slice a slice instance to be associated with this ROI