def translate(x, y, z)
      @slices.each do |s|
        s.translate(x, y, z)
      end
    end
def translate(x, y, z)
      @slices.each do |s|
        s.translate(x, y, z)
      end
    end
Moves the ROI by applying the given offset vector to its coordinates.

 @param [Float] x the offset along the x axis (in units of mm)
 @param [Float] y the offset along the y axis (in units of mm)
 @param [Float] z the offset along the z axis (in units of mm)