def add_ssd(value, item)
      DICOM::Element.new('300A,0130', "#{value.to_f * 10}", :parent => item) if value && !value.empty?
    end
def add_ssd(value, item)
      DICOM::Element.new('300A,0130', "#{value.to_f * 10}", :parent => item) if value && !value.empty?
    end
Adds a Source to Surface Distance element to a Control Point Item.
 Note that the element is only added if the SSD attribute contains
 real (non-empty) value.

 @param [String, NilClass] value the SSD attribute
 @param [DICOM::Item] item the DICOM control point item in which to create an element