      &lt;!-- The horizontal distance in the subject of the image, in
             millimeters, represented by one pixel at the center of the
             image --&gt;
        &lt;!ATTLIST "HorizontalPhysicalPixelSpacing" "value" #CDATA #REQUIRED&gt;
          &lt;!-- Data type: Float --&gt;

      &lt;!ELEMENT "VerticalPhysicalPixelSpacing" EMPTY&gt;
        &lt;!-- The vertical distance in the subject of the image, in
             millimeters, represented by one pixel at the center of the
             ima