Certain Data Elements are no longer supported in the current Standard. These Data Elements are retired and are denoted as such (RET) in the VR column in PS3.6. Implementations may continue to support these Data Elements for the purpose of backward compatibility with older versions of this Standard, but this is not a requirement of the current Standard. If a retired Data Element is used it must contain valid data as specified in older versions of this Standard. Any other use of a retired Data Element, and its associated Data Element Tag, is reserved by this Standard. Retired Data Element Tags shall not be redefined in later versions of this Standard.