The DICOM UID encoding rules are defined as follows:
⎯ Each component of a UID is a number and shall consist of one or more digits. The first digit of each component shall not be zero unless the component is a single digit.
Note: Registration authorities may distribute components with non-significant leading zeroes. The leading zeroes should be ignored when being encoded (ie. “00029” would be encoded “29”).
⎯ Each component numeric value shall be encoded using the characters 0-9 of the Basic G0 Set of the International Reference Version of ISO 646:1990 (the DICOM default character repertoire).
⎯ Components shall be separated by the character "." (2EH).
⎯ If ending on an odd byte boundary, except when used for network negotiation (See PS 3.8), one trailing NULL (00H), as a padding character, shall follow the last component in order to align the UID on an even byte boundary.
UID's, shall not exceed 64 total characters, including the digits of each component, separators between components, and the NULL (00H) padding character if needed.