DICOM PS3.4 2022c - Service Class Specifications
C.2.2.2.7 Empty Value Matching

If Extended Negotiation of Empty Value Matching is successful, and for Attributes with VR of AE, CS, DA, DT, LO, LT, PN, SH, ST, TM, UC, UR, or UT, a Key Attribute value of exactly two QUOTATION MARK characters (22H in the Default Character Repertoire) specified in a request shall indicate matching to an empty value. Such a match is successful to entities with a zero-length value for the corresponding Attribute, or for which the Attribute is not present.

Note

  1. Other quotation mark characters defined in an expanded or replacement character set, such as double angle quotation marks, left and right curved quotation marks, etc., are not valid for specifying empty value matching.

  2. VRs of AE, LO, LT, PN, SH, ST, UC, and UT allow the QUOTATION MARK character. Matching of a string of two QUOTATION MARK characters in those Attributes can be done with wild card matching using the ASTERISK character (e.g., ""*).

DICOM PS3.4 2022c - Service Class Specifications