The parameter name shall be “transferSyntax".
The Transfer Syntax to be used within the DICOM image object, as specified in PS 3.6. This parameter is OPTIONAL. It shall not be present if contentType is other than application/dicom.
By default the DICOM object(s) returned shall be encoded in Explicit VR Little Endian. Neither Implicit VR, nor Big Endian shall be used. The response shall be the Transfer Syntax requested if possible. If it is not possible for the response to be sent using the requested transfer syntax then the Explicit VR Little Endian Uncompressed Transfer Syntax shall be used.
The value shall be encoded as an unique identifier (UID) string, as specified in PS 3.5, except that it shall not be padded to an even length with a NULL character.