In order to ensure the integrity of the DICOM UID system, DicomObjects incorporates a mechanism for the automatic allocation of unique identifiers.  This is used in the following circumstances:

• When a new DicomImage is created from scratch.
  This can be due to any type of OLE object creation such as Visual Basic’s “CreateObject” method, or via the DicomViewer’
  s New method.  New UIDs are automatically allocated for the Instance UID, StudyUID and SeriesUID.  Commonly, of course, the Study and Series UIDs for images other than the 1st of a series will be replaced by those from the first image.
• When a lossy image is generated. This can be due either to saving to a file, field, etc., or to network transmission.  In these circumstances, the original instance UID is stored in item (0028,2112), as required by the DICOM standard, and the lossy flag, and lossy image type items are also set.
• When the Capture or SubImage methods are used.
  As above, the details of the original image are stored in item (0028,2112).
• When the DicomGlobal.NewUID method is used.

In order to guarantee that UIDs generated are unique, it is important that the machine is given a unique UID root under the registry entry:
HKEY_LOCAL_MACHINE/SOFTWARE/Medical Connections/DicomObjects/UIDRoot
As a service to its customers, Medical Connections will provide a guaranteed unique UID root to anyone needing one for use with DICOM, and if you do not have one, you are strongly advice to obtain one by visiting:

http://www.medicalconnections.co.uk/html/free_uid.html

Of course, you must then devise a system for allocating machine roots below this, but addition of simple sequential number to your root from Medical Connections is simple and effective.  E.g. if you are given UID 1.2.826.0.1.3680043.2.50, then machines could be allocated

1.2.826.0.1.3680043.2.50.1

1.2.826.0.1.3680043.2.50.2 etc.

under the above registry key.

The UIDs generated use the date, time and an incrementing counter appended to these vales to ensure that each UID is unique.  These may use up to 20 characters, so please make sure that each machine’s UID root is less than 43 characters to ensure that the resulting UIDs comply with DICOM’s 64 character limit (all lengths include the dots).