A sequence in DICOM is represented by DicomDataSets Object in DicomObjects and a sequence item is represented by a DicomDataSet Object.

Following is sample code showing how ot add sequence items using DicomObjects.

.NET version

DicomDataSetCollection ReferencedImageSequence = new DicomDataSetCollection();
DicomDataSet ReferencedImageA = new DicomDataSet();
DicomDataSet ReferencedImageB = new DicomDataSet();
DicomDataSet DataSet = new DicomDataSet();

// Add attributes to ReferencedImageA  
ReferencedImageA.Add(Keyword.ReferencedSOPClassUID, "Referenced SOP Class UID A");
ReferencedImageA.Add(Keyword.ReferencedSOPInstanceUID, "Referenced SOP Instance UID A");
ReferencedImageA.Add(Keyword.RetrieveAETitle, "Retrieve AE A");
ReferencedImageA.Add(Keyword.StorageMediaFileSetID, "Storage Media File-Set ID A");
ReferencedImageA.Add(Keyword.StorageMediaFileSetUID, "Storage Media File-Set UID A");

// Add attributes to ReferencedImageB  
ReferencedImageB.Add(Keyword.ReferencedSOPClassUID, "Referenced SOP Class UID B");
ReferencedImageB.Add(Keyword.ReferencedSOPInstanceUID, "Referenced SOP Instance UID B");
ReferencedImageB.Add(Keyword.RetrieveAETitle, "Retrieve AE B");
ReferencedImageB.Add(Keyword.StorageMediaFileSetID, "Storage Media File-Set ID B");
ReferencedImageB.Add(Keyword.StorageMediaFileSetUID, "Storage Media File-Set UID B");

// ...
// Add Sequence Items to Sequences

// ...      
// Add Referenced Image Sequence to DataSet
DataSet.Add(Keyword.ReferencedImageSequence, ReferencedImageSequence);

.COM version

Dim ReferencedImageSequence As New DicomDataSets
Dim ReferencedImageA As New DicomDataSet
Dim ReferencedImageB As New DicomDataSet
Dim DataSet As New DicomDataSet

' Add attributes to ReferencedImageA  
ReferencedImageA.Attributes.Add &H0008, &H1150, "Referenced SOP Class UID A"
ReferencedImageA.Attributes.Add &H0008, &H1155, "Referenced SOP Instance UID A"
ReferencedImageA.Attributes.Add &H0008, &H0054, "Retrieve AE A"
ReferencedImageA.Attributes.Add &H0088, &H0130, "Storage Media File-Set ID A"
ReferencedImageA.Attributes.Add &H0088, &H0140, "Storage Media File-Set UID A"

' Add attributes to ReferencedImageB  
ReferencedImageB.Attributes.Add &H0008, &H1150, "Referenced SOP Class UID B"
ReferencedImageB.Attributes.Add &H0008, &H1155, "Referenced SOP Instance UID B"
ReferencedImageB.Attributes.Add &H0008, &H0054, "Retrieve AE B"
ReferencedImageB.Attributes.Add &H0088, &H0130, "Storage Media File-Set ID B"
ReferencedImageB.Attributes.Add &H0088, &H0140, "Storage Media File-Set UID B"

' ...
' Add Sequence Items to Sequences
ReferencedImageSequence.Add ReferencedImageA 
ReferencedImageSequence.Add ReferencedImageB 

' ...      
' Add Referenced Image Sequence to DataSet
DataSet.Attributes.Add &H8, &H1140, ReferencedImageSequence   

Note: NOT all Sequences can have multiple items in DICOM, for example the “Scheduled Procedure Step Sequence” (0040, 0100) can have only 1 sequence item. Check the DICOM Standard Part 3 (for stored items) or Part 4 (for services such as Modality Worklist) for the rules for particular sequences. The “value multiplicity” found in part 6 does not apply to sequences.