How to decide if a DICOM series is a 3D volume or a series of images?

We are writing an importer for dicom files.

How does one generally deceide if a series of images forms a 3D-Volume or is just a series of 2D images?

Is there a universal way to decide this for most vendors? I looked a the DICOM tags and could no find an apparent solution.

Solution

The DICOM standard defines UIDs for describing the hierarchy. These are from top to bottom:

Study UID - Identifier of the study or scanning session.
Series UID - The same within a series acquired in one scan.
Image UID - Should be unique for any image.

A DICOM image saved by a standard-conforming implementation should have all these IDs. If multiple images have the same SeriesUID, they are a volume (or time-series) as defined in the standard. Some software of course is not standard-conforming and you'll have to look at other things like timestamps and patient position, but it is usually best to start by following the standard.

For ordering the series after identifying it, GDCM (as malat suggested) or dcmtkdicom are pretty well-established libraries.