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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.
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Images in the DICOM format can be processed using 2D or 3D methods.
The Dicom image (or file) is a 2D image even though it has a volume but in reality it is a 2D image because it has only one slice of a MRI, CT, TEP… Instead of that, the Nifti file can contain a set of these Dicom images.
A series generally equates to a specific type (modality) of data, or the position of a patient on the acquisition device. Each series contains 1..n DICOM object instances (most commonly images, but also reports, waveform objects, etc.). All of this information is contained in each DICOM object of a study.
dcm.” DICOM differs from other image formats in that it groups information into data sets. A DICOM file consists of a header and image data sets packed into a single file. The information within the header is organized as a constant and standardized series of tags.
The DICOM standard defines UIDs for describing the hierarchy. These are from top to bottom:
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.
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In MR, you'll want to look for:
MR Acquisition Type (0018,0023). It has two enumerated values:
I'm not as sure about CT.
Most of the time, malat's answer is what you'll want to do (i.e. organize the slices by position and orientation and treat them in a 3D fashion through multi-planar reconstruction).
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