How to determine DICOM / DICOMDIR images relationship?

0
votes

The DICOM images have "Slice location" parameter recorded in addition to the "Slice Thickness".

Question: "Slice location" in where? I understand it's in the body depth - but it must be in images as well, right?

I think a series must or may have a corresponding series in which we can find a reference of the "Slice Location".

If I am right, How to find that those images? And then how to establish the point of the slice in the corresponding images?

As well, if you know a well written refference guide to dicom image structure, please share.

Thanks a lot.

4
dicom
The written refference guide to dicom image structure is here: medical.nema.org/medical/dicom/2009 – ruslik
@ruslik: I agree with the posting of the written reference guide to dicom image structure; however, I should point out that the OP asked for a "well written" reference guide, which the reference guide most certainly is not. Written, yes; well, no. – Paul Sonier
@McWafflestix: yeah, this is why I ommited this word from the comment :) – ruslik
thanks guys. the keyword was "well written" indeed. after i read the one you pointed out, the only thing that stopped me from shooting myself was my mortgage obligation :-) I just need to regroup and read again. Cheers – val

4 Answers

0
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The standard specifies that the unit for Slice Location is millimeters. Usually there is a special scout image that is refferenced by slices with an overlay that looks like a grid, that shows where each slice is mapped.

And a suggestion: don't expect it to work "in theory", without trying on real samples. DICOM is rather a collection of all standards that existed at the time it was created. Also, many modalities use their own private tags for additional info. If you need to process the output of a certain modality then you are lucky, you just have to find its DICOM Conformance Statement. If it's for a viewer.. then good luck :)

EDIT: Also, CT series usually have one image with LOCALIZER in the Image Type tag that refferences the rest of images in the series that are slices (or is reffered by them).

0
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Here's a page that contains some good information on DICOM:

http://www.thefullwiki.org/DICOM

As to your question; I think you're looking for the "image number", which defines an order to the image. The "slice location" is a spatial coordinate as to the offset of the image slice; the "image number" is an integer indicating the order of an image in reference to other images. YMMV; DICOM is a very loosely adhered to standard.

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I suspect the slice position is for thick slab acquisitions, where the extents of each slice overlap with the next slice. The axial resolution of current scanners is high enough that this does not happen anymore. Hence the slice thickness is used more frequently now as opposed to slice position.

0
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Please look at http://medical.nema.org/dicom/2003/03_10PU.PDF. Especially Annex A.

The method I usually follow is as follows. I access DICOMDIR for the dcm file paths. This can be accessed at tag [0004, 1500]. Once I get all the paths, I iterate through each dcm image to access any property I want. The slice location might be a property in dcm image but without knowing the modality it is quiet difficult to figure out the tag.

dcmtk is a nice library written in C++ that can help to get specific tags or to extract pixel data from dcm images. You can use it to make your life easier.