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- CT/PET Links:
[Correlating CT and PT series]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/50bd859e0232a735/6040b545240c8fa4
Quote:
For completeness, there are three ways an application can
correlate CT and PET (or other sets) using DICOM only:

1) Code all the images with the same Frame of Reference UID.
At least one major vendor does this now.

2) Make assumptions based on specific implementation behavior
based on data elements that match (e.g. perhaps Study Time, or
matching values in the General Equipment Module).
Without actual trial and experience verifying the correlation,
I agree, that an assumption is not wise

3) Use the recent Supplement 73 Spatial Registration Storage SOP Classes.
This capability allows explicitly specifying the spatial transformation
from one Frame of Reference to another. However, this supplement
is probably too recent to be in use. 

[Is there a SOP class for CT-PET images?]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/bb96abb730624a8a/5a78f1ff0199a727

[Everything you have always hated about the DICOM PET SOP Class, but were afraid to ask]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/dc3a07d4999445ae/560fd0a064145d61

[fMRI Dicom objects]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/30897c138442daad/27382b21968ce0b3
Quote:
WG 17 is considering the matter of registration of images
in 3D, including rigid (and probably non-rigid) body
transformations. This effort has been prioritized over
WG 17's other work on multi-dimensional representation
as a consequence of the prevalence of PET-CT fusion
applications. See:

ftp://medical.nema.org/medical/dicom/supps/sup73_05.pdf
broken link use instead: ftp://medical.nema.org/medical/dicom/final/sup73_ft4.pdf

[4 PET/CT questions]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/56d07d5686e2ec67/b4c131f3e711716f


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- Spatial registration oriented:
[Spatial Registration]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/ab94a61d33082e29/d929474e92c30b24

[presentation context ID]
http://groups.google.com/group/comp.protocols.dicom/browse_thread/thread/a4bb2647d5a91001/d0fbff58a644ce7c

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Adding comment by Doug Sluis (dsluis at clinical-knowledge.com)
To your numbered questions:
1.  Yes they are separate SOP Instances. (What is alternative?)
2. Yes. (although the recent Spatial Registration SOP Class is a possible option)

There is no guarantee that CT and PET slices are one-to-one or
that the slices are spatially coincident. Attempts to spatially sort
may not succeed.

> I am trying to gather some information about CT-PET acquisition and how
> to order/link slices together properly(*).
>
> 1. I understand there is not and there won't be any SOP Class for
> CT-PET. But should we still consider this as two *independent* SOP
> Class Instances ?
>
> 2. Image acquired in this dual modality *have* to have the same Frame
> of Reference UID, right ?
>
> In this case I'll add the following strategy in gdcm to organize the
> slices:
>
> 1. Open a DICOM file A
> 2. Open another DICOM file B
> 3. Same Serie/Study ?
>  * No -> return
>  * Yes -> continue
> 4. Same Frame of Reference ?
>  * No -> Return
>  * Yes -> continue
> 5 A is CT and B is PT ?
>  * No -> return
>  * Yes -> continue
> 6 Same Image Position ?
>  * No -> Return
>  * Yes: We found a match !