There is a SOP Class for MPPS.

The Modality is the SCU of the SOP Class - it sends the N-CREATE
request to the RIS (or PACS) which is the SCP of the SOP Class.

The instance of the MPPS that is created then "lives" in the SCP,
i.e., the RIS.

Later, the Modality (SCU) will update the information with N-SET
commands to the RIS (SCP), until it is is finished, at which time
it will N-SET the status to completed.

In addition to creating an MPPS instance that lives on the SCP,
the Modality should also be including a reference to the UID
of that MPPS in the image objects, since these objects may be
stored somewhere else than the recipient of the MPPS, and this
helps link everything together (though the complete set of such
images will have been N-SET in the SCP MPPS before the step is
completed, which gives a link in the other direction).

The M2.2 scenario is describing the case where the Modality
internally models the concept of an MPPS, and hence has a
UID to put in the images, but does not for some reason have
a means of actually creating an MPPS on an MPPS SCP for some
reason (e.g., the RIS or PACS is not an MPPS SCP, or the link
to the SCP is down temporarily); obviously if the Modality were
not an SCU of the MPPS SOP Class, it would be unlikely to have
a UID to put in the images.

One reason to put the MPPS UID in the images even if the Modality
cannot N-CREATE an MPPS on the RIS is that there may be some
device or box looking at the images that can extract this
information and make use of it in some way, now or in the future,
even though MPPS is not formally supported in the system, or as
mentioned, to allow recovery from a transient failure on the MPPS
link.

Note that the SCU is required in MPPS to supply the SOP Instance UID
of the MPPS being created; this is not true of all N-CREATE operations
in DICOM but is a specific requirement for MPPS in order to make sure
that the SCU knows the UID (for inclusion in the images), as described
in PS 3.4 F.7.2.1.2, although the SCU could easily capture and cache
the Affected SOP Instance UID that is required to be returned in the
N-CREATE response were it not supplied by the SCU. The additional
requirement anticipates that the images might already have been
encoded before the MPPS N-CREATE is actually sent (undesirable, but
possible).

David

Radde wrote:

> HI,
> I want to know where exactly MPPS instance is been created(Modality
> or IS(RIS)). I was reading PS3.4 Annex M. Iam not able to understand
> these statements.
>
> M.2.1
> The modality may:
> - N-CREATE a MPPS SOP Instance and include its SOP Instance UID in
> the Image SOPInstances within the Referenced Performed Procedure Step
> Sequence Attribute
>
> What does this "N-CREATE a MPPS SOP Instance" sentence mean?. Is it
> modality has to create or IS will create it..
>
> M2.2
> In the absence of the ability to N-CREATE a MPPS SOP Instance, generate
> a MPPS SOP Instance UID and include it into Referenced Performed
> Procedure Step Sequence Attribute of the Image SOP Instances.A system
> that later N-CREATEs a MPPS SOP Instance
> may use this UID extracted from the related Image SOP Instances.
>
> In the above situtaion who actually creates MPPS instance? If modality
> is not supporting MPPS or if there is no RIS or MPPS SCP, whats the
> point in creating this MPPS instance.
>
> Again the below sentence says creating MPPS Instance, its already
> created in the previous sentence.
> "A system that later N-CREATEs a MPPS SOP Instance
> may use this UID extracted from the related Image SOP Instances".
>
> Its really confusing. Pls help me..
>
> Regards
>

David Clunie wrote:
> There is a SOP Class for MPPS.
>
> The Modality is the SCU of the SOP Class - it sends the N-CREATE
> request to the RIS (or PACS) which is the SCP of the SOP Class.
>
> The instance of the MPPS that is created then "lives" in the SCP,
> i.e., the RIS.
>
> Later, the Modality (SCU) will update the information with N-SET
> commands to the RIS (SCP), until it is is finished, at which time
> it will N-SET the status to completed.
>
> In addition to creating an MPPS instance that lives on the SCP,
> the Modality should also be including a reference to the UID
> of that MPPS in the image objects, since these objects may be
> stored somewhere else than the recipient of the MPPS, and this
> helps link everything together (though the complete set of such
> images will have been N-SET in the SCP MPPS before the step is
> completed, which gives a link in the other direction).
>
> The M2.2 scenario is describing the case where the Modality
> internally models the concept of an MPPS, and hence has a
> UID to put in the images, but does not for some reason have
> a means of actually creating an MPPS on an MPPS SCP for some
> reason (e.g., the RIS or PACS is not an MPPS SCP, or the link
> to the SCP is down temporarily); obviously if the Modality were
> not an SCU of the MPPS SOP Class, it would be unlikely to have
> a UID to put in the images.
>
> One reason to put the MPPS UID in the images even if the Modality
> cannot N-CREATE an MPPS on the RIS is that there may be some
> device or box looking at the images that can extract this
> information and make use of it in some way, now or in the future,
> even though MPPS is not formally supported in the system, or as
> mentioned, to allow recovery from a transient failure on the MPPS
> link.
>
> Note that the SCU is required in MPPS to supply the SOP Instance UID
> of the MPPS being created; this is not true of all N-CREATE
operations
> in DICOM but is a specific requirement for MPPS in order to make sure
> that the SCU knows the UID (for inclusion in the images), as
described
> in PS 3.4 F.7.2.1.2, although the SCU could easily capture and cache
> the Affected SOP Instance UID that is required to be returned in the
> N-CREATE response were it not supplied by the SCU. The additional
> requirement anticipates that the images might already have been
> encoded before the MPPS N-CREATE is actually sent (undesirable, but
> possible).
>
> David
>
> Radde wrote:
>
> > HI,
> > I want to know where exactly MPPS instance is been
created(Modality
> > or IS(RIS)). I was reading PS3.4 Annex M. Iam not able to
understand
> > these statements.
> >
> > M.2.1
> > The modality may:
> > - N-CREATE a MPPS SOP Instance and include its SOP Instance UID in
> > the Image SOPInstances within the Referenced Performed Procedure
Step
> > Sequence Attribute
> >
> > What does this "N-CREATE a MPPS SOP Instance" sentence mean?. Is it
> > modality has to create or IS will create it..
> >
> > M2.2
> > In the absence of the ability to N-CREATE a MPPS SOP Instance,
generate
> > a MPPS SOP Instance UID and include it into Referenced Performed
> > Procedure Step Sequence Attribute of the Image SOP Instances.A
system
> > that later N-CREATEs a MPPS SOP Instance
> > may use this UID extracted from the related Image SOP Instances.
> >
> > In the above situtaion who actually creates MPPS instance? If
modality
> > is not supporting MPPS or if there is no RIS or MPPS SCP, whats the
> > point in creating this MPPS instance.
> >
> > Again the below sentence says creating MPPS Instance, its already
> > created in the previous sentence.
> > "A system that later N-CREATEs a MPPS SOP Instance
> > may use this UID extracted from the related Image SOP Instances".
> >
> > Its really confusing. Pls help me..
> >
> > Regards
> >


When the modality is SCU and there is SCP(RIS/PACS) and is running, and
the flow is fine..Here MPPS instance is created in SCP(RIS) and stored.
Same MPPS instance UID is sent back to SCU with N-CREATE-RSP and
modality uses this MPPS Instance UID as a reference UID(Referenced
Performed Procedure Step Sequence Attribute) in all image instances it
generates. Hope this correct.

In second scenerio, when there is no SCP(RIS) or SCP is down...In this
case what do you mean by modality or SCU creating MPPS SOP instance
UID, Is it just creating one UID or is it creating MPPS Object(i mean
is it same as how SCP creates MPPS instance). I got stuck up here..

Assuming if modality create MPPS instance, then what does this sentence
mean
"A system that later N-CREATEs a MPPS SOP Instance
may use this UID extracted from the related Image SOP Instances".
MPPS Instance is already created by modality, again who will create or
which system will create MPPS instance UID.


Regards