does SOP instance contain image and services?

Question

I know that sop class is a combination of services(C-GET,C-MOVE..etc) and object.

i've prepared this link for SOP instance. it wasn't enough to me to understand sop instance.

What about SOP Instance please describe?

Answer 1

An SOP Instance is an instantiation of an SOP Class.

Comparing it with terms usually found in software development, an SOP Class is a class description, while the SOP Instance is an actual object and its type is described by the class description.

So, the SOP Class UID identifies the type and is well known (available in the DICOM standard) while the SOP Instance UID is unique for each object (there can be several SOP Instances with the same Class UID but each of them needs a unique SOP Instance UID).

The SOP Class does not describe just the object type, but also how the object is used (the service that can use the object):

• Storage SOP classes identify objects that can be stored by the PACS, so yes, they can contain also images and any data relevant to the medical case
• Move SOP classes identify object types that contain a MOVE command description: they don't contain objects that are stored in PACS and usually contain only the command parameters needed for a MOVE operation
• Find SOP classes identify object types used in the FIND operations
• etc...

So, when you negotiate an association with a PACS and tell it that you want to use a specific SOP Storage Class and a specific SOP Move class, you are saying to the PACS that:

• you want to be able to set/retrieve objects of the specific SOP Storage class (e.g. XRAYS)
• you want to be able to perform MOVE operations according to the specifications of the selected MOVE SOP class (e.g. Patient root or Study root)