
are able to connect to another device, the next step is trying to exchange certain information between the two devices using the DICOM protocol. Here is where things can go wrong as well.
Before we discuss details, let’s go over the DICOM protocol
steps that include the handshake. There are two separate levels of
communication, the first one being the connection management, which can be
considered the “session” layer of a protocol, whereby a connection is properly
established and released. Establishing the connection includes an agreement of
what information will be exchanged and how it is being encoded. The negotiation
of the information exchange is a simple “proposed” and either “accepted” or
“rejected” step. We’ll discuss the handshake about the filetype to be exchanged
first.
There are three terms that are important in this context:
the “Presentation Context” which is the set of parameters being proposed by the
client device which includes the type of information to be exchanged, such as
“CT Images,” a “Dose Report,” an image “Presentation State,” and many others. The
second term to know is the “Abstract Syntax” that identifies the information to
be exchanged, and the third term is the “SOP Class” identifying the requested service,
such as “Store these CT images.” Incompatibility issues are typically reported
by the device as “Presentation Context,” “Abstract Syntax,” or “SOP Class” not
supported.
These are some commonly encountered issues:
·
The image type that is proposed by the client is not supported. The
error that might come back
![]() |
Example of "Abstract Syntax" not supported log using Modality Simulator (OT-DICE) |
·
A non-image file type is not supported by the
server (PACS, Workstation). You’ll see the same errors as listed for the file
types, but they refer to a non-image file such as a Dose Report, a CAD
Structured report for mammography or chest, a Presentation State containing
image manipulation and display information, ultrasound measurements, a DICOM
encapsulated PDF, and many others. These objects are typically meant to be sent
with the images in the same study, and it is likely that the images will make
it to its destination, but not the corresponding non-image files, so you probably
will get a “DICOM error.” You’ll use the
same tools to diagnose and/or simulate this as for the image type issue.
·
A private image or non-image file is being
proposed. Vendors frequently create private or proprietary file types. This is
common for some CR vendors, ultrasound, and others. If the images are sent to a
PACS from the same vendor, the PACS will most likely support and display them,
but subsequent viewers very likely will not. Imagine that a private file is
sent from Vendor A modality to a Vendor A PACS successfully, if forwarded to an
enterprise archive from Vendor B, it might fail to connect. The same tools
apply, to diagnose and simulate
·
A non-appropriate SOP Class is used as an
interim solution. Some vendors create a different modality and corresponding image
format, e.g. CT instead of mammography, a screen-save (Secondary Capture)
instead of an ultrasound, or other SOP Class that was not intended to cover a
specific modality. There is not much you can do about this except for upgrading
your PACS as soon as you can, and at that time try to convert these anomalies
back to the original, intended file type.
·
CD’s are inoperable. Instead of trying to
exchange these different file types over a network and being rejected by the
intended receiver, you also may experience exactly the same problem when trying
to read images from a DICOM CD. After diagnosing the issue, the problem might
be harder to solve because you might need to contact the creator of the CD,
which is likely not local, to resolve the issue.
Filetype issues are sometimes a little bit hard to diagnose
as you might not always be able to or be allowed to use the tools mentioned.
You could change that of course, I know of one vendor who installs a modality
simulator (OT-DICE) and Wireshark on each of its modalities, just in case you might
need them.
The next in this series will be on Transfer Syntax (such as
compression) incompatibility issues.
Additional information can be found in the
DICOM textbook, or you can sign up for our on-line or face-to-face PACS and/or DICOM
training classes.