1.IHE Y4 Topic: General Purpose Worklist (GP-WL) for CAD Author: Janet Keyes Date: 28-Dec-2001 Version: 2

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1.

IHE Y4 Topic: General Purpose Worklist (GP
-
WL) for CAD

Author: Janet Keyes

Date: 28
-
Dec
-
2001

Version: 2


2.

Scope Refinement

The first workflow management communication mechanism defined in DICOM was Modality
Worklist, which is limited to the communication

of information regarding scheduled image
acquisition procedures. In this case, a digital image acquisition device obtains information about
scheduled imaging procedures from a scheduling system, and can report completion of the
requested procedures back
to the scheduling system, as modality performed procedure steps
(MPPS). This information can be used for billing purposes.


The DICOM General Purpose Worklist provides for the communication of information regarding
post
-
image acquisition procedures, such
as Image Processing, Quality Control, Computer Aided
Detection, Computer Aided Diagnosis, Interpretation, Transcription, Report Verification, and
Print. In this case, a softcopy reading workstation or CAD device obtains information about
scheduled interpr
etations or CAD processing from a workflow manager, and can report
completion of the requested tasks back to the workflow manager, as general purpose performed
procedure steps (GP
-
PPS). This information could be used for billing purposes for CAD
processin
g.


Computer
-
aided detection or diagnosis (CAD) of medical images, specifically in the area of
mammography x
-
ray, has entered the clinical workflow over the past 2
-
3 years. CAD
processing occurs after the images have been acquired, and before the images

are interpreted by
a radiologist, and is a billable procedure.


In order for CAD processing to be efficient for users to incorporate within the healthcare
enterprise, it must be integrated into the electronic clinical workflow. Standardized workflow
mech
anisms would allow the workflow user to schedule CAD processing, the CAD processing
system to obtain the information needed to perform the work and provide the results for
interpretation by the radiologist along with the images, and to record CAD processin
g tasks
performed for billing purposes.


3.

Use Cases

A mammography exam (e.g., screening) is scheduled, the images are taken, and CAD processing
is to be performed on the images. The images and CAD processing results are to be sent to a
review workstation f
or the radiologist to interpret the exam. The specific actors in this case are
Acquisition Modality (digital mammography image acquisition system), Report Creator (CAD
processing system), Reporting Worklist Manager, Image Archive, and Image Display (revie
w
workstation). The DICOM Standard services used are Storage of Digital Mammography X
-
Ray
images, Query/Retrieve, General Purpose Worklist, and Storage of Mammography CAD SR
(Structured Report).


The CAD processing results are stored as a DICOM Mammograph
y CAD Structured Report.
The report content includes references to the images that were analyzed (typically for
mammography screening, the MLO and CC views of the left and right breasts), a summary of the
algorithms that were executed, including algorithm

identification, whether they succeeded or
failed, and the findings detected by the algorithms. The current capabilities of CAD processing
for mammography include identification of the locations of suspected densities (masses) and
micro
-
calcifications on
the images.


The Acquisition Modality obtains scheduled procedures via Modality Worklist, and the images
are taken. The following sequence ensues:


1.

The Acquisition Modality reports to the GP
-
Worklist Manager (perhaps indirectly via the
Image Manager/Image

Archive, which in turn notifies the GP
-
Worklist Manager) that the
images are taken, via Modality Performed Procedure Step (MPPS).

2.

The Acquisition Modality stores the images to the Image Archive, CAD Processor, and
Image Display.

3.

MPPS triggers the GP
-
Workl
ist Manager to create GP
-
WL items for CAD processing. The
CAD Processor retrieves a list of tasks (GP
-
WL) that reference the images to be analyzed.

4.

The CAD Processor matches received images to a corresponding GP
-
WL item, and retrieves
any images that were

not automatically sent to the CAD Processor, based on references in the
GP
-
WL item.

5.

The CAD Processor notifies the GP
-
Worklist Manager which task it intends to work on (GP
-
SPS update).

6.

The CAD Processor performs the task, and then stores CAD results to th
e Image Display and
Image Archive, in the form of a Mammography CAD SR.

7.

The CAD Processor creates a GP
-
PPS, and reports to the GP
-
Worklist Manager when it is
completed. The GP
-
PPS includes a reference to the Mammography CAD SR.

8.

The CAD Processor sends not
ification to the GP
-
Worklist Manager that a scheduled task is
completed (GP
-
SPS update).

9.

A review workstation acts as Image Display and Report Reader, matching image SOP
instances with the corresponding Mammography CAD SR SOP instance, to display CAD
proce
ssing results with the images.


The GP
-
SPS completed and GP
-
PPS information can be used for billing of CAD processing.


The Transaction Summary is illustrated in the following diagram:

Acquisition Modality
Image Manager/
Image Archive
CAD Processor/
Report Creator
Image Display/
Report Reader
MPPS Completed
Images Stored
Images Stored
Query images
Perform CAD
CAD SR Stored
CAD SR Stored
GP-Worklist
Manager
GP-WL Provided
GP-SPS in progress
GP-PPS completed
GP-SPS completed
GP-PPS in progress
Images Stored
MPPS Completed
Images Available
Retrieve images


4.

Technical approach

New actors

1)

General Pur
pose Worklist Manager: The definition is provided in the document that
describes the Interpretation, Transcription, Report Verification package.

2)

No new generic General Purpose Worklist User. The CAD Processor can be considered as a
specific instance of Re
port Creator.


New transactions (standards used)

1)

General Purpose Worklist Provided: The Report Creator (CAD Processor) queries the GP
-
WL Manager for Scheduled Procedure Steps. The CAD Processor requires that the
following information be returned with ea
ch Scheduled Procedure Step:

1.

All Type 1 Return Key attributes

2.

Input Information Sequence (0040,4021): a sequence item
identifying each image to be analyzed as a collective group (e.g.,
the typical four images for screening mammography)

3.

Scheduled Processing

Applications Code Sequence (0040,4004):
potentially, a billable code that specifies the type of CAD
processing requested


The CAD Processor may also use information from the DICOM image header, from
attributes that are Type 1 for Digital Mammography, such

as: Image Pixel module attributes,
Presentation Intent Type (0008,0068), Anatomic Region Sequence (0008,2218), Patient
Orientation (0020,0020), Image Laterality (0020,0062), Imager Pixel Spacing (0018,1164),
Burned in Annotation (0028,0301), Lossy Image C
ompression (0028,2110), and View Code
Sequence (0054,0220).




2)

General Purpose Scheduled Procedure Step In Progress/Suspend: upon starting to work on
the item, the Report Creator (CAD Processor) updates the GP
-
SPS status to IN PROGRESS.
This allows the G
P
-
WL Manager to update its Worklist and permits other worklist SCUs to
detect that this GP
-
SPS is already being worked on. The SCU can also set the status to
SUSPEND.


3)

GP
-
PPS In Progress: upon starting to work on the GP
-
SPS, the Report Creator (CAD
Proce
ssor) creates a GP
-
PPS with status IN PROGRESS. This status information is
communicated to the DSS and IM.


GP-WL Manager
Report Creator
(CAD Processor)
Query
Scheduled GP-WL
Scheduled GP-WL Response
GP-WL Manager
Report Creator
(CAD Processor)
GP-SPS N-ACTION


4)

GP
-
PPS Completed/Discontinued: after completing or discontinuing the performed step, the
Report Creator (CAD Processor) updates the GP
-
PPS statu
s to COMPLETE or
DISCONTINUED and references any results. The CAD Processor will populate the
following information in the GP
-
PPS instance:

1.

All Type 1 attributes

2.

Patient’s Name, Patient ID (from the corresponding GP
-
SPS)

3.

Performed Station Name Code Sequen
ce (0040,4028) sequence
item

4.

Performed Station Class Code Sequence (0040,4029) sequence
item

5.

Performed Processing Applications Code Sequence (0040,4007)
sequence item, identifying the billable CAD processing code

6.

Performed Workitem Code Sequence (0040,4019
) sequence item

7.

Output Information Sequence (0040,4033) sequence item,
identifying the Mammography CAD SR instance created




5)

GP
-
SPS Completed/Discontinued: after completing or discontinuing the performed step, the
Report Creator (CAD Processor) updates t
he GP
-
SPS status to COMPLETE or
DISCONTINUED.

Report Creator
(CAD Processor)
GP-WL Manager
GP-PPS N-CREATE
Department System
Scheduler/Order Filler
GP-PPS N-CREATE
Image
Manager
GP-PPS N-CREATE
Report Creator
(CAD Processor)
GP-WL Manager
GP-PPS N-SET
Department System
Scheduler/Order Filler
GP-PPS N-SET
Image
Manager
GP-PPS N-SET

Impact on existing integration profiles

This profile picks up where the Scheduled Workflow profile ends.

This profile can be considered a pre
-
cursor to profiles that involve Reporting (e.g., the Year 4
Interp
retation, Transcription, and Report Verification package).

Check for possible interaction with the new Charge Posting profile.


New integration profiles needed

1 new profile would be added for the CAD Processing workflow.


5.

Open Issues

1)

Is the storage of ima
ges to an actor other than the Image Archive considered to be part of the
“Modality Images Stored” transaction [No], or should a separate transaction be defined?
[Yes, if permitted]

2)

Notes from Kevin:
A push model from Acquisition Modality to CAD processor
assumes that
the modality knows that CAD has been scheduled and knows which workstation will be
assigned the task for this particular study. A pull model requires that the CAD processor
query the Worklist Manager on a regular basis to get timely reaction.

There have been past
discussions on whether it is sufficient for worklist users to poll the list on a regular basis
(every few minutes) or whenever they are about to start some work, or whether it would be
better for the Worklist Manager to broadcast som
e kind of notification that there is
new/changed data. That would likely require the manager to maintain a list of users.

3)

From Kevin: Is there any value to including the Image Availability Query transaction in this
profile? Or is it sufficient to allow q
uery/retrieve to be attempted until successful?

4)

If there are concerns with the Acquisition Modality sending images directly to the CAD
Processor and Image Display, and the CAD Processor sending results directly to the Image
Display (rather than each actor
interacting only with the Image Archive): it is imperative that
CAD processing be completed as quickly as possible, so that images and CAD results are
available at the Image Display by the time the radiologist is ready to read the images.

5)

Is a new transa
ction required for the storage of Mammography CAD SR (or any other SR) to
the Image Archive or Image Display?

6)

What is the trigger mechanism for the GP
-
WL Manager to generate CAD processing work
items? How does the GP
-
WL Manager determine which images to gr
oup together in a CAD
processing work item? Is it triggered automatically by the completion of certain types of
Requested Procedures, and the availability of the corresponding images? Might there be user
interaction with a GP
-
WL Manager that could trigge
r this action?

GP-WL Manager
Report Creator
(CAD Processor)
GP-SPS N-ACTION
7)

From Kevin: I
s there a requirement for CAD processing to be explicitly ordered by a
physician (since it is a billable procedure)? If so, could CAD processing be just another
Scheduled Procedure Step in the original order? Some of the relat
ed questions are: Who
decides if CAD processing will be done? When (in the workflow) do they make the
decision? Where (in the organization/what system are they at) when they decide? It's OK if
some of these have multiple possible answers. Maybe the Or
der Filler automatically adds the
CAD step as standard procedure when filling/scheduling certain orders.

8)

From Kevin: Should there be a separate QC Profile, Post
-
Processing Profile, CAD profile,
and Reporting Profile, or is there some way to group them toge
ther? Perhaps a Processing
and Interpretation Workflow Profile, with various actors that can participate. So when a
CAD system participates in the PIW profile, allowing CAD, a QC system participates in the
PIW profile allowing QC, etc. Would a prolifera
tion of new profiles add too much
complexity by the time we get to IHE Year 5 or 6? What is the effect of creating fewer, but
more complex profiles? Topic for discussion.

9)

Will there be instances of Acquisition Modality actors that will support storage of

Digital
Mammography X
-
ray images as SCU?

10)

Will there be instances of Image Display actors that will support storage of Digital
Mammography X
-
ray images and Mammography CAD SR as SCP?

11)

Will there be instances of Image Archive actors that will support storage

of Digital
Mammography X
-
ray images and Mammography CAD SR as SCP?


Note: The CAD Processor will support storage of Digital Mammography X
-
ray images as SCP
and storage of Mammography CAD SR as SCU.