Mammography CAD Workflow - Detailed Proposal

1. Proposed Profile: Mammography CAD Workflow

Proposal Editor: Carolyn Reynolds
Date: N/A (Wiki keeps history)
Version: N/A (Wiki keeps history)
Domain: Radiology/Mammography

2. Summary

Problem

CAD processing of Full Field Digital Mammography (FFDM) images is a common practice in the US and is deployed in many parts of the world. Users and vendors have examined applying existing IHE profiles to mammography CAD workflow, such as Post Processing Workflow (PWF), without success. The PWF profile is based upon a query model that presumes the Post Processing Manager to be paired with a Department System Scheduler (DSS) or Image Manager (IM). In the PWF use case 12.4.1, a Modality Performed Procedure Step (MPPS) Complete message would trigger the work item order for which the CAD server would query and claim. The CAD would then retrieve images from the Image Manager, and generate CAD results. CAD results would then be stored on the image manager, for later query by the Image Display.

The above model does not work for mammography because in practice, users do not archive the “MG for processing” images necessary for CAD processing. The images are simply not available from the Image Manager to retrieve. Also, many users also do not wish to archive CAD results for a variety of reasons (i.e. many false positives, legal), and therefore they are not available for the Image Display to retrieve.

The model also introduces other inefficiencies. CAD servers are typically “headless,” creating the need to constantly be polling the DSS or IM for work items. Another complication is that CAD servers may be licensed to only process images from particular FFDM machines by serial number (found in Gantry ID or Detector ID). A burden would exist on the scheduling system to understand this relationship, or CAD servers could end up claiming work items and then later discontinuing them if not properly licensed. Image Displays also experience inefficiencies. CAD results usually take several minutes to process after receiving the images. The user at the Image Display may have access to the images but will have to poll the Image Manager over time until the CAD results become available for retrieval.

In addition to PWF not providing an optimal workflow for CAD as practiced for mammography, there are a few, very common use cases that could benefit from having an industry endorsed implementation. Such examples include:

How to handle images added to a case after initial CAD results have been produced
How to handle diagnostic (as opposed to screening) cases
How to handle retakes

Proposed Solution

Today, all mammography CAD vendors deploy a push model workflow for mammography CAD processing. The efficiency of this model, coupled with the lack of enabling PWF actors explains its wide acceptance. This model can easily be represented through existing IHE transactions and actors. Recognizing and adopting a different profile for mammography CAD other than PWF keeps customers from demanding an inefficient, impractical solution, and also keeps vendors from developing functionality that doesn’t serve its customers needs.

However, the currently practiced model is not without its own issues. Determining what objects should and should not be included in case level processing can be a challenge to CAD vendors. The generation of multiple CAD results can be confusing when determining what should be taken into consideration during diagnosis. Because the IHE Mammography Committee is made up of users and vendors that represent nearly all related actors and industry vendor participants, it is the perfect forum to determine if specifying use cases and industry practices for such cases can overcome some of the issues introduced by the push model.

3. Use Cases

The problem domain for this proposal is the workflow associated with generating, distributing, and interpreting mammography CAD reports. Below are descriptions of typical use cases.

Use Case #1 – normal screening – all images sent within same association

The technologist acquires 4 views as part of a screening exam – 2 views per breast. The technologist completes the exam. The raw, “for processing” image data is sent to the CAD server, while the processed “for presentation” data objects are distributed among PACS and diagnostic workstations. The CAD server begins image level processing, followed by case level processing. The CAD server sends the CAD results to the workstation(s) where the study will be read. The “for presentation” images arrive at the workstation first. The CAD report arrives a few minutes later. The radiologist interprets the case, reviews the CAD report, and finalizes his/her diagnosis.

Use Case #2 – normal screening – images sent as acquired

The technologist acquires 4 views as part of a screening exam. As each image is captured, the raw, “for processing” image data is sent to CAD. The CAD server begins image level processing, followed by case level processing of all images. All acquired images arrive before the case level processing begins (usually determined by a time out strategy in between images received). The CAD server sends results to the workstation(s) where the study will be read.

Use Case #3 – normal screening, delay in image acquisition

The technologist acquires 4 views as part of a screening exam. As each image is captured, the raw, “for processing” image data is sent to CAD. The CAD server begins image level processing, followed by case level processing. Positioning and getting the patient to stand still are particularly difficult for this patient. Several retakes must be done to acquire an acceptable image, requiring longer than normal time between images sent to CAD. The CAD server times-out waiting for any more case level images and generates a CAD report. After distributing the CAD report, additional images are received for the already processed study. The CAD server still has the original case images, reprocesses the case with the additional images, and sends a second CAD report that contains results for all images, processed as a single case.

For use cases 1 – 3, it is proposed that a mechanism such as MPPS can be used to communicate between the modality and CAD server as to exactly when the screening procedure has been completed and which “for processing” data objects are contained within the completed procedure.

Use Case #4 – follow-up views

While taking a patient’s history information for a screening exam, the patient reveals to the technologist that she is concerned about something that she feels in her right breast. The technologist acquires the 4 traditional screening views and completes the procedure. CAD results are generated for the 4 acquired views and are sent to the radiologist. The patient is held by the technologist until she can have a consultation with the radiologist. The radiologist reviews the case and CAD results, and decides that additional views should be acquired. Additional views are acquired as part of an appended procedure. The additional views are sent through the CAD server. The modality could send all case images, or the CAD can associate the additional views with cached images it still has from before. The additional images are processed as a case with the original images. A second CAD report is sent to the workstation where the radiologist can view the additional images (received from the modality) and both CAD reports. The radiologist has information readily displayed that helps him/her discern among the multiple CAD results.

Note: in the above case, the additional images may or may not be acquired on the same modality as the original images.

Note: a variance on the above case may be that patient is not held and that additional views may be acquired on a subsequent day.

Use Case #5 – generalized PACS workstations

A user already has an enterprise PACS solution in which she has invested a lot of money. Her PACS is approved for use in diagnosing FFDM images and can even display CAD results. However, her workstation may have the following undesirable behavior for mammography diagnosis:

CAD results arrive before the associated images arrive. The patient appears on the list without indication that the images are not available. Upon opening the study, the radiologist has not explanation as to why images are not presented. In some cases, the workstation discards the report if it does not have associated images.

CAD results are viewable upon opening the case. CAD results should be turned off until impressions are made. Users should be able to toggle CAD markers on and off and include this function in their hanging protocol

The user does not have access to important CAD header data such as Manufacturer (0008,0070), Algorithm, Operating Point, Content Date (0008,0023) and Content Time (0008,0033), or if this information is present, it covers breast tissue when displayed.

The user does not have access as to whether or not the CAD processing was deemed successful or not.

The CAD marks have undesirable appearance changes during window/center or zoom in/out operations. The CAD marks do not follow rotation, flip, and mirror operations.

The workstation is not capable of rending all marks contained in the report.

Multiple CAD reports were generated due to follow-up views on the same visit. The workstation provides no indication to the user that multiple reports exist, or when known, does not provide enough information to help the radiologist know if any reports are inferior/superior to the other reports present.

Use Case #6 – mosaic views

The patient is too large to be imaged within just one expose per view. To image the entire breast, multiple exposures of the same view type are required. The modality does not support supplying partial view information, and therefore, the CAD server can not process or incorrectly processes the exam.

Use Case #7 – CAD to technologist communication

CAD could communicate back to the technologist if the positioning was sufficient for processing.
CAD could communicate back to the technologist if there were image quality issues.

4. Standards & Systems

Most currently available systems have applications that support a push model for data objects associated with mammography CAD.

DICOM 2007 and existing IHE transactions will be used within this profile. The IHE mammography committee has representation from DICOM Working Groups 15 (Digital Mammography) and 6 (Base Standard). When mechanisms are not presently available to support desired workflow, it is hoped that these relationships can help address solutions compatible with DICOM or assist in sponsoring CP’s to the DICOM standard.

5. Technical Approach

Additional work will need to be done to address all concerns, details, and use cases. Below is just one possible baseline approach for a push model for CAD workflow. This approach should be compared to the present PWF profile along with other possible ideas from the committee.

1. The FFDM modality can send an “in progress” MPPS message (RAD-9) to a CAD server.

2. The Acquisition Modality uses the images store transaction (RAD-8) to send “for processing” image data to the CAD server. RAD-8 has already been expanded to include additional required fields that support the Mammography Image profile. The committee will examine if additional field support is needed for CAD workflow.

3. The Acquisition Modality sends an MPPS complete message to the CAD server, which can indicate the instance UIDS of the images that should be used for CAD processing.

4. Upon receiving an MPPS complete message with the relevant UID’s the CAD server can confidently begin case level processing and generate results for the completed procedure.

5. The CAD server can distribute the CAD reports to multiple locations where the CAD report could be accessed (Image Manager, multiple workstations if not archiving CAD results). The CAD report content should contain all necessary fields to support CAD workflow.

6. Image Managers would be required to support mammography CAD SR’s to participate in the workflow profile.

7. Image Displays would be required to support receiving and properly rendering CAD reports. Image display should communicate the availability of both images and reports as to avoid inefficiencies in reading. Upon receipt of multiple CAD reports, the image display would be required to appropriately communicate fields that help radiologist discern among multiple reports.

8. If follow-up views are required to complete a same day exam, the modality would follow the “Append Case” from the scheduled workflow profile to indicate the nature of the additional images. The Append Case (same study, accession number) would indicate to the CAD server the relationship to the previously sent images. The modality could be required to resend all case level images to the CAD server, or conversely, the CAD server could be required to retain an image cache where it could associate previously processed images with additional images received.

New actors

None identified at this time.

Existing actors

Acquisition Modality, Evidence Creator, Image Manager, Image Display

New transactions (standards used)

It is expected that extensions would be made to existing transactions to specifically enable mammography CAD workflow

If CAD to technologist communications are included in the profile, new transactions would be likely.

Impact on existing integration profiles

None expected except that PWF is not officially endorsed as a solution for mammography CAD workflow

New integration profiles needed

It is desired to create a new profile for this workflow to help the user community describe the specific extensions to transactions and actor requirements to specifically support CAD processing as practiced for mammography.

Breakdown of tasks that need to be accomplished

1. Validate proposed use cases and collect all desires and requirements related to mammography CAD workflow with the user and vendor community.

2. Identify existing DICOM services and IHE transactions that already perform desired functions.

3. Perform a gap analysis on whether or not new transactions or transaction modifications are required to enable CAD workflow.

4. Determine if specific fields in data objects should be specified beyond already existing standards and IHE requirements.

5. Write and refine profile.

Risks

Lack of existing standard or mechanism to communicate necessary trigger in workflow

7. Open Issues

Mechanism for declaring end of case
- Potentially add a new Transaction from the Modality for end of case -- PPS Transaction
Mechanism for handling added views
Mechanism for specifying type of CAD to process (just calcs, just masses, both)
Mechanism for CAD to technologist communication

8. Effort Estimates

Effort Evaluation (as a % of Tech Cmte Bandwidth):

35% (This includes both the definition of the case and the distribution.

Responses to Issues:

See italics in Risk and Open Issue sections and Minutes from the Sept 26 T-Con

Candidate Editor:

Carolyn Reynolds/Paul Morgan/John Paganini/Ron Hitzelberger Assumes that only the Mammo Acquisition or the Mammo CAD will occur in the 2007-2008 time-frame.