Mammography Acquisition Workflow - Detailed Proposal

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1. Proposed Profile: Mammography Acquisition Workflow

  • Proposal Editor: John Paganini/Ron Hitzelberger/Carolyn Reynolds
  • Profile Editor: Carolyn Reynolds/Paul Morgan
  • Date: N/A (Wiki keeps history)
  • Version: N/A (Wiki keeps history)
  • Domain: Radiology


2. Summary

Mammography Acquisition Workflow is about handling scheduled and unscheduled image acquisition in Mammography. Acquired images serve as input to potentially any other subsequent event such as post-processing/ CAD, interpretation/ reporting, and billing. Optimal integration of acquisition steps into the overall workflow is critical.

After initial image acquisition re-takes, additional views or CAD results may be appended to the imaging study subsequently. Studies are not complete until the Radiologist is satisfied.

There are common practices in digital mammography which can have a wide variety of workflow results. Despite technical means defined in the Scheduled Workflow and Mammography Image Profiles, variances in the way users and systems behave can lead to department inefficiencies, ambiguous data, special cases for automated billing, and less than optimal acquisition and reading environments.

Because additional views are common in mammography, there is no easy, practical mechanism within mammography to declare a scheduled procedure complete. Performed Procedure Steps can continually be added to a study. MPPS complete messages and PACS distribution mechanisms can inhibit access to images, CAD result reports, and study annotations. Inconsistent study statuses and study structures have also been an issue with many PACS.

Different implementations of workflow functions and semantics can be reduced by guiding or defining which data and semantics is exchanged and used by interacting systems. IHE can facilitate the exchange of information required for efficient workflow especially for solving the problem of additional views.

One approach might be to define how to apply more generalized Scheduled Workflow use cases (e.g. Append Case) to mammography practices. IHE may re-use existing IHE work, add IHE specification based on existing standards, or identify gaps in standardization that could be handed off to the appropriate resources (i.e. DICOM committees).


3. Use Cases

1. A patient comes in for a screening mammogram which is converted to a diagnostic exam upon the technologist discovering a lump. The technologist adds an extra view, but no exam type, so the hanging protocol at the workstation is unacceptable. For example, a screening mammogram typically has 4 standard views. The hanging protocol for a screening mammogram very possibly is triggered by the exam type at the diagnostic workstation. If another view is added by the technologist and the exam type is not altered, either the physician may not see that extra view in the hanging protocol or the additional view may disrupt the normal hanging steps and force the user to drag and drop images.

  • Additional views may effectively change the type of the exam (i.e. screening to diagnostic, or uni-lateral to bi-lateral). The resulting final exam type is not evident to systems and users.


2. A radiologist views a screening exam and toggles on CAD which indicates findings. The radiologist requests additional images to better demonstrate the abnormality. Should the technologist add the views to the existing order? Does it depend upon whether or not the patient is still available for imaging that day? How should the exam type (and billing) change from screening to diagnostic if this is necessary?

  • Using another study or accession number to add the views leads to archiving, billing, and display presentation problems. The additional views may not hang simultaneously with the original study, or the extra views may make the study that happened just a few minutes prior the “old” study.


3. A patient comes in for a follow-up exam on one breast. Since she is close to her yearly exam date, the radiologist calls for imaging of the other breast too, while the patient is waiting. The original room is unavailable, so another machine is used. The technologist generates a new study and accession number. The right and left breasts do not hang together at the diagnostic workstation. The following year, the prior images are hung as two prior studies, not as one complete comparison study.

  • Additional views can later be mistaken for complete prior exams.


4. The technologist labels a view incorrectly and doesn’t realize it until after the case is completed and sent to PACS. The view information is corrected at the acquisition modality and resent. The images do not hang properly on the workstations and multiple copies of the same image exist, one of which is labeled incorrectly.

  • Additional views may be data corrections or retakes on previously acquired views. Image Managers and Workstations do not have a mechanism to understand and properly treat images produced as a result of such conditions.
  • Additional views may generate additional CAD result reports. This creates confusion as to which objects should be considered for case level processing and which CAD reports should be considered when reading.
  • Some CAD outputs consider only the most recent of the four standard views sent and so, for example, if a Right MLO view is done twice and the second one turns out worse than the first, the CAD may only be applied to the the less diagnostic image. If the hanging protocol prescribes that the first image for any one view be hung in the vieport, the CAD is not readily visible to the radiologist who then has to figure out where the CAD is.


5. A PACS will not distribute images until a study is complete. A technologist wants the radiologist to view the images before completing the exam. The radiologist can not access the images from the diagnostic workstation. If the technologist completes the exam for the radiologist to view then the problems already ellucidated apply.

  • Some workstation behaviors are incompatible with the needs of mammography, such as not allowing the addition of images to studies that are open or have already been viewed.


6. CAD objects and markups are persistent. Many sites want to have them available until after the study is completed then they no longer wish to keep or store them.

  • ACR does not require that mammography facilities archive CAD objects and image markups (overlays or Presentation States).
  • PACS vendor assumes responsibility.
  • Deletion is possible based on SOP Class but maybe there is a better way to deal with this situation.


7. Study objects (images, CAD SR, digitized films) for the same patient can arrive at a PACS from multiple stations, creating a ‘mixed’ station name.

  • Mixed station names complicate the ability to address the individual needs of stations, i.e. body part mapping, specialty mapping, compression and archiving, etc.


8. Not all mammography modalities create markers that are ‘burnt’ into the image data per the ACR QC Manual. It states that the view and laterality should be placed on the image near the axilla.

  • Radiologists are used to the ‘look’ of conventional markers and dislike the variability that exists. They prefer that this information is not hidden amongst other demographic information.
  • While the markers are supposed to be in the axilla and radiologists are accustomed to the look of the conventional markers, the markers should not be distracting and should not ever exist inside the skin line, no matter the resolution or mode of display.


9. Workstations often include a means to indicate to a radiologist that there are additional views during dictation.

  • A standardized means of indicating wheteher images, objects, and presentation states have been viewed would be useful to radiologists once they begin dictation. It is not the dictation that should cue this but the moving on to another case or better yet marking the case as read. Most systems do not have integrated dictation to like these two functions.


10. A patient has an ultrasound. The tech does the ultrasound and completes the exam to send it to the radiologist. The radiologist decides to scan the patient and wants to add more images but can’t because the exam has been changed from in progress to completed.


11. The radiologist wants to delete US images that the tech took because they are not representative of real findings, but the tech completed the exam to send to the radiologist and so the study cannot be altered in that way.

12. The patient presents for a unilateral breast ultrasound and the RIS indicates right or left bresat ultrasound. The doctor decides that he/she wants to scan the other side. Another exam needs to be ordered in the RIS and so the left and right ultrasounds hang separately on the workstation.

13. It is typical for a mammography site to have an acquisition modality, diagnostic display station, and a PACS system from different vendors. The modality is expected to store images to multiple destinations (display station, CAD server, and archive). The CAD server also requires multiple destinations (display station and archive). The diagnostic display station must querry for then retrieve relevant prior studies. Multiple destination wokflow causes excess network traffic and creates multiple instances of images, objects, markups and status.


4. Standards & Systems

Existing standards and mechanisms to consider include:

  • DICOM <Be specific>
  • Existing IHE profiles, actors, and transactions <Be specific>


Existing systems that could be involved in the problem/solution include: FFDM modalities, Mammography CAD servers, Diagnostic and Technologists’ workstations, PACS, and RIS.


5. Technical Approach

The committee will first try to apply the existing Scheduled Workflow Profile transactions and actors to mammography and then address gaps requirements not met. The committee will seek to stay aligned with any applicable developments associated with Scheduled Workflow 2.0 activity. However, because mammography is a screening modality and a highly regulated field, the committee believes that some of its unique challenges and most urgent issues would not be completly addressed by SWF 1.0/2.0. We would expect that SWF 2.0 alone would seek to resolve common issues among radiology practices, not those unique to mammography.


Below are some possible ideas that could be used to address some of the problems. Better ideas may be available, but these are provided to demonstrate profile feasibility.


Normal Screening Use Case (scheduled case w/o pre-fetching priors)

1. The ADT, OP, and DSS/OF, actors work as detailed in SWF to register the patient and then schedule and fill the screening order.


2. The full field digital mammography modality (FFDM MOD actor) queries the DSS/OF for the modality worklist (RAD-5)


3. When the technologist begins the exam, the modality sends a Modality Performed Procedure Step message (RAD-6) to those systems desiring such information. It is believed that PACS, RIS, and CAD may all desire MPPS data for different reasons. To date, it has not been viable to rely upon a PPS Manager to distribute MPPS messages among these multiple systems. Where a PPS manager exists, having the modality send to once to the PPS manager is preferred, but the non-existence of an enterprise wide PPS manager should not limit the other systems from having access to this needed information.


4. The technologist begins acquiring the typical 4 view images for the exam. Images may be sent to destinations (RAD-8) as they are captured and accepted (one DICOM association per image), or images may be held and sent at once at the end of the exam (one association per exam). There are benefits to both methods, and destinations should be compatible with either method, giving users the choice of which method benefits them best.


5. “For processing” images are sent from the modality to CAD (RAD-8).


6. “For presentation” images are sent to the Image Manager from the modality (RAD-8) and “for processing” images can be sent per the user’s choice.


7. Store Commitment (RAD-10) message(s) are sent to the Image Manger from the modality


8. A preferred next step would be for the Image Manager to forward the image on to the Image Manager actor (RAD-8) along with any relevant priors not pre-fetched already to an image display. The committee would not seek to define the application that would do this, but would recommend guidance from our user community on what to consider when identifying relevant priors and intelligent routing to an image display(s). Since this is a preferred and not required operation, defining an actor/transaction pair as an option would be an effective way for the committee to communicate to the user community a preferred, but not required method of data transfer and distribution.


9. In the absence of the option described in the previous step, the modality will need to be required to distribute images to not only CAD systems and an Image Manager, but would also be required to send images directly to the Image Display. This would require support of RAD-8 by the Image Display actor which is not currently part of SWF. (Note: diagnosis of mammography images from remote locations is a forceful market demand gaining momentum, even when PACS are not shared among facilities. The committee should consider how the Image Manager actors and Image Display actor relationships play not only within one facilities, but among facilities that may or may not have integrated PACS).


10. The technologist would complete the procedure, thus sending an MPPS complete message (RAD-7) to the systems requiring such information. Comments similar to those in Step 3 apply here.


11. Although potentially outside the scope of this profile, the CAD system would process the screening exams and send a mammo CAD SR report to the Image Display (RAD-43). The CAD should also have the ability to optionally send the report to the Image Manager and perform a Storage Commitment (RAD-10) for those users wishing to archive CAD reports. For those archiving reports, the same comments from Step 8 apply to relaying prior CAD results to Image Display(s).


Follow-up images:

To address the problems that additional images case systems, the follow approach could be considered:


1. The data flow for the initial images will be assumed to be the same as described for the standard screening exam. Previously acquired images would belong to a completed performed procedure step.


2. The addition of follow-up views would follow the data structure similar to the Append Use Case in scheduled workflow. Several scenarios could play out:

  • Upon confirming the need for additional views, the technologist returns to the equipment where the original views were captured and are still available on the system. The technologist appends a modality performed procedure step to the original study.
  • Instead of returning to the original system to take the extra shots, the technologist uses the only room open that has a modality of a different manufacturer. The technologist is able to still see the worklist item for the order, selects the worklist item, and prepares the additional views.
  • The technologist uses a system to take the additional views (original or different room). The original study is not available and the worklist item is not longer available [because the worklist SCP does not follow the OF requirements for this profile). The technologist is able to retrieve the original image information from the Image Manager from which then the system is able to append a modality performed procedure step.


3. In all the scenarios above, the modality will create a new procedure step and send out appropriate MPPS messages (RAD-6 and RAD-7). Per the Append Use Case data structure, the added images will contain the same study UID and accession number as the original images.


4. The images will be sent to the Image Manager and Image Display in ways similar to the standard screening use case.


5. The images could be sent to CAD in one of at least 3 approaches:

  • The modality could simply send all the images that it has for a specific study and all images from that study would then be processed as a case. Note: this would be true whether or not the original images were taken on the equipment that acquired the additional views.
  • The technologist could be given the ability to select among all available images (original set and additional views) and send just the selected images to CAD to be processed as a case.
  • The CAD could be required to either 1) retain images in cache for a configurable period of time or add all images of the same study UID to the case for processing, or 2) the CAD could be required to query the Image Manager and retrieve all case level images before processing the additional images with the case. Note: the first behavior is present in virtually all installed CAD systems, today.


Optimally, the committee could search for a DICOM mechanism that allows the technologist to communicate [from the modality] to the CAD system, which images from a reference study should be considered for CAD case processing.


6. If not deemed outside the scope of this profile, the CAD system will be required to have behaviors that populate header information that would assist a radiologist in understanding how this CAD report may relate to any other CAD reports that may have been processed on the same study. The fields would be expected to already be within the scope of existing DICOM services or minor enhancements not expected to generate controversy.


7. The Image Manager and Image Display will be required to have behaviors consistent with this use case. For example, some PACS will complete a study upon receipt of a completed procedure step. The exam must not be completed at the study level when it is a sub-study component that is completed. Image Displays will need to be able to help the radiologist not miss when views have been added to a study if the study is being viewed or has been marked viewed or read. The Image Display will also be required to display enough header information in from the CAD results to help the radiologist understand which report is most appropriate to use. The committee will not seek to define application requirements, but will aim to help vendors avoid behaviors that break mammography workflow and encourage behaviors that reduce ambiguity and increase efficiency and contribute to patient care.


Pre-fetching prior images:


Screening exam turned diagnostic on the same day:

Screening exam turned diagnostic on the same day:

In the US, there are specific rules regarding billing for exams that begin as screening exams, but then turn diagnostic should the patient mention a problem or the technologist or radiologist quickly identify a concern and move within the same day for follow-up. The committee would want to perform limited research to appreciate practices in other parts of the world.

One approach to this challenge is to have an agreed upon method of assigning codes to the performed procedure step for the additional views that can be used by down stream systems (Image Manager, Image Display, CAD, Billing systems) so that their applications the necessary special treatment necessary for this use case. If no additional views are required, and the original screening views are enough for diagnostic purposes, the original MPPS could be discontinued and the images could be reassigned (through a new instance UID) to a different MPPS that could communicate a different performed procedure code. This approach would require a CP to DICOM MPPS to allow a DISCONTINUED status to be sent after a final COMPLETED status has already been received.


Screening exam turned diagnostic on subsequent day:


Existing actors

<Indicate what existing actors could be used or might be affected by the profile.>

New actors

<List possible new actors>

Existing transactions

<Indicate how existing transactions might be used or might need to be extended.>

New transactions (standards used)

<Describe possible new transactions (indicating what standards would likely be used for each. Transaction diagrams are very helpful here. Feel free to go into as much detail as seems useful.>

Impact on existing integration profiles

<Indicate how existing profiles might need to be modified.>

New integration profiles needed

<Indicate what new profile(s) might need to be created.>

Breakdown of tasks that need to be accomplished

<A list of tasks would be helpful for the technical committee who will have to estimate the effort required to design, review and implement the profile.>

The original profile proposal, “Mammography Acquisition and CAD Workflow” has been separated into two different IHE proposals, although there are several overlapping concerns.

The following options and issues need to be clarified and resolved, including boundaries/ interfaces to a potential CAD profile:

  • What mechanisms solve which part of the problem:
    • Dataflow: reliably get images to a CAD box, workstation, PACS, etc. This includes clarifying the data lifecycle, e.g. retaining acquired images (or relevant data) on the modality so that in the append case, this previous Study and Procedure information can be re-used. Where to send which data to (PACS as single data sink or additional push to few known systems performing single next steps, e.g. CAD)?
    • Workflow: tell another system to do something, including references to input data. Which systems query for worklists (CAD worklist)? What scheduled steps are needed (e.g. schedule potential re-takes/ additional views, or CAD)? Which systems send and receive work status (MPPS to CAD and PACS)?
    • Internal logic of querying/ sending and receiving actors in order to determine when all images are available. For instance, compare MPPS references to available images, or query/ send image availability status.
  • It does not seem realistic to assume that IHE Technical Specifications can solve all variability in the field. Thus, users and vendors need to know how local practices and habits impact system use and departmental efficiency.
  • In acquisition and subsequent steps - how to access the images:
    • Pull: query/ retrieve, e.g. by CAD. This implies that PACS is required to retrieve images that match the query, irrespective of "Study complete" internal logic.
    • Push: store to one/ more receivers. This implies that the modality has internal logic to know when to send images or appended images, e.g. by using a waiting queue, by providing an interactive function for a user to manually send images.
  • For Workflow: prefer re-use and established things.
    • SWF
      • normal case - for scheduled acquisitions without re-takes or additional views
      • unscheduled case - is it relevant in Mammography at all?
      • append case - for re-takes or additional views (unscheduled or scheduled cases)
      • group case - is it relevant in Mammography at all?
      • Are Mammo-specific codes for procedures/ steps needed?
    • There are no other relevant IHE workflow profiles to be reused for acquisition workflow (PWF, RWF do other things).
    • If Modality Worklist and SWF do not solve the Mammo acquisition problems, is it worth while looking for less-established mechanisms? E.g. opportunities and risks of using UPS (still not finalized); dataflow (push images and MPPS to CAD).
  • Study complete - define the concept, i.e. relation of MPPS and "all images available". Only a human user can finally reliably state that a study is complete. If additional views are taken at a 2nd, different modality, does IHE need to cover this case (is it 80% routine?)? If a CAD system receives an MPPS from one modality, how sure can it be that there won't follow another MPSP from a 2nd modality notifying the CAD box of additional images/ views?
  • Exam type - clarify what this means exactly (screening <--> diagnostic). What are implications and required behavior?

6. Support & Resources

<List groups that have expressed support for the proposal and resources that would be available to accomplish the tasks listed above.>

7. Risks

<List technical or political risks that will need to be considered to successfully field the profile.>

8. Open Issues

<Point out any key issues or design problems. This will be helpful for estimating the amount of work and demonstrates thought has already gone into the candidate profile.>

9. Tech Cmte Evaluation

<The technical committee will use this area to record details of the effort estimation, etc.>

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