PDI large data sets - Detailed Proposal

1. Proposed Workitem: Large data sets on Portable Media

• Proposal Editor: Christoph Dickmann
• Profile Editor:
• Date: 2007-09-12
• Version: N/A (Wiki keeps history)
• Domain: Rad, incl. Mammography, Card, RO

Summary

IHE PDI does not describe what to do if a patient's study data exceeds the size of a CD (~700MB)

• Some studies significantly exceed DVD size, needing spanning
• Some studies significantly exceed CD size and could be handled by spanning and/or DVD support
• Some studies slightly exceed CD size (e.g. Cardiology diagnostic exams often have a size of 800 MB) and could be handled by spanning and/or DVD support and/or compression
• Some studies fit on a single PDI CD

Tradeoffs include the convenience and efficiency of a single disk vs the compatibility/reliability of a single format.

DICOM defines media application profiles with compression and with DVDs. DICOM has not specifically addressed issues of spanning.

PDI should be extended to address handling large data sets by using one or multiple media in a reliable manner.

2. The Problem

IHE Radiology has defined a reliable mechanism to create, (transport,) present, and import DICOM data on CD-ROM (cheap and widely used media) in the original, uncompressed format.
PDI does not explicitly define or recommend what to do in case the data to be burned by a Media Creator does not fit on a single media. However, the PDI Use Case 3 describes a scenario where voluminous data is to be exchanged by CD. Of course, this does not disallow a product implementing the Portable Media Creator to be able to burn CDs with additional DICOM media application profiles that allow compression.

IHE PDI was intended for general-purpose "simple" CD exchange to any unknown recipient with or without sophisticated workstations. Therefore, it was a design principle to use as few as possible DICOM media application profiles (i.e. exactly one: STD-GEN-CD).
PDI does not contain compression because

• there was no general DICOM CD media profile that includes compressed images
• modality-specific media profiles were considered inappropriate for a general/ simple CD exchange
• DVD compression media profiles suffer from hardware incompatibilities.

Meanwhile, users have reacted to this fact and

• requested PDI to explicitly cover a compression mechanism (which may reflect their local habits)
• add extensions to otherwise PDI-using frameworks, which may result in wrong use of DICOM media (e.g. DVD compression on a PDI CD).

It seems helpful if IHE clarifies this situation.

3. Key Use Case

Use Case 3 - Operating Room Viewing (RAD TF-1, 15.3.1):
"Media data is used to enable diagnostic or therapeutic processes in environments without a reliable network connection. The volume of data can be very large and may contain image data, post-processing results and reports. In the operating room, the surgical staff receives the media and reads its contents using advanced viewing capabilities, which may include manipulating or processing images."
Even data of one single patient may not fit on 1 CD.
Media user perspective:

• Preparation time increases if media content from more than one media is loaded onto the computer in order to have the images readily available during surgery.
• Reading in DICOM objects from a newly inserted media is slower than accessing DICOM objects from internal storage or from an already accessed media.
• Changing CDs in the operating theater also interrupts the procedure as this is done by a non-sterile person that may not be immediately at hand.

Media creator perspective:

• At time of media writing, it often is not exactly known who will use the media in what way. Therefore, there is a tendency to write the complete study data to media instead of selecting a few key images that may rather serve a special target user group.
• If a Tech burns the media, then she will often not select key images but just burn the whole study and report to the media.

Cardiologist practice and specialist referral:
After a cardiovascular diagnostic catheterization examination was completed, the Tech wants to give the patient her images on CD to be handed over to the referring general medicine physician.
Due to the large volume of the acquired images, the Portable Media Creator system needs to burn 2 CDs due to the volume of the acquired images. The Tech's preparation for the next patient is disturbed by needing to remove the completed first CD and to insert a second CD in order to burn all examination images.
For interventional studies, even more CDs may need to be produced (3 CDs).
Therefore, the Cardiologist practice will check if the Portable Media Creator function in the product can be switched off and instead, image compression can be switched on so that most patient studies will fit on one single CD.
During the next consultation, the referring physician who has cared for this patient over many years, wants to demonstrate the improvement to the patient who brings in the 2 CDs. As the physician has no imaging system, she reads in the first media on the office computer to show the patient the key images. Unfortunately, these are on the 2nd media, so she has to switch the CDs, which takes time.

4. Standards & Systems

There exist several DICOM media application profiles that allow storing compressed images, e.g. for CT, MR, XA, US images (DICOM part 11). However, none of them matches the STD-GEN-CD profile that is used in the current PDI specification. DICOM viewers that support JPEG-compressed images are not uncommon today.

DICOM does not define a general-purpose CD profile that allows storage of compressed images. A similar DVD profile exists, however, DVDs still show a considerable number of read errors.

DICOM allows data from one patient to be written on multiple media. However, there is no media-spanning information in the DICOMDIR, so that a receiver of one CD does not know

• if there exist additional CDs that complete the study data of a patient
• on which CD the priors, a subset of images, measurements or the report can be found.

5. Technical Approach

The technical approach should tackle these two issues of large data sets exceeding one piece of CD:

• compression: if DICOM objects can be compressed on a CD, this solves the problem of producing more than one CDs in many cases. Generally, it reduces the number of CDs to be burnt for large datasets.
• media spanning: if the DICOMDIR contains information on all objects burnt to a number of media, applications and users may easier navigate and do less media flipping.
• information, education: creators and users of media may benefit from finding key images and reports on media only, i.e. from avoiding information overload. IHE may promote selecting and burning key images for certain situations, e.g. for situations where CDs are produced for imformative rather than diagnostic or therapeutic follow-up.

Existing actors

PDI: Portable Media Creator, Image Display, Portable Media Importer, Print Composer

New actors

none.

Existing transactions

RAD-47 can be extended by options if

• existing DICOM compression mechanisms (media application profiles) are to be used
• an extensions of STD-GEN-CD that allows compression is created by DICOM
• media spanning gets specified by DICOM.

New transactions (standards used)

Distribute imaging information by DVD would require a new transaction.

Impact on existing integration profiles

PDI: Informative text should be added that describes pros and cons of different ways to handle large data sets with PDI actors (e.g. see use cases)

• CD for key images, small studies and unknown receiver or general use (less advanced applications expected)
• DVD for large studies and advanced reading applications of specialists as target receivers.

A reference to a "large volume media (DVD)" Integration Profile should be added.

IWRF:

• No changes necessary, as the IWRF Importer depends on a PDI actor or non-IHE defined functions to get the DICOM objects.

New integration profiles needed

If DVD is used for large data sets, a new separate profile is preferred over adding options to the existing PDI. The profile should reuse the actor names/ concepts from PDI.

Breakdown of tasks that need to be accomplished

Main workitems:

• Evaluate how existing DICOM media application profiles can be used.
• Evaluate how media spanning contributes to solving the large dataset problem.
• Check the DICOM plans for large datasets on CD, on media and with relation to general, non-modality specific media profiles. Also check options for DICOM development.
• Check if additional informative text to PDI can help users to decide how to reduce image volumes for media export.
• Evaluate how additional information in README.TXT, INDEX.HTM or CD labelling can help.

6. Support & Resources

DICOM support is necessary for advice or specification.
It should be checked how DRG/ OFFIS can help.
Request opinions/ input/ review from IHE Cardiology, IHE Pathology, IHE Eyecare, IHE Radiation Oncology, ITI XDM experts.

7. Risks

If new DICOM Supplements are necessary, the DICOM timeline may not match the IHE timeline. If no reliable technical solution can be found, adding informative text only may be considered insufficient for the practice.

There is the potential to reduce the reliability of the current install base.

8. Open Issues

Reliability of DVD does not seem to have improved sufficiently. This should be re-evaluated (access to experts?).

Media seems to be more of an issue than drive.

Should IHE organize a DVD "compatibility test" to better understand the problems with DVD?

9. Tech Cmte Evaluation

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

• 25% ...

Responses to Issues:

See italics in Risk and Open Issue sections

Candidate Editor:

TBA