Tuesday, October 11, 2011

Introduction to DICOM - Chpater 2 - Why is it this way in DICOM?

Introduction to DICOM
Chpater 2 - Why is it this way in DICOM?
Many times when I explain features and aspects of DICOM I get questions like, “Why do you need DICOM if you have JPEG and XML?”; or, ”why is DICOM so complicated?”. Many variants of such questions continually come up over and over again. These types of questions can be very broad or very specific and relate to all kind of choices that the people who write the standard make and the options that they take.

Here’s an example. In DICOM there’s a command called C-FIND that is used to make queries to another system, to search for images and other entities. You would naturally think of SQL, but in DICOM there’s a different way of doing it.

Let’s continue with the C-FIND example. The DICOM C-FIND command has three variants, each with its own data model. These variants are ‘Patient Root’, ‘Study Root’ and ‘Patient Study Only Root’. I’m always asked why do we need three variants and I really can’t give a simple answer. Luckily, the third model, ‘Patient Study Only Root’ is now obsolete so we are left with only two models.

There are many more examples like the C-FIND Query Model where DICOM just have too many options and redundancies. But as the standard became more and more common and dominant, developers just took care of all the options and degenerate the redundancies. Many PACS implementation simply treat all three models using the same code. The answer that I have come to use for that kind of questions is:
"That’s the way it is in DICOM and let’s just get on with it"

12 comments:

  1. I am a software engineer and new to DICOM. The question as to why DICOM is the way it is very intriguing. Why don't you write some better explanation regarding the subject?

    ReplyDelete
  2. Dear Divakar,
    The question "Why DICOM?" is a philosophical question that I didn't even try to address. Why XML? There are alternatives like JSON (see http://www.json.org/).
    The question "Why DICOM is the way it is?" that I discuss briefly here, is a technical question that is more interesting but still interesting enough. Why XML use < and > instead of for example { and } like JSON does? Why the ratio between syntax and data in XML is usually so small, typically much less than 1?
    If we were to redesign XML or DICOM I'm sure we could have make better work but we are not asked to do so. We are only users and we use what they give us and try to make the most out of it. In a way, my attitude towards practical engineering is like real politics: make the most of what you've got.
    Regards,
    Roni

    ReplyDelete
  3. It's also good to mention that DICOM was around much before possible alternatives like XML or JSON were popular (or even existed). Design considerations were different then (ie. saving a few bytes here and there could be significant), and DICOM evolved to meet those considerations. Replacing DICOM with one of these alternatives now would be an enormous undertaking, and even if attempted, the chances it would get adopted are probably slim. (HL7 v3 anyone?)

    ReplyDelete
  4. my question is :
    if i did an exam on such MRI for (X-Vendor), can isee the same exam thru MRN by DICOM standard on anther MRI for (Y-Vendor).
    i mean can i see the exam without using PACS viewer or PACS interface

    ReplyDelete
    Replies
    1. Dear Ahmed,
      In order to get DICOM images rrom the MRI you need either to copy the files on a CD or some other removable media (USB for example) or to send it to a DICOM Storage SCP using DICOM protocol.
      In order to view DICOM images you need a software that can do that. It can be from any vendor as long as it can read the files and display the images properly.
      Regards,
      Roni

      Delete
  5. my question is :
    if i did an exam on such MRI for (X-Vendor), can isee the same exam thru MRN by DICOM standard on anther MRI for (Y-Vendor).
    i mean can i see the exam without using PACS viewer or PACS interface

    ReplyDelete
  6. my question is :
    if i did an exam on such MRI for (X-Vendor), can isee the same exam thru MRN by DICOM standard on anther MRI for (Y-Vendor).
    i mean can i see the exam without using PACS viewer or PACS interface

    ReplyDelete
    Replies
    1. If I understand correctly (and I'm not sure I do) you can.
      Theoretically, if Y-Vendor MRI is a Storage SCP then you can send the images from X to Y directly.
      I don't know why you would like to do this but that's another story.

      Delete
    2. By means of DICOM, provided the imaging device and the viewing device are both connected to the same network, and properly configured, you could simply "pass" the images from one to the other... Equally, by means of DICOM you can simply have a given study from one source in say a CD/DVD/USB disk and import that data set to another machine with a DICOM viewer or DICOM set of applications.

      Delete
  7. I have some non dicom videos (MPEG) I want to convert and store this video into PACS for this I required to convert it into Dicom with multi-frame dicom image and stored into PACS.
    How Can I do this?

    ReplyDelete
  8. Excuse me ,Could you explain me ,how can i choose (Group,Element)Tag for right to my parameter project?

    ReplyDelete
  9. this really helpful , my doubt is why can't we use color images instead of gray scale images. event we will get some more clarity details and better diagnosis.

    ReplyDelete