Saturday, June 30, 2012

Convert DICOM to Bitmap in 3 lines of code

In an earlier post I covered how to convert JPEG to DICOM and also PDF and Bitmap to DICOM. In this very short post I'm going to show the opposite direction, which is much simpler,  converting DICOM to Bitmap.
With RZDCX this is very simple. Here's the C# code:

            DCXIMG img = new DCXIMG();
            img.SaveBitmap(0, bmpFile.Text);

dcmfile and bmpFile in this example are text boxes.
SaveBitmap first parameter is the frame number (0 based index) as a DICOM file may have many frames in it.
The DCXIMG class takes care of all conversions and decoding of the image if the pixel data in the DICOM file is compressed.
That's it on this subject. Comments and questions are most welcome.

Sunday, June 24, 2012

Web Site Upgrade - Broken links hazard

My new web site design for just went live. I hope its better than the old one. However, this may cause many of the links in the blog to get broken.
If you run into such broken link, just replace to which should take you to the old web site.

Thursday, June 21, 2012

Storage Commitment

What is DICOM Storage Commitment Service and why is it needed

Storage commitment (SCM) is a DICOM service that lets you verify if files that were previously sent to the PACS using the DICOM Storage Service were indeed stored by the application you sent it to. The SOP Class UID of this Service is “1.2.840.10008.1.20.1”. One can argue if it is necessary or not because when you send a DICOM image using C-STORE command and get a success status (0x0000) then it is supposed to be stored so the existence of Storage Commitment raises doubts about the meaning of that status in the first place. However, I can defiantly think of reasons for having such service, first because better safe than sorry and second because I already had some programming experience in the days when the DICOM standard was specified, Thanks god, we did make a long way since then. For example, some engineers, for the sake of efficiency and performance considerations, may have decided to first puts the files in a temporary storage or a queue, without even looking at their content and reply immediately with success and then later, when some batch or another thread processes the files in the queue and try to fill the database errors occur. I wouldn’t implement it this way, and I’ll give you reasons for that at the end of this post, but I did run into such implementations. The DICOM standard gives us the service but doesn’t go into the details of what is the implementation meaning should be but IHE does. IHE says that if your application creates instances and send it to somewhere, before deleting them from your local disk it should send a Storage Commitment and if all instances are OK, go ahead and make some space on your hard drive. Sounds like a good idea to me, it’s like double booking. Storage is the transaction and Storage Commitment is the reconciliation, Why not.

Storage Commitment Data Flow

All together SCM is pretty straight forward. All we need to do is to send a list of the instances and get back a reply saying which are in the PACS database and which are not, and that’s exactly how it works. Well, almost.  

Tuesday, June 5, 2012

Modality Performed Procedure Step


After the post on Modality Worklist, I felt that it wouldn’t be a complete without explanation on Modality Performed Procedure Step. MWL without MPPS is like a task list without checkboxes, and after all, striking a checkbox on a completed task is great fun. Talking of which, I once red this article about productivity and task lists and since then I’m using a circular checkbox on my paper to do notes because it’s 4 times faster. Instead of 4 lines you only need one. Think of it.

IHE Comes to Rescue

Though the DICOM standard states that it doesn’t go into the details of the implementation and what should be the implications of MPPS on workflow it is very clear from reading the details of the standard that an MPPS is the checkmark of MWL. The gap is closed by IHE radiology technical framework that does a great job and details exactly what should be the workflow and how the implementation should look like. If you are not familiar with IHE, I strongly recommend navigating to their web site and start digging. Getting familiar with the IHE Technical Frameworks can save a lot of expensive software architect hours and more important, save you from implementing things wrong. The IHE TF is high quality software specification document that you can use almost as is for your healthcare IT software projects.

Anyway, if you don’t have time to dig inside the long documents of IHE and DICOM and HL7, here’s a short data and program flow summary:

  1. The modality makes a MWL Query. Each result is a requested procedure object with one or more Scheduled Procedure Steps (SPS).
  2. The user picks one SPS to perform.  
  3. The modality creates a new Modality Performed Procedure Step (MPPS) that references the Study, the requested procedure, and the SPS.  This is done using the N-CREATE command. 
  4. There’s a state machine for MPPS with three states:
    1. In Progress (A dot at the center of the circular checkbox)
    2. Completed (A dash on the checkbox)
    3. Discontinued (Back to the beginning)
  5. After the images acquisition is done the modality sends an updated status for the MPPS using N-SET command. The N-SET must include a performed series sequence with at least one series in it, even if the procedure was aborted (in which case the series will have no images).
  6. At this point the Scheduler should dash the checkbox to mark the task as completed (or discontinued).
  7. Though usually you would have a 1-to-1 relationship between a scheduled procedure and a performed procedure, the DICOM data model has a n-to-m relationship between SPS and MPPS. The connection is made by the MPPS that references the SPS that it was performed for.

The DIMSE-N Protocol

Unlike all the other command that we’ve discussed so far in this tutorial namely C-ECHO, C-STORE, C-FIND and C-MOVE that are DIMSE-C commands, MPPS uses the normalized, DIMSE-N protocol commands N-CREATE and N-SET to create and update the Modality Performed Procedure Step normalized  information entity. We’ve discussed the normalized data model (aka DICOM Model of the Real World) briefly in chapter 4 when discussing DICOM Objects and stating that image objects are composites of modules from different information entities.
Like, in MWL before, here’s where MPPS fits into the DICOM Data Model: