DICOM Simple Notes

DICOM Important Components

The DICOM standard primarily consists of:

1. A file format detailing the storage of medical images and associated metadata. For example: A ultrasound machine creates an image and stores it as a DICOM file (.dcm).
2. A network protocol that governs communication between imaging devices. For example: Ultrasound machine sends it to a PACS (Picture Archiving and Communication System) via the DICOM protocol.

Typical DICOM Workflow

1. Order created in HIS/RIS: The workflow begins when a doctor orders a medical imaging exam (e.g., a CT scan, MRI, or X-ray) for a patient. This order, including patient demographics, the type of exam, and clinical history, is entered into the Radiology Information System (RIS) or the hospital's central electronic health record (EHR). The orders are stored as Modality Worklist entries in RIS system.
2. Modality queries MWL (C-FIND): When the patient arrives for their appointment, the imaging technologist prepares the imaging device(imaging modality like CT, MRI, Ultrasound etc.). Instead of manually typing in the patient's information, the modality sends a DICOM network query (a C-FIND request) to the RIS. The RIS, acting as a DICOM server, responds with a Modality Worklist entries. This worklist contains all the necessary metadata for each procedure.
3. Procedure performed: The technologist selects the correct patient from the worklist displayed on the imaging machine's console. This action automatically populates the imaging device with the patient and exam information. The imagine device then performs the scan and acquires the pixel data (the actual image) with metadata from the Modality Worklist (e.g., patient name, ID, and study description). This combination of metadata and pixel data is what creates the final DICOM .dcm file. The file is then sent to a PACS (Picture Archiving and Communication System) for storage and review by a radiologist.
4. Images sent to PACS (C-STORE).
5. MPPS sent to RIS (N-CREATE/N-SET): marks procedure done.
6. Radiologist retrieves images from PACS (C-FIND / C-MOVE).

Questions List

What's Modality Worklist(MWL) and its relation to DICOM .dcm file?

The Modality Worklist(MWL) is a DICOM service that provides a list of scheduled patient exams to imaging equipment, So the technologist doesn’t have to manually re-type patient details on the machine. The service is defined in the DICOM standard. This list is typically generated by a RIS (Radiology Information System).

A .dcm file is a DICOM image or related data file. It contains Metadata (DICOM tags) like patient name, ID, modality type, acquisition parameters, etc and Pixel Data(the actual image).

Here’s how they connect in the real workflow:

1. Modality Worklist(MWL) Query (C-FIND):
   • Imaging machine(Imaging Modality) sends a DICOM network query (a C-FIND request) to the RIS. This query asks for a list of scheduled exams.
   • RIS sends back a list of worklist items (patient name, procedure description, accession number, etc.).
2. Exam Acquisition:
   • The modality operator selects one Modality Worklist(MWL) entry.
   • The modality copies patient and study details from MWL into the DICOM header when generating .dcm files.
3. Image Creation:
   • The scanner captures images and stores them as .dcm files with the metadata filled in from Modality Worklist(MWL).
4. Send to PACS (C-STORE):
   • The .dcm files are sent to PACS or other storage.