Exploring DICOM’s Service Class Framework
After learning about the DICOM Communication Model, we now dive deeper into the mechanism that ensures every interaction between medical devices works smoothly — DICOM Service Class Specifications. This is the essential component that enables devices like MRI, CT, and PACS/MIMPS to not only exchange data but also perform specific actions as defined by the DICOM standard.
Roles of SCU and SCP in DICOM
In DICOM, SCU (Service Class User) and SCP (Service Class Provider) are two critical roles that determine who requests and who provides services in the communication process.
- SCU (Service Class User): Acts as the client that initiates a service request, for example, a modality (like an MRI) requesting a PACS/MIMPS to store newly captured images.
- SCP (Service Class Provider): Acts as the server that accepts the request and provides the requested service, for instance, a PACS/MIMPS storing or processing the images sent by the SCU.
In the Service Class Specification, each SOP Class defines whether a device must act as an SCU, SCP, or both. For example, in the image storage SOP Class (C-STORE), the device sending the image acts as the SCU, while the device storing it acts as the SCP.
DICOM Protocols
Here are some common DICOM SOP Classes related to communication and storage:
- C-STORE: This command is used to send and store medical images. The SCU sends the image to the SCP for storage.
- C-FIND: This command searches for data within a database, such as looking up patient information in a PACS/MIMPS.
- C-GET and C-MOVE: These commands retrieve or move data from one location to another. C-GET pulls data to the SCU, while C-MOVE sends data to another SCP.
- C-ECHO: This command acts as a “ping” between devices, verifying that network communication is functioning properly. It checks the connectivity between DICOM devices.
Each SOP Class has a specific purpose and function that drives the digital medical workflow.
DICOM Normalised Operations
In addition to standard operations, DICOM also supports Normalised Operations, which allow for more complex interactions. These operations deal with non-image objects like patient reports or procedural information.
- N-CREATE: Used to create a new instance of a DICOM object, such as generating a new report.
- N-GET: Requests and retrieves specific information from an existing DICOM object.
- N-SET: Modifies or updates information in an existing DICOM object, like updating patient data.
- N-ACTION: Instructs the SCP to perform a specific action on an object, such as processing an existing report.
- N-DELETE: Deletes an existing DICOM object from the database.
- N-EVENT-REPORT: Provides an event report or status update about a DICOM object to the SCU, such as reporting the status of an ongoing procedure.
Conformance and SOP Classes
DICOM ensures interoperability by allowing medical devices to declare their conformance to SOP Classes. This is critical in ensuring that devices from different vendors can communicate and exchange data seamlessly.
For media exchange (offline), devices can take on the roles of:
- File Set Creator (FSC): Responsible for creating and writing to storage media like CDs or USB drives.
- File Set Reader (FSR): Reads data from such media.
- File Set Updater (FSU): Updates data on the storage media.
Conclusion and Next Steps
By understanding Service Class Specifications, we can see how the structured communication in the DICOM model translates into actions such as sending, storing, and processing medical images. After grasping these fundamentals, we’ll explore DICOMweb, the modern web-based implementation of DICOM, which is increasingly relevant in today’s cloud-driven technology landscape.
Thank you for reading until the end. What do you think of this article? Please share your feedback in the comments below.
