DICOM 3.0 & HL7 Integration Standards for Hospitals in Pakistan
Almost every integration question in a hospital imaging project comes down to two standards: DICOM for images and imaging workflow, and HL7 for patient, order and result data. This guide explains what each one does, which parts of them a hospital network actually relies on, and what to ask a vendor before you buy.
Two Standards, Two Jobs
| DICOM | HL7 | |
|---|---|---|
| Carries | Images and their metadata; worklists; imaging status | Patient registrations, orders, results and reports |
| Between | Modalities, PACS, RIS worklist, viewers, other archives | HMIS / EMR, RIS, laboratory and billing systems |
| Maintained by | NEMA (the DICOM Standards Committee) | HL7 International |
| Current form | DICOM 3.0, updated in regular editions | HL7 v2.x messaging; HL7 FHIR for web APIs |
DICOM Services a Hospital Network Uses
DICOM defines many services. These are the ones that matter in day-to-day radiology:
| Service | What it does |
|---|---|
| Storage (C-STORE) | Sends a study from a modality to the PACS, or between archives and sites. |
| Query/Retrieve (C-FIND, C-MOVE / C-GET) | Lets a workstation or another system search the archive and pull studies, for example priors. |
| Modality Worklist (MWL) | The modality asks the RIS for scheduled patients, so demographics are never typed at the console. |
| Modality Performed Procedure Step (MPPS) | The modality reports that an exam has started or finished, so the RIS status updates automatically. |
| Storage Commitment | The archive confirms it has safely stored a study, so the modality can delete its local copy. |
| Verification (C-ECHO) | A "ping" that tests the DICOM connection between two systems. |
| DICOMweb (QIDO-RS, WADO-RS, STOW-RS) | The same search, retrieve and store operations over HTTP, used by web viewers and newer integrations. |
DICOM Concepts to Know
- AE title. The DICOM name of each system. Together with the IP address and port it identifies who may talk to whom.
- SOP class. A combination of a service and an object type, for example "CT Image Storage". Two systems interoperate for a task only if they share the SOP class, in complementary roles.
- SCU and SCP. The Service Class User sends a request and the Service Class Provider answers it. A PACS is typically a Storage SCP; a modality is a Storage SCU.
- Transfer syntax. How the pixel data is encoded: uncompressed, lossless compressed, or lossy compressed. Diagnostic archives normally keep studies uncompressed or losslessly compressed.
- Unique identifiers. Every study, series and image carries a globally unique UID, so it can never be confused with another, even across hospitals.
- Conformance statement. The document (DICOM PS3.2) in which a product declares which SOP classes, roles and transfer syntaxes it supports. No body certifies DICOM; conformance is declared by the vendor and proven by testing.
HL7 v2 Messages in Radiology
HL7 version 2 is still the most widely supported way hospital systems exchange data. A typical radiology integration uses:
| Message | Typical direction | Purpose |
|---|---|---|
ADT^A04 / ADT^A01 | HMIS → RIS | Patient registered (outpatient) or admitted |
ADT^A08 | HMIS → RIS | Patient details updated |
ADT^A40 | HMIS → RIS / PACS | Duplicate patient records merged |
ORM^O01 or OMI^O23 | HMIS / EMR → RIS | Imaging order placed, changed or cancelled (OMI is the imaging-specific order from v2.5) |
SIU | Either way | Appointment scheduling |
ORU^R01 | RIS → HMIS / EMR | Signed report returned to the patient record |
ACK | Both | Acknowledgement of each message |
Which messages and fields are used is agreed per project in an interface specification. Pacslink uses HL7 v2 to connect its HMIS, RIS and PACS with each other and with third-party systems.
How DICOM and HL7 Meet
The two standards are joined by identifiers that travel with the patient through the workflow:
- The HMIS sends the order to the RIS over HL7. The order carries the patient ID and an accession number for the exam.
- The RIS publishes the exam on the DICOM modality worklist, including the same patient ID and accession number.
- The modality copies them into the DICOM header of every image it acquires, and sends the study to the PACS.
- The PACS and RIS match the study to the order by accession number; the radiologist reports, and the RIS returns the report over HL7.
When the worklist is not used and details are typed at the console, this chain breaks: studies arrive with misspelt names or wrong IDs and must be fixed by hand. Using the worklist on every modality is the single most effective integration step.
Where HL7 FHIR Fits
HL7 FHIR exposes the same kinds of data as web resources (REST and JSON). For imaging, the relevant
resources include ServiceRequest (the order), ImagingStudy (a reference to the DICOM
study) and DiagnosticReport (the report). FHIR is increasingly used for mobile apps, patient
portals and data sharing between organisations, while HL7 v2 remains the norm inside most hospital
radiology workflows. If you need a FHIR interface, raise it at scoping so the resources and security
model are agreed early.
Practical Points for Hospitals in Pakistan
- Mixed-vendor fleets. Hospitals often run modalities from several manufacturers and generations. Check each one's conformance statement for Storage and Modality Worklist support; older units may need a DICOM option enabled by the vendor.
- Patient identifiers. Decide which identifier is primary, typically the hospital's MR number, and how others (such as CNIC) are recorded, before go-live. Changing this later means re-matching studies.
- Connectivity between sites. For multi-site networks and teleradiology, choose routing that queues and retries studies when a link drops, rather than failing silently.
- Power. Keep modalities' network equipment, the PACS and the RIS on UPS so transfers are not interrupted mid-study.
Questions to Ask Any PACS or RIS Vendor
- Can we see your DICOM conformance statement for the version you are offering?
- Which SOP classes do you support as Storage SCP, and do you provide Modality Worklist, MPPS and Storage Commitment?
- Which transfer syntaxes do you accept, and do you ever store our studies with lossy compression?
- Which HL7 version and messages do you support, and do you have an interface specification we can review?
- Do you offer FHIR or DICOMweb interfaces, and on what terms?
- At the end of the contract, can we export every study in DICOM and every report in a standard format?
- How are access, audit trails and encryption handled for images and reports?
Want this checked against your own modalities and HMIS? Our engineers can review your equipment list and interfaces: contact the Lahore team.
