Short answer: a PACS (Picture Archiving and Communication System) receives images from scanners, stores them and shows them to radiologists. A RIS (Radiology Information System) runs the department's paperwork: orders, appointments, worklists, the dictated report, billing codes. A VNA (Vendor Neutral Archive) is a long-term store for images and documents from all departments (radiology, cardiology, pathology, dermatology photos), independent of any single PACS vendor. The HIS or EHR is the hospital-wide record that orders the exam and receives the report. They talk to each other with HL7 v2 messages, DICOM services and, increasingly, FHIR.
Who does what
In radiology IT, the HIS or EHR holds the whole patient record and orders the exam, the RIS manages radiology orders, scheduling, worklists, reports and billing, the PACS stores and displays DICOM images, the VNA archives images and documents from many departments for decades in standard formats, and the scanner itself stores nothing long-term.
| System | Stores | Main users | Speaks |
|---|---|---|---|
| HIS / EHR | The patient's whole record, orders, results, notes | All clinicians, administration | HL7 v2, FHIR, CDA |
| RIS | Radiology orders, schedule, protocols, reports, radiation dose, billing | Radiology reception, technologists, radiologists | HL7 v2 (ORM/OML, ORU, SIU), DICOM MWL/MPPS |
| PACS | Images (DICOM), hanging protocols, measurements, key images | Radiologists, referring clinicians | DICOM (C-STORE, C-FIND, C-MOVE), DICOMweb |
| VNA | Images and documents from many departments, for 10–30 years, in standard formats | IT, archiving, other departments | DICOM, DICOMweb, IHE XDS / XDS-I, FHIR |
| Modality (scanner) | Nothing long-term | Technologists | DICOM (MWL, C-STORE, MPPS, Storage Commitment) |
Many vendors sell RIS and PACS as one product, and some EHRs have absorbed the RIS function. The roles still exist even when the boxes merge.
The life of one CT scan
One CT scan runs through seven steps: the EHR sends an HL7 v2 order to the RIS, the RIS schedules it, the scanner reads the patient from a DICOM Modality Worklist, images go to the PACS by C-STORE with MPPS updates, the radiologist reports in the RIS, the report returns as ORU, and the study later migrates to the VNA.
- Order. A clinician orders a chest CT in the EHR. The EHR sends an HL7 v2 ORM^O01 (or OML^O21) to the RIS, with the patient, the requested procedure and the clinical question. See HL7 v2 order messages.
- Schedule. The RIS books the slot and sends an SIU message back if the EHR tracks appointments.
- Worklist. The scanner queries the RIS with DICOM Modality Worklist (MWL), so the technologist picks the patient from a list instead of typing a name. This is where most identity errors are prevented.
- Acquire and store. The scanner sends the images to the PACS with C-STORE and tells the RIS the exam is in progress and then complete through MPPS (Modality Performed Procedure Step), including dose data.
- Read. The radiologist opens the study in the PACS viewer, dictates the report in the RIS (often with speech recognition), and signs it.
- Report out. The RIS sends an HL7 v2 ORU^R01 with the report text to the EHR; some sites also produce a DICOM SR or a FHIR DiagnosticReport. The referring clinician reads it in the EHR; the patient may see it in the portal.
- Archive. After weeks or months, the study migrates from the PACS's fast storage to the VNA, from where it can be retrieved by any PACS or web viewer through DICOMweb or IHE XDS-I.
IHE wrote this flow down as the Scheduled Workflow (SWF) profile; most radiology integrations follow it even when nobody calls it by name.
Why a VNA exists
A VNA exists because a PACS stores images in its vendor's internal structure, so replacing the PACS means migrating terabytes with vendor-specific quirks. A vendor neutral archive stores everything as standard DICOM with standard metadata, holds non-DICOM documents alongside, serves several departments, lets a hospital change PACS vendors without touching the archive, and shares images between hospitals.
A PACS stores images in its vendor's internal structure. Replacing the PACS after ten years means migrating terabytes, often with vendor-specific quirks (private tags, compressed formats). A VNA stores everything in standard DICOM with standard metadata, holds non-DICOM documents alongside, serves several departments and lets the hospital change PACS vendors without touching the archive. In large regions, the VNA is also the node that shares images between hospitals.
Where FHIR enters
FHIR is arriving from the EHR side. Orders become ServiceRequest, appointments become Appointment, the finished study is described by an ImagingStudy and the report by a DiagnosticReport, all pointing to the DICOMweb endpoint of the PACS or VNA. Inside the department, HL7 v2 and DICOM will remain for years, because every scanner and every RIS already speaks them.
What reaches a patient's record
What reaches a patient's record from radiology is the signed report, with its codes, dates and the radiologist's name, plus a reference to the imaging study. In Anpheros this is a DiagnosticReport or DocumentReference in the patient's FHIR record; the images themselves stay in the hospital's PACS or VNA under its access rules.
The report, with its codes, dates and the radiologist's name, and a reference to the study. In Anpheros, that is a DiagnosticReport or DocumentReference in the patient's FHIR record; the images stay in the hospital's PACS or VNA. To obtain the images yourself, see How to get your CT or MRI images, and for the report itself, CT scan report explained or MRI results explained.
Related pages
- DICOMweb explained
- FHIR ImagingStudy vs DICOMweb
- HL7 v2 ORM and OML order messages
- HL7 v2 messages: ADT and ORU
- DICOM tags explained
- How to get your CT or MRI images (DICOM)
Sources
- IHE Radiology: Scheduled Workflow (SWF)
- IHE Radiology technical framework
- DICOM PS3.4: Service Class Specifications (Modality Worklist, MPPS)
- HL7 FHIR R4: DiagnosticReport
Frequently asked questions
Is a VNA just a bigger PACS?
No. A PACS is optimised for fast display and reading in one department; a VNA is optimised for long-term, standards-based storage across departments and vendors, and usually has no diagnostic viewer of its own.
Where is the radiology report stored?
The signed report lives in the RIS and is sent to the EHR as an HL7 v2 ORU (and sometimes as a FHIR DiagnosticReport). The PACS may keep a copy for display next to the images, but the RIS or EHR is the source of truth.
What is a modality worklist?
A DICOM service through which a scanner fetches the list of scheduled patients from the RIS, with their identifiers and the requested procedure. It removes manual typing at the scanner and is the main protection against images being filed under the wrong patient.
Can a patient portal show the images?
Yes, when the portal calls the PACS or VNA through DICOMweb with the right authorisation and renders them in a web viewer. The portal's FHIR record only needs the ImagingStudy and the report; it does not copy the images.
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