DICOM vs HL7, in short
The short answer
DICOM is the standard for medical images: how they are formatted, stored and sent between scanners, the PACS and viewers. HL7 is the standard for clinical and administrative messages between systems: in radiology, registrations, orders, scheduling and reports. A CT scan travels as DICOM; the order that requested it and the report that interprets it travel as HL7.
DICOM carries
- The images (pixel data) from every modality
- Image details: patient, exam, series, technique
- The scanner’s worklist (Modality Worklist)
- Image storage, query and retrieval between systems
HL7 carries
- Patient registration and updates (ADT)
- Imaging orders from the EHR to the RIS
- Scheduling notices to the PACS and reporting system
- Signed reports back to the RIS and EHR (ORU)
What is DICOM?
DICOM stands for Digital Imaging and Communications in Medicine. In its own words, DICOM “is the standard for the communication and management of medical imaging information and related data” (DICOM PS3.1). It is also published as ISO 12052, and NEMA serves as the DICOM Secretariat (About DICOM).
A DICOM file holds both the image pixels and a header of metadata: the patient, the accession number, the exam, the series and how the images were acquired. DICOM also defines network services, so a scanner can store images on a PACS, a viewer can query and retrieve priors, and a scanner can pull its list of scheduled patients.
- 1983ACR and NEMA form a joint standards committee
- 1985ACR-NEMA 300 released
- 1993third version renamed DICOM
Dates from the DICOM history page. The 1993 version moved image communication onto standard networks (TCP/IP), which is what made PACS networks practical.
What is HL7?
HL7 refers both to Health Level Seven International and to its family of standards. HL7 International, “founded in 1987,” describes itself as “a non-profit, ANSI-accredited standards development organization,” and says that in the US “the HL7 Version 2 messaging standard is deployed at most healthcare facilities” (HL7 International). HL7 version 2 messages are short, structured text messages: each has a type (such as ADT, ORM or ORU) and segments for the patient, the order and the results.
The newer HL7 standard is FHIR (Fast Healthcare Interoperability Resources), which exchanges data through web APIs. FHIR has an ImagingStudy resource that “provides information on a DICOM imaging study,” so other systems can see that a study exists and where to get it, while the images themselves stay in DICOM.
The radiology messages, step by step
- 01
Register · HL7 ADT
The patient is registered or admitted. ADT messages (for example ADT^A01, A04 or A05) tell the RIS and PACS who the patient is.
- 02
Order · HL7 ORM or OMG
The order goes from the EHR to the RIS. Older interfaces use ORM^O01 (HL7 v2.3.1); the current IHE profile uses OMG (v2.5.1).
- 03
Schedule · HL7 OMI
The RIS tells the PACS and the reporting system that a procedure is scheduled, so they expect the images.
- 04
Worklist · DICOM MWL
The scanner queries the DICOM Modality Worklist and gets the patient and exam details for the scheduled study.
- 05
Images · DICOM C-STORE
The scanner sends the images to the PACS with the DICOM storage service. Modality Performed Procedure Step (MPPS) messages can report when the exam starts and finishes.
- 06
Report · HL7 ORU
The signed report goes back to the RIS and EHR as an ORU^R01 results message.
The message names follow the IHE Radiology Technical Framework, Volume 2, which defines these transactions (RAD-1 registration, RAD-2 order, RAD-4 procedure scheduled, RAD-8 image storage, RAD-28 report export). The IHE Scheduled Workflow profile ties them together and uses the DICOM Modality Worklist, Modality Performed Procedure Step and Storage Commitment services. Real interfaces vary; your interface specification is the final word.
DICOM vs HL7, side by side
| DICOM | HL7 | |
|---|---|---|
| Stands for | Digital Imaging and Communications in Medicine | Health Level Seven |
| Maintained by | DICOM Standards Committee; NEMA is the Secretariat | HL7 International (founded 1987) |
| Carries in radiology | Images and image metadata; scanner worklists | Registrations, orders, scheduling, reports |
| Typical traffic | Scanner → PACS, PACS → viewer, PACS → PACS | EHR → RIS, RIS → PACS, reporting → RIS and EHR |
| Web-era version | DICOMweb (WADO-RS, STOW-RS, QIDO-RS) | FHIR (including ImagingStudy) |
| Formal status | Also published as ISO 12052 | Developed by an ANSI-accredited standards organization |
DICOMweb and FHIR: the web versions
DICOMweb is “the DICOM Standard for web-based medical imaging,” a set of RESTful services: WADO-RS to retrieve DICOM objects, STOW-RS to store them, and QIDO-RS to search for them. It is what lets zero-footprint browser viewers and cloud archives work with images over ordinary web connections. FHIR does the same for clinical data, and the two meet in resources such as ImagingStudy. Most hospitals still run classic DICOM and HL7 v2 interfaces alongside the newer ones.
What this means for teleradiology
Connecting a hospital to a teleradiology group is mostly a DICOM and HL7 project. The hospital routes images as DICOM to the reading group’s PACS, sends orders as HL7 so the radiologist sees the request and the clinical history, and receives the signed report back as HL7 so it lands in the RIS and EHR in the hospital’s format. The usual work is mapping identifiers (the accession number and patient ID) so each image, order and report match. Our guide to switching teleradiology providers covers the timeline.
Orders come to us by HL7 and images by secure routing to our PACS. Signed reports go back into your system. We read on our PACS, so there is nothing for your staff to install or run. We sign a HIPAA Business Associate Agreement (BAA) with every hospital, and our technology runs on SOC 2-compliant platforms. Every TeleRads report is a signed final; we read finals only, never preliminaries.
Questions
What is the difference between DICOM and HL7?
DICOM is the standard for medical images and how they are stored and sent. HL7 is the standard for clinical and administrative messages between systems. In radiology, images travel as DICOM; registrations, orders and reports travel as HL7.
What is DICOM?
DICOM (Digital Imaging and Communications in Medicine) is the international standard for medical imaging information and related data, published as ISO 12052. It defines the image file format with its metadata and the network services scanners, PACS and viewers use to exchange images.
What is HL7?
HL7 is both Health Level Seven International, a non-profit standards organization founded in 1987, and its family of standards for exchanging clinical and administrative data. HL7 version 2 messaging is deployed at most US healthcare facilities; FHIR is its newer web-based standard.
Which HL7 messages are used in radiology?
Common ones are ADT for patient registration, ORM or OMG for orders, OMI for scheduled procedures, and ORU for reports. The IHE Radiology Technical Framework defines how these are used in a standard radiology workflow.
What is the DICOM Modality Worklist?
A DICOM service that lets a scanner download its list of scheduled exams, with patient and exam details, from the RIS. It avoids retyping and keeps images matched to the right order.
What is DICOMweb?
DICOMweb is the web version of DICOM: RESTful services to retrieve (WADO-RS), store (STOW-RS) and search for (QIDO-RS) imaging objects over HTTP. Browser-based viewers and cloud archives rely on it.
Does teleradiology use DICOM and HL7?
Yes. Images go to the teleradiology group’s PACS as DICOM, and orders and reports travel as HL7. With TeleRads, orders come to us by HL7 and images by secure routing to our PACS, and signed reports go back into your system.