DICOM Basics - How do HL7, DICOM, and IHE come together

Dec 15, 2025

Introduction

This is part of my series of articles on the DICOM standard. In this article, we'll explore how three major healthcare standards - HL7, DICOM, and IHE - work together to enable interoperability in medical imaging workflows. Understanding the relationship between these standards is essential for anyone working in healthcare IT.

While each standard has its own focus and purpose, they are designed to complement each other. Together, they form the foundation of modern healthcare information exchange, particularly in radiology and imaging departments.

The Three Standards at a Glance

Before diving into how they integrate, let's understand what each standard does:

Standard	Focus	Primary Use
HL7	Clinical and administrative data	Patient demographics, orders, results, billing
DICOM	Medical imaging	Image acquisition, storage, display, printing
IHE	Integration profiles	Defines how HL7 and DICOM work together

HL7 (Health Level Seven)

HL7 is the standard for exchanging clinical and administrative healthcare information. Key versions include:

HL7 v2.x: Message-based format widely used for ADT (Admit/Discharge/Transfer), orders, and results
HL7 v3: XML-based with RIM (Reference Information Model)
HL7 FHIR: Modern RESTful API-based standard

In imaging workflows, HL7 is typically used for:

Patient registration and demographics (ADT messages)
Radiology orders (ORM messages)
Results and reports (ORU messages)
Scheduling (SIU messages)

DICOM (Digital Imaging and Communications in Medicine)

DICOM is the standard for medical imaging. It defines:

File format for storing medical images with metadata
Network protocols for image exchange (C-STORE, C-FIND, C-MOVE, etc.)
Services for printing, worklist management, and more
Structured reports for encoding clinical findings

DICOM is used by:

Imaging modalities (CT, MR, US, X-ray, etc.)
PACS (Picture Archiving and Communication Systems)
Diagnostic workstations
Image archives

IHE (Integrating the Healthcare Enterprise)

IHE is not a standard itself but an initiative that creates Integration Profiles. These profiles specify exactly how to use HL7 and DICOM together to solve real-world integration challenges.

IHE profiles define:

Which transactions to use
Which actors (systems) are involved
Required and optional attributes
Expected behavior and error handling

The Typical Radiology Workflow

Here's how these standards work together in a typical radiology workflow:

1. Patient Registration (HL7 ADT)
   HIS → RIS: Patient demographics via HL7 ADT message

2. Order Placement (HL7 ORM)
   HIS/EMR → RIS: Radiology order via HL7 ORM message

3. Worklist Query (DICOM MWL)
   Modality → RIS: Query scheduled procedures via DICOM Modality Worklist

4. Image Acquisition (DICOM)
   Modality: Creates DICOM images with patient/order information

5. Image Storage (DICOM C-STORE)
   Modality → PACS: Store images via DICOM C-STORE

6. Procedure Status (DICOM MPPS or HL7)
   Modality → RIS: Report procedure completion

7. Report Creation
   Radiologist interprets images on PACS workstation

8. Results Distribution (HL7 ORU)
   RIS → HIS/EMR: Final report via HL7 ORU message

Key IHE Radiology Profiles

IHE defines several profiles for radiology integration:

Profile	Purpose
SWF (Scheduled Workflow)	Basic radiology workflow from order to report
PIR (Patient Information Reconciliation)	Handle patient ID discrepancies
RWF (Reporting Workflow)	Manage reporting process
SINR (Simple Image and Numeric Report)	Structured reporting
XDS-I (Cross-Enterprise Document Sharing for Imaging)	Share images across enterprises
PDI (Portable Data for Imaging)	Patient CD/DVD creation

SWF (Scheduled Workflow) Profile

The Scheduled Workflow profile is the foundation of radiology integration. It defines these actors:

Actor	Role	Typical System
ADT	Patient registration	HIS
Order Placer	Creates orders	HIS/EMR
Department System Scheduler	Schedules procedures	RIS
Acquisition Modality	Acquires images	CT, MR, US
Image Manager/Archive	Stores images	PACS
Image Display	Views images	Workstation

Where HL7 and DICOM Meet

The critical integration points between HL7 and DICOM are:

1. Patient Demographics

HL7 ADT messages carry patient information
RIS stores this information
DICOM Modality Worklist returns it to modalities
Modalities embed it in DICOM images

2. Order Information

HL7 ORM messages carry order details
RIS creates scheduled procedure steps
DICOM MWL returns order info to modalities
Accession number links HL7 orders to DICOM images

3. Results and Reports

DICOM Structured Reports encode findings
HL7 ORU messages distribute text reports
Both reference the same study/order

Common Integration Challenges

Real-world integration often encounters these challenges:

Patient ID Mismatches: Different IDs in HIS vs. modality
Character Encoding: HL7 and DICOM handle special characters differently
Date/Time Formats: Slight variations in formatting
Name Components: Different handling of name parts
Missing Data: Optional fields in one system, required in another

The Role of RIS

The Radiology Information System (RIS) is the bridge between HL7 and DICOM:

HIS ←→ [HL7] ←→ RIS ←→ [DICOM MWL] ←→ Modality
                 ↓
            [DICOM]
                 ↓
               PACS

The RIS:

Receives patient/order info via HL7
Provides worklist to modalities via DICOM MWL
Tracks procedure status
Manages reporting workflow
Sends results back via HL7

Best Practices for Integration

Use IHE Profiles: Follow established integration patterns
Consistent Identifiers: Use accession numbers consistently across systems
Test Thoroughly: Participate in IHE Connectathons or use testing tools
Document Interfaces: Maintain interface specifications
Monitor Transactions: Log all HL7 and DICOM exchanges
Handle Errors: Implement proper error handling and notifications

Conclusion

HL7, DICOM, and IHE are complementary standards that together enable comprehensive healthcare interoperability. HL7 handles clinical and administrative data, DICOM manages medical imaging, and IHE profiles define how to use them together effectively.

Understanding how these standards interact is essential for implementing successful healthcare integration projects, particularly in radiology and imaging departments where both standards are heavily used.