slug: dicom-vs-pacs title: DICOM vs PACS: Understanding the Difference titleZh: DICOM vs PACS：理解差异 category: dicom description: Understanding the relationship between DICOM (the standard) and PACS (the system) in medical imaging. descriptionZh: 了解医学影像中 DICOM（标准）和 PACS（系统）之间的关系。 keywords: [DICOM vs PACS, medical imaging storage, PACS system, radiology workflow] last_updated: January 2025 difficulty: beginner readTime: 8 relatedArticles: [what-is-dicom, open-dcm-files]
DICOM vs PACS: Understanding the Difference
In medical imaging, DICOM and PACS are often mentioned together, but they serve fundamentally different roles. Understanding the distinction is key to grasping how medical images are created, stored, and accessed.
The Short Answer
| Aspect | DICOM | PACS | |--------|-------|------| | What is it? | A standard/format | A system/server | | Analogy | JPEG format | Photo cloud storage | | Purpose | Defines image structure | Stores and manages images | | Scope | Universal standard | Organizational system |
What is DICOM?
DICOM (Digital Imaging and Communications in Medicine) is:
- A file format for medical images
- A communication protocol for transmitting images
- An international standard (NEMA standard)
DICOM answers: "How is the image structured and transmitted?"
DICOM File (.dcm)
├── Header (metadata)
│ ├── Patient Name
│ ├── Study Date
│ ├── Modality (CT, MRI, etc.)
│ └── Acquisition Parameters
└── Pixel Data (the actual image)
What is PACS?
PACS (Picture Archiving and Communication System) is:
- A server/software that stores medical images
- A management system for image workflows
- An organizational solution for radiology departments
PACS answers: "Where and how do we store, retrieve, and manage images?"
PACS Components:
┌─────────────────────────────────────────────────┐
│ PACS Server │
│ ┌───────────────────────────────────────────┐ │
│ │ Image Storage │ │
│ │ (stores DICOM files from all modalities) │ │
│ └───────────────────────────────────────────┘ │
│ ┌───────────────────────────────────────────┐ │
│ │ Database │ │
│ │ (indexes images for fast retrieval) │ │
│ └───────────────────────────────────────────┘ │
│ ┌───────────────────────────────────────────┐ │
│ │ Web/Mobile Viewer │ │
│ │ (displays images to users) │ │
│ └───────────────────────────────────────────┘ │
└─────────────────────────────────────────────────┘
How They Work Together
┌──────────────┐ DICOM ┌──────────────┐
│ CT │ ============> │ │
│ Scanner │ (C-STORE) │ │
└──────────────┘ │ │
│ PACS │
┌──────────────┐ DICOM │ Server │
│ MRI │ ============> │ │
│ Scanner │ (C-STORE) │ │
└──────────────┘ │ │
│ │
┌──────────────┐ DICOM │ │
│ X-Ray │ ============> │ │
│ Machine │ (C-STORE) │ │
└──────────────┘ └──────────────┘
│
│ DICOM
│ (C-FIND/C-MOVE)
▼
┌──────────────┐
│ Radiologist │
│ Workstation │
└──────────────┘
Key Differences in Detail
1. Nature
DICOM:
- A specification or standard
- Defines data structure and communication
- Can be implemented by any vendor
PACS:
- A product or system
- Actual software implementation
- Provided by specific vendors (GE, Philips, Siemens, etc.)
2. Function
DICOM:
- Standardizes image format
- Enables interoperability
- Defines communication protocols
PACS:
- Stores images long-term
- Manages image workflows
- Provides viewing capabilities
- Handles routing and prefetching
3. Scope
DICOM is universal:
- Used worldwide
- Same standard for all vendors
- Enables cross-system communication
PACS is organizational:
- Each hospital has its own PACS
- May be on-premise or cloud-based
- Vendor-specific features and limitations
Types of PACS
| Type | Description | Best For | |------|-------------|----------| | On-Premise | Local servers | Large hospitals with reliable IT | | Cloud-Based | Hosted by vendor | Small practices, telemedicine | | Hybrid | Combination | Organizations with multi-site needs | | Enterprise | Multi-facility | Health systems with multiple locations |
Workflow Example
1. Image Acquisition
CT Scanner → [Creates DICOM file] → Sends to PACS
2. Storage
PACS → [Stores DICOM file] → [Updates database index]
3. Retrieval
Radiologist Workstation → [Queries PACS via DICOM] → [Receives DICOM file]
4. Distribution
PACS → [Sends DICOM to referral] → [Archives to long-term storage]
Common Questions
Can PACS exist without DICOM?
Technically yes, but modern PACS all use DICOM. Non-DICOM PACS are legacy systems.
Do I need PACS to use DICOM?
Not necessarily. You can:
- View DICOM files locally with a viewer
- Send DICOM files via email/CD (with proper security)
- Use DICOM for research/development
Are images in PACS always DICOM?
Almost always. Some systems may convert for display, but the original is DICOM.
Vendor Examples
| PACS Vendor | Notable Features | |-------------|-----------------| | GE Healthcare | Centricity, AI integration | | Philips | IntelliSpace, enterprise solutions | | Siemens | syngo, workflow optimization | | Agfa | enterprise imaging, multi-department | | IBM/Merge | cloud-based solutions | | Ambra (Canon) | cloud-native PACS |
Summary
- DICOM = The language/format (universal standard)
- PACS = The system/server (organizational solution)
Think of it this way:
- DICOM is like PDF format—anyone can create and read PDFs
- PACS is like Google Drive—a specific service that stores your PDFs
Both are essential for modern medical imaging:
- DICOM ensures compatibility between systems
- PACS provides management and access for images