What is DICOM?
DICOM (Digital Imaging and Communications in Medicine) is the standard for medical image storage and transmission.
What is DICOM?
DICOM (Digital Imaging and Communications in Medicine) is the international standard for medical images and related information. It defines the formats for medical images that can be exchanged between different systems, ensuring compatibility across imaging equipment, hospitals, and healthcare facilities.
Why DICOM Matters
Before DICOM, each medical imaging manufacturer used proprietary formats—making it nearly impossible to share images between different systems. DICOM solved this by:
- Standardizing formats: All modalities (CT, MRI, X-ray, etc.) use the same structure
- Enabling interoperability: Images can be shared between any DICOM-compatible systems
- Including metadata: Patient information, acquisition parameters, and more travel with images
- Ensuring quality: Standards for compression and image integrity
How DICOM Works
DICOM Files (.dcm)
A DICOM file contains both:
- Header metadata: Patient info, study details, equipment parameters
- Pixel data: The actual image data
DICOM File Structure:
┌─────────────────────────────┐
│ Meta Information Group │
│ (Transfer Syntax, etc.) │
├─────────────────────────────┤
│ Data Set │
│ ├─ Patient Name │
│ ├─ Study Date │
│ ├─ Modality (CT, MRI, etc.) │
│ ├─ ... │
│ └─ Pixel Data (Image) │
└─────────────────────────────┘
DICOM Network Communication
DICOM also defines how systems communicate:
- DICOM Service Class Users (SCUs): Clients that request services
- DICOM Service Class Providers (SCPs): Servers that provide services
- DICOM Associations: Connections between SCUs and SCPs
Common operations include:
- C-STORE: Send/store images
- C-FIND: Search for studies
- C-MOVE: Retrieve images
- C-GET: Query/retrieve images
Key Components
Modalities
DICOM supports all major imaging modalities:
| Modality | DICOM Code | Description | |----------|------------|-------------| | CT | CT | Computed Tomography | | MRI | MR | Magnetic Resonance | | X-ray | CR/DR | Computed/Digital Radiography | | Ultrasound | US | Ultrasound imaging | | PET | PT | Positron Emission Tomography | | Mammography | MG | Mammography |
Tags
DICOM uses tags (hexadecimal codes) to identify data elements:
| Tag | Name | Example | |-----|------|---------| | (0010,0010) | Patient Name | Smith^John | | (0010,0020) | Patient ID | 12345678 | | (0008,0060) | Modality | CT | | (0028,0010) | Rows | 512 | | (0028,0011) | Columns | 512 |
DICOM vs PACS
While often mentioned together, they serve different purposes:
- DICOM: The standard/format for medical images
- PACS (Picture Archiving and Communication System): The system that stores, retrieves, and manages DICOM images
Think of DICOM as the file format and PACS as the server that manages those files.
Working with DICOM
Opening DICOM Files
Standard image viewers can't open .dcm files. You need specialized software:
Free viewers:
- RadiAnt: Windows (trial)
- Horos: macOS
- MicroDICOM: Windows
- Weasis: Cross-platform, web-based
Programmatic access:
- pydicom (Python)
- fo-dicom (C#)
- dcm4che (Java)
Common Issues
"Why can't I open this DICOM file?"
Common reasons:
- Missing transfer syntax: The file header is incomplete
- Compression: Some older viewers can't handle compressed DICOM
- Corrupted data: File transfer errors
- Proprietary formats: Some vendors add non-standard extensions
File Size
Uncompressed DICOM files are large. Consider:
- Lossless compression: For diagnostic quality
- Lossy compression: For storage/transmission (may affect diagnosis)
- Exporting to standard formats: For sharing with patients
Summary
DICOM is the backbone of medical imaging—ensuring that images can be created, stored, transmitted, and displayed consistently across the healthcare ecosystem. Whether you're a radiologist, IT professional, or developer working with medical images, understanding DICOM is essential.
For more information, see: