What Is DICOM? The Medical Imaging Standard That Connects Healthcare

• DICOM = Universal language for medical images: Every imaging modality (CT, MRI, X-ray, ultrasound) uses DICOM
• DICOM files contain both images AND patient data: Name, exam date, scan parameters embedded in file
• DICOM enables image sharing: Between hospitals, doctors, specialists - worldwide compatibility
• Viewing DICOM images: Requires special software (DICOM viewer) - can't open like regular photos
• Getting your images: Ask for "DICOM CD" or "electronic DICOM export" - not just JPEG
• DICOM standards: Managed by NEMA (National Electrical Manufacturers Association)
• PACS uses DICOM: Picture Archiving and Communication System stores/retrieves DICOM images

Our DICOM guide is based on technical standards, clinical workflows, and health IT best practices.

Data Sources Analyzed:

DICOM (Digital Imaging and Communications in Medicine) is the international standard for:

• Storing medical images
• Transmitting medical images
• Printing medical images
• Displaying medical images

Think of DICOM as:

• The "USB of medical imaging" - universal connector
• The "PDF of medical images" - standard format everyone uses
• The "language of medical imaging" - all systems understand DICOM

Why DICOM Matters

Before DICOM (pre-1990s):

• Each imaging manufacturer had proprietary formats
• GE images couldn't be read on Siemens equipment
• Films were physically carried between departments
• Sharing images between hospitals was difficult

After DICOM (1993-present):

• Universal format: Any system can read any DICOM image
• Digital sharing: Images sent instantly between facilities
• PACS possible: Digital storage and retrieval systems
• Teleradiology: Images read remotely by radiologists

Bottom line: DICOM made medical imaging interoperable. Without DICOM, modern digital imaging wouldn't exist.

DICOM Files Are Special

Regular image files (JPEG, PNG):

• Contain pixel data (colors, brightness)
• That's it - just the image

DICOM files:

• Contain pixel data (the image)
• AND metadata (patient information, scan parameters)
• AND headers (identifying information)

What's in a DICOM file:

DICOM Information Object Definitions (IODs)

DICOM defines how different types of images are stored:

Each modality has unique parameters stored in DICOM file.

DICOM Communication (DICOM Network)

DICOM defines how imaging devices talk to each other:

DICOM network communication:

• DICOM Service Class Users (SCUs): Requesting devices (workstations, viewers)
• DICOM Service Class Providers (SCPs): Providing devices (PACS, modalities)
• DICOM associations: Like network connections for image transfer

Real-world example:

1. CT scanner (SCU) sends images to PACS (SCP)
2. Radiologist workstation (SCU) retrieves images from PACS (SCP)
3. Referring physician viewer (SCU) queries PACS (SCP) for images

All use DICOM protocol - like all web browsers use HTTP.

DICOM vs. JPEG/PNG

Key difference: DICOM is a medical record, not just an image.

Why you can't email medical images:

• Email attachments usually JPEG (loses DICOM metadata)
• JPEG is not a legal medical record (missing information)
• DICOM files too large for email (typically 10-50 MB each)
• Must use secure transfer or DICOM-compliant systems

DICOM vs. NIfTI (Research Imaging)

NIfTI used in brain imaging research because:

• Simpler format
• Easier to process in analysis software
• Doesn't require all clinical metadata

DICOM used clinically because:

• Complete medical record
• Legal requirements
• Interoperability between systems

How Your Images Travel Through Healthcare

Typical DICOM workflow:

1. Imaging Modality (CT/MRI/X-ray)
   ↓ Creates DICOM files
2. Modality sends to PACS (via DICOM network)
   ↓ Stores images
3. Radiologist retrieves from PACS (DICOM workstation)
   ↓ Interprets images, creates report
4. Report linked to DICOM images in PACS
   ↓
5. Ordering physician views images (DICOM viewer or EMR integration)
   ↓
6. If needed: Export to CD/DICOM for patient or referral

All steps use DICOM (except report, which is usually text/HL7).

PACS: Picture Archiving and Communication System

PACS is:

• Server that stores all DICOM images
• Software that manages image storage, retrieval
• Network that connects imaging devices to viewing stations

PACS capabilities:

Without PACS:

• Images stored on individual modality workstations
• Films printed and physically transported
• No central archive
• Difficult to find old studies

With PACS:

• All images stored centrally
• Instant retrieval from anywhere
• Comparison with prior studies
• No films (mostly)

Requesting Your Images

When you need copies of your images (for second opinion, specialist, personal records):

For medical use (second opinion, specialist):

• ✅ Ask for DICOM format
• ✅ Request "full DICOM export" or "DICOM CD"
• ✅ Ensure includes all series (all images from exam)

For personal use (sharing with family, keeping memento):

• JPEG/PNG OK
• But keep DICOM for medical purposes

Reading DICOM Files

DICOM viewers required to open DICOM files:

Can't open DICOM files in:

• ❌ Photos app
• ❌ Preview app
• ❌ Paint, Photoshop (can open with plugins but loses metadata)
• ❌ Email attachments (usually converted to JPEG)

Must use:

• ✅ DICOM-specific viewer
• ✅ Web portal from hospital/EMR
• ✅ Hospital-provided viewing software

PHI in DICOM Files

DICOM files contain PHI (Protected Health Information):

HIPAA requires protection of DICOM files containing PHI.

De-identifying DICOM (Anonymization)

Before using images for research, education:

• Remove PHI from DICOM files
• Process called "de-identification" or "anonymization"
• Follows DICOM confidentiality standards

De-identified DICOM:

• Patient name replaced with "anonymous" or removed
• Patient ID replaced with random code
• Birth dates removed or shifted
• Images can be used for research, education without privacy concerns

Real-world example:

• Teaching files on Radiopaedia: De-identified DICOM
• Research datasets: De-identified DICOM
• Medical education: De-identified DICOM

Who Maintains DICOM?

DICOM standards managed by:

• NEMA (National Electrical Manufacturers Association)
• DICOM Standards Committee (expert working groups)
• Annual updates (new features, capabilities added)

DICOM is:

• International standard: Used worldwide
• Voluntary standard: Not law, but universally adopted
• Continuously evolving: New modalities, features added

DICOM Conformance

Medical imaging devices claim "DICOM conformance":

• Can send/receive DICOM images
• Support specific DICOM service classes
• Follow DICOM standard specifications

Conformance statements:

• Document what DICOM services device supports
• Specify which SOP classes supported
• Identify transfer syntaxes (compression, etc.)

Real-world importance:

• Before buying imaging equipment, check DICOM conformance
• Ensures compatibility with existing PACS
• Prevents interoperability problems

Asking for DICOM Images

When you need your images (second opinion, moving, personal records):

What to ask for:

1. "Can I get a copy of my images in DICOM format?"
2. "Will the CD include all DICOM files from my exam?"
3. "Can you export to DICOM for electronic download?"
4. "Will the images include all series ( scout images, 3D reconstructions)?"

What to avoid:

• ❌ "Can I get my X-rays?" (confusing - may get JPEG)
• ❌ "Can I get my scans?" (ambiguous - may get JPEG)
• ❌ "Email me my images" (usually JPEG, incomplete)

Best request:

”

"I'd like a complete DICOM export of my recent [CT/MRI/X-ray] exam for my records. Can you put this on CD or provide electronic download in DICOM format?"

Viewing Your DICOM Images

On your computer:

1. Download DICOM viewer (free options available)
2. Import DICOM files from CD or download
3. View images with all metadata preserved

Free DICOM viewers:

• RadiAnt (Windows) - popular, easy to use
• Horos (Mac) - full-featured, used by radiologists
• MicroDICOM (Windows) - lightweight
• Radiopaedia web viewer - browser-based, no install

Mobile DICOM viewers (iOS/Android):

• Available but less common
• Useful for quick viewing
• Not for primary diagnosis

Sharing Your Images with Doctors

When seeing a specialist or getting second opinion:

Best practice:

• Call ahead: Ask specialist's office how they prefer to receive images
• Bring CD: As backup even if arranging transfer
• Confirm receipt: Ensure images arrived before appointment

FAQ

Q: Can I convert DICOM to JPEG? A: Yes, DICOM viewers can export JPEG. But JPEG loses medical metadata and isn't a legal medical record. Keep original DICOM.

Q: Why are my DICOM files so large? A: Each file is a full slice (typically 10-50 MB). A CT scan may have 100-500 files = 1-25 GB total.

Q: Can I email my DICOM files? A: Generally no - files too large for email. Use secure transfer, CD, or upload to patient portal.

Q: Why won't my images open in Photos/Preview? A: DICOM is a special format requiring DICOM viewer. Regular image apps don't support DICOM.

Q: Can I view DICOM files on my phone? A: Yes, with mobile DICOM apps, but experience better on computer with larger screen.

Q: Do all hospitals use DICOM? A: Yes, universally. DICOM is the international standard for medical imaging.

Q: Can I edit my DICOM files? A: You shouldn't. Editing alters medical record. Use DICOM viewer to view, measure, annotate without altering original.

Q: What's the difference between DICOM and PACS? A: DICOM is the file format/communication standard. PACS is the system that stores and manages DICOM files.

Q: How long are DICOM images kept? A: Varies by hospital (usually 5-15+ years). Ask about retention policy if you need old images.

DICOM is:

• ✅ Universal language of medical imaging
• ✅ Enables digital storage and sharing of images
• ✅ Contains complete medical record (image + metadata)
• ✅ Required for interoperability between systems
• ✅ Standard you'll encounter whenever you have medical imaging

For patients:

• ✅ Ask for DICOM format when requesting images
• ✅ Use DICOM viewer to open image files
• ✅ Keep DICOM files for your records (not just JPEG)
• ✅ Understand DICOM is why images can be shared between hospitals

Key takeaways:

• DICOM makes modern medical imaging possible
• Without DICOM, we'd still be using film
• DICOM is why you can get copies of your scans
• DICOM is why your doctors can share your images

Most important: DICOM is the invisible technology that makes medical imaging work. As a patient, you don't need to understand the technical details, but knowing about DICOM helps you navigate the healthcare system and advocate for your medical records.

Related articles on WellAlly:

• PACS and Medical Imaging: Understanding Image Storage
• How to Get Your Medical Imaging Records
• Medical Imaging Data Security and Privacy
• Second Opinion Guide: Preparing Your Imaging Records