Quick answer: A PACS (picture archiving and communication system) is the medical imaging IT system that captures, stores, distributes, and displays diagnostic images — X-ray, CT, MRI, ultrasound, and more — electronically, replacing physical film. It works alongside a radiology information system (RIS), which handles scheduling and reporting workflow, and a hospital’s EHR/HIS, which holds the full patient chart; PACS itself is only responsible for the images. Every PACS relies on DICOM (Digital Imaging and Communications in Medicine) as its underlying format and transfer standard, which is what lets scanners, workstations, and archives from different vendors exchange images at all.
What Is a PACS System?
PACS stands for picture archiving and communication system. It is the software and storage infrastructure a radiology department (or any imaging-heavy clinical or research service — cardiology, pathology, dermatology, and others increasingly use PACS-style systems too) uses to manage the full lifecycle of a diagnostic image: acquisition from the scanner, transmission across the network, long-term storage, retrieval, and display on a diagnostic workstation for interpretation.
Before PACS became standard, radiology departments stored and moved physical film — a single study could mean multiple large film jackets, physically routed between reading rooms, referring clinicians, and file rooms, with no way to view the same study in two places at once. PACS digitized that entire chain. A radiologist can now pull up a study from any authorized workstation, a comparison prior from years earlier is retrieved automatically rather than searched for by hand, and the same image set is simultaneously available to a referring physician’s EHR viewer.
How a PACS System Works
A PACS deployment has four functional components, regardless of vendor:
- Imaging modalities — the CT, MRI, X-ray, ultrasound, mammography, or other scanners that generate the images and send them into the system, almost always as DICOM-formatted files.
- A secure network — the infrastructure that moves image data (routinely tens to hundreds of megabytes per study) between modalities, archive, and workstations without loss or corruption, with access controls appropriate to protected health information (PHI).
- Archive/storage — where studies live long-term. Storage architecture is the single biggest design and cost variable in a PACS: retention requirements (many jurisdictions require adult imaging records be kept 5-10+ years, longer for pediatric studies), redundancy, and whether storage is proprietary to the PACS vendor or vendor-neutral (see the vendor neutral archive (VNA) entry) all shape this layer.
- Diagnostic and clinical workstations — the viewers radiologists use to interpret studies (calibrated diagnostic-grade monitors, specific hanging-protocol and measurement tools) and the lighter-weight viewers referring clinicians use elsewhere in the hospital.
The standard that makes all of this interoperate across vendors is DICOM (Digital Imaging and Communications in Medicine), maintained by NEMA (the National Electrical Manufacturers Association) with the American College of Radiology. DICOM defines both the image file format itself and the network protocol for querying, retrieving, and transmitting studies — it is the reason a CT scanner from one manufacturer can send a study into a PACS from a different manufacturer and have it display correctly. Non-image data (orders, reports, patient demographics) typically moves alongside PACS via HL7 messaging or, increasingly, HL7 FHIR.
PACS vs. RIS vs. EHR/HIS
These three systems are frequently confused because they sit side by side in the same imaging workflow, but each has a distinct job:
| System | What it manages | Primary users |
|---|---|---|
| PACS | Storage, transmission, and display of the diagnostic images themselves | Radiologists, imaging technologists |
| RIS (radiology information system) | Scheduling, order tracking, exam status, department billing and resource management | Radiology schedulers, technologists, department administrators |
| EHR/HIS | The full longitudinal patient chart across every department, not just imaging | All clinical staff hospital-wide |
In practice, a radiology exam typically touches all three: it is ordered and scheduled in the RIS, the images are acquired and stored in the PACS, the signed report is routed back to the RIS and into the EHR, and referring clinicians view both the report and the images through EHR-embedded viewers. Many vendors now sell combined RIS/PACS platforms, but they remain functionally distinct layers even when bundled under one product name.
PACS vs. VNA: Where Vendor-Neutral Archiving Fits
Early PACS deployments bundled image storage and the viewing/workflow software from a single vendor, which meant switching PACS vendors later meant migrating years of stored studies out of a proprietary database — often a costly, multi-year project. A vendor neutral archive (VNA) separates those layers: images are normalized into standards-based formats on ingest and made available through standard protocols, so the PACS viewer/workflow layer on top can be replaced, or extended to additional service lines (cardiology, pathology, dermatology), without re-migrating the underlying archive each time. A growing share of new PACS procurements are explicitly architected around a VNA as the storage layer, with PACS as a thinner front-end application on top — worth understanding as a distinct procurement decision, not an afterthought, before signing a multi-year PACS contract.
PACS Deployment Models
| Model | How it works | Typical trade-off |
|---|---|---|
| On-premise | Servers and storage hosted in the facility’s own data center | Full control and predictable latency; the facility owns hardware refresh, redundancy, and disaster-recovery costs directly |
| Cloud-hosted | Traditional PACS software run on infrastructure hosted by a cloud provider or the vendor | Shifts hardware maintenance off-site; still largely mirrors on-prem workflow and licensing |
| Cloud-native | PACS built from the ground up as a multi-tenant cloud application, typically subscription-priced | Faster scaling and multi-site rollout, lower up-front capital cost; long-term data egress and vendor-lock-in terms need close review |
| Hybrid | Local (edge) storage for fast retrieval of recent/active studies, cloud archive for long-term retention | Balances read-speed for active cases against the storage economics of cloud archiving for older studies |
What to Evaluate When Selecting a PACS
A PACS is typically one of the largest single IT capital or subscription commitments an imaging department makes, and switching later is expensive precisely because of the migration problem described above. Procurement teams evaluating vendors should look closely at:
- DICOM and HL7/FHIR conformance — ask for the vendor’s DICOM conformance statement and confirm it covers every modality type currently and prospectively in use.
- Storage architecture and scalability — proprietary vs. vendor-neutral storage, and whether capacity and pricing scale predictably as study volume and resolution (e.g. higher-resolution CT/MRI protocols) grow.
- Interoperability beyond DICOM basics — support for IHE (Integrating the Healthcare Enterprise) integration profiles such as XDS-I for cross-enterprise image sharing, which matters for multi-site health systems and referral networks.
- Integration with existing RIS and EHR — confirmed, tested interfaces rather than a generic claim of “integrates with any EHR.”
- Vendor lock-in and exit terms — what it actually costs, contractually and technically, to export the full archive if the facility later switches PACS vendors; a VNA architecture substantially reduces this risk.
- Security and HIPAA Security Rule compliance — encryption at rest and in transit, access logging/audit trails, and role-based access controls, since PACS stores protected health information.
- Disaster recovery and redundancy — documented recovery point/time objectives, and whether failover has actually been tested, not just specified.
- Multi-site and enterprise imaging support — if the organization has (or plans) more than one imaging location, confirm the architecture supports shared worklists and a single logical archive rather than per-site silos.
- AI/CAD tool integration — whether the PACS supports third-party AI-assisted detection or triage tools through a standard integration path, increasingly a differentiator among vendors.
- Total cost of ownership — licensing model (perpetual vs. subscription), storage costs at projected volume, migration/implementation cost, training, and ongoing support/maintenance — not just the headline license price. See X-Ray Machine Cost for how imaging capital costs are typically budgeted alongside systems like PACS.
Regulatory and Compliance Considerations
In the United States, PACS software is regulated by the FDA as medical device software (picture archiving and communication systems fall under 21 CFR 892.2050, Class II). Because a PACS stores and transmits protected health information, it is also subject to the HIPAA Security Rule’s requirements for access controls, audit controls, and transmission security. Procurement and compliance teams should confirm a vendor’s FDA clearance status for any diagnostic-display or AI-enabled features and review the vendor’s HIPAA Business Associate Agreement (BAA) terms before contracting — requirements and enforcement details can change, so verify current status directly with the FDA and with legal/compliance counsel rather than relying on vendor marketing claims alone.
Frequently Asked Questions
What does PACS stand for?
PACS stands for picture archiving and communication system — the medical imaging IT system used to store, retrieve, distribute, and display diagnostic images electronically.
What is a PACS system used for in radiology?
In radiology specifically, a PACS is used to receive images directly from imaging modalities (X-ray, CT, MRI, ultrasound, mammography, and others), archive them long-term, and make them available to radiologists for interpretation and to referring clinicians for review — replacing physical film entirely.
Is PACS the same as a picture archiving and communication system?
Yes — “PACS” is simply the acronym for “picture archiving and communication system.” They are the same thing; PACS is how the term is used in practice.
What is the difference between PACS and RIS?
PACS stores and displays the diagnostic images. A radiology information system (RIS) handles the surrounding operational workflow — scheduling, order tracking, and reporting. See the full RIS definition for the complete breakdown.
What is a healthcare PACS system used for outside radiology?
Beyond radiology, cardiology, pathology, dermatology, and other image-heavy specialties increasingly use PACS or PACS-like enterprise imaging platforms to store and share their own diagnostic images, often on a shared vendor-neutral archive rather than separate department-specific systems.
Do all PACS systems use DICOM?
Effectively yes. DICOM is the universal standard for medical image formatting and transmission; a PACS that cannot receive, store, and transmit DICOM-conformant studies would not be able to interoperate with standard imaging modalities and viewers.
