What Is PACS and DICOM?
DICOM (Digital Imaging and Communications in Medicine) is the international standard format used to store, transmit, and display medical images such as X-ray, CT, MRI, and ultrasound files. PACS (Picture Archiving and Communication System) is the system that stores, indexes, and retrieves those DICOM files so clinicians can access imaging studies from a workstation instead of physical film.
DICOM is the file format and communication protocol; PACS is the storage and retrieval system built around it. Together they explain how the diagnostic images mentioned on our medical data backup page are actually produced, stored, and made available for backup.
PACS vs. DICOM: What's the Difference?
DICOM
DICOM is a file format and network protocol. Every CT, MRI, X-ray, or ultrasound scanner ("modality") that follows the standard produces DICOM files, each carrying both the image data and embedded metadata such as patient identifiers, study date, and acquisition settings.
PACS
PACS is the software and storage infrastructure that receives DICOM files from modalities, archives them, and lets radiologists and physicians search, view, and share studies across a hospital or clinic network. A PACS typically includes an image archive and a separate database that indexes studies for fast retrieval.
How Medical Imaging Data Flows
Modality. A CT, MRI, X-ray, or ultrasound scanner acquires an image and saves it as a DICOM file.
Transmission. The modality sends the DICOM file to the PACS over the hospital or clinic network using the DICOM protocol.
Archive. PACS stores the DICOM file in its image archive and records the study in its database for indexing and search.
Retrieval. A radiologist or physician opens the study from a workstation or diagnostic viewer connected to the PACS.
What This Means for Backup Planning
A PACS archive is usually large, made up of many individual DICOM files plus a separate database that indexes them. Backing up only the file storage without the database — or the other way around — can leave a PACS unable to locate or reassemble studies after a restore. Organizations backing up medical imaging data typically need to:
- Back up both the DICOM image archive and the PACS database as a coordinated task, not as separate, unrelated jobs
- Confirm whether the PACS vendor requires a specific export method, a supported database connector, or allows direct file-level backup of the archive
- Account for the volume of imaging data when planning storage capacity, retention, and backup windows
- Treat DICOM files as ePHI when they are linked to an identifiable patient, applying the same encryption and access-control safeguards as other medical data
- Test restoring a study end-to-end — image and index together — rather than only verifying that backup files exist
Diagnostic images are one of several data types covered in our medical data backup guide, alongside clinic databases, patient documents, and application data. For the regulatory side of storing and retaining this data, see our overview of backup compliance standards and the HIPAA glossary entry.
FAQ
Is a DICOM file the same as a regular image file like JPEG?
No. A DICOM file contains the pixel data plus structured metadata such as patient identifiers, study and series information, and acquisition parameters, all in one file. This metadata is what lets a PACS index and retrieve studies correctly.
Does backing up the PACS file storage back up the whole system?
Not on its own. Most PACS systems separate the image archive from a database that indexes studies. Both need to be included in the backup plan, and ideally kept consistent with each other, or a restore may leave images that cannot be found or opened.
Are DICOM images considered ePHI?
Yes, when the embedded metadata links the image to an identifiable patient, which is the case for standard clinical DICOM studies. See our ePHI / PHI glossary entry for what that means for backup handling.
Can PACS data be backed up to the cloud?
It depends on the organization's storage policy, contracts, and risk analysis for regulated health data, not just on whether a cloud destination is technically supported. See our backup compliance standards guide for the considerations that apply before choosing a storage destination.
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