PACS meaning, in one paragraph
The short answer
A PACS (picture archiving and communication system) is the system that acquires medical images from the scanners, archives them, transmits them across the network and displays them on reading workstations. Images move in the DICOM standard; orders and reports move between the PACS, the RIS and the EHR as HL7 messages. A radiologist reads a study from the PACS viewer and dictates a report that goes back into the patient’s record.
- 1981first international PACS conference, Newport Beach, CA
- 1993DICOM, the image standard PACS runs on, takes its name
- Class IIFDA class for medical image management systems
Sources: the first PACS conference date is from a history of PACS in the Journal of Medical Imaging (2023); the DICOM date from the DICOM Standards Committee; the FDA class from 21 CFR 892.2050.
What does a PACS do?
A PACS does four jobs, which map onto its main parts. A review in the Journal of Medical Imaging describes the components of a PACS as “image acquisition, archival, transmission, and display elements.”
- Acquire
- Receives images from the modalities: CT and MRI scanners, ultrasound machines, X-ray rooms, mammography units. Each study arrives as DICOM objects carrying the pixels plus the patient, exam and technique details.
- Archive
- Stores every study, short term for fast access and long term for priors and records retention. Many hospitals now keep the long-term copy in a vendor neutral archive (VNA) that more than one system can read.
- Transmit
- Moves studies across the hospital network and out to remote readers, other hospitals and image-sharing services, and fetches relevant prior studies for comparison.
- Display
- Shows the images on diagnostic workstations and in viewers elsewhere in the hospital, with tools such as hanging protocols, measurements, multi-planar reconstruction and side-by-side priors.
A paper in Cureus (2022) puts it simply: “The PACS serves as a primary tool for the radiologist to view and interpret medical images.”
How a study moves through PACS
- 01
The order is placed
A clinician orders the exam in the EHR. The order travels to the radiology information system (RIS) as an HL7 message. See RIS vs PACS.
- 02
The scanner gets its worklist
The RIS sends the scheduled exam to the scanner through the DICOM Modality Worklist, so the patient’s name and exam details don’t have to be typed in again.
- 03
Images go to the PACS
The technologist acquires the images and the scanner sends them to the PACS using DICOM. The PACS files them under the patient and the order.
- 04
The radiologist reads
The study appears on the radiologist’s worklist. The radiologist opens it in the PACS viewer, compares priors and dictates the report.
- 05
The report goes back
The signed report goes from the reporting system to the RIS and the EHR as an HL7 message, where the ordering clinician sees it. Our guide to DICOM and HL7 in radiology explains each message.
This sequence follows the order-to-report flow described in Cureus (2022) and in the IHE Scheduled Workflow profile, the integration profile vendors use to make the RIS, PACS and scanners agree.
A short history of PACS
Radiology ran on film for most of the 20th century. Research on digital image archiving grew through the 1980s; the first international conference and workshop on PACS was held in January 1981 in Newport Beach, California. In 1983 the American College of Radiology and the National Electrical Manufacturers Association formed a joint standards committee, released the ACR-NEMA 300 standard in 1985, and in 1993 renamed the third version DICOM (DICOM history). The same year the Baltimore VA Medical Center moved to filmless operation, one of the first hospitals to do so.
The same journal review notes that present-day PACS use thin-client architectures and that cloud storage has become a feasible option.
Is PACS regulated by the FDA?
Yes. In the US, PACS software falls under 21 CFR 892.2050, “Medical image management and processing system”, defined as “a device that provides one or more capabilities relating to the review and digital processing of medical images.” It is a Class II device with special controls, and the regulation names the DICOM standard among its voluntary standards. The FDA product code for these systems is LLZ. Vendors usually list their FDA clearances on their own regulatory pages.
PACS, RIS, VNA and the EHR: the radiology systems
- PACS
- Stores, moves and displays the images.
- RIS
- The radiology information system handles scheduling, patient tracking, results and billing. See RIS vs PACS.
- VNA
- A vendor neutral archive keeps images in standard formats in one central archive, so they can outlive any one PACS and be shared across departments and sites.
- EHR / EMR
- The hospital’s main patient record, where exams are ordered and the final report is read by the care team.
- Reporting / dictation
- Speech-recognition software in which the radiologist dictates and signs the report.
- Viewer
- The application the radiologist reads in. Some PACS viewers are installed on the workstation; others are zero-footprint web viewers. For one vendor’s products, see Intelerad PACS, explained.
On-premises vs cloud PACS
A traditional PACS runs on servers in the hospital’s own data center. A cloud PACS runs on a cloud provider’s infrastructure, either as the same software hosted elsewhere or as a fully managed service the vendor runs and upgrades. Cloud models move hardware refresh and disaster recovery to the vendor; in exchange, the hospital depends more on its internet link and needs a Business Associate Agreement with every party that stores patient images. Our PACS vendors comparison shows which vendors offer which model, and lists 12 questions to ask before you choose a PACS.
PACS and teleradiology
Teleradiology depends on the same plumbing. When a hospital sends studies to an outside reading group, the images travel as DICOM to that group’s PACS, and the signed reports return as HL7 messages. The hospital keeps its own PACS; the teleradiology group reads on its own system.
Orders come to us by HL7 and images by secure routing to our PACS. Signed reports go back into your system. We read on our PACS, so there is nothing for your staff to install or run. We sign a HIPAA Business Associate Agreement (BAA) with every hospital, and our technology runs on SOC 2-compliant platforms. Every TeleRads report is a signed final; we read finals only, never preliminaries.
For the full picture, see what is teleradiology and how TeleRads works.
Questions
What does PACS stand for?
PACS stands for picture archiving and communication system. It is the system hospitals and imaging centers use to receive, store, move and display medical images such as CT, MRI, ultrasound and X-ray.
What is PACS in radiology?
In radiology, the PACS is where images from every scanner are stored and where radiologists read them. Radiologists open studies from the PACS worklist in a diagnostic viewer, compare them with prior exams and dictate a report that goes back to the patient’s record.
What are the main components of a PACS?
Image acquisition from the scanners, an archive for storage, a network for transmission, and workstations and viewers for display. Most hospitals add a vendor neutral archive for long-term storage and connect the PACS to the RIS and EHR.
What is the difference between PACS and DICOM?
DICOM is the standard for medical images and how they are sent; PACS is the system that uses DICOM to receive, store and display them. A scanner sends DICOM images to the PACS.
What is the difference between PACS and RIS?
The PACS handles images; the RIS handles the radiology workflow around them: scheduling, tracking, results and billing. They exchange information so the right images match the right order and report.
What is a cloud PACS?
A PACS that runs on a cloud provider’s infrastructure instead of servers in the hospital. Some are fully managed services where the vendor runs and upgrades everything; others are the same PACS software hosted in the cloud.
Is PACS a medical device?
Yes. In the US, PACS software is regulated under 21 CFR 892.2050 as a medical image management and processing system, a Class II device.
Do hospitals need their own PACS to use teleradiology?
Most hospitals already have one for their own radiologists. A teleradiology group reads on its own PACS: with TeleRads, images route securely to our PACS and signed reports go back into your system, with nothing for your staff to install.