A PACS (Picture Archiving and Communication System) requires four core components working together: image acquisition devices, a communication network, an archive server, and display workstations. Each piece handles a different stage of the medical imaging workflow, from capturing a scan to storing it long-term and displaying it for diagnosis. Beyond these four pillars, a functional PACS also depends on standardized communication protocols, security infrastructure, and integration with other hospital systems.
Image Acquisition Devices
Image acquisition is where everything starts. These are the imaging modalities that generate the pictures: CT scanners, MRI machines, ultrasound units, computed radiography systems, and nuclear medicine scanners. Each device produces digital images that need to flow into the PACS for storage and viewing.
The acquisition layer also includes gateway computers that sit between the imaging equipment and the network. These gateways prepare the image data for transmission, converting it into a standardized format so the rest of the system can read it regardless of which manufacturer built the scanner. Older analog equipment that can’t output digital files natively requires a digitizer at this stage to convert film-based images into a compatible format.
The Communication Network
Medical images are large files, and a PACS network needs enough bandwidth to move them quickly. For general radiography, CT, and MRI work, current guidelines recommend at least 100 Mbps of sustained download bandwidth. Mammography workflows need 150 Mbps or more, and subspecialty imaging like multiphase CT or cardiac MRI calls for speeds above 200 Mbps. Upload speeds of 20 to 50 Mbps support report transmission and video consultations.
Speed alone isn’t enough. Network latency, the round-trip delay for data requests, should stay below 50 milliseconds for images to load and respond fluidly when a radiologist scrolls through a study. Jitter (variation in that delay) should remain under 15 milliseconds. Without these performance thresholds, even a technically “fast” connection can make image interaction sluggish and frustrating during diagnosis.
Most PACS installations use a combination of local area networks within the hospital and wide area network links for remote reading sites. Redundant connections and failover paths are standard because any network downtime means radiologists can’t access studies.
DICOM and HL7: The Communication Protocols
Two standards make the entire system possible. DICOM (Digital Imaging and Communications in Medicine) provides a universal language for medical imaging. It defines not just how image files are formatted but how devices talk to each other: how a scanner sends images to an archive, how a workstation requests a specific study, and how that study gets delivered. DICOM isn’t a cable or plug. It’s a set of rules governing the form and flow of electronic messages between computers, which means equipment from different manufacturers can share data without proprietary converters.
HL7 (Health Level Seven) handles the text-based side. It structures messages between the PACS, the hospital information system (HIS), and the radiology information system (RIS). When a physician orders an imaging exam, HL7 carries that order from the HIS to the RIS and ultimately tells the PACS which patient and study to expect. When a radiologist finalizes a report, HL7 routes it back. Together, DICOM moves the images while HL7 moves the patient data and clinical messages around them.
The Archive Server
The archive is the central repository where every image study is stored, indexed, and made retrievable. A PACS archive server manages both short-term storage (for studies being actively read) and long-term storage (for the years or decades that regulations require images to be kept). Most systems use a tiered approach: fast storage like solid-state drives for recent studies and slower, higher-capacity storage for older ones.
One limitation of traditional PACS archives is that they often use proprietary formats. If a hospital decides to switch PACS vendors, migrating years of stored data into the new system’s format is expensive and time-consuming. A Vendor Neutral Archive (VNA) solves this by sitting between the imaging modalities and the PACS itself. A VNA stores everything in standard DICOM 3.0 format with an open database schema, so the data belongs to the hospital rather than being locked into one vendor’s ecosystem. VNAs can also store non-DICOM objects like PDFs and scanned documents, and they interface directly with RIS and HIS systems, which traditional DICOM archives typically cannot do.
Display Workstations
Radiologists read images on diagnostic workstations, and the monitors on these stations must meet strict technical standards. The American College of Radiology recommends diagnostic displays maintain a maximum brightness of at least 350 candelas per square meter for general imaging and 420 for mammography. The ratio between the brightest and dimmest areas a screen can show should be around 350 to 1, ensuring subtle differences in tissue density remain visible.
Ambient lighting in the reading room matters too. The ACR recommends 25 to 75 lux, dim enough that room light doesn’t wash out the screen but bright enough that radiologists aren’t working in total darkness. Screen brightness uniformity should vary by less than 15% across the display surface, and the luminance response must closely follow a standardized curve (the DICOM Grayscale Standard Display Function) so that a given shade of gray looks the same on every calibrated monitor in every facility. Consumer off-the-shelf monitors are discouraged for diagnostic reading because they lack the internal calibration hardware to maintain these standards over time.
Workstations also provide basic image processing tools: window and level adjustment, zoom, pan, measurement, and the ability to compare a current study against prior exams side by side.
Integration With RIS and HIS
A PACS doesn’t operate in isolation. Its real value emerges when it connects to the radiology information system (which manages exam scheduling, tracking, and reporting) and the broader hospital information system (which holds patient demographics, clinical notes, and orders). Full integration means a radiologist can sit at one workstation and pull up a patient’s images alongside their relevant clinical history, surgical records, and prior reports without switching between separate applications.
At the most basic level of integration, images live on the PACS and text records live on a separate browser-based system. The radiologist switches between them manually. More advanced integration merges these into a single workflow: a worklist automatically populates with unread studies, and selecting a patient brings up both the images and filtered clinical documents relevant to the case. Some systems use intelligent filtering to surface only the most pertinent notes, such as flagging surgical history for a brain tumor patient, so the radiologist isn’t scrolling through hundreds of irrelevant records. This kind of tight integration is what moves a department toward a genuinely paperless workflow.
Security and Compliance Requirements
Because PACS stores and transmits protected health information, it falls squarely under HIPAA’s Security Rule. Three technical safeguards are non-negotiable. Access controls must ensure only authorized users can view patient images and data, typically through role-based permissions and unique login credentials. Audit controls require the system to log and track all activity, recording who accessed which study and when. Transmission security means that any image or data sent over a network must be protected against interception, which in practice means encryption during transit.
These aren’t optional checkboxes. HIPAA distinguishes between “required” and “addressable” implementation specifications, but “addressable” does not mean optional. It means a facility must evaluate whether a particular safeguard is reasonable for their setup, and if it is, they must implement it. For a system handling thousands of imaging studies daily, virtually all of these safeguards apply.