Fundamental PACS architecture and design

• 4 major ingredients in the PACS infrastructure design concept are: industry standards, connectivity and open architecture, reliability, security
• INDUSTRY STANDARDS: Minimize the need of customized software
• INDUSTRY STANDARDS: Increases the portability of the system to other computer platforms
• Open Network Design: allows a standardized method for data and message exchange between heterogenous systems
• To be sure that a contemplated PACS is well designed and allows for future connectivity, the following questions should be kept in mind all the time:

  1. Can we transmit images from this PACS module to other modules, and vice versa?
  2. Does this use HL7 standard fortextual data and DICOM forimages?
  3. Does this computer in the module use a standard communication protocol?
• RELIABILITY: system must be reliable, accurate, and secure. When we upload images or data to the PACS, it should not be corrupted
• in order for systems to be reliable, it is important to use fault tolerant measures, including error detection and logging software, external auditing programs, hardware redundancy, and intelligent software recovery blocks
• Some fail recovery mechanisms that can be used include automatic retry of failed jobs with alternative resources and algorithms and intelligent bootstrap routines that allow a PACS computerto automatically continue operations after a power outage or system failure
• intelligent bootstrap routines: a software block executed by a computer when it is restarted
• Security: Patient confidentiality, is an important consideration because of medicolegal issues and the HIPAA (Health Insurance Portability and Accountability Act) mandate
• Application programs may supply additional layers of protection. Privilege control refers to granting and revoking the user’s access to specific tables, columns, or views from the database
• SYSTEM ARCHITECTURE: Defined as the hardware and software infrastructure of a computer system
• In a PACS, the system architecture normally consists of acquisition devices, storage, display workstations, and an image management system
• STAND-ALONE MODEL: AKA thick client model
• thick client model: one of the most flexible models
• 3 major features of stand-alone model:

  1. Images are automatically sent to the designated diagnostic and review WSs from the server
  2. WSs can also query/retrieve images from the archive server
  3. WSs have short-term cache storage
• first step of general data workflow of stand-alone model:

  • RIS notifies the imaging modality and the PACS server of a patientregistration
• second step of general data workflow of stand-alone model:

  • Afterthe examination, the modality sends images to the PACS server for archiving of the images
• third step of general data workflow of stand-alone model:

  • PACS server archives the images
• fourth step of general data workflow of stand-alone model:

  • Multiple copies of the images are distributed to selected diagnostic and review WSs. The server performed this images distribution function automatically based on the default setting
• fifth step of general data workflow of stand-alone model: Server also prefetches pertinent historical images and sends copies to selected WSs
• sixth step of general data workflow of stand-alone model: WSs can also use DICOM query/retrieve function through the server to obtain images for review. In addition, if automatic prefetching fails, a WS can query/retrieve historical images from the server
• seventh step of general data workflow of stand-alone model: Each WS contains a local storage to hold a preset number of PACS exams
• eighth step of general data workflow of stand-alone model: WS returns the diagnosis to the server then to the RIS
• In a stand-alone model, if the PACS server goes down, imaging modalities or acquisition GWs have the flexibility to send images directly to designated WSs so that radiologist scan continues reading new cases
• In a stand-alone model, because multiple copies of the PACS exam are distributed throughout the system, there is less risk of losing PACS image data
• In a stand-alone model, some historical PACS exams will still be available in WSs because they have local storages
• In a stand-alone model, system is less susceptible to daily variations of network performance because PACS exams are preloaded onto the WSs local storage and available for viewing immediately
• In a stand-alone model, modification to the DICOM header can be performed if necessary during the quality control before archiving
• In a stand-alone model, users mustrely on correct image distribution and prefetching of historical PACS exams based on the preset default table, which is not possible all the time.
• In a stand-alone model, because images are sent to designated WSs, each WS may have a different worklist, which makes it inconvenient for radiologists to read/review all examinations assigned to him/her at any WS in one setting
• In a stand-alone model, users sometime need to use query/retrieve function to retrieve pertinent PACS exams from the archive, this task can be a complex function compared to the client-server model
• In a stand-alone model, radiologist may duplicate the reading of the same case from a different WS because the same exam may be sen to several WSs.
• CLIENT-SERVER MODEL: AKA thin client model
• 3 major features of client-server model:

  1. Images are centrally archive in the PACS server
  2. From a single worklist at the client WS has a single worklist of all examinations where a user selects the patient anf images via the PACS server
  3. WSs have no local storage, images are flushed after reading
• first step of general data workflow of client-server model: RIS notifies the imaging modality and the PACS server of a patient registration
• second step of general data workflow of client-server model: After the examination, the modality sends images to the PACS server
• third step of general data workflow of client-server model: PACS server archives the images
• fourth step of general data workflow of client-server model: Client WSs have access to the complete worklist from where images, and exams can be retrieved from the PACS server and archive. For more efficient image retrievals, the worklist can be shortened by a preset filter
• fifth step of general data workflow of client-server model: Once the exam is selected, images from the PACS archive are loaded directly into the image memory of the client WS for viewing. Prefetched historical exams are loaded to the WS in the same manner