An image as stored on a picture archiving and communication system (PACS)The same image following contrast adjustment, sharpening and measurement tags added by the system
A picture archiving and communication system (PACS) is a medical imaging technology which provides economical storage and convenient access to images from multiple modalities (source machine types).[1]Electronic images and reports are transmitted digitally via PACS; this eliminates the need to manually file, retrieve, or transport film jackets, the folders used to store and protect X-ray film. The universal format for PACS image storage and transfer is DICOM (Digital Imaging and Communications in Medicine). Non-image data, such as scanned documents, may be incorporated using consumer industry standard formats like PDF (Portable Document Format), once encapsulated in DICOM. A PACS consists of four major components: The imaging modalities such as X-ray plain film (PF), computed tomography (CT) and magnetic resonance imaging (MRI), a secured network for the transmission of patient information, workstations for interpreting and reviewing images, and archives for the storage and retrieval of images and reports. Combined with available and emerging web technology, PACS has the ability to deliver timely and efficient access to images, interpretations, and related data. PACS reduces the physical and time barriers associated with traditional film-basedimage retrieval, distribution, and display.
Hard copy replacement: PACS replaces hard-copy based means of managing medical images, such as film archives. With the decreasing price of digital storage, PACS provide a growing cost and space advantage over film archives in addition to the instant access to prior images at the same institution. Digital copies are referred to as Soft-copy.
Remote access: It expands on the possibilities of conventional systems by providing capabilities of off-site viewing and reporting (distance education, telediagnosis). It enables practitioners in different physical locations to access the same information simultaneously for teleradiology.
Radiology Workflow Management: PACS is used by radiology personnel to manage the workflow of patient exams.
PACS is offered by virtually all the major medical imaging equipment manufacturers, medical IT companies and many independent software companies. Basic PACS software can be found free on the Internet.
Architecture
PACS workflow diagram
The architecture is the physical implementation of required functionality, or what one sees from the outside. There are different views, depending on the user. A radiologist typically sees a viewing station, a technologist a QA workstation, while a PACS administrator might spend most of their time in the climate-controlled computer room. The composite view is rather different for the various vendors.[2]
Typically a PACS consists of a multitude of devices. The first step in typical PACS systems is the modality. Modalities are typically computed tomography (CT), ultrasound, nuclear medicine, positron emission tomography (PET), and magnetic resonance imaging (MRI). Depending on the facility's workflow most modalities send to a quality assurance (QA) workstation or sometimes called a PACS gateway. The QA workstation is a checkpoint to make sure patient demographics are correct as well as other important attributes of a study. If the study information is correct the images are passed to the archive for storage. The central storage device (archive) stores images and in some cases reports, measurements and other information that resides with the images. The next step in the PACS workflow is the reading workstations. The reading workstation is where the radiologist reviews the patient's study and formulates their diagnosis. Normally tied to the reading workstation is a reporting package that assists the radiologist with dictating the final report. Reporting software is optional and there are various ways in which doctors prefer to dictate their report. Ancillary to the workflow mentioned, there is normally CD/DVD authoring software used to burn patient studies for distribution to patients or referring physicians. The diagram above shows a typical workflow in most imaging centers and hospitals. Note that this section does not cover integration to a Radiology Information System, Hospital Information System and other such front-end system that relates to the PACS workflow.
More and more PACS include web-based interfaces to utilize the internet or a wide area network (WAN) as their means of communication, usually via VPN (Virtual Private Network) or SSL (Secure Sockets Layer). The clients side software may use ActiveX, JavaScript and/or a Java Applet. More robust PACS clients are full applications which can utilize the full resources of the computer they are executing on and are unaffected by the frequent unattended Web Browser and Java updates. As the need for distribution of images and reports becomes more widespread there is a push for PACS systems to support DICOM part 18 of the DICOM standard. Web Access to DICOM Objects (WADO) creates the necessary standard to expose images and reports over the web through truly portable medium. Without stepping outside the focus of the PACS architecture, WADO becomes the solution to cross platform capability and can increase the distribution of images and reports to referring physicians and patients.
PACS image backup is a critical, but sometimes overlooked, part of the PACS Architecture (see below). Within the United States, HIPAA requires that backup copies of patient images be made in case of image loss from the PACS. There are several methods of backing up the images, but they typically involve automatically sending copies of the images to a separate computer for storage, preferably off-site.
Querying (C-FIND) and Image (Instance) Retrieval (C-MOVE and C-GET)
The communication with the PACS server is done through DICOM messages that are similar to DICOM image "headers", but with different attributes. A query (C-FIND) is performed as follows:
The client establishes the network connection to the PACS server.
The client prepares a C-FIND request message which is a list of DICOM attributes.
The client fills in the C-FIND request message with the keys that should be matched. E.g. to query for a patient ID, the patient ID attribute is filled with the patient's ID.
The client creates empty (zero length) attributes for all the attributes it wishes to receive from the server. E.g. if the client wishes to receive an ID that it can use to receive images (see image retrieval) it should include a zero-length SOPInstanceUID (0008,0018) attribute in the C-FIND request messages.
The C-FIND request message is sent to the server.
The server sends back to the client a list of C-FIND response messages, each of which is also a list of DICOM attributes, populated with values for each match.
The client extracts the attributes that are of interest from the response messages objects.
Images (and other composite instances like Presentation States and Structured Reports) are then retrieved from a PACS server through either a C-MOVE or C-GET request, using the DICOM network protocol. Retrieval can be performed at the Study, Series or Image (instance) level. The C-MOVE request specifies where the retrieved instances should be sent (using separate C-STORE messages on one or more separate connections) with an identifier known as the destination Application Entity Title (AE Title). For a C-MOVE to work, the server must be configured with mapping of the AE Title to a TCP/IP address and port, and as a consequence the server must know in advance all the AE Titles that it will ever be requested to send images to. A C-GET, on the other hand, performs the C-STORE operations on the same connection as the request, and hence does not require that the "server" know the "client" TCP/IP address and port, and hence also works more easily through firewalls and with network address translation, environments in which the incoming TCP C-STORE connections required for C-MOVE may not get through. The difference between C-MOVE and C-GET is somewhat analogous to the difference between active and passive FTP. C-MOVE is most commonly used within enterprises and facilities, whereas C-GET is more practical between enterprises.
In addition to the traditional DICOM network services, particularly for cross-enterprise use, DICOM (and IHE) define other retrieval mechanisms, including WADO, WADO-WS and most recently WADO-RS.
Image archival and backup
PACS-Server with 35-terabyte RAID Archive and high-speed fiber optic switch
Digital medical images are typically stored locally on a PACS for retrieval. It is important (and required in the United States by the Security Rule's Administrative Safeguards section of HIPAA) that facilities have a means of recovering images in the event of an error or disaster. While each facility is different, the goal in image back-up is to make it automatic and as easy to administer as possible. The hope is that the copies won't be needed; however, disaster recovery and business continuity planning dictates that plans should include maintaining copies of data even when an entire site is temporarily or permanently lost.
Ideally, copies of images should be maintained in several locations, including off-site to provide disaster recovery capabilities. In general, PACS data is no different than other business critical data and should be protected with multiple copies at multiple locations. As PACS data can be considered protected health information (PHI), regulations may apply, most notably HIPAA and HIPAA Hi-Tech requirements.[3]
Images may be stored both locally and remotely on off-line media such as disk, tape or optical media. The use of storage systems, using modern data protection technologies has become increasingly common, particularly for larger organizations with greater capacity and performance requirements. Storage systems may be configured and attached to the PACS server in various ways, either as Direct-Attached Storage (DAS), Network-attached storage (NAS), or via a Storage Area Network (SAN). However the storage is attached, enterprise storage systems commonly utilize RAID and other technologies to provide high availability and fault tolerance to protect against failures. In the event that it is necessary to reconstruct a PACS partially or completely, some means of rapidly transferring data back to the PACS is required, preferably while the PACS continues to operate.
Modern data storage replication technologies may be applied to PACS information, including the creation of local copies via point-in-time copy for locally protected copies, along with complete copies of data on separate repositories including disk and tape based systems. Remote copies of data should be created, either by physically moving tapes off-site, or copying data to remote storage systems. Whenever HIPAA protected data is moved, it should be encrypted, which includes sending via physical tape or replication technologies over WAN to a secondary location.
Other options for creating copies of PACS data include removable media (hard drives, DVDs or other media that can hold many patients' images) that is physically transferred off-site. HIPAA HITECH mandates encryption of stored data in many instances or other security mechanisms to avoid penalties for failure to comply.[4]
The back-up infrastructure may also be capable of supporting the migration of images to a new PACS. Due to the high volume of images that need to be archived many rad centers are migrating their systems to a Cloud-based PACS.
Integration
A chest image displayed via a PACS
A full PACS should provide a single point of access for images and their associated data. That is, it should support all digital modalities, in all departments, throughout the organisation.
However, until PACS penetration is complete, individual islands of digital imaging not yet connected to a central PACS may exist. These may take the form of a localized, modality-specific network of modalities, workstations and storage (a so-called "mini-PACS"), or may consist of a small cluster of modalities directly connected to reading workstations without long term storage or management. Such systems are also often not connected to the departmental information system. Historically, Ultrasound, Nuclear Medicine and Cardiology Cath Labs are often departments that adopt such an approach.
More recently, Full Field digital mammography (FFDM) has taken a similar approach, largely because of the large image size, highly specialized reading workflow and display requirements, and intervention by regulators. The rapid deployment of FFDM in the US following the DMIST study has led to the integration of Digital Mammography and PACS becoming more commonplace.
All PACS, whether they span the entire enterprise or are localized within a department, should also interface with existing hospital information systems: Hospital information system (HIS) and Radiology Information System (RIS). There are several data flowing into PACS as inputs for next procedures and back to HIS as results corresponding inputs:
In: Patient Identification and Orders for examination. These data are sent from HIS to RIS via integration interface, in most of hospital, via HL7 protocol. Patient ID and Orders will be sent to Modality (CT,MR,etc) via DICOM protocol (Worklist). Images will be created after images scanning and then forwarded to PACS Server. Diagnosis Report is created based on the images retrieved for presenting from PACS Server by physician/radiologist and then saved to RIS System. Out: Diagnosis Report and Images created accordingly. Diagnosis Report is sent back to HIS via HL7 usually and Images are sent back to HIS via DICOM usually if there is a DICOM Viewer integrated with HIS in hospitals (In most of cases, Clinical Physician gets reminder of Diagnosis Report coming and then queries images from PACS Server).
Interfacing between multiple systems provides a more consistent and more reliable dataset:
Less risk of entering an incorrect patient ID for a study – modalities that support DICOM worklists can retrieve identifying patient information (patient name, patient number, accession number) for upcoming cases and present that to the technologist, preventing data entry errors during acquisition. Once the acquisition is complete, the PACS can compare the embedded image data with a list of scheduled studies from RIS, and can flag a warning if the image data does not match a scheduled study.
Data saved in the PACS can be tagged with unique patient identifiers (such as a social security number or NHS number) obtained from HIS. Providing a robust method of merging datasets from multiple hospitals, even where the different centers use different ID systems internally.
An interface can also improve workflow patterns:
When a study has been reported by a radiologist the PACS can mark it as read. This avoids needless double-reading. The report can be attached to the images and be viewable via a single interface.
Improved use of online storage and nearline storage in the image archive. The PACS can obtain lists of appointments and admissions in advance, allowing images to be pre-fetched from off-line storage or near-line storage onto online disk storage.
Recognition of the importance of integration has led a number of suppliers to develop fully integrated RIS/PACS. These may offer a number of advanced features:
Dictation of reports can be integrated into a single system. Integrated speech-to-text voice recognition software may be used to create and upload a report to the patient's chart within minutes of the patient's scan, or the reporting physician may dictate their findings into a phone system or voice recorder. That recording may be automatically sent to a transcript writer's workstation for typing, but it can also be made available for access by physicians, avoiding typing delays for urgent results, or retained in case of typing error.
Provides a single tool for quality control and audit purposes. Rejected images can be tagged, allowing later analysis (as may be required under radiation protection legislation). Workloads and turn-around time can be reported automatically for management purposes.
Acceptance testing
The PACS installation process is complicated requiring time, resources, planning, and testing. Installation is not complete until the acceptance test is passed. Acceptance testing of a new installation is a vital step to assure user compliance, functionality, and especially clinical safety. Take for example the Therac-25, a radiation medical device involved in accidents in which patients were given massive overdoses of radiation, due to unverified software control.[5]
The acceptance test determines whether the PACS is ready for clinical use and marks the warranty timeline while serving as a payment milestone. The test process varies in time requirements depending on facility size but contract condition of 30-day time limit is not unusual. It requires detailed planning and development of testing criteria prior to writing the contract. It is a joint process requiring defined test protocols and benchmarks.
Testing uncovers deficiencies. A study determined that the most frequently cited deficiencies were the most costly components.[6] Failures ranked from most-to-least common are: Workstation; HIS/RIS/ACS broker interfaces; RIS; Computer Monitors; Web-based image distribution system; Modality interfaces; Archive devices; Maintenance; Training; Network; DICOM; Teleradiology; Security; Film digitizer.
History
One of the first basic PACS was created in 1972 by Dr Richard J. Steckel.[7]:6
The principles of PACS were first discussed at meetings of radiologists in 1982. Various people are credited with the coinage of the term PACS. Cardiovascular radiologist Dr Andre Duerinckx reported in 1983 that he had first used the term in 1981.[8]:9–18 Dr Samuel Dwyer, though, credits Dr Judith M. Prewitt for introducing the term.[9]:2–9
Dr Harold Glass, a medical physicist working in London in the early 1990s secured UK Government funding and managed the project over many years which transformed Hammersmith Hospital in London as the first filmless hospital in the United Kingdom.[10]:469–478 Dr Glass died a few months after the project came live but is credited with being one of the pioneers of PACS.
The first large-scale PACS installation was in 1982 at the University of Kansas, Kansas City.[2]
Regulatory concerns
In the US PACS are classified as Medical Devices, and hence if for sale are regulated by the USFDA. In general they are subject to Class 2 controls and hence require a 510(k), though individual PACS components may be subject to less stringent general controls.[11] Some specific applications, such as the use for primary mammography interpretation, are additionally regulated[12] within the scope of the Mammography Quality Standards Act.
The Society for Imaging Informatics in Medicine (SIIM) is the worldwide professional and trade organization that provides an annual meeting and a peer-reviewed journal to promote research and education about PACS and related digital topics.
Digital Imaging and Communications in Medicine (DICOM) is a technical standard for the digital storage and transmission of medical images and related information. It includes a file format definition, which specifies the structure of a DICOM file, as well as a network communication protocol that uses TCP/IP to communicate between systems. The primary purpose of the standard is to facilitate communication between the software and hardware entities involved in medical imaging, especially those that are created by different manufacturers. Entities that utilize DICOM files include components of picture archiving and communication systems (PACS), such as imaging machines (modalities), radiological information systems (RIS), scanners, printers, computing servers, and networking hardware.
Radiology is the medical specialty that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography, but today it includes all imaging modalities, including those that use no ionizing electromagnetic radiation, as well as others that do, such as computed tomography (CT), fluoroscopy, and nuclear medicine including positron emission tomography (PET). Interventional radiology is the performance of usually minimally invasive medical procedures with the guidance of imaging technologies such as those mentioned above.
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to reveal internal structures hidden by the skin and bones, as well as to diagnose and treat disease. Medical imaging also establishes a database of normal anatomy and physiology to make it possible to identify abnormalities. Although imaging of removed organs and tissues can be performed for medical reasons, such procedures are usually considered part of pathology instead of medical imaging.
A hospital information system (HIS) is an element of health informatics that focuses mainly on the administrational needs of hospitals. In many implementations, a HIS is a comprehensive, integrated information system designed to manage all the aspects of a hospital's operation, such as medical, administrative, financial, and legal issues and the corresponding processing of services. Hospital information system is also known as hospital management software (HMS) or hospital management system.
OsiriX is an image processing application for the Apple MacOS operating system dedicated to DICOM images produced by equipment. OsiriX is complementary to existing viewers, in particular to nuclear medicine viewers. It can also read many other file formats: TIFF, JPEG, PDF, AVI, MPEG and QuickTime. It is fully compliant with the DICOM standard for image communication and image file formats. OsiriX is able to receive images transferred by DICOM communication protocol from any PACS or medical imaging modality.
A radiological information system (RIS) is the core system for the electronic management of imaging departments. The major functions of the RIS can include patient scheduling, resource management, examination performance tracking, reporting, results distribution, and procedure billing. RIS complements HIS and PACS, and is critical to efficient workflow to radiology practices.
Teleradiology is the transmission of radiological patient images from procedures such as x-rays photographs, Computed tomography (CT), and MRI imaging, from one location to another for the purposes of sharing studies with other radiologists and physicians. Teleradiology allows radiologists to provide services without actually having to be at the location of the patient. This is particularly important when a sub-specialist such as an MRI radiologist, neuroradiologist, pediatric radiologist, or musculoskeletal radiologist is needed, since these professionals are generally only located in large metropolitan areas working during daytime hours. Teleradiology allows for specialists to be available at all times.
The American College of Radiology (ACR), founded in 1923, is a professional medical society representing nearly 40,000 diagnostic radiologists, radiation oncologists, interventional radiologists, nuclear medicine physicians and medical physicists.
BI-RADS is an acronym for Breast Imaging-Reporting and Data System, a quality assurance tool originally designed for use with mammography. The system is a collaborative effort of many health groups but is published and trademarked by the American College of Radiology (ACR).
CEN ISO/IEEE 11073 Health informatics - Medical / health device communication standards enable communication between medical, health care and wellness devices and external computer systems. They provide automatic and detailed electronic data capture of client-related and vital signs information, and of device operational data.
VistA Imaging is an FDA-listed Image Management system used in the Department of Veterans Affairs healthcare facilities nationwide. It is one of the most widely used image management systems in routine healthcare use, and is used to manage many different varieties of images associated with a patient's medical record. The system was started as a research project by Ruth Dayhoff in 1986 and was formally launched in 1991.
Imaging informatics, also known as radiology informatics or medical imaging informatics, is a subspecialty of biomedical informatics that aims to improve the efficiency, accuracy, usability and reliability of medical imaging services within the healthcare enterprise. It is devoted to the study of how information about and contained within medical images is retrieved, analyzed, enhanced, and exchanged throughout the medical enterprise.
GIMIAS is a workflow-oriented environment focused on biomedical image computing and simulation. The open-source framework is extensible through plug-ins and is focused on building research and clinical software prototypes. Gimias has been used to develop clinical prototypes in the fields of cardiac imaging and simulation, angiography imaging and simulation, and neurology
Radiation Exposure Monitoring (REM) is a framework developed by Integrating the Healthcare Enterprise (IHE), for utilizing existing technical standards, such as DICOM, to provide information about the dose delivered to patients in radiology procedures, in an interoperable format.
A Vendor Neutral Archive (VNA) is a medical imaging technology in which images and documents are stored (archived) in a standard format with a standard interface, such that they can be accessed in a vendor-neutral manner by other systems.
Medical image sharing is the electronic exchange of medical images between hospitals, physicians and patients. Rather than using traditional media, such as a CD or DVD, and either shipping it out or having patients carry it with them, technology now allows for the sharing of these images using the cloud. The primary format for images is DICOM. Typically, non-image data such as reports may be attached in standard formats like PDF during the sending process. Additionally, there are standards in the industry, such as IHE Cross Enterprise Document Sharing for Imaging (XDS-I), for managing the sharing of documents between healthcare enterprises. A typical architecture involved in setup is a locally installed server, which sits behind the firewall, allowing secure transmissions with outside facilities. In 2009, the Radiological Society of North America launched the "Image Share" project, with the goal of giving patients control of their imaging histories by allowing them to manage these records as they would online banking or shopping.
Ginkgo CADx is an abandoned multi platform DICOM viewer (*.dcm) and dicomizer. Ginkgo CADx is licensed under LGPL license, being an open source project with an open core approach. The goal of Ginkgo CADx project was to develop an open source professional DICOM workstation.
DICOMweb is a term applied to the family of RESTful DICOM services defined for sending, retrieving and querying for medical images and related information.
Oncology Information System (OIS) is a software solution that manages departmental, administrative and clinical activities in cancer care. It aggregates information into a complete oncology-specific electronic health record to support medical information management. The OIS allows the capture of patient history information, the documentation of the treatment response, medical prescription of the treatment, the storage of patient documentation and the capture of activities for billing purposes.
↑ "HITECH Act Enforcement Interim Final Rule". hhs.gov. United States Department of Health and Human Services. 16 June 2017 [2009-02-18]. Archived from the original on 30 January 2023. Retrieved 11 February 2023. The Health Information Technology for Economic and Clinical Health (HITECH) Act, enacted as part of the American Recovery and Reinvestment Act of 2009, was signed into law on February 17, 2009, to promote the adoption and meaningful use of health information technology
↑ Dwyer III, Samuel J. (18 May 2000). Siegel, G. James; Blaine, Eliot L. (eds.). "A personalized view of the history of PACS in the USA". Proceedings of SPIE Medical Imaging 2000: PACS Design and Evaluation: Engineering and Clinical Issues. 3980: 2–9. doi:10.1117/12.386388. eISSN1996-756X. ISSN0277-786X.
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