Picture archiving and communication system

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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

In medical imaging, picture archiving and communication systems (PACS) are computers or networks dedicated to the storage, retrieval, distribution and presentation of images. The medical images are stored in an independent format. The most common format for image storage is DICOM (Digital Imaging and Communications in Medicine).

Contents

[edit] Types of images

Most PACSs handle images from various medical imaging instruments, including ultrasound (US), magnetic resonance (MR), positron emission tomography (PET), computed tomography (CT), endoscopy (ENDO), mammograms (MAMMO), digital radiography (DR), computed radiography (CR) etc. (see DICOM Application areas).

[edit] Uses

PACS has two main uses:

  • Hard copy replacement: PACS replaces hard-copy based means of managing medical images, such as film archives. With the decreasing price of digital storage, PACSs 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.

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.

One difficult area in PACS is interpreting the DICOM image format. DICOM does not fully specify the metadata tags stored with images to annotate and describe them, so vendors of medical imaging equipment have latitude to create DICOM-compliant files that differ in the meaning and representation of this metadata. A feature common to most PACS is to read the metadata from all the images into a central database, allowing the PACS user to retrieve all images with a common feature no matter the originating instrument. The differences between vendors' DICOM implementations make this a difficult task.

A PACS can store volume data from exams and reconstruct 3D images

Some medical modality vendors have defined private DICOM tags to introduce added features. Tags like this are permitted according to DICOM protocol and will not impact on the images in most cases, but will not operate when the image is viewed on a different platform.

[edit] Architecture

Typically a PACS network consists of a central server that stores a database containing the images connected to one or more clients via a LAN or a WAN which provide or utilize the images.

More and more PACS include web-based interfaces to utilize the Internet as their means of communication, usually via VPN (Virtual Private Network) or SSL (Secure Sockets Layer). The client side software is often using ActiveX, JavaScript and/or Java.

Definitions vary, but most claim that for a system to be truly web based, each individual image should have its own URL.[citation needed]

Client workstations can use local peripherals for scanning image films into the system, printing image films from the system and interactive display of digital images. PACS workstations offer means of manipulating the images (crop, rotate, zoom, window, level and others).

Modern radiology equipment and modalities feed patient images directly to the PACS in digital form. For backwards compatibility, most hospital imaging departments and radiology practices employ a film digitizer.

PACS image backup is a critical, but sometimes overlooked, part of the PACS Architecture (see below). 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.

Some of the largest sites are based on Unix, which is very stable and secure about viruses. The wintel platforms are gaining space with the help of the modern powerful processors.

[edit] Image Backup

Digital medical images are typically stored on a Picture Archiving and Communication System (PACS) for retrieval. Computer images are fragile and can be lost very quickly. It is important (and required in the USA by the Security Rule's Administrative Safeguards section of HIPAA) that facilities have a backup copy of the images.

While each facility is different, the goal in image backup is to make it automatic and as easy to administer as possible. The hope is that the copies won't ever be needed. But, as with other disaster planning, they need to be available if needed.

Ideally, copies of images should be streamed off-site as they are created. (If using the internet, the Security Rule's Technical Safeguards section of HIPAA requires that the images be encrypted during transmission.) Depending on bandwidth and image volume, this may not be practical. Other options include removable media (hard drives, DVDs or other media that can hold many patients' images) and/or separate computers. These copies need to be protected.[1]

As hard drive and computer prices continue to fall, RAID is losing acceptance as a backup mechanism. RAID doesn't backup the images to a fully redundant device, but rather writes some redundant information on multiple drives within the same computer. This added complexity brings its own vulnerabilities.[2] The redundant data written on RAID is subject to the same virus, hardware or software problems as the original image, except that it is protected from hard drive failure. Another way to backup data in the PACS environment is using LTO libraries, which uses digital tapes storing up to 800 GB each with the LTO3 type. This puts their stored images on ´near line´ status, meaning that the user has to wait some minutes to get their study.

In the event that it is necessary to reconstruct a PACS from the backup images, the backup system should be able to be turned into a "super modality" that simply blasts all of its images back to the PACS.[3] This will allow the PACS to continue receiving current images while also rebuilding its historical images at the same time.

When migrating images from one PACS to another, it is sometimes very difficult to get the old PACS to blast the images to the new one. This is another application where backup can be used to "restore" the images to the new PACS.

Backup should be inexpensive, automatic, require no downtime and flexible enough to be used for partial or full restores, as well as migrating images to a new PACS.

[edit] Integration

A chest image displayed via a PACS

A full PACS should provide a single point of access for images and their associated data (i.e. it should support multiple modalities). It 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 nearline storage (for example, tape libraries or DVD jukeboxes) onto online disk storage (RAID array).

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. The recording is 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.

[edit] DICOM Viewers

There are several DICOM Viewers available both free and proprietary. Some of the DICOM Viewers include: DICOM Works, Osirix, SureVistaVision , UniPACS, Syngo Imaging, VRRender, ImageJ and MicroDicom. Various viewers can connect directly to a PACS server or retrieve images from local storage.

[edit] History

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.[4] Dr Samuel Dwyer, though, credits Dr Judith M. Prewitt for introducing the term.[5]

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.[6] Dr Glass died a few months after the project came live but is credited with being one of the pioneers of PACS.

[edit] References

  1. ^ HHS cracks down: provider to pay $100,000 in HIPAA penalties over lost laptops
  2. ^ As the number of drives increase, image inconsistency increases
  3. ^ "Blast" images to a PACS
  4. ^ Duerinckx AJ, Pisa EJ. Filmless Picture Archiving and Communication System (PACS) in Diagnostic Radiology. Proc SPIE 1982;318;9-18. Reprinted in IEEE Computer Society Proceedings of PACS'82, order No 388.
  5. ^ Samuel J. Dwyer III. A personalized view of the history of PACS in the USA. In: Proceedings of the SPIE, "Medical Imaging 2000: PACS Design and Evaluation: Engineering and Clinical Issues", edited by G. James Blaine and Eliot L. Siegel. 2000;3980:2-9.
  6. ^ Bryan S, Weatherburn GC, Watkins JR, Buxton MJ (1999). "The benefits of hospital-wide picture archiving and communication systems: a survey of clinical users of radiology services". Br J Radiol 72 (857): 469–78. PMID 10505012. 

[edit] See also

[edit] External links

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