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Accession number A unique number given to each patient study. This is a portion of the information required to define the patient's identification in the imaging modality.

ACR See American College of Radiology

ACR-NEMA See American College of Radiology - National Electrical Manufacturers Association.

ADC See Analogue to Digital Converter.

Admit Discharge Transfer (ADT) Many PACS use patient location information, for example in the management of online storage and the creation of worklists. This information can be obtained from other hospital information systems in the form of messages containing details of patient admissions, discharges, or transfers between wards. These messages are usually referred to as ADT messages.

ADT See Admit Discharge Transfer.

Advanced Intelligent Tape (AIT) Advanced Intelligent Tape is tape technology that comes in two formats (AIT-2 and AIT-3) which hold 50 and 100 GB respectively. The tape has firmware that contains the indexing information and tape status, thus enabling rapid retrieval of data from anywhere on the tape. See Digital Versatile Disk (DVD), Linear Tape Open (LTO), Jukebox, Digital Linear Tape (DLT), Magneto Optical Disk (MOD), Firmware and Digital Audio Tape (DAT).

AIT See Advanced Intelligent Tape.

Algorithm The series of rules that a computer follows to solve a problem. The rules in an algorithm should be clear and have a definite stopping point.

American College of Radiology (ACR) This is the professional institute for radiologists in the USA. Its primary goal is the advancement of radiology to provide better patient care ( http://www.acr.org/ ). See British Institute of Radiology (BIR) and Radiological Society of North America (RSNA).

American College of Radiology - National Electrical Manufacturers Association (ACR-NEMA) These two bodies together produced the ACR-NEMA standards that have evolved into the DICOM standards. See Digital Imaging and Communications in Medicine (DICOM).

American National Standards Institute (ANSI) This standards agency creates standards for all equipment and goods sold in the USA. The ANSI standard has been adopted as the de facto world standard for some products such as software and technological equipment ( http://www.ansi.org/ ). See British Standards Institute (BSI).

Analogue A physical object or quantity, which varies in a continuous manner and is not limited to discrete steps. An example of an analogue device is a mercury thermometer.

Analogue to Digital Converter (ADC) A device converting an analogue electrical signal into its digital representation so that it can be processed by a digital system. An example is the conversion of the light emitted from a CR plate during the read process, which is read by a PMT to form a digital image. See Photo Multiplier Tube (PMT) and Computed Radiography (CR).

ANSI See American National Standards Institute.

Application Service Provider (ASP) An organisation which provides and manages archive storage space for image data. This archive space will frequently be located off-site, and may serve more than one independent PACS. See Data warehousing.

Archive The storage of large amounts of data. This data can be stored on various types of devices, examples being RAID, optical disk or digital tape. The use of the archiving media is dependant on the status of the images stored. Several terms are associated with archiving in PACS and are often used. See Long Term Archive (LTA), Short Term Storage (STS), Online Storage, Everything Online (EOL), Nearline archive, and Offline archive.

ASP See Application Service Provider.

Asynchronous Transfer Mode (ATM) A network technology based on transferring data in packets of a fixed size. The size of the data packets in ATM are relatively small compared to units used with older technologies. The small, constant size allows ATM equipment to transmit video, audio, and computer data over the same network. See Packet.

ATM See Asynchronous Transfer Mode.