Below is a list of some of the commonly used terms related to the medical imaging industry today. For a more comprehensive list, please click here.
Commonly Used Terms
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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.

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.

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/ ).

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.

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).

Application Service Provider (ASP)
An organization 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.

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.

The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or more commonly Mbps. This is also known as transfer rate.

Bits per second (bps)
A measure of the transfer rate that data travels over networks. It is usually expressed in Megabits per second, or Mbps.

Computed Radiography (CR)
CR uses an imaging plate instead of film to capture an image. The plate is made of a storage phosphor that captures x-ray energy. When scanned with a laser the plate emits light. This is captured by the plate reader in order to build up an image from measurements made on the released energy.

Computer Aided Diagnosis (CAD)
A sophisticated program which can aid the diagnosis of images. It usually has some artificial intelligence base.

Conformance statement, DICOM conformance statement
A formal statement, provided by a vendor, associated with a specific implementation of the DICOM Standard. It specifies the service classes, information objects, and communication protocols supported by the implementation. This statement is usually several pages long, and specifies precisely how any item of equipment will implement the various options allowed within the DICOM standard.

The extent to which adjacent areas of an image on a display screen differ in relative brightness.

Contrast resolution
This is the minimum perceptible difference in the luminance between two adjacent pixels a display.

Factual information, usually organized for analysis. It can also be thought of as information which is in a suitable form for processing by a computer.

A collection of information organized in such a way that a computer program can quickly select desired pieces of data. A database can be constructed using several methods, examples are a relational database and a flat database; a relational database stores data in related tables whereas a flat database stores data in a single table.

DICOM gateway
An interface between a modality and PACS. This will allow the transfer of images or data when the PACS and the modalities have DICOM conflicts.

Digital Imaging and Communications in Medicine (DICOM)
The ACR-NEMA standard protocol adopted by all manufacturers of equipment associated with medical imaging. The standard provides a method of linking a series of heterogeneous modalities, workstations and printers without the need for customized hardware to allow them to communicate and transfer images (http://medical.nema.org/dicom.html).

A device used to scan a traditional X-ray film to create a digital image data file. There are two types of film digitizers in common use. Both use lasers to scan the film to create the digital image; however one uses photo-multiplier tubes (PMT) to capture the light whereas the other uses charged coupled device (CCD) technology.

Direct Attached Storage (DAS)
This a term used to describe a storage device (usually a disk) attached to a server which can respond quickly to random requests for data.

This is the most widely used architecture in local area networks (LAN). It is defined by the IEEE as the 802.3 standard. Ethernet operates over various types of physical media such as coaxial, shielded or unshielded twisted pair and fiber optics. It normally operates at 10 or 100 Mbps but new versions can operate at Gbit (1000 Mbps) transfer rates.

gigabyte (1000 MB).
Graphical User Interface (GUI)
This allows the user to interact with a computer through pictorial means. This can be done in the form of windows with drop down menus and icons.

Hanging protocol
When the images in a PACS are displayed on a workstation for reporting they will be placed in a standard or default format known as the Default Display Protocol. This is also referred to as the hanging protocol.

Health Insurance Portability and Accountability Act (HIPAA)
This is a USA law that comes into effect in 2002. Principally the goals are the standardization of information management and exchange in medicine, to maintain security, improve accuracy and assure privacy (http://www.hipadvisory.com/ and http://www.scarnet,org/).

Health Level 7 (HL7)
This is an ANSI accredited standard developed to allow transfer of data between different systems in healthcare. This operates at the top level of the open system integration model, the application layer (http://www.hl7.org/ and http://www.hl7.org.uk/).

HealthCare Information and Management Systems Society (HIMSS)
This is a society which provides a forum for multidisciplinary professionals in healthcare information services to discuss problems and provide educational facilities for its members. It also aids in the advancement of standards and initiative such as IHE (http:www.himss.org/)

Hospital Information System (HIS)
A computer system which stores demographic information on all patients It may also store appointment details, clerical data or pathology reports.

A general definition is a visual representation of a real world entity. However a more appropriate definition of a digital image would be an array of numerical values which may be meaningfully rendered as a visible image by means of an algorithm that maps between the array values and the displayed pixel values. The information in each of the pixels will be contained in bytes which will determine its level of grey on the greyscale.

Integrating the Healthcare Enterprise (IHE)
An initiative by HIMSS and RSNA to establish the integration of all hospital information and imaging systems. Its aim is to encourage manufacturers to establish common protocols that will allow this integration to take place.

Joint Photographic Experts Group (JPEG)
JPEG is a group of experts which was formed to produce a standard for compressing images, (ISO/IEC JTC1 SC29). JPEG is also a lossy compression technique that reduces the size of the image data file. However the cost of this is the loss of some information. JPEG is never used for text compression (http://www.jpeg.org/).

An archiving jukebox can contain one of many types of media (CD-ROM, tape or disks). The jukebox moves the media from its location by means of a robot or carousel to a reading /writing area. The time for this movement of disk to read is usually 10 - 20 seconds.

Local Area Network (LAN)
A computer network that spans a small area, e.g. an office, with each computer being a node on the network.

Lossless compression
A data compression technique which results in data being returned to its original form without any loss of information when it is decompressed. The decompressed file and the original file are identical.

Lossy compression
This is a data compression technique; which results in data not being returned to its original form when it is decompressed. The benefit of using this technique is that it provides a high degree of compression, saving on storage space and transmission time over a network.

MAC Address
This is a unique serial number residing in the firmware of a network interface card that identifies the network card on the network.

Magneto Optical Disk (MOD)
A type of disk that combines magnetic disk technologies and CD-ROM technologies. MO disks can be read from and written to and are removable. Their storage capacity is approximately 1.3 GB, (650 MB per side).

megabyte (1000 000 bytes).

If it assumed that a PACS must be as a minimum hospital wide, a mini-PACS can refer to a department based system, such as Radiology, A & E or Orthopedics, or to a modality based system such as CT and MRI or CR.

A generic term used to describe an imaging device such as MRI, CT, Ultrasound, DR and CR.

Modality Interface Unit (MIU)
All modern imaging modalities will be DICOM compliant. However specific DICOM interpretations may have compatibility problems. A MIU will allow modalities to be interfaced to the PACS where any areas of DICOM conflicts occur.

National Electrical Manufacturers Association (NEMA)
This is a trade organization in the USA who make a significant contribution to the development of industry standards affecting the imaging community. They also develop and promote new technologies (http://www.nema.org/).

Network Attached Storage (NAS)
This is a device that contains a number of disk units attached to a dedicated server. The NAS device appears as a server on the network. It is possible to communicate with it using standard file sharing protocols, therefore no specialized hardware is required.

Network Interface Card (NIC)
This is a circuit board that allows a computer to communicate on the network. There are NICs available for all network protocols.

Picture Archiving and Communication System (PACS)
The acquisition, archival and retrieval of digital images over a computer network, for diagnosis and review at dedicated workstations.

PACS broker
A device that allows the PACS to interface with the Hospital Information System (HIS) and/or the Radiology Information System (RIS). This is not essential in all systems as the RIS and HIS may be able to interface directly with the PACS using the HL7 standard.

This is a word defined from the term "picture element" and is the smallest viewable element, rectangular or square in an image or display. The function of a workstation will determine the number of pixels required in its display.

This is a DICOM service class. It supports the ability to query a device for a list of patients, studies or series and to initiate the transfer instances of patients, studies or series, this is the MOVE operation.

Radiological Society of North America (RSNA)
An organization based in the USA whose purpose is to promote radiology and related sciences through education and research, and forward research in both clinical and basic sciences including IT to improve and promote healthcare (http://www.rsna.org/).

Radiology Information System (RIS)
A computer system which stores the appointment information for a radiology department and may be linked to the HIS. A PACS may take exam booking information and demographics from the RIS to form worklists.

Redundant Array of Inexpensive Disks (RAID)
A RAID is a multi disk system where one or more of the disks provide fault tolerance. A RAID should be able to withstand disk failure and have the ability to reconstruct the data from a failed disk.

Request For Proposal (RFP)
This is a detailed document from both a technical and business perspective. A document that has been written thoroughly will ensure the organization gains valuable information about the vendors. It will also aid the vendors to provide the system that the organization requires.

This defines the ability to discern the detail in an image.

A device which is used to link heterogeneous networks. Routers use headers and a forwarding table to determine where packets go. They use ICMP to communicate with each other and configure the best route between any two hosts.

A computer which controls the function of network resources. A server is often applied to a dedicated task, e.g. a file server controls delivery of files and a network server controls network traffic. However it is possible for servers to fulfill more than one task if they have a multiprocessing operating systems.

SMPTE test image
A standard test image used in the television industry. It allows the user to make judgments on the quality of the display monitor by looking at the contrast resolution, spatial resolution and any distortion.

Society for Computer Applications in Radiology (SCAR)
This a multi-disciplinary body involved in the advancement of computer applications and information technology in medicine. This is achieved through educational bodies and conferences (http://www.scarnet.org/).

Spatial resolution
Defines the smallest feature that can be detected in an image. This is usually defined as line pairs per mm.

Storage Area Network (SAN)
A network topology which has a series of servers linked through a series of switches through a dedicated network to a central storage. This allows all servers to access a large storage and improves access times. This topology would be most suitable in a distributed PACS, with the PACS servers at remote locations accessing a central data store. A dedicated high speed network, usually fiber channel connects the storage elements (RAID, JBOD and tape), to the servers.

A device that filters and forwards packets between LAN segments. Switches, because of their design, support any packet protocol.

The delivery of healthcare and the sharing of knowledge over a distance using telecommunications network. This is much more comprehensive than teleradiology in that it allows a broad range of medical information, including radiological, to be shared. This allows remote sites access to major centers of excellence.

The ability to acquire a diagnostic image at one location and review it at a remote location that is not part of a LAN. This allows an information system to be spread over a large distributed area, and is most effective in allowing small hospitals access to centers of excellence.

Transmission Control Protocol/Internet Protocol (TCP/IP)
TCP is one of the main protocols in TCP/IP networks. Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.

Uninterruptible Power Supply (UPS)
A device which provides back-up power in the event of failure in the primary power supply system. If there is a power-cut or drop-out the UPS will keep the system running for a finite period of time, allowing the primary power supply to be repaired and/or the system to be powered-off gracefully. This protects the equipment and the stored data.

Voice recognition
A process which takes the spoken word as its input and produces text as the output. It can be used in an imaging department to aid in the production of clinical reports.

Web browser
An application used to display images in clinical environments. The workstations used are normal PCs with high quality monitors. The application used is similar to the web browser used in the world wide web, for example Netscape Navigator or Internet Explorer.

Wide Area Network (WAN)
A computer network that spans a relatively large geographical area and typically consists of more than one LAN.

The list of patient studies sent from the RIS and displayed at the appropriate acquisition modality.

In a PACS there are several types of workstations that are used for differing purposes. These workstations are described below:

Reporting workstation
A workstation used for viewing images for primary diagnosis and/or production of clinical reports. A reporting workstation will commonly have multiple display monitors, usually 2 or 4 screens, to allow for the simultaneous display of multiple images. These monitors will be of high quality and resolution.

Review workstation
A workstation used for checking that acquired images are of the required quality and that all necessary views have been performed, or a workstation used on a ward or in a clinic to view images in conjunction with the associated clinical report. A review workstation will usually have one or two display monitors, which are likely to be of lower display quality than the monitors used in reporting workstations.

QA workstation
A workstation dedicated to quality assurance of the PACS, i.e. used by support staff to ensure that the PACS is functioning correctly. The display monitor used for the QA workstation should be of equivalent quality to the monitors used for the reporting workstations.
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