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Universal C-mount
Enables a video camera to be attached to any medical peripheral device that uses the same connector. These are increasingly common.

Unsharp Mask
Despite the name, this is an edge enhancing filter frequently used in teleradiology. It is created by first generating a low-pass filtered image, which is then subtracted from the original image. This effectively removes part of the background, leaving an image where contours are emphasized.

V.11
ITU-T Rec. V.11 describing Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s.

V.24
ITU-T Rec. V.24 listing definitions for interchange circuits between terminal equipment (DTE) and data circuit-terminating equipment (DCE).

VCR record source control
One-source control
 
indicates if the system allows the user to push one button and start or stop recording either end of the video conference. Several systems require entering a complex series of commands (multiple button pushes) to initiate or stop recording the conference, or to change which end of the conference is being recorded. This is very cumbersome when a user only remembers shortly after the start of a conference to turn the tape on, or when trying to record sequential segments of the participants at both ends of a video conference. We have not found an off the shelf system that allows the user to record both ends of a video conference simultaneously on one tape.

VCR Simultaneous playing of pre-recorded tape and recording of conference
relates to the ability to have one VCR playing a pre-recorded tape into the system as a video source, while simultaneously having another VCR connected and recording the videoconference in progress. This is necessary for those telemedicine programs that maintain a policy of recording all consults and which periodically use pre-recorded tapes of patient procedures or educational tapes as part of a video conference.

Vector Adaptive Predictive Coding (VAPC)
A proprietary audio coding algorithm primarily intended for use at the lowest transmission aggregate bit rates.

Video Cassette Recorder (VCR)
 

Video Conferencing
Real time, usually two-way, transmission of digitized video images between two or more locations. This requires a wideband transmission facility (frequently satellite) and bandwidths from 56 Kbps (freeze frame) to T1 rates (full motion).

Video on Demand
The ability to provide instantaneous access to remotely stored sources of video. A video server stores and manages large amounts of multimedia data and delivers it on demand to one, or many, users. Limitations to deployment are bandwidth availability, video server price, and video compression protocols .

Videophone
Small, stand-alone video appliance with a small camera and circulation, not part of a computer or larger videoconferencing system, that enables interactive audio-video communications over POTS or ISDN.

Video Server
An audio and video file server with hard disk capacities often measured in the terabytes, connected to LANs and WANs with high-speed facilities like ATMor FDDI. Usually uses H.320, MPEG or Motion-JPEG video compression. Used for training on demand to the desktop and many other purposes including marketing and entertainment.

Video Signal
Currently there are three, established standards in the word for composite, color encoded video: NTSC, PAL, SECAM. HDTV is a new international standard that has been developed and adopted in Japan. More recently, MPEG has appeared as a world standard for digital television broadcasting. The adoption of a common, international standard for video transmission has been one primary focus of the IETF.

Virtual Circuit
Packet switching, network facilities that give the appearance of an actual end-to-end circuit. A dynamically variable, network connection where sequential user data packets may be routed differently.

Virtual Private Network (VPN)
Private, software defined network dedicated to connecting two or more high volume, long distance client sites.

Visualization
Graphics and visualization technologies consist of the software and hardware which permits effortless generation of fast, high quality graphic images from data.

Voice Grade Channel
A telephone channel of sufficient bandwidth to transmit human voice, usually an analog signal ranging from 300 Hz to 3,400 Hz.

Voice Over Internet Protocol (VOIP)
A series of techniques permiting transmission of telephony over the internet. Often makes use of ITU-T G.7xx audio compression recommendations.

Voice Switching
An electrical technique for opening and closing a circuit, such as changing from one microphone to another microphone or from one video camera to another video camera, in response to the presence or absence of sound.

Wavelets
An image compression technique that enables more or less lossless compression ratios of 10:1 or even 20:1, compared to the standard 3:1 maximum for lossless JPEG compression.

Wide Area Network (WAN)
Wider in geographic scope than a LAN. Provides digital communications (voice / video / data) over switched (ISDN, switched 56) or unswitched (fractional T1, T1) networks. Some consider commercial dial-up networks (America OnLine, the Internet) to be WANs.

Windowing
A software manipulation technique, using mathematical algorithms, to compensate for a teleradiology monitor's inability to provide the same contrast and bit depth as the original hardcopy X-ray. Pixels within a certain range of bit-depth values are assigned the full range of possible grayscale values, while those outside that range are either white or black. This allows emphasis of contrast for those structures that lie within the grayscale "window". (Torbjшrn Sund article, this issue)

Working Storage Unit (WSU)
A file server that provides enough capacity and speed to combine the functions of short term and local workstation storage by using disks (magnetic media) operating in parallel. Digital images are stored redundantly so that single bit errors (e.g., a single disk failure) can be detected and corrected without any loss of RIS operations. Total capacity and retrieval bandwidth should be sufficient for peak requests from multiple workstations (CR image equivalent requests per minute).

X.Protocol
A CCITT standard that specifies the interface between the data terminal and packet switching, data circuit, and terminating equipment.

XLR
A circular three-conductor shielded connector commonly used in professional applications for connection of low-level balanced audio signals to and from equipment.

 


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