Glossary

Analog signal ?€“ a form of information transmission in which the signal varies in a continuous manner and is not limited to discrete steps.

Archive ?€“ a repository for digital medical images in a PACS, typically with a specific purpose of providing either short-term or long-term (permanent) storage of images. Erasable or nonerasable media may be utilized in an archive.

Bandwidth ?€“ (the width of a band of electromagnetic frequencies) is used to mean how fast data flows on a given transmission path

Baud ?€“ the number of events processed in 1 second, usually expressed in kilobits per second (kbps). Typical rates are 14.4 kbps, 28.8 kbps, and 56 kbps.

Bit (Binary digit) ?€“ the smallest piece of digital information that a computing device handles. It represents off or on (0 or 1). All data in computing devices are processed as bits or strings of bits.

Bit depth ?€“ the number of bits used to encode each pixel of the image.

Bits per second ?€“ see Throughput, Baud.

Byte ?€“ a grouping of 8 bits used to represent a character or value.

Carrier ?€“ see Data carrier.

CCD (charge-coupled device) ?€“ a photoelectric device that converts light information into electronic information. CCDs are commonly used in television cameras and image scanners and consist of an array of sensors that collect and store light as a buildup of electrical charge. The resulting electrical signal can be converted into digital values and processed digitally in a computer to form an image.

CCD scanner ?€“ a device that uses a CCD sensor to convert film images into electronic data.

Clock ?€“ a component in a computers processor that supplies an oscillating signal used for timing, command execution and information handling.

Clock speed ?€“ the rate at which the clock oscillates or cycles. Clock speed is expressed in MHz, equal to 1 million clock cycles per second.

Compression ratio ?€“ the ratio of the number of bits in an original image to that in a compressed version of that image. For example, a compression ratio of 2:1 would correspond to a compressed image with one-half the number of bits of the original.

Consultation system ?€“ a teleradiology system used to determine the completeness of examinations, to discuss findings with other physicians, or for other applications with the knowledge that the original images will serve as the basis for the final official interpretation rendered at some later time by the physician responsible for that report.

Co-processor ?€“ a device in a computer to which specialized processing operations are delegated, such as mathematical computation or video display. The advantage of a co-processor is that it significantly increases processing speed.

CPU (central processing unit) ?€“ the device in a computer that performs the calculations. It executes instructions (the program) and performs operations on data.

CR (computed radiography) ?€“ a system that uses a storage phosphor plate contained in a cassette instead of a film-screen cassette. A laser beam scans the exposed plate to produce the digital data that is then converted into an image.

CRT (cathode ray tube) ?€“ refers to the monitor or display device in the teleradiology system.

Data carrier ?€“ the signal that is used to transmit the data. If this signal is not present, there can be no data communication between modems.

Data communication ?€“ all forms of computer information exchange. Data communication may take place between two computers in the same building via a local area network (LAN), across the country via telephone, or around the world via satellite.

Data compression ?€“ methods to reduce the data volume by encoding it in a more efficient manner, thus reducing the image processing and transmission times and storage space required. These methods may be reversible or irreversible.

Data transfer rate ?€“ the speed at which information is transferred between devices, such as a scanner and a computer; between components within a device such as between storage and memory in a computer; or between teleradiology stations.

Dedicated line ?€“ a telephone line that is reserved for the exclusive use of one customer. It can be used 24 hours a day and usually offers better quality than a standard dial-up telephone line but may not significantly increase the performance of data communication.

DICOM (Digital Imaging and Communications in Medicine) ?€“ a standard for interconnection of medical digital imaging devices, developed and sponsored by the American College of Radiology and the National Electrical Manufacturers Association.

Digital signal ?€“ a form of information transmission in which the signal varies in discrete steps, not in a continuous manner.

Digitize ?€“ the process by which analog (continuous value) information is converted into digital (discrete value) information. This process is a necessary function for computer imaging applications because visual information is inherently in analog format and most computers use only digital information.

Direct image capture ?€“ the capture or acquisition of digital image data that has been acquired in digital format by an imaging modality. The image produced from the data, regardless of the modality that produced it, (CT, MRI, CR, US) is identical to the original.

Dpi (dots per inch) ?€“ while in conventional radiography resolution is commonly expressed in line pairs per millimeter (lp/mm), film digitizer resolution is commonly expressed as dots (pixels) per inch.

Dynamic range ?€“ the ability of a communication or imaging system to transmit or reproduce a range of information or brightness value.

File ?€“ a set of digital data that have a common purpose, such as an image, a program, or a database.

Floppy diskette ?€“ a data storage device made of metal-coated plastic that can store computer information and can be physically transported from one place to another. The storage capacity of floppy diskettes is usually in the range of 360 K to 1.5 MB, which is too small to be of use in imaging applications.

Floppy diskette drive ?€“ the device on a computer that can read and write to floppy diskettes. It is used to import and export data.

G (giga) ?€“ stands for the number 1 billion. It is used primarily when referring to computer storage capacities; for example, 1 GB = 1 billion bytes or 1000 megabytes.

Gray scale ?€“ the number of different shades of levels of gray that can be stored and displayed by a computer system. The number of gray levels is directly related to the number of bits used in each pixel: 6 bit = 64 gray levels, 7 bits = 128 gray levels, 8 bits = 256 gray levels, 10 bits = 1024 gray levels, and 12 bits = 4096 gray levels.

Hard disk drive ?€“ an internal computer device that is used for storage of data.

Hardware ?€“ a collective term used to describe the physical components that form a computer. The monitor, CPU, disk drives, memory, modem, and other components are all considered hardware. If you can touch it, it is hardware.

HIS (hospital information system) ?€“ an integrated computer-based system to store and retrieve patient information, including laboratory and radiology reports.

IDE (integrated device electronics) ?€“ a type of interface used for hard disk drives that integrates the control electronics for the interface on the drive itself. Its purpose is to increase the speed at which information can be transferred between the hard disk and the rest of the computer.

Image ?€“ a computers digital representation of a physical object.

Image compression ?€“ reduction of the amount of data required to represent an image. This is accomplished by encoding the spatial and contrast information more efficiently or discarding some non-essential information or both.

Interface ?€“ the connection between two computers or parts of computers. It consists mainly of electronic circuitry.

Irreversible compression ?€“ some permanent alteration of digital image data. This is sometimes referred to as lossy.

ISDN (integrated services digital network) ?€“ a switched network with end-to-end digital connection enabling copper wiring to perform functions such as high-speed transmission, which frequently requires higher capacity fiber optic cable.

K (kilo) ?€“ stands for the number 1000. It is used primarily when referring to computer storage and memory capacities: for example, 1 kbps = 1024 bytes.

LAN (local area network) ?€“ computers in a limited area linked by cables that allow the exchange of data.

Laser film scanner ?€“ a device that uses a laser beam to convert an image on X-ray into digital image data.

Leased line ?€“ same as a dedicated line.

Login - a method for authenticating a user's identity with a system before provided access to it

Lossless ?€“ see reversible compression.

Lossy ?€“ see irreversible compression.

M (mega) ?€“ stands for the number 1 million. It is used primarily when referring to computer storage and memory capacities: for example, 1 MB = 1 million bytes. 1 MB = 1024 thousand bytes or 1000 kbytes.

Matrix size:
Small ?€“ defined as images from CT, MR, ultrasound, nuclear medicine, and digital fluorography.
Large ?€“ defined as images from computed radiography and digitized radiographic films.

Memory ?€“ electronic circuitry within a computer that stores information.

Modem ?€“ a device that converts digital signals from a computer to pulse tone signals for transmission over telephone lines.

Monochrome monitor ?€“ a computer display in which an image is presented as different shades of gray from black to white. (see also gray-scale monitor)

Mouse ?€“ an input device that allows the computer user to point to objects on the screen and execute commands.

NIC - a Network Interface Card is an expansion board inserted into a computer so the computer can be connected to a network.

Operating system ?€“ software that allocates and manages the resources available within a computer system. UNIX, MS-DOS, Macintosh, and Windows are examples of operating systems.

Optical disk ?€“ a computer data storage disk used primarily for large amounts (GB) of data.

PACS ?€“ Picture Archiving and Communication System.

Peripheral ?€“ a device that is connected to a computer and performs a function. Scanners, mouse pointers, printers, keyboards, and monitors are examples of peripherals.

Phosphor ?€“ the coating on the inside of a CRT or monitor that produces light when it is struck by an electron beam.

Pixel (picture element) ?€“ the smallest piece of information that can be displayed on a CRT. It is represented by a numerical code within the computer and displayed on the monitor as a dot of a specific color or intensity. An image is composed of a large array of pixels of differing intensities or colors.

Protocol ?€“ a set of guidelines by which two different computer devices communicate with each other.

RAM (random access memory) ?€“ a type of temporary memory in a computer in which programs are run, images are processed, and information is stored. The amount of RAM that a computer requires varies widely depending on the specific application. Information stored in RAM is lost when the power is shut off.

Resolution ?€“ the ability of an imaging system to differentiate between objects.

Reversible compression ?€“ no alteration of original image information upon reconstruction. This is sometimes referred to as lossless.

RIS ?€“ Radiology Information System.

Roam and zoom ?€“ the ability to select and magnify a region in the display.

ROM (read only memory) ?€“ a permanent memory which is an integral part of the computer. Programs and information stored in ROM are not lost when the power is removed.

SCSI (small computer systems interface) ?€“ SCSI is an interface protocol that is used to link dissimilar computer devices so that they can exchange data. SCSI interfaces are most common in image scanners and mass storage devices. This type of interface is well suited for imaging applications.

Secondary image capture ?€“ the capture in digital format of image data that originally existed in another primary format (e.g., a digital image data file on a CT scanner, or a screen-film radiographic film) through the process of video capture or film digitization.

Software ?€“ a name given to the programs or sets of programs that are executed on a computer.

Tera (T) ?€“ stands for approximately 1 trillion. It is used primarily when referring to archive storage capabilities; for example, 1 TB = 1 trillion bytes, 1 million MB, or 1000 GB.

Thin client - a computer (client) in client-server architecture networks which depends primarily on the central server for processing activities. The word "thin" refers to the small boot image which such clients typically require.

Thick or fat client - a computer (client) in client-server architecture networks which does as much processing as possible and passes only data required for communications and archival storage to the server.

Throughput ?€“ a measure of the amount of data that is actually being communicated, expressed in bits per second. It is related to the baud rate, but is usually somewhat less in value due to non-ideal circumstances. Typically, modems with higher baud rates can attain a higher throughput.

Video capture ?€“ the process by which images are digitized directly from the video display console of a modality, such as CT, MRI, or ultrasound. The video signal is converted to a digital signal. This process is more efficient and produces better quality images than scanning films that are produced by the same equipment.

Voxel (volume element, derived from pixel) ?€“ a voxel is, as the name would imply, a three-dimensional version of a pixel. Voxels are generated by computer-based imaging systems, such as CT and MRI. Using voxels, three-dimensional simulations of objects can be reconstructed by imaging systems.

WAN (wide area network) ?€“ a communication system that extends over large distances (covering more than a metropolitan area), often employing multiple communication link technologies such as copper wire, coaxial cable, and fiber optic links. The cost of these WANs is presently dominated by transmission costs.

WORM (write once read many times) ?€“ a peripheral memory device that stores information permanently.