Digital Radiography and PACS
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| acceptance testing | testing that occurs to ensure equipment or processes are functioning within acceptable limits
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| archive | historical collection of images stored in PACS
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| archive query | software function that allows historical information to be gathered from digital storage, i.e. multiple exams, range of dates, or by pathology
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| aspect ratio | ratio of width of the monitor to the height of the monitor
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| automatic data recognition | processing mode in which computer analyzes data according to set parameters
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| automatic rescaling | occurs when exposure is greater or less than the optimal amount to produce a diagnostic image; it is the effort of the computer to "fix" exposure errors
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| backing layer | soft polymer that protects the back of the cassette
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| barium fluorohalide | photostimulable phosphor located in the imaging plate
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| basic input/output system (BIOS) | contains a simple set of instructions for the computer to perform several basic functions, i.e. boot up, run hardware diagnostics, interpret keyboard signals, and so on
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| central processing unit (CPU) | small chip found on the motherboard that manipulates data sent from a program; brains of the computer
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| cesium iodide scintillator (CsI) | newer type of amorphous silicon detector that uses this; scintillator is made by growing very thin crystalline needles (5 μm wide) that work as light-directing tubes, much like fiberoptics
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| charge-coupled device (CCD) | coupling devices that act as cameras that link phosphor signals to a signal
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| collimation | type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire; shield minimizes electrical and radio frequency interference
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| color layer | area within the conductive layer where electrons are trapped
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| computed radiography (CR) | or cassette-based digital radiography is the digital acquisition modality that uses storage phosphor plates to produce projection images
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| conductive layer | layer of material that will absorb and reduce static electricity
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| continuous quality improvement | alternative set of terms for total QM that includes maintenance of equipment, image acquisition, and processing standards
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| detective quantum efficiency (DQE) | measurement of how efficiently a system converts x-ray input signal into a useful output image
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| detector size | actual physical size, length, and width of x-ray detector
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| digital imaging and communications in medicine (DICOM) | global information technology standard that allows network communication between modality and PACS
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| digital imaging | any imaging acquisition process that produces an electronic image that can be viewed and manipulated on a computer
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| digital radiography (DR) | or cassette-less systems use an x-ray absorber material coupled to a flat panel detector or a charged-coupled device to form the image
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| direct capture digital radiography | these devices convert incident x-ray energy directly into an electrical signal, typically using a photoconductor as x-ray absorber and a thin-film transistor as signal collection area, and send electrical signal to computer for processing and viewing
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| direct conversion | conversion of x-ray energy to electrical signals without the light-conversion step
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| display workstation | generally a display monitor where postprocessing occurs or where images can be viewed
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| distributed system | PACS workflow where acquisition modalities send the images to a designated reading station and possibly review stations
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| dot pitch | measurement of how close the dots are located to one another within a pixel
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| dry imager | printer that uses heat to develop the film
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| edge enhancement | enhancement occurs when fewer pixels in the neighborhood are included in the signal average; the smaller the neighborhood, the greater the enhancement
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| exposure index (EI) | term used by Kodak to express exposure values
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| exposure indicator number | numerical representation of the amount of exposure, usually the mean value
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| field effect transistor (FET) | device within an iamging detector that isolates each pixel element and reacts like a switch to send the electrical charges to the image processor
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| film digitizer | device that scans hard copy x-ray images and converts them to digital images
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| fixed mode | postprocessing mode in which the user selects exposure index: latitude is set by the menu selection; no histogram is generated, and there is no recognition of imaging plate division; resultant image is direct reflection of exposure value
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| flat panel detector | detector that consists of a photoconductor, which holds a charge on its surface that can then be read out by a thin-film transistor
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| focused grid | grid in which the scatter absorbing lead lines are tilted so that at a prescribed distance, the lines will converge
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| grid frequency | number of grid lines per inch
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| grid ratio | ratio of height of grid line to width of interspace material
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| high-pass filtering | technique for enhancement of contrast and edge that amplifies the frequencies of areas of interest that are known and suppresses frequencies outside the area of interest
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| histogram | graphic representation of all of the digitally recorded signals of a digital ex-ray exposure
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| image sampling | amount of information gathered from pixel storage
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| image stitching | process of "sewing" together multiple images to form one continuous image
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| imaging plate | thin piece of plastic with several layers of material that capture and store image data
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| indirect capture digital radiography | devices that convert absorb x-rays & convert them into light; light is then detected by area-charged-coupled device or thin-film transistor array in concert w/photodiodes, & then converted into electrical signal thats sent to comp for processing & viewing
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| indirect conversion | two-step process in which x-ray photos are converted to light and then the light photons are converted to an electrical signal
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| laser | amplification of stimulated emission of radiation, a device that creates and amplifies a narrow, intense beam of coherent light
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| latitude | amount of error that can be made in exposure factor choice and still result in the capture of a quality image
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| logarithm of the median exposure (IgM) | term used by Agfa to express exposure to the imaging plate
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| look-up table (LUT) | reference histogram of luminance values derived during image acquisition
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| low-pass filtering | result of averaging each pixel's frequency with surrounding pixel values to remove high frequency noise; the result is a reduction of noise and contrast; useful for viewing small structures i.e. fine bone
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| matrix | rectangular or square table of numbers that represent the pixel intensity to be displayed on the monitor
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| modulation transfer function | ability of a system to record available spatial frequencies
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| moire | grid line or image noise pattern that occurs when either the alignment of the grid to the laser scan direction is incorrect or when spatial frequency is greater than the Nyquist frequency; a wraparound image will result
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| Nyquist theorem | when sampling a signal such as the conversion from an analog to digital image, the sampling frequency must be greater than twice the bandwidth of input signal so that reconstruction of original image will be nearly perfect
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| picture archival and communications system (PACS) | consists of digital acquisition, display workstations, and storage devices interconnected through a network; networked groups of computers, servers, and archives that can be used to manage digital images
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| phosphor layer | layer of photostimulable phosphor that "traps" electrons during exposure; usually made of phosphors from the barium fluorohalide family
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| photometer | device used to measure the luminescence of areas on the monitor
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| photomultiplier | electronic device that amplifies light energy
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| photostimulable luminescence (PSL) | light produced by a phosphor when stimulated by light or x-ray photons
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| pixel | basic picture element on a display
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| protective layer | very thin, tough, clear plastic covering in the imaging plate for protection of the phosphor layer
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| quality control (QC) | subdivision of QM that focuses on equipment functions
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| quantum mottle | failure of imaging system to record densities usually caused by a lack of x-ray photons
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| quantum noise | recording error in the digital image
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| raster | zigzag electron scanning pattern
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| reflective layer | layer in imaging plate that sends light in a forward direction when released in cassette reader; this may be black to reduce spread of stimulating light and escape of emitted light; some detail is lost in this process
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| refresh rate | measure of how fast the monitor rewrites the screen or the number of times that the image is redrawn on the display each second
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| resolution | number of pixels contained on a display
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| S, sensitivity number | term used by Fuji Medical to express exposure
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| semiautomatic mode | postprocessing mode in which latitude value of histogram is fixed, & only small reading area is used; no collimation detection; proper kV must be used to maintain subject contrast because latitude value does not change
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| shuttering | used to blacken out the white collimation borders in a digital image, effectively eliminating veil glare
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| smoothing | AKA low-pass filtering; result of averaging each pixel's frequency with surrounding pixel values to remove high frequency noise
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| spatial frequency resolution | amount of detail or sharpness in a digital image
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| speed (in conventional radiography) | determined by size and layers of crystals in the film and screen
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| speeds (in CR system) | reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
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| support layer | semirigid material in the imaging plate that gives the imaging sheet some strength
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| thin-film transistor (TFT) | photosensitive array, made up of small (about 100 to 200 μm) pixels, converts light into electrical charges
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| wet imager | printer that uses chemicals to develop the film
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| window | image manipulation parameter that changes screen image brightness usually through the use of a mouse
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