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RAD 122-Definitions
| Question | Answer |
|---|---|
| algorithm | step by step procedure or mathematical process for solving a problem or accomplishing a specific task. computer adapted math calculation applied to raw data during image reconstruction |
| Amorphous Selenium - (a-Se) | capture and coupling element for direct DR; xray beam interacts directly w/a-Se producing a charged pair converts x-ray energy to electrical charge (direct photoconductor) |
| Amorphous silicon (a-Si) | Coupling element semiconductor; liquid form of silicon painted onto surface to capture xray photons indirect photoconductor; coupling element for indirect DR |
| histogram | Orth p 295/Papp p264 graphic representation of optimal densities (patient tissues). built by counting pixels w/in image at each brightness level as computer scans. Step by step procedure/math process for solving a problem or accomplishing specific task |
| histogram analysis | computer generates histogram from data in scanned area and compares it to existing histogram for programmed body parts. values vary from part to part and patient to patient Histogram IS the algorithm (set of rules) |
| x axis in histogram represents ? | range of pixel brightness value (range of exposures captured by plate) related to dynamic range and related to contrast resolution |
| y axis in histogram represents? | number of pixels with that brightness value for each exposure frequency or number of pixels counted at that range level (pixel value) |
| LUT (look up table) | Orth p 295 Papp p 164 ALGORITHM-how to select values of interest histogram of luminance values derived from IR values, adjust correct grayscale contrast; lists parameters used to produce ideal histogram for anatomy imaged CONTROLS IMAGE CONTRAST |
| describe x-axis histogram values right to left | left (lower #s) - (whites) represents low pixel #s (absorption) right (higher #s) - (blacks) represents high pixel #s (transmission) she may ask - on this side of histogram, what can conclude about subject contrast? high or low transmission |
| analog | Selman p297 processing data on unfolding events, REAL TIME, IE hands of a clock constantly changing - each time I look it's different vs DIGITAL - indicates time at defined intervals |
| What is purpose of LUT? | change contrast (grayscale, pixel values) to accentuate something in the image goal is to accentuate the tissues for a sharp, clear image |
| Histogram/LUT - how does it work? | image generates; histogram knows what to exclude (collimation (white), outside skin line (blacks)) LUT - applies appropriate contrast for specific exam knows to include from S1 to S2 |
| Automatic rescaling (aka auto ranging, rescaling, scaling, normalization) | process of using algorithms to reprocess image to acceptable diagnostic level |
| Bit | binary digit smallest unit of computer memory that holds 1 of 2 values - 0 or 1 |
| Bit depth (pixel bit depth) | # of bits that determine the precision with which exit radiation is recorded; controls pixel brightness or gray level |
| Brightness | amount of luminance or light emission of a display monitor; the level of bright white of the image displayed on monitor |
| Capture elements (and materials) | The material that captures xray photon In CR, the photostimulable phosphor, BaF In DR, top portion of an active matrix array IR that absorbs remnant radiation Ex: a-Se, CeI, GdOS, NaI |
| Charge Coupled Device (CCD) | solid state device that converts visible light photons to electrons; 2 dimensional electronic array for converting light patterns into electronic signals |
| Collection element | Bottom portion of active matrix array IR that collects the charge and sends it through analog to digital converter into computer to be processed into image may be a photodiode, a CCD, or TFT (thin film transistor) |
| Contrast resolution | ability of system to distinguish structures with similar transmission as separate objects ability of detector to separately image similar tissues/objects with similar subject contrast |
| CNR | contrast to noise ratio ratio between contrast and noise can be used to describe image quality method of describing contrast resolution compared to amount of noise in digital image increased CNR = increased spatial resolution |
| DQE | Detective Quantum Efficiency radiation exposure level required to produce optimal image measurement of efficiency of IR in converting xray exposure to quality image |
| DEL | detector element (dexel, pixel) determines spatial resolution of acquisition medium in FPD; elements in detector may be processed, recombined, resampled or manipulated to produce an image |
| Digital | Discreet sampling processing data at defined intervals |
| DR | digital radiography static images produced with area xray beam intercepted by photostimulable phosphor plate or direct capture solid state device |
| indirect acquisition | 2 steps to convert xrays into image a) xrays to light (phosphor) b) light to electrical signal machine absorbs xrays and converts to light; CCD or TFT converts light to electrical signal; computer processes |
| direct acquisition | X-ray energy is directly converted into electrical signal photoconductor absorbs x-rays; TFT collects and sends to computer |
| DAP | dose area product measurement that incorporates TOTAL dose of radiation along with area of field being used |
| Dynamic Range | CONTRAST RESOLUTION range of gray levels available to construct an image range of values that can be displayed by an imaging system; shades of gray; range of exposures that can be captured by detector |
| Exposure latitude | Range of exposure latitudes to receptor that will produce an acceptable range of densities for diagnostic purposes |
| Europium | PSP plate activator in phosphor layer Capture element in CR absorbs xray photon via photoelectric interaction (ionization) ionized Europium hold electrons until stimulated by reader to release light electrons (will release ie PORTABLES) |
| Exposure Indicator | EI # represents exposure level to image receptor method by which digital radiography estimates exposure on the image detector amount of light given off IR from radiation exposure received (converted to signal used to calculate EI#) |
| Fill factor | % of pixel area that is sensitive to image signal; approximately 80% due to other areas devoted to electronic conductors and thin film transistors |
| FPD | flat panel detector plates used in digital imaging |
| FOV | field of view the size of the monitor (can swell/shrink the pixels which affects spatial resolution) can also refer to anatomy within collimated field |
| Fluorescence | emission of visible light only during stimulation by radiation |
| Helium-neon laser (solid state laser) | inside CR reader - high energy laser beam that scans plate stimulating phosphors (BaF and Europium) to release electrons (light) 2nd fluorescence *photostimulable luminescence* unique to CR |
| Image noise Orth p 272 | deterioration of image Main cause is scatter. Sources quantum noise xray photon absorbed/scattered latent image fading IR noise phosphor structure phosphor crystal size phosphor crystal distribution overcoat, reflection, or base layers |
| Light guide (CR optical system) | located inside the CR reader and guides light from IP to PMT (photomultiplier tube); collects light emitted from IP when it's scanned by laser |
| Log Mean Exposure (LgM) | AGFA logarithmic calculation for exposure level; each .3 is 2x exposure EX 2.0 vs 2.3 calibrated in mGy; values directly related to exposure to IR |
| Luminance | amount of luminous intensity emitted by light source; brightness; expressed as units of candela/sq meter or nits |
| Luminescence | Emission of light from exit radiation, energizing the phosphor crystals occurs via fluorescence/phosphorescence |
| Matrix size | # pixels allocated to each linear dimension (columns/rows) in digital image dependent on FOV and pixel density increased matrix size = increased spatial resolution |
| MTF | modulation transfer function math procedure for measuring resolution; measure of imaging system ability to display contrast of different anatomic structure of various sizes |
| Photodiode | solid-state device that converts light into electronic current |
| Photomultiplier tube (PMT) | device used in radiation detection applications that converts low level of light into electronic pulses |
| Photostimulable phosphor (PSP) | a plate made of several layers that stores x-ray energy as a latent image (not visible to naked eye) for CR BaF and Europium |
| Pixel | picture elements small cells of info make up digital image on computer monitor |
| Pixel density | quantity of pixels per unit area number of pixels/mm in a given area; determined by pixel size and pitch increased pixel density = increased spatial resolution |
| Pixel pitch | pixel spacing or distance measured from center of a pixel to center of adjacent pixel |
| Phosphorescence | BAD delayed emission of light (afterglow or lag) causes image noise; the continuum of light emission after the stimulation ceases |
| Photoconductor | device that absorbs xrays and creates electrical charges in proportion to xray exposure received material that conducts electrons when illuminated |
| Photostimulable luminescence (PSL) | release of trapped energy from trapped electrons by Helium Neon laser during scanning of PSP only happens with BaF and Europium Unique to CR |
| Quantization | process of assigning discrete numerical values to data points in proportion to energy/signal received Orth p 277 |
| Raw data | unprocessed information (no algorithms yet applied) |
| Sensitivity | indicates likelihood of obtaining a positive diagnosis in patient with disease ability of IR to respond to very low levels of light |
| sensitivity number | S# represents exposure level to plate for Fuji, Philips, Konica INVERSELY related to exposure level S# of 200 - 1mRad of exposure to IR |
| Scintillator | a material that exhibits luminescence when excited by xrays, lens then focuses onto detector Cesium Iodide and Gd2O2S are scintillators |
| Spatial Resolution | ability to system to distinguish small adjacent, high contrast structures in the patient The smallest object that can be recorded on image |
| Sampling frequency | rate at which laser extracts image data from IR; Process of selecting data points on continuum at regular time intervals; how often analog signal is reproduced in its discrete digitized form INCREASED sampling frequency = decreased sampling pitch |
| Sampling pitch | the distance between the sampling points increased sampling frequency = decreased sampling pitch = decreased pixel pitch = increased spatial resolution |
| Signal to Noise ratio (SNR) | describes relative contributions to a detected signal of true signal and random superimposed signals or noise method of describing strength of radiation exposure compared to amount of noise apparent in digital image |
| Structured phosphor (needle) | Indirect FPD; columnar phosphor crystals within active layer that funnel directly to a-Si, then converted to light |
| Thin Film Transistor (TFT) | switches for each pixel of array connected to circuitry allows all switches in row to be operated simultaneously the electronic switch that detects electrons in direct radiography FPD |
| Turbid Phosphor | a phosphor layer with random distribution of phosphor crystals within active layer (low spatial resolution) |
| Window width | value in digital image selects width of band of values in digital signal can be represented as gray tones in image range of grays visible on image |
| Window level | value in digital imaging that selects level of displayed band of values within complete range; allows tech to adjust brightness level of image |
| VOI | values of interest Established values within histogram models that determine what part of data set should be incorporated in displayed image determines range of histogram data set included in image |
| Where is algorithm? | Located in computer when you pull up patient requisition - processes digital information for that specific image |
| Screen speed | a term used to describe how much light is obtained from a given xray exposure. Range from 50 (slow and detailed) to 1200 (fast) Standard speed is 100 Controlled by phosphor size, layer thickness, kVp and temperature |
Created by:
Larobbins
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