In each blank, try to type in the
word that is missing. If you've
typed in the correct word, the
blank will turn green.
If your not sure what answer should be entered, press the space bar and the next missing letter will be displayed. When you are all done, you should look back over all your answers and review the ones in red. These ones in red are the ones which you needed help on. Question: silicon (a-Si)Answer: the devel. of a-si materials,have the same structure as single crystals over short distances but are less ordered over larger distances, has enabled fabrication of flat-panel TFT arrays large enough to be used as the basis for all flat panel XR Question: Amorphous (a-Se)Answer: Amorphous selenium layers have the same structure as single crystals over short distance, but are less over larger distances. As a result, amorphous selenium layers provide uniform x-ray detection over the large areas needed by flat-panel x-ray de Question: Automatic rescaling (Auto ranging, , scaling, normalization)Answer: software function maps the gray-scale to the values of interest (VOI) in the histogram. This feature provides image brightness that is at a prescribed level over a large range of exposure. With some digital systems the image brightness will be Question: Bit Answer: the available for image acquisition and display. Bit depth is equal to 2n, where 'n' is the number of bits. Bit depth cannot be changed after equipment is purchased and is a vendor-specific system characteristic (i.e., 8 bits = 256 shades of gra Question: Complimentary -oxide semi-conductor (CMOS)Answer: a photgraphic detector. None are in use for intraoral dental imaging. Question: resolutionAnswer: the exposure change (signal difference) that can be captured by a detector. Ultimately, contrast resolution is limited by the dynamic range and the quantization (number of bits per pixel) of the detector. Increased contrast resolution is consider Question: quantum efficiency (DQE)Answer: an indicator of the "speed class" or dose level required to acquire an optimal image. The DQE performance is obtained by comparing the image noise of a detector with that expected for an "ideal" detecor having the same signal-response characteri Question: detector size or of view (FOV)Answer: the detector size and FOV describe the useful image acquisition area of an imaging device. Cassette-less digital systems have a fixed OV which makes some projections difficult, while cassette-based CR have flexible FOVs like screen/film. Question: Detector (DEL)Answer: the detector element is the smallest resolvable area in a TFT- or CCD-based imaging device Question: Dynamic Answer: the range of exposure over which a detector can acquire image data. Digital image acquisition systems are capable of capturing an image across a much larger range of exposures than film-screen. The dynamic range allows more anatomical structures Question: exposure Answer: the range of receptor exposures that provides a quality, low-noise imageat an appropriate patient exposure consistent with ALARA. Exposure latitude is not the exposure range which will be to consistent image brightness. Question: Answer: a data set, in a graphical form, of the digital values vs. the prevalence number of those values inthe image. The horizontal axis represents pixel exposure, the vertical axis represents incidence of those values. The software has histogram models fo Question: noiseAnswer: all images have unwanted fluctuations in brightness that are unrelated to the object being imaged. These are collectively described as noise. Question: look up (LUT)Answer: the default gradient curve applied to the data set of your image determining the intial display . The LUT can be adjusted after the initial image processing has been applied. Question: sizeAnswer: the matrix size is the number of pixels that make up the image; this is normally expressed in terms of the number of pixels in two orthogonal directions (length and width of the image). The matrix size is on VOV and pixel size. Question: modulation transfer (MTF)Answer: a of the ability of the imaging system to preserve signal contrast as a function of the spatial resolution. every image can be described in terms of the amount of energy for each of its spatia frequency components. Question: Nyquist Answer: the highest spatial frequency that can be recorded by a digital detector. Determined by the pixel pitch. The pixel pitch is determined by sampling frequency for cassette-based PSP and by DEL spacing for TFT flat panel. half the # of pixels/mm Question: photodiodeAnswer: an electronic element that converts light into charge. With indirect TFT detectrs this is accomplished by a -sensitive amorphous silicon photodiode on top of the TFT array. Question: photoconductorAnswer: amorphous selenium TFT detectors, the a-Se layer forms a continuous x-ray-sensitive photoconductor that x-ray energy directly to charge. This charge can be directly "read out" by the TFT array. A photodiode is not necessary with a-Se detectors. Question: Answer: a "picture element", or pixel, the smallest area represented in a image. A digital radiography image consists of a matrix of pixels, which is typically several thousand pixels in each direction Question: pixel Answer: a term that describes the number of pixels/mm in an image. pixel density is determined by the pitch. Question: pitchAnswer: the space from the center of a to the center of the adjacent pixel. It is measured in microns (um). Pixel pitch is determined by the DEL size or the sampling frequency. Question: processing Answer: the mathematical codes used by the software to the image appearance desired by the viewer. The processing algorithm includes gradient processing (brightness and contrast), frequency processing (edge enhancement and smoothing), and others Question: Answer: all xray digital receptors respond smoothly and continuously to the incident exposure. Digital images require each pixel to be a unique value (quantized), so that a unique gray shade is assigned to that pixel. Question: sampling Answer: the frequency that a data sample is acquired from the exposed detector. Sampling frequency is in pixel pitch and pixels per mm. may be determined by receptor size, depending on the vendor. As receptor size dec., samp freq ^, spat res ^ Question: Answer: a that absorbs x-ray energy and re-emits part of that energy as visible light. Indirect TFT flat panel detectors use a scintillator. 2 modern high-eff x-ray scintillators are cesium iodide & gadolinim oxysulfide. Question: signal to noise (SNR)Answer: noise, especially noise, ultimately limits our ability to see an object's edge (signal difference); SNR can be used to describe the edge conspicuity of a particular obj. under well defined exposure conditions. Question: resolutionAnswer: a characteristic of the imaging system. Max spat. res. (Nyquist freq-line pairs per mm)is equal to half the of pixel/mm. Spa res depends on the sampling freq for cassette-based systems & the detector element size for cassette less Question: structured (needle) Answer: a phosphor layer with columnar phosphor crystals within the active layer. Resembles needles lined up on end and together. Question: thin film (TFT)Answer: an electronic switch on flat panel detectors commonly made of amorphous silicon. The TFT allows the charge collected at each to be independently transferred to external electronics, where it is amplified and quantized. Question: Answer: a prcess several flat panel detectors are joined to obtain one larger detector. Tiling results in segments tha have unequal response requiring flat-field correction for flat panel detectors. Question: turbid Answer: a phosphor layer with a random distribution of phosphor crystals within the active . this layer can be used in both cassette-based and cassette-less systems and is similar to a standard intensifying screen used with film. |
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