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Digital Radiography

Digital Radiography Test

QuestionvAnswer
*graphic representation of prevalence of signal vs exposure *horizontal-exposure in mR *vertical-prevalence of signal histogram
scintillator absorbs xrays and re-emits part of energy as visible light
charged couple device (CCD) solid state chip that converts analog information into electronic signal
thin film transistor (TFT) electronic switch to allow charges to be collected at each pixel, directly converted to an image
software function designed to even the brightness (density). light areas are made darker and dark areas lighter *good for tube placement in chest imaging equalization
*artificial increase in contrast at edge of structures *diamond view is the siemens term *also called high pass filtering(convolution) edge enhancement
*software function to reduce the appearance of noise but causes loss of fine detail *also call low pass filtering(convolution) Smoothing
*software that allows RT to place images together if too long for IR *scoliosis pt's *long bone measurement stitchgin
*auto-ranging or normalization *software that adjusts gray scale to values of interest(VOI) in histogram *provides density/brightness at a prescribed level over large range of exposures *check exposure index to make sure you aren't over exposing auto re-scaling
default gradient curve or code applied to the data set of your image determining the initial display contrast *can be adjusted by changing window width or range after initial processing *image data from histogram is rescaled look up table(LUT)
*method to convert data, permits reconstruction of portions of data when other portions and their relationships are known, use inverse fourier transformation to change back data *used to demonstrate different attenuation coefficients *allows default pro fourier tranformation
what are the two attenuation coefficients *LAC-linear attenuated coefficients *MAC-mass attenuated coefficients
window level controls brightness -direct relationship
window width contrast(gray scale)(visibility of detail) -inverse relationship
latent image invisible image after exposure, before processing
halide gives off light when stimulated by xray energy
manifest image visible image on the look up table
phosphor converts xrays to light
*smallest exposure change or signal difference that can be detected *main advantage of DR/CR *linear response contrast resolution
how do you change window level & window width and what do they control *use the sun and moon icon *vertical movement up and down(window level) controls brightness/density.(up for more brightness and down for mor density) *horizontal movement side to side(window width)to control gray scale(left more gray, right less gray)
what is the advantage of high DQE in a detector *higher DQE allows more absorbtion of xrays and allows you to use lower mAs
grid aliasing moire *parallel motion of grid is equal to the frequency of the scanning of the grid by the electronic imaging system *easily caused by using wrong size grid(higher frequency grid for higher kV)
what types of DR scintilators can we use today *cesium iodide(indirect)(CCD) *godolinium oxysulfide(indirect)(CCD or TFT) *amorphous selenium(direct)(TFT)
what are coupling elements *transfers xray signal to collection element using: -lens and mirror or fiber optics
what are the collection elements *photodiode(PSP) *CCD(amorphus silicone) *TFT(amorphus silicone)
what are the different types of DR systems *PSP *CCD *CMOS *flat pannel detector
what are the advantages of electronic imaging vs film imaging *improved contrast resolution *cost savings
amorphus no definate size or shape
exit radiation beam coming from pt and striking the image receptor
photoconductor TFT detectors that convert xray energy directly to e- charge without photodiode(direct capture amorphus sileneum system)
why is collimation important *incorrect collimation can cause histogram error, which can result in image that is too light or too dark *collimation can also reduce the area of exposure *reduces scatter and personell dose *improves contrast *gives a more accurate EXI
fill factor percentage of pixel that is sensitive to x-radiation
DAP(AKA: EXI,EI,REX or S value for CR) *Dose Area Product *pt dose related to volume of tissue irradiated, dependant upon exposure and field size. measured in R-cm squared
cropping cutting out uneeded areas of image, such as white edges of image that were collimated out prior to exposure, without cutting out any anatomy
what is the default tube rating for DR systems 80%
what can cause histogram errors *part not centered *inapropriate collimation *selecting wrong histogram
what is pixel shifting computer shifts pixel back into alignment to compensate for motion
quantum xray photon
Created by: Adrian Dykeman Adrian Dykeman on 2012-02-05



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