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Imaging 2 - digital

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show After X-ray exposure, latent image is formed, Laser beam extracts image information signal, Signal is digitized and sent to a computer for preprocessing.  
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Two categories of flat panel DR detectors:   show
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Indirect and direct are based on the type of x-ray absorber used, what do each use?   show
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Systems that use phosphor (indirect detectors) and systems that use photoconductors (direct) differ by converting x-rays to electrical how?   show
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show charged coupling device (CCD) digital detector, and the flat-panel thin film transistor (TFT) digital detector. (difference between them is technical factors on how to convert light to electrical)  
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CCD digital detector is based on an _____ conversion process and uses a _______ to convert light to electrical signal.   show
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Which detector is not classified as a flat-panel digital detector but is available commercially?   show
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4 main components of a CCD detector?   show
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show captures the light, and is also an electrical charge readout device.  
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Scintillator screen does what in CCD detectors? ****   show
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An indirect flat-panel (TFT) digital detector uses several components to convert x-rays into light that is subsequently converted into electrical charges, these components are:   show
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show cesium iodide (Csl) or gradolinium oxysulfide (Gd2O2S)  
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(indirect flat panel (TFT) detectors) ______ crystals are deposited in a needle like fashion (_______ phosphor) and run in the direction of the x-ray beam.   show
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show gradolinium oxysulfide crystals, (turbid phosphors)  
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Csi crystals (______ phosphor). Gradolinium oxysulfide (_____ phosphor).   show
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show X-ray detection of CR is inefficient and this affects image quality and dose, Spatial resolution of CR is less than FS radiography. CR IPs can easily be damaged. CR IPs must be transported to a separate image processor for image data extraction  
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(flat panel DR) Selenium drum technology developed specifically for:   show
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CCD indirect digital detector order:   show
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CCD. Silicon chip is made of millions of pixels forming a matrix array of pixels. Light from the _____ falls upon each pixel to produce __________ (charges) in direct proportion to the amount of light falling upon them.   show
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CCD. Bucket brigade?   show
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CCD. What happens after the bucket brigade?   show
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show powdered. (this is why structured phosphor like Csi crystals are better)  
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show thin-film transistor  
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Indirect flat panel TFT detectors: following the x-ray scintillator (x-ray detection medium) is what?   show
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Indirect flat panel TFT detectors: a-Si photodiode layer is for what?   show
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show collect and store the electrical charge produced in the a-Si photodiode array.  
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show scintillator phosphor such as CsI, a-Se photoconductor to convert x-rays directly  
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Indirect TFT: the purpose of the a-Si photodiode layer is ?   show
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show To collect and store the electrical charge produced in the a-Si photodiode array.  
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show amorphous selenium (a-Se)  
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Direct TFT: the photoconductor (a-Se) does what?   show
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show consists of rows and columns that play a role in addressing and readout of the signal from each pixel.  
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Flat panel TFT: each pixel contains what 3 things?   show
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The sensing area (in each pixel of a TFT) will detect the light from the CsI scintillator in the indirect TFT detector, or in the case of a direct TFT, ______________.   show
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The sensing/storage element (of a pixel...) of an indirect TFT detector is the _________, and it is the ____________ in the direct TFT that uses the a-Se photoconductor.   show
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show sensing area  
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show defined as the ratio of sensing area of the pixel to the area of the pixel itself  
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Fill factor is expressed how?   show
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show spatial resolution and contrast resolution (detail and signal-to-noise)  
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Detectors with ____ fill factors (____ sensing areas) will provide better spatial and contrast resolution.   show
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Indirect TFT detectors use a light sensitive ___________ to capture light from the scintillator phophor (such as CsI) to produce _________. Direct TFT detectors use an a-Se ___________ to convert the x-rays _________.   show
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x-ray attenuation depends on what 3 factors?   show
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show CsI and Gd2O2S (gradolinium)  
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General operating principles/steps of indirect TFT?   show
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General operating principles/steps of direct TFT?   show
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Before the flat panel detector can be used, it must be prepared. This is referred to as __________.   show
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What is exposure latitude?   show
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EI does or does not represent an equivalent for patient dose entrance exposure?   show
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show "for processing" image.  
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show post processing, "for presentation" image.  
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____ processing improves contrast/appearance for the radiologist.   show
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Image obtained initially from the detector is referred to as what?   show
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You base scaling the histogram on what?   show
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Third step in image processing is ___________, where the adjusted or scaled raw data values are mapped to the "for presentation" values to display an optimum image.   show
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"processing optimization rules" are what   show
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show spatial resolution  
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show bar test pattern, sharp-edged object, narrow slit.  
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What is the modulation transfer function? ***   show
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show 1  
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High frequencies contain _____, low frequencies contain ______.   show
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show better  
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show contrast resolution  
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Dynamic range of a digital detector is what   show
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What is DQE?   show
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It is important to have low or high SNR?   show
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show DQE= SNR 2out / SNR 2in  
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A perfect digital detector would have a DQE of __.   show
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As the spatial frequencies increase, the DQE ______   show
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show memory effect  
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show the persistance of the image, that is, charge is still being produced after the radiation beam from the tube has been turned off.  
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