Digital Radiography: An Introduction Chapter 5 (Euclid Seeram)
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| Indirect Detector | A system that uses phosphors to convert x-ray energy into an electrical signal through an intermediate stage that utilizes light photons.
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| Direct Detector | A system that uses photoconductors to convert x-ray energy directly into electrical charge without the intermediate stage.
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| Amorphous Silicon | An Indirect detector has a layer of ______.
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| Selenium | A direct detector converts x-ray to electrical signal with amorphous _____.
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| CCD Chip | The CCD digital detector is based on an indirect conversion process and uses a ____ to convert light to electrical charge.
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| Scintillation Screen | The ______ detects x-rays and converts them into light.
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| Cesium Iodide, Gradolinium oxysulfide | The x-ray scintillation layer used in the direct flat-panel digital detector is usually either _____ ______ or _________ _______.
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| Structured Phosphor/Scintillator | Cesium Iodide crystals are arranged in a needle-like fashion and run in the direction of the x-ray beam.
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| Turbid Powdered Unstructured Phosphor | Gradolinium oxysulfide crystals are deposited as powdered particles in the photodiode array.
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| Turbid Powdered Phosphor | Which type of phosphor or scintillation screen causes lateral spreading of light and decreases the spatial resolution of the image?
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| Photodiode layer | The purpose of a a-Si ______ ______ is to convert the light from the x-ray detection scintillator into electrical charges.
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| Photoconductor | The ______ in a direct digital detector system converts the x-ray to an electrical signal.
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| Thin Film Transistor | An array for readout of electrical charges generated by the photodiode layer in an indirect detector system, or by the storage capacitor from the photoconductor of the direct detector system.
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| Photodiode | The sensing/storage element of an indirect flat-panel TFT detector is the _______.
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| Storage Capacitor | The sensing/storage element of a direct flat-panel TFT detector is the _____ ________ in the photoconductor.
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| Fill Factor | The ratio of sensing area of the pixel to the area of the pixel itself.
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| high | Detectors with ____ fill factors will provide better spatial and contrast resolutions.
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| light optics | The _____ ______ in a CCD digital detector system reduces the output image from the scintillator phosphor to the size of the CCD array thereby reducing the image quality.
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| Signal noise ratio | The light optics reduces the image quality by reducing the ______to_____ _____.
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| photodiode | Indirect detectors use a light-sensitive __________ to capture light and then produce electrical charges.
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| photoconductor | The direct detectors use a a-Se ____________ to convert x-ray energy directly into electrical charges.
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| amorphous selenium | X-ray scintillators are CsI and Gradolinium oxysulfide for indirect flat-panel TFT detectors and a _______ for direct flat-panel TFT detectors.
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| Exposure latitude | The response of the image receptor to the radiation falling upon it.
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| wider | The exposure latitude for digital detectors is much _____ compared to the film-screen receptors.
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| Flat fielding | A pre-processing technique properly referred to as system calibration that ensures detector performance integrity by removing artifacts.
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| size | The spatial resolution depends on the ____ of the pixels in the matrix.
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| Spatial Resolution | The ability of an imaging system to resolve fine details present in an object. It's also referred to as the sharpness of the image.
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| Modulation Transfer Function | A mathematical function that measures the ability of a detector to transfer its spatial resolution characteristics to the image.
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| one | An MTF of __ represents a perfect detector.
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| decreases | As spatial frequency increases, the MTF _______.
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| one | A perfect digital detector would have a DQE of __.
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| Image lag | also known as memory effect;The persistence of an image in a flat-panel detector due to charge still being produced after the x-ray radiation beam has been turned off
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| dynamic range | The response of a detector to different levels of radiation exposure.
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| Pre-processing | ____________ operations deal with applying corrections to the raw data.
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| Post-processing | _____________ operations address the appearance of the image displayed on a monitor for viewing and interpretation by a radiologist.
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| detector elements | The flat-panel TFT digital detector is designed as a matrix of ______ _______.
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| ______ ________ involves the digital subtraction of images in time. A pre-contrast image(mask image) and post contrast images are digitally subtracted from the mask image. | Temporal subtraction
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| The _____ _______ operation is based on subtraction of images taken at different kVps. | energy subtraction
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