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Digital Radiography

Digital Radiography: An Introduction Chapter 5 (Euclid Seeram)

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