'Filter' p2 Searchterm 'Filter' found in 3 terms [ • ] and 15 definitions [• ]Result Pages : •
Image quality is an important value of all radiographic imaging procedures. Accurate measures of both image quality and patient radiation risk are needed for effective optimization of diagnostic imaging. Images are acquired for specific purposes, and the result depends on how well this task is performed. The imaging performance is mainly influenced by the imaging procedure, examined object, contrast agents, imaging system, electronic data processing, display, maintenance and the operator. Spatial resolution (sharpness), contrast resolution and sensitivity, artifacts and noise are indicators of image quality.
A high image contrast provides the discrimination between tissues of different densities. The image resolution states the distinct visibility of linear structures, masses and calcifications. Noise and artifacts degrade the image quality. In computed tomography (CT), high spatial resolution improves the visibility of small details, but results in increased noise. Increased noise reduces the low contrast detectability. Noise can be reduced by the use of large voxels, increased radiation dose, or an additional smoothing filter, but this type of filter increases blurring. An image acquisition technique taking these facts into account maximizes the received information content and minimizes the radiation risk or keeps it at a low level. See also As Low As Reasonably Achievable. • View NEWS results for 'Image Quality' (8). Further Reading: Basics:
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Raw data are the values of all measured detector signals during a scan. After calibration for fluctuations in tube output and beam hardening, the attenuation properties of each x-ray signal are accounted and correlated with the ray position. From these data the CT images are reconstructed including the use of mathematical procedures like convolution filtering and back projection.
Raw data can also be used for later reconstruction of additional planes and images by using a different convolution filter, zoom reconstruction, or an alternative CT number scale. See also Magnification, Archiving, Number of Measurements and Convolution. • • •
A computed tomography (CT) scanner is used to create cross-sectional
slices of different objects. The medical version of CT system scans the human body for tumors or other abnormalities, other versions are used for non-destructive testing in the industry. The CT imaging system includes the moveable gantry and patient table or couch. The gantry is a frame that contains the x-ray source, collimators, filters, detectors, a data acquisition system (DAS), rotational components including slip ring systems and all associated electronics. The x-ray tube and detector system are mounted opposite each other, allowing a rapid and synchronous rotation around the patient table. In older CT scanners a small generator supplied power to the x-ray tube and the rotational components via cables for operation. Up to the 4th generation the CT tube and detectors rotate together around the patient for each slice. CT systems with slip ring technology (the x-ray tube rotates around a stationary ring of detectors) operate without cables and provides continuous rotation of the gantry components without interference of cables. Spiral CT scanners work with a continuous table movement while the x-ray tube is rotating around the patient. Overview about CT scanner generations:
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1st generation has a pencil beam and one detector;
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2nd generation has a narrow fan beam and multiple detectors;
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3rd generation has a wide fan beam;;
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4th generation is equipped with a detector ring;
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6th generation is the helical (or spiral) CT scanner;
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7th generation is the multi-detector row CT.
See also Contrast Media Injector, Dual-Head CT Power Injector, Syringeless CT Power Injector. Further Reading: News & More:
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