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Analytical reconstruction algorithms
Published in Daniele Panetta, Niccoló Camarlinghi, 3D Image Reconstruction for CT and PET, 2020
Daniele Panetta, Niccoló Camarlinghi
Exact 3D CT reconstruction has limited application in real-world CBCT imaging. The most used source trajectory for most CT and micro-CT scanners is a circle, which does not fulfill the Tuy-Smith sufficiency condition. Several scanning trajectories have been evaluated by investigators in order to handle the data incompleteness, such as perpendicular circles or circles plus lines (Kudo and Saito 1994 [18]), a circle plus arc (Wang 1999 [37]), or a helix with constant or variable pitch and radius (Katsevich 2004 [16]). Among them, only the circle and helix with constant pitch and radius have found significant applications. Even though the helical cone beam scan is performed on modern multi-slice CT (MSCT) scanners the computational burden of exact algorithms is still an issue. Hence, approximate algorithms are by far most used rather than exact ones for practical cone beam reconstruction. The most widespread method for approximate cone beam reconstruction was derived by Feldkamp, Davis and Kress (Feldkamp 1984 [6]) and is described in this section.
Cardiovascular PET-CT
Published in Yi-Hwa Liu, Albert J. Sinusas, Hybrid Imaging in Cardiovascular Medicine, 2017
Etienne Croteau, Ran Klein, Jennifer M. Renaud, Manuja Premaratne, Robert A. Dekemp
Fan-beam image reconstructions has been successfully employed for decades on single-slice CT and scanners with few slices, where the x-ray beam can be assumed to be thin in the axial direction. However, with multislice CT (>four slices) with large axial coverage, the x-ray beam covers a conical volume in order to illuminate all the detectors. Off-center objects are projected onto different rings as the gantry is rotated, and therefore, standard 2D reconstruction produces artifacts (Kalender 2005). Specialized cone-beam reconstruction is required for cone-beam geometries; typically, these algorithms “rebin” the projection data into parallel off-axis slices before employing fast 2D reconstruction algorithms to generate slice images.
Polymer Gel Dosimetry
Published in Ben Mijnheer, Clinical 3D Dosimetry in Modern Radiation Therapy, 2017
A faster optical CT scanner makes use of a charge-coupled device (CCD) camera that records entire images for each angular increment of the phantom instead of transmission line profiles in the optical laser scanner (Figure 5.4c and d). In this cone-beam optical CT scanner (Wolodzko et al., 1999), the dosimeter phantom is placed between a diffuse light source and a pinhole camera. The pinhole camera receives the transmitted light from a cone. CT images are reconstructed using a cone-beam reconstruction algorithm. With the cone-beam optical CT scanner, an entire 3D volume can be scanned in less than 10 min. The cone-beam image reconstruction is in the order of a few minutes on a modern PC but has currently been sped up by use of parallel computing (graphics processor unit [GPU]—CUDA). A cone-beam optical scanner has been marketed by the company Modus Medical Devices (London, Ontario, Canada) under the name “Vista scanner.”
Diagnostic imaging in infective endocarditis: a contemporary perspective
Published in Expert Review of Anti-infective Therapy, 2020
Natalia E. Castillo Almeida, Pooja Gurram, Zerelda Esquer Garrigos, Maryam Mahmood, Larry M. Baddour, M. Rizwan Sohail
In one cohort of patients with native valve IE, the sensitivity and specificity of MDCT were 97% and 88%, respectively [9]. The sensitivity and specificity of MDCT were also high for the detection of vegetations and perivalvular extension of infection in this investigation [9]. MDCT includes ECG gating to eliminate movement artifact during the cardiac cycle. In patients with irregular heart rhythms and tachycardia in which the cardiac cycle is variable, image acquisition may be more challenging [6]. The potential risk of iodine contrast exposure may limit the use of CT in patients with underlying renal dysfunction. Radiation is also a concern, but radiation doses of prospective gating MDCT are significantly lower than that of retrospective ECG-gate helical scan [9,26]. Retrospective gating uses the backward-looking measurement of R wave timing, spiral scanning during table motion, and a more traditional cone-beam reconstruction. The x-ray beam is turned on throughout the R-R interval, thus using higher radiation doses [27]. In contrast, prospective gating MDCT scans use forward-looking prediction of R wave timing, step-and-shoot acquisition with no table motion during imaging, and a different cone-beam reconstruction [28]. The x-ray beam turns on for only a small portion of diastole and turns off during the rest of the R-R cycle with lower radiation doses that are equivalent to a routine chest CT.