Publications (4)1.6 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: The spatial resolution of diagnostic Computed Tomography (CT) has increased substantially, and 3D isotropic sub-millimeter spatial resolution in both axial and helical scan modes is routinely available in the clinic. However, driven by advanced clinical applications, the pursuit for higher spatial resolution and free of aliasing artifacts in diagnostic CT has never stopped. A method to accommodate focal spot wobbling at an arbitrary number of projection views per gantry rotation in CT is presented and evaluated here. The method employs a beta-correction scheme in the row-wise fan-to-parallel rebinning to transform the native cone beam geometry into the cone-parallel geometry under which existing 3D weighted cone beam filtered backprojection algorithms can be utilized for image reconstruction. The experimental evaluation shows that the row-wise fan-to-parallel rebinning with the beta-correction can increase the quantitative in-plane spatial resolution (Modulation Transfer Function) substantially, while the visual spatial resolution can be enhanced significantly. Consequently, the architectural designers of CT scanners are no longer constrained to choosing the number of projection views per rotation determined by gantry geometry. Instead, they can choose the number of projection views per rotation to optimize the trade-offs between in-plane spatial resolution and noise characteristics. Therefore, the presented method is of practical relevance in the architectural design of state-of-the-art diagnostic CT.
- [Show abstract] [Hide abstract] ABSTRACT: With increasing longitudinal detector dimension available in diagnostic volumetric CT, step-and-shoot scan is becoming popular for cardiac imaging. In comparison to helical scan, step-and-shoot scan decouples patient table movement from cardiac gating/triggering, which facilitates the cardiac imaging via multi-sector data acquisition, as well as the administration of inter-cycle heart beat variation (arrhythmia) and radiation dose efficiency. Ideally, a multi-sector data acquisition can improve temporal resolution at a factor the same as the number of sectors (best scenario). In reality, however, the effective temporal resolution is jointly determined by gantry rotation speed and patient heart beat rate, which may significantly lower than the ideal or no improvement (worst scenario). Hence, it is clinically relevant to investigate the behavior of effective temporal resolution in cardiac imaging with multi-sector data acquisition. In this study, a 5-second cine scan of a porcine heart, which cascades 6 porcine cardiac cycles, is acquired. In addition to theoretical analysis and motion phantom study, the clinical consequences due to the effective temporal resolution variation are evaluated qualitative or quantitatively. By employing a 2-sector image reconstruction strategy, a total of 15 (the permutation of P(6, 2)) cases between the best and worst scenarios are studied, providing informative guidance for the design and optimization of CT cardiac imaging in volumetric CT with multi-sector data acquisition.
- [Show abstract] [Hide abstract] ABSTRACT: PURPOSE It has been well aware that there exists over-ranging/over-beaming in helical CT imaging. With increasing longitudinal coverage of the x-ray detector in volumetric CT, the helical over-ranging/over-beaming may increase proportionally if it is not addressed appropriately. A hybrid cone beam (CB) reconstruction solution to reduce such over-ranging/over-beaming significantly and its experimental evaluation are presented here. METHOD AND MATERIALS The helical over-ranging/over-beaming refers to the indention of image zone, i.e., the zone covered by the tomographic images is smaller than the actually irradiated zone. The hybrid CB reconstruction integrates the 3D weighted CB filtered backprojection (FBP) algorithms previously proposed for helical and axial scans, in which the 3D weighting depends on helical pitch and the distance between the reconstruction plane and the central plane (namely z-offset), respectively. In the hybrid CB reconstruction, the 3D weighting becomes dependent on both the helical pitch and z-offset simultaneously. Consequently, the indented image zone can be recovered substantially by dealing with the asymmetric z-truncation in a detector appropriately. The performance of the hybrid CB reconstruction, including its accuracy, noise characteristics and spatial resolution along the longitudinal direction, is evaluated with phantoms and clinical data acquired on a volumetric CT scanner (Lightspeed VCT, GE Healthcare, Waukesha, WI). RESULTS Phantom study shows that 63.5% and 45.5% of the image zone indention can be recovered at helical pitch 63/64:1 and 88/64:1, respectively. An analysis on reconstruction accuracy shows that the images in the extended zone are as good as those within the indented zone, while their other image qualities are quite comparable. In addition, the evaluation by clinical data shows results consistent with the phantom study. CONCLUSION In comparison to other hardware-based methods that may impose challenges in mechanical and temporal accuracy, the hybrid CB reconstruction, a software-based solution, can reduce helical over-ranging/over-beaming significantly. Moreover, it can be combined with the hardware-based approaches to avoid tight mechanical and temporal requirements. CLINICAL RELEVANCE/APPLICATION With increasing detector dimension in volumetric CT for diagnostic imaging, the reduction of over-ranging/over-beaming is of great clinical relevancy to meet the ALARA criteria in helical scans.
- [Show abstract] [Hide abstract] ABSTRACT: A 3D weighting scheme have been proposed previously to reconstruct images at both helical and axial scans in stat-of-the-art volumetric CT scanners for diagnostic imaging. Such a 3D weighting can be implemented in the manner of either ray-driven or pixel-drive, depending on the available computation resources. An experimental study is conducted in this paper to evaluate the difference between the ray-driven and pixel-driven implementations of the 3D weighting from the perspective of image quality, while their computational complexity is analyzed theoretically. Computer simulated data and several phantoms, such as the helical body phantom and humanoid chest phantom, are employed in the experimental study, showing that both the ray-driven and pixel-driven 3D weighting provides superior image quality for diagnostic imaging in clinical applications. With the availability of image reconstruction engine at increasing computational power, it is believed that the pixel-driven 3D weighting will be dominantly employed in state-of-the-art volumetric CT scanners over clinical applications.