This paper examines the use of the Algebraic Reconstruction Technique (ART) and related techniques to reconstruct 3D objects from a relatively sparse set of cone-beam projections. Although ART has been widely used for cone-beam reconstruction of high-contrast objects, e.g. in computed angiography, the work presented here explores the more challenging low-contrast case which represents a little investigated scenario for ART. Preliminary experiments indicate that for cone angles greater than 20, traditional ART produces reconstructions with strong aliasing artifacts. These artifacts are in addition to the usual off-midplane inaccuracies of cone-beam tomography with planar orbits. We find that the source of these artifacts is the non-uniform reconstruction grid sampling and correction by the conebeam rays during the ART projection/backprojection procedure. A new method to compute the weights of the reconstruction matrix is devised which replaces the usual constant-size interpol...

This paper examines the use of the algebraic reconstruction technique (ART) and related techniques to reconstruct 3-D objects from a relatively sparse set of cone-beam projections. Although ART has been widely used for cone-beam reconstruction of high-contrast objects, e.g., in computed angiography, the work presented here explores the more challenging low-contrast case which represents a little-investigated scenario for ART. Preliminary experiments indicate that for cone angles greater than 20 ffiffiffi , traditional ART produces reconstructions with strong aliasing artifacts. These artifacts are in addition to the usual off-midplane inaccuracies of cone-beam tomography with planar orbits. We find that the source of these artifacts is the nonuniform reconstruction grid sampling and correction by the cone-beam rays during the ART projection--backprojection procedure. A new method to compute the weights of the reconstruction matrix is devised, which replaces the usual constant-size in...

Cone-beam computed tomography (CT) is an emerging imaging technology, as it provides all projections needed for three-dimensional (3D) reconstruction in a single spin of the Xray source-detector pair. This facilitates fast, low-dose data acquisition as required for imaging fast moving objects, such as the heart, and intra-operative CT applications. Current cone-beam reconstruction algorithms mainly employ the Filtered-Backprojection (FBP) approach. In this dissertation, a different class of reconstruction algorithms is studied: the algebraic reconstruction methods. Algebraic reconstruction starts from an initial guess for the reconstructed object and then performs a sequence of iterative grid projections and correction backprojections until the reconstruction has converged. Algebraic methods have many advantages over FBP, such as better noise tolerance and better handling of sparse and non-uniformly distributed projection datasets. So far, the main repellant for using algebraic methods...

The prime motivation of this work is to devise techniques that make the Algebraic Reconstruction Technique (ART) and related methods more efficient for routine clinical use, while not compromising their accuracy. In particular, we strive to push the overall cost for a ART reconstruction as close as possible to the theoretical cost for a reconstruction obtained with Filtered Backprojection (FBP). While we focus mostly on fast implementations of ART-type methods in the context of 3D cone-beam reconstruction, different parts of the material presented here is also applicable to speed up reconstruction from fan-beam and parallel-beam data. It was shown in previous research that three iterations are sufficient to obtain a high quality reconstruction for low-contrast cone-beam. Based on the observation that ART typically only requires only half the projections of FBP, we conclude that if the overall cost for ART's projection-backprojection operations could be cut in half, then one ...

This paper examines the use of the Algebraic Reconstruction Method (ART) and related techniques to reconstruct 3D objects from a relatively sparse set of cone-beam projection data. Although ART has been widely used for cone-beam reconstruction of high-contrast objects, e.g. in computed angiography, we are interested in the more challenging low-contrast case which represents a little investigated scenario for ART. Preliminary experiments indicate that for cone angles greater than 20, traditional ART produces reconstructions with strong aliasing artifacts, obliterating much object detail. By analyzing the reconstruction process using signal processing principles it is revealed that the source of these artifacts is the non-uniform reconstruction grid sampling of the cone-beam rays. To eliminate these errors, we devise a new way of computing the weights of the reconstruction matrix. This new method is more adequate for cone-beam and replaces the usual constant-size interpolation...

This study investigates the feasibility and applicability of cone beam CT for a megavoltage therapeutic LINAC. A Rando head phantom was irradiated using the 15 MV beam of a Varian 2100C LINAC at MSKCC for gantry angles from -102 to 102 with a 2 increment. The projection image for each gantry angle was obtained using a Varian Mark II EPID. Reference images without phantom were also collected at different angles. Pixel readings of each image were converted to dose rate using the EPID calibration curve. The ray sum (sum of linear attenuation coefficients along the ray from the source to a pixel) is calculated as the negative logarithm of the ratio of dose rate of that pixel to that of the corresponding pixel in the reference image. The ray sums were then used for volumetric reconstruction using ART. ART is an iterative method that solves a system of linear equations by iteratively updating the volume to reduce the errors between the measured and calculated ray sums. Our results indicate...

The prime motivation of this work is to devise techniques that make the algebraic reconstruction technique (ART) and related methods more efficient for routine clinical use, while not compromising their accuracy. Since most of the computational effort of ART is spent for projection/backprojection operations, we first seek to optimize the projection algorithm. Existing projection algorithms are surveyed and it is found that these algorithms either lack accuracy or speed, or are not suitable for cone-beam reconstruction. We hence devise a new and more accurate extension to the splatting algorithm, a wellknown voxel-driven projection method. We also describe a new three-dimensional (3-D) ray-driven projector that is considerably faster than the voxel-driven projector and, at the same time, more accurate and perfectly suited for the demands of cone beam. We then devise caching schemes for both ART and simultaneous ART (SART), which minimize the number of redundant computations for projecti...