Missing Projection Data Research Articles

A new reconstruction method in the Fourier domain for 3D positron emission tomography

This article describes a new exact 3D reconstruction algorithm dedicated to cylindrical positron emission tomographs that does not require an estimation of missing projection data nor complex 3D interpolation procedures. This algorithm uses the 2D Fast Fourier Transform of non-transaxial projections to place suitable voxel values in the 3D FFT of the radioactive distribution. This leads to a direct fully 3D reconstruction algorithm with a limited amount of computation that requires only 1D interpolation procedures and benefits from redundant projection data to improve the signal to noise ratio in the radioactive distribution. To cite this article: D. Mariano-Goulart, J.-F. Crouzet, C. R. Physique 6 (2005).

Total hip prosthesis metal-artifact suppression using iterative deblurring reconstruction.

CT of total joint prostheses is limited by metal artifact produced mainly by missing projection data. Iterative deblurring reconstruction is less sensitive to missing projection data than filtered backprojection. A software CT simulator was used to compare total hip prosthesis images reconstructed using standard filtered backprojection, filtered backprojection after linear interpolation of missing data, and iterative deblurring. Unilateral and bilateral total hip replacements with metal-backed or all-polyethylene acetabular prostheses were simulated using bone, metal, and polyethylene annuli and circles of metal and water (soft tissue). Material attenuation properties were taken from the literature. The simulation assumed that no X-rays penetrated the metal. Simulated projection data were reconstructed using filtered backprojection, filtered backprojection after linear interpolation of missing data, and iterative deblurring. Visual observations and objective region-of-interest analyses were made. Even with no X-rays penetrating the metal, iterative deblurring produced almost no visible artifact within the bone or soft tissues. Bone edge detection and sizing were more easily and accurately done from the iterative deblurring images. All reconstruction techniques underestimated bone and water CT attenuation values. Metal artifact was worse for the bilateral or metal-backed prostheses. Iterative deblurring generated nearly metal-artifact-free images in this simulation. Filtered backprojection, even after linear interpolation, produced typical clinical metal-artifact images.

Constrained Fourier space method for compensation of missing data in emission computed tomography

A method is introduced to compensate for missing projection data that can result from gas between detectors or from malfunctioning detectors. This method uses constraints in the Fourier domain to estimate the missing data, thus completing the data set so that the filtered backprojection algorithm can be used to reconstruct artifact-free images. The image reconstructed from estimates using this technique and a data set with gaps is nearly indistinguishable from an image reconstructed from a complete data set without gaps, using a simulated brain phantom.

Evaluation of CT techniques for reducing artifacts in the presence of metallic orthopedic implants.

Metallic intramedullary orthopedic implants generate artifacts that can markedly degrade transaxial CT images. The artifacts, typically seen as starburst streaking, result primarily from reconstructions involving missing projection data. Two approaches are clinically available to reduce the artifacts around orthopedic implants. These are (a) the imaging of implants with lower attenuation coefficients or smaller path lengths (less attenuating objects) and (b) the planar reformatting of image data. The sizing accuracy of these two approaches was quantified using phantoms and the efficacy using cadaveric femoral specimens. Results demonstrated that metal artifacts may be reduced and accurate bony dimensional data obtained.

Maximum Entropy Image Reconstruction for an Object with Opaque Obstructions

In the case of image reconstruction from missing projection data such as imaging an object with opaque obstructions, the conventional maximum entropy technique reconstructs a degraded image, which results from missing projection data. In this paper, we propose an improved maximum entropy technique based on a good estimation of missing projection data. Computer simulation using the proposed algorithm shows a significant improvement in image quality and convergence behavior over the conventional algorithms. This algorithm is also applied successfully to ultrasound attenuation CT (computed tomography) using a sponge phantom.

Reduction of CT artifacts caused by metallic implants.

A technique to reduce metallic implant artifacts on computed tomography scans is presented. The implant boundaries are determined semiautomatically; the missing projection data are replaced by linear interpolation. The complete procedure requires 1-2 minutes per scan. Images with greatly improved quality were obtained in the presence of surgical clips and pelvic implants; success is limited in highly structured regions, such as the facial skull.