Weighted Backprojection Research Articles

The Effect of Overabundant Projection Directions on 3D Reconstruction Algorithms

The experimental process of collecting images from macromolecules in an electron microscope is such that it does not allow for prior specification of the angular distribution of the projection images. As a consequence, an uneven distribution of projection directions may occur. Concerns have been raised recently about the behavior of 3D reconstruction algorithms for the case of unevenly distributed projections. It has been illustrated on experimental data that in the case of a heavily uneven distribution of projection directions some algorithms tend to elongate the reconstructed volumes along the overloaded direction so much as to make a quantitative biological analysis impossible. In answer to these concerns we have developed a strategy for quantitative comparison and optimization of 3D reconstruction algorithms. We apply this strategy to quantitatively analyze algebraic reconstruction techniques (ART) with blobs, simultaneous iterative reconstruction techniques (SIRT) with voxels, and weighted backprojection (WBP). We show that the elongation artifacts that had been previously reported can be strongly reduced. With our specific choices for the free parameters of the three algorithms, WBP reconstructions tend to be inferior to those obtained with either SIRT or ART and the results obtained with ART are comparable to those with SIRT, but at a very small fraction of the computational cost of SIRT.

Recovery of loss of spatial resolution at depth in planar images

Resolution and contrast recovery in planar nuclear images at depth with a high purity germanium (HPGe) camera has been achieved through use of a weighted back projection (WBP) method. The algorithm is derivable from Bayes' theorem using the point spread function of the camera. Three variations in the formulation of WBP are presented. The characteristics and performance of each method are discussed. Application of WBP is shown to increase spatial resolution and contrast without a concomitant reduction in signal to noise. The algorthm has been applied to the scintillation camera, yielding significant resolution and contrast recovery despite the presence of scatter and textured noise not present in the HPGe images.