Spectral effects on three-dimensional reconstruction from x rays

Abstract

Continuous bremsstrahlung spectra were calculated for 120 kVp for constant and sinusoidal potentials. Fluorescent radiation for the tungsten target was added to the bremsstrahlung, and the spectra were attenuated through various filter materials. A drawing of an object to be scanned was divided into an array of small squares in which the composition was assumed to be constant. Transmission data for 120 rays at each of 120 angles spanning a range of 180 degrees were calculated. Two algorithms for the reconstruction of attenuation coefficients from projection data, an algebraic reconstruction technique (ART) and the convolution method, were utilized to reconstruct effective coefficients. The effect of spectral filtration on the quality of the reconstruction was evaluated. Lightly filtered x-ray beams give rise to severe distortions in image quality, with values of the reconstructed coefficients rising toward the periphery of the object. Highly filtered beams give rise to images with less pronounced distortion.