Quantitative image reconstruction with weighted backprojection for single photon emission computed tomography

A new method of image reconstruction for single photon emission computed tomography is presented. The method is basically a filtered backprojection with some modifications. The algorithm consists of three steps: normalization of observed projections, modified convolution operation, and weighted backprojection. The weighting function for backprojection is determined to provide perfect attenuation compensation for a uniform attenuation medium and to keep the statistical noise in the reconstructed image low. The relative contributions of two conjugate projections to the image can be controlled by the reconstruction parameters, enabling improvement of the signal-to-noise ratio and spatial resolution at off-center area compared with the conventional averaging method of two conjugate projections. Simulation studies indicated that the method provides a satisfactory image for an extended source of 99mTc (mu = 0.15 cm-1) having a diameter of up to approximately 35 cm. A myocardium phantom is adequately reconstructed from a 180 approximately 225 degrees angle scan. The effect of nonuniform attenuation medium surrounding the source region can be corrected. This paper presents the mathematical basis of the procedure, the evaluation of the statistical noise, and some illustrative computer simulations.