A QUANTITATIVE COMPARISON OF ATTENUATION-WEIGHTED BACKPROJECTION WITH MULTIPLICATIVE AND ITERATIVE POSTPROCESSING ATTENUATION COMPENSATION IN SPECT

Comparisons are made between different analytic attenuation compensation methods used in SPECT imaging. The methods include a multiplicative technique and a single-iterative technique, both applied after filtered backprojection, and two different implementations of an attenuation-weighted filtered backprojection technique (A-W FBP). The methods are compared using simple phantoms of line sources and water-filled circular and elliptical cylinders. Both simulated data (without scatter) and experimental data (with scatter) are reconstructed. The weighted backprojection methods eliminate nearly all deformation due to nonisotropic attenuation for a line source centered in an ellipse. However, the measured noise is amplified by A-W FBP, unless the method is further modified to reduce the amplification. The multiplicative technique does not increase image noise, and runs quickly, but it is not exact for distributed sources and is unable to remove the deformation caused by a nonisotropic attenuation. The single-iteration technique improves the reconstruction of distributed sources and nonsotropic geometries, but increases the image noise.