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Three-dimensional simulations of multidetector point-focusing SPECT imaging.

We have applied an efficient algorithm for mathematically simulating the three-dimensional (3-D) response of a SPECT imaging system with a depth-dependent 3-D point spread function (3-DPSF). The input object whose reconstructed image is to be simulated is restricted to a binary map; more complex objects may be treated as linear combinations of binary maps. The 3-D convolution reduces to a sequence of additions of a 3-D line spread function (3-DLSF), appropriately translated, to the 3-D response. We have simulated the projection data from a multidetector SPECT system with point-focusing collimators. The simulated projection data were then reconstructed using the manufacturer's software. The objects simulated included simple geometrical solids such as spheres and cylinders, as well as the distribution of muscarinic cholinergic receptors in a realistic brain slice. The results of these simulations indicate the existence of significant qualitative and quantitative artifacts in reconstructed human brain images.