1. A method for model-based scatter correction in a single photon emission computed tomography (SPECT) system, the method comprising: detecting, with a SPECT detector having a non-parallel-hole collimator, emissions from a patient; generating an image object from the emissions; forward projecting from the image object to a first data model in data space; forming a model-based scatter source from convolution of the image object with scatter kernels, the scatter kernels being kernels from a simulation of scatter with a parallel hole collimator normalized by sensitivity as a function of location measured for the non-parallel-hole collimator; determining a model of scatter from a vector map measured from the non-parallel-hole collimator and the model-based scatter source; combining the first data model with the model of scatter into a projection data model; and displaying a SPECT image of the patient as a function of the projection data model.