An essential feature of SPECT imaging is collimation of gamma photons, allowing detection of only those photons propagating in the appropriate direction. Parallel beam collimators are widely used in different applications, because reconstruction is straightforward. Fan-beam collimators focus on a focal line parallel to the axis of rotation. For organs centered within the field of view this enhances the sensitivity. We propose a new, more sophisticated model for calculating the sensitivity of

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... -beam collimation throughout the whole field of view of an Anger gamma camera and compare it with a previously published model. Projection measurements of a uniform flood source near the face of a fan-beam collimator demonstrate that this new model is more accurate.