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Multi-segment slant-hole (MSSH) collimators provide much higher detection efficiency of breast lesions at a single view than conventional low-energy high-resolution (LEHR) parallel-hole collimators. The purpose of this study is to evaluate rotating MSSH (RMSSH) SPECT mammography using Monte Carlo Simulation methods. We modified the SIMIND Monte Carlo code to generate RMSSH projection data including the effects of attenuation, collimator-detector response and scatter from a realistic NCAT phantom with an attached breast and a lesion placed at locations at the center and at the near and far walls of the breast. The projection data were reconstructed using analytic and iterative image reconstruction methods. For comparison, we examine an LEHR collimator with a resolution of 1 cm at 15.2 cm, which is the same as that of the MSSH at the center of the common volume-of-view. Also, we simulated the inclusion of a lead shield that covers the body to keep photons emitted from the other organs from reaching the MSSH collimator. Our results indicated that RMSSH SPECT provides greater breast lesion contrast than that of a planar image taken using a conventional LEHR collimator at all lesion locations. Depending on the lesion location, the spatial resolution of the RMSSH SPECT images may be comparable or slightly poorer than that of the planar scintimammographic images obtained using a LEHR collimator. Shielding of photon emissions from the other organs substantially improves the RMSSH SPECT image quality. We conclude that the Monte Carlo simulation methods are useful in evaluating the application of RMSSH SPECT to breast imaging as compared to conventional planar scintimammography and that RMSSH SPECT may enhance lesion detectability.