We previously developed an OS-EM reconstruction method for rotating multi-segment slant-hole SPECT with compensation for non-uniform attenuation and collimator-detector response. In this study we performed simulations to investigate the imaging characteristics of RMSSH SPECT mammography using signal-to-noise ratio as a criterion. We varied the breast lesion size and the lesion to background uptake ratio in the 3D NCAT phantom, reconstructed RMSSH SPECT projection data using OS-EM reconstruction with and without various compensations, and calculated the SNR of the breast lesion from the reconstructed images. For comparison, we also calculated the SNR values using projection images from planar scintimammography. Our calculations showed progressive improvement in terms of SNR values when more compensation for image degrading factors were applied, and RMSSH SPECT offered higher image contrast and SNR values as compared to planar scintimammography. The results from this study may help to design an efficient and economical ROC study for further evaluating the performance in a lesion detection task for RMSSH SPECT mammography.