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Non uniform photon attenuation and Compton scatter degrade nuclear medicine SPECT images by removing true counts or adding unwanted counts, respectively. For quantitative SPECT, iterative reconstruction algorithms, such as OSEM, allow 3D collimator modeling and compensation of the effects of scatter and attenuation. In this work, we investigate, through ROI and SPM analysis of phantom and computer simulation studies, how a combination of compensation strategies affects image quality and quantitative accuracy. Phantoms were imaged with a SPECT and a CT scanner. With these acquisitions, semi-quantitative analysis was performed for the following reconstruction strategies: OSEM-3D without attenuation and scatter compensation; OSEM-3D CTAC (with attenuation correction); and OSEM-3D with attenuation and scatter compensation (CTACSC). For the simulated dataset, the SNR was 50.5 with CTACSC compared to 27.5 without any compensation and OSEM-3D CTACSC produced reconstructed images with contrast within 0.23% of the true image with a standard error of 21 counts. Without compensation, the error increases to 2382 counts. The implementation and design of the OSEM-3D CTACSC approach proved effective, with improved visual quality and quantitative accuracy of the SPECT images.