## 6 Conclusions  
The characteristics of myocardial perfusion imaging devices and reconstruction algorithms necessitate a comprehensive image quality evaluation of _MPI systems_. The results of the image analysis of selected image quality descriptors in both normal and pathological heart simulations showed the intrinsic characteristics of the evaluated systems. An extended quantitative evaluation of the self-attenuation and perfusion detection capability of different _MPI systems_ was performed concerning intrinsic contrast and net contrast. This investigation revealed minimal self-attenuation artifacts and better signal uniformity in the _LV_ wall over all short-axis images when IQ-IRR-SC-AC was used (_IC_ < 1% for anterior, lateral, and posterior positions), except for the septal position. In the latter, an underestimation of the signal intensity was observed, resulting in an unexpectedly higher intrinsic contrast value in the septal part of the heart (2.38 \(\pm\) 0.53%). Concerning the perfusion detection capability, the net contrast values for the _MPI systems_ were found to be perfusion-defect-position-dependent: 32.09 \(\pm\) 2.05%, 28.80 \(\pm\) 2.13%, 21.64 \(\pm\) 2.21%, and 35.13 \(\pm\) 3.57%, for anterior, lateral, posterior, and septal positions, respectively. The results show that IQ-IRR-SC-AC and SPECT-IRR-SC have the highest net contrast means overall at 31.11 \(\pm\) 3.22% and 30.97 \(\pm\) 2.75%, respectively. In the case of IQ-IRR-SC-AC, it was found that corrections made a difference in the posterior and septal positions when evaluating net contrast (26.61% and 39.07% for IQ-IRR-SC-AC vs. 14.03% and 30.78% for IQ-IRR). This fact enables better perfusion detection capability over all short-axis images of IQ-IRR-SC-AC and minimizes the lack of perfusion detection capability for that particular _MPI system_ in the posterior part of the heart, which is present otherwise. A substantial deterioration in image data quality was observed for IQ-IRR compared to IQ-IRR-SC-AC, and the performance could be compared to SPECT-IRR. The results of this investigation suggest that there is also a gain in terms of image quality and perfusion detection capability from the use of a double-energy window in SPECT devices with IRR for scatter correction (\(C_{LV/LVIC}\): 57.43 \(\pm\) 2.87% and 63.76 \(\pm\) 2.87% for SPECT-IRR and SPECT-IRR-SC, respectively; _NC_: 27.40 \(\pm\) 4.50% and 30.97 \(\pm\) 2.75% for SPECT-IRR and SPECT-IRR-SC, respectively).  
The results of the comprehensive evaluation of _MPI systems_ using the standard phantom presented in this study will be used as reference values in further research.  
**Author Contributions:** Conceptualization, D.D.D., R.M. and S.J.; Investigation, D.D.D.; Methodology, D.D.D., R.M. and S.J.; Validation, D.D.D.; Data curation, D.D.D. and I.P.; Formal analysis, D.D.D. and I.P.; Resources, S.J.; Visualization, D.D.D.; Project administration, D.D.D. and S.J.; Resources, S.J.; Writing--Original draft, D.D.D.; Writing--Review and editing, D.D.D., R.M., S.J., M.B. and I.P. Supervision, S.J. and R.M. All authors have read and agreed to the published version of the manuscript.  
Part of the investigation was performed within the scope of the projects IAEA CRO6021 and UniRi-Iskusni-Priord-23-8.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
The authors declare no conflicts of interest.