## 1 Introduction  
The application of physics in nuclear cardiology aims to improve the quality of the image data obtained using different combinations of tomographic systems, reconstruction algorithms, and corrections used in myocardial perfusion imaging (MPI). The characterization of imaging systems and the evaluation of image data through the application of formalisms and metrices of radiation physics is crucial for the investigation of system performance and the determination of possible limitations. MPI is a non-invasive tomographic nuclear medicine procedure dedicated to identifying early asymptomatic coronary artery disease (CAD) or examining the clinical impact of previously diagnosed CAD. Single-photon emission computed tomography (SPECT) is used to assess the blood flow through the myocardium, and to locate areas where it is diminished by stenosed or obstructed coronary arteries, i.e., areas of perfusion defects. The blood flow information is obtained by the analysis of radiopharmaceutical accumulation and distribution in the myocardium. Therefore, the quality of the image data and the capability of the system to detect PDs are essential. Image quality is related to system performance and can be expressed by several physical parameters. The most important are related to the imaging system, i.e., contrast, spatial resolution, sensitivity, and uniformity [1; 2; 3; 4; 5; 6; 7]. When performing MPI on a SPECT system with NaI-crystal and parallel-hole collimators, only a small portion of the detector area is used. In addition, the loss of spatial resolution due to source-to-detector distance when using parallel-hole collimators must be considered. Cardio-centric acquisition and multi-focal collimators have improved the sensitivity and resolution of NaI-crystal detector systems by the specific convergent collimator geometry in the center of the detector area. Moreover, they have allowed the acquisition time or the administered activity to be reduced [8; 9; 10; 11]. The performance of systems with NaI-crystal detectors has been further enhanced by the introduction of iterative reconstruction algorithms with resolution recovery (IRR). These algorithms enable three-dimensional collimator response function modeling and account for the spatial resolution of the system in the reconstruction process [1; 12; 13; 14; 15]. Collimator response function modeling is performed using the physical and geometric features of the detector and collimator along with orbit shape, detector rotation radius, and patient-detector distance to improve the accuracy of the radiopharmaceutical distribution visualization on reconstructed images [1; 16]. Resolution recovery is particularly important for MPI procedures, where the change in the position of the organ can cause reconstruction artifacts due to differences in spatial resolution [17]. In addition, IRR algorithms allow the correction of various degrading factors such as noise, scatter, and attenuation [1; 13; 14; 15]. The contribution of the scattered gamma rays originating in adjacent organs can be corrected using multiple energy windows that enable scatter contribution estimation during IRR and compensation for it [18; 19]. Gamma ray attenuation in tissues can be corrected using transmission data acquired through computed tomography (CT). Although mandatory for some cardio-centric systems [13], this is still an open question due to the possible mismatch between emission and transmission data that may result in attenuation correction (AC)-induced artifacts [17]. A comprehensive characterization of nuclear cardiology imaging systems should include the evaluation of system diagnostic performance in terms of perfusion detection capability. The aim of this study was to quantify self-attenuation characteristics, non-uniformities of the signal intensity and maximum contrast between the perfusion defect (_PD_) and the _LV_ wall for nuclear cardiology imaging systems, in reproducible and controlled clinical conditions with an anthropomorphic SPECT phantom.