Abstract Funding Acknowledgements Spectrum Dynamics Background Traditional relative assessment of regional myocardial perfusion by single photon emission computed tomography (SPECT) has limited ability to identify multivessel coronary artery disease, as well as diffuse atherosclerosis and coronary microvascular dysfunction. Current gamma cameras with cadmium-zinc-telluride (CZT) detectors have higher temporal resolution and sensitivity and allow the acquisition of multi-frame images and quantification of absolute myocardial blood flow (MBF) and coronary flow reserve (CFR Purpose The aim of this study was to assess the accuracy and reproducibility of quantitative measurements of MBF and CFR obtained with a CZT SPECT system compared to PET in a cohort of patients with known or suspected coronary artery disease. Methods Accuracy was assessed in 22 patients who underwent dynamic rest/stress 99mTc-sestamibi-SPECT and 13N-ammonia PET myocardial perfusion imaging within two weeks of each other. Fourteen patients comprised the reproducibility cohort and underwent two dynamic 99mTc-sestamibi SPECT scans within two weeks. A rest/pharmacological stress single-day SPECT protocol was performed, using a 1:3 dose ratio. SPECT image reconstruction was performed using a spline-fitting method and SPECT MBF was quantified using a net retention kinetic model in commercially available software. Rest MBF and CFR were adjusted for heart-rate pressure product. Results Global MBF at rest and stress showed a good correlation between SPECT and PET (r = 0.814, p < 0.001). For global rest MBF the mean difference between the two techniques was -0.25 ± 0.24 ml/min/g, while for stress MBF mean difference was -0.21 ± 0.40 ml/min/g. We also observed a significant correlation between global SPECT and PET CFR measurements (r = 0.745, p < 0.001), with no significant difference between the two (mean difference: 0.16 ± 0.50). Regarding the reproducibility cohort, the correlation between global CFR measured by two SPECT scans was also significant (r = 0.616, p = 0.019), with a mean difference of 0.14 ±0.51. The mean difference between scans for rest MBF (-0.05 ± 0.19) and stress MBF (0.01 ± 0.42) were also not significant. Conclusion MBF and CFR quantification is feasible using a CZT gamma camera and provides accurate and reproducible results that correlate with 13N-ammonia PET. This may be of special relevance in sites where PET is not available, enabling MBF and CFR quantification with CZT SPECT cameras. Abstract P361 Figure.