Objectives: This study aimed to investigate the accuracy of myocardial extracellular volume (ECV) quantification using a prototype photon-counting detector (PCD) computed tomography (CT) and examine the association between radiation dose and spectral image settings. Material and Methods: A multi-energy CT phantom that simulated the blood pool and myocardium was used. The tube voltage was set at 120 kVp and three types of tube current-time products (105, 150, and 300 mAs) were applied for pre- and post-contrast scans. Virtual monoenergetic images (VMIs) at 50-100 keV were reconstructed. The ECV value was calculated from the CT numbers between pre-contrast and post-contrast. We compared the accuracy of ECV values at each VMI level. Results: Each radiation dose setting demonstrated a small but significant difference in ECV values at each keV level. ECV was overestimated at higher keV in all radiation dose settings. A significant difference in ECV value variabilities was found among keV levels in all three radiation dose settings, with higher keV exhibiting greater variability. The variation was particularly large in the low-dose setting. The residual values were significantly larger at higher keV levels in all radiation dose settings. The residual values were smaller at 50 and 60 keV with no significant difference in 150- and 300-mAs settings. Conclusion: Setting appropriate VMI keV and radiation dose settings was necessary when quantifying myocardial ECV with PCD-CT because the keV levels caused differences in the quantification value and measurement variation.
