Myocardial Extracellular Volume Quantification Using Cardiac Computed Tomography: A Comparison of the Dual-energy Iodine Method and the Standard Subtraction Method

Rationale and Objectives: To clarify the accuracy of two measurement methods for myocardial extracellular volume (ECV) quantification (ie, the standard subtraction method [ECVsub] and the dual-energy iodine method [ECViodine]) with the use of cardiac CT in comparison to cardiac magnetic resonance imaging (CMR) as a reference standard.Materials and Methods: Equilibrium phase cardiac images of 21 patients were acquired with a dual-layer spectral detector CT and CMR, and the images were retrospectively analyzed. CT-ECV was calculated using ECVsub and ECViodine. The correlation between the ECV values measured by each method was assessed. Bland-Altman analysis was used to identify systematic errors and to determine the limits of agreement between the CT-ECV and CMR-ECV values. Root mean squared errors and residual values for the ECVsub and ECViodine were also assessed.Results: The correlations between ECVsub and ECViodine for both septal and global measurement were r = 0.95 (p < 0.01) and 0.91 (p < 0.01), respectively, while those between the mean ECVsub and CMR-ECV were r = 0.90 (septal, p < 0.01) and 0.84 (global, p < 0.01), and those between ECViodine and CMR-ECV were r = 0.94 (septal, p < 0.01) and 0.95 (global, p < 0.01). Bland-Altman plots showed lower 95% limits of agreement between ECViodine and CMR-ECV compared with that between ECVsub and CMR-ECV in both septal and global measurement. The root mean squared error of ECVsub was higher than that of ECViodine. The mean residual value of ECVsub was significantly higher than that of ECViodine.Conclusion: ECViodine yielded more accurate myocardial ECV quantification than ECVsub, and provided a comparable ECV value to that obtained by CMR.