Estimation of myocardial extracellular volume fraction with cardiac CT in subjects without clinical coronary artery disease: A feasibility study.

Background: Use of CT for assessment of extracellular volume fraction (ECV) is a new approach toward the evaluation of diffuse and focal myocardial fibrosis. It has recently been demonstrated that a hybrid algorithm of half- and full-scan reconstruction can improve image quality of delayed-phase CT.

Objective: The purpose of this study was to evaluate reproducibility of CT measurement of ECV of the myocardium using pre-contrast and delayed-phase CT, and to investigate the association between ECV and location, age and gender in subjects without clinical coronary artery disease.

Methods: Thirty-eight subjects (ages 45-78, mean 65 years, 14 females) without coronary artery stenosis, stress perfusion deficits or myocardial delayed enhancement on comprehensive cardiac CT comprise the study population. Delayed-phase CT was reconstructed with the hybrid algorithm. ECV was calculated as a ratio of the change in Hounsfield unit of the myocardium and the left ventricular (LV) blood before and after contrast administration, multiplied by (1-hematocrit).

Results: Good inter- and intra-observer agreement was observed in CT measurement of ECV (intraclass correlation coefficient: 0.968 and 0.971, respectively). Mean ECV was 26.1 ± 2.0% (range 22.6-30.0%), and was positively related to age (r = 0.46, p = 0.003). Mean ECV in males was lower compared with females (25.5 ± 2.0% vs. 27.1 ± 1.8%, p = 0.02). There was no statistically significant difference in ECV between anterior, septal, inferior, and lateral segments.

Conclusions: CT measurement of myocardial ECV showed high inter- and intra-observer reproducibility, and age-related increase and gender-related difference of ECV were demonstrated. This might enable additional CT evaluation of diffuse and focal myocardial fibrosis in various pathological conditions as part of a comprehensive cardiac CT examination.