Synthetic extracellular volume fraction as an imaging biomarker of the myocardial interstitium without blood sampling: a systematic review and meta-analysis

The calculation of conventional extracellular volume fraction (ECV) requires blood hematocrit (Hct) measurement. Based on the relationship between Hct and blood T1 relaxivity for cardiac magnetic resonance (CMR), a synthetic ECV could be estimated without a blood sampling. The aim of this study was to evaluate the correlation and agreement in the quantification of synthetic ECV and laboratory ECV from conventional Hct measurements. Electronic database searches of PubMed, Web of Science Core Collection, Cochrane advanced search, and EMBASE were performed. The authors employed a meta-analysis using the generic inverse variance method with a random-effects model to estimate the summary correlation coefficient and mean absolute difference between synthetic and laboratory ECV. Of 38 papers, 10 studies comprising 4492 patients were identified. Overall, there was an excellent correlation between synthetic ECV and laboratory ECV (0.95 [95% confidence interval (CI): 0.92 to 0.97]) at 1.5T CMR and (0.91 [95% CI: 0.86 to 0.94]) at 3.0T CMR. The pooled mean difference between synthetic ECV and laboratory ECV was 0.61% (95% CI: 0.23 to 0.98%, I 2 = 0%, p for heterogeneity = 0.67) at 1.5T CMR and 0.24% (95% CI: −0.13 to 0.61%, I 2 = 19%, p for heterogeneity = 0.25) at 3.0T CMR. This study is the first comprehensive systematic review and meta-analysis of synthetic ECV evaluation at CMR. Synthetic ECV demonstrated an excellent correlation with laboratory ECV, with a mean difference of less than 1%, and offers noninvasive and instantaneous quantification of the myocardial extracellular space without the need for blood sampling.