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

Background: 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.

Methods: 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.

Results: 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%, I² = 0%, p for heterogeneity = 0.67) at 1.5T CMR and 0.24% (95% CI: -0.13 to 0.61%, I² = 19%, p for heterogeneity = 0.25) at 3.0T CMR.

Conclusion: 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.