Quantification of myocardial extracellular volume without blood sampling

Wensu Chen; Alessandro Faragli; Collin Goetze; Victoria Zieschang; Karl Jakob Weiss; Djawid Hashemi; Rebecca Beyer; Lorena Hafermann; Philipp Stawowy; Sebastian Kelle; Patrick Doeblin

doi:10.1093/ehjimp/qyad022

Quantification of myocardial extracellular volume without blood sampling

Eur Heart J Imaging Methods Pract. 2023 Sep 15;1(2):qyad022. doi: 10.1093/ehjimp/qyad022. eCollection 2023 Sep.

Authors

Wensu Chen^{1

2

3}, Alessandro Faragli^{1

2

4

5}, Collin Goetze^{1

2}, Victoria Zieschang^{1

2}, Karl Jakob Weiss^{1

2

5}, Djawid Hashemi^{1

2

5}, Rebecca Beyer^{1

2}, Lorena Hafermann⁶, Philipp Stawowy^{1

2

5}, Sebastian Kelle^{1

2

4

5}, Patrick Doeblin^{1

2

5}

Affiliations

¹ Department of Cardiology, Angiology and Intensive Care Medicine, Deutsches Herzzentrum der Charité, Augustenburger Platz 1, Berlin 13353, Germany.
² Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Charitéplatz 1, Berlin 10117, Germany.
³ Department of Cardiology, Affiliated Hospital of Xuzhou Medical University, Xuzhou, China.
⁴ Berlin Institute of Health at Charité-Universitätsmedizin Berlin, Charitéplatz 1, Berlin 10117, Germany.
⁵ DZHK (German Center for Cardiovascular Research), Partner Site Berlin, Potsdamer Str. 58, Berlin 10785, Germany.
⁶ Institute of Biometry and Clinical Epidemiology, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Charitéplatz 1, Berlin 10117, Germany.

Abstract

Aims: Cardiac magnetic resonance (CMR) T1 relaxation time mapping is an established technique primarily used to identify diffuse interstitial fibrosis and oedema. The myocardial extracellular volume (ECV) can be calculated from pre- and post-contrast T1 relaxation times and is a reproducible parametric index of the proportion of volume occupied by non-cardiomyocyte components in myocardial tissue. The conventional calculation of the ECV requires blood sampling to measure the haematocrit (HCT). Given the high variability of the HCT, the blood collection is recommended within 24 h of the CMR scan, limiting its applicability and posing a barrier to the clinical routine use of ECV measurements. In recent years, several research groups have proposed a method to determine the ECV by CMR without blood sampling. This is based on the inverse relationship between the T1 relaxation rate (R1) of blood and the HCT. Consequently, a 'synthetic' HCT could be estimated from the native blood R1, avoiding blood sampling.

Methods and results: We performed a review and meta-analysis of published studies on synthetic ECV, as well as a secondary analysis of previously published data to examine the effect of the chosen regression modell on bias. While, overall, a good correlation and little bias between synthetic and conventional ECV were found in these studies, questions regarding its accuracy remain.

Conclusion: Synthetic HCT and ECV can provide a 'non-invasive' quantitative measurement of the myocardium's extracellular space when timely HCT measurements are not available and large alterations in ECV are expected, such as in cardiac amyloidosis. Due to the dependency of T1 relaxation times on the local setup, calculation of local formulas using linear regression is recommended, which can be easily performed using available data.

Keywords: CMR; ECV classification description; T1 mapping; cardiac magnetic resonance (CMR); synthetic HCT; tissue characterization.