Synthetic Extracellular Volume in Cardiac Magnetic Resonance Without Blood Sampling: a Reliable Tool to Replace Conventional Extracellular Volume

Abstract

BACKGROUND: The calculation of extracellular volume (ECV) in cardiac magnetic resonance requires hematocrit, limiting its applicability in clinical practice. Based on the linear relationship between hematocrit and blood T1 relaxivity, a synthetic ECV could be estimated without a blood sample. We aim to develop and test regression models for synthetic ECV without blood sampling in 1.5-T and 3.0-T scanners. METHODS: A total of 1101 subjects who underwent cardiac magnetic resonance scanning with native and postcontrast T1 mapping and venous hematocrit within 24 hours were retrospectively enrolled. Subjects were randomly split into derivation (n=550) and validation (n=551) subgroups for each scanner. Different regression models were derived controlling for sex, field strength, and left ventricle/right ventricle blood pool and validated in the validation group. We performed additional validation analyses in subgroups of patients with histological validation (n=17), amyloidosis (n=29), anemia (n=185), and reduced ejection fraction (n=322). RESULTS: In the derivation group, 8 specific models and 2 common estimate models were derived. In the validation group, using specific models, synthetic ECV had high agreement with conventional ECV (R 2 , 0.87; P <0.0001 and R 2 , 0.88, P <0.0001; −0.16% and −0.10%, left ventricle and right ventricle model, respectively). Common models also performed well (R 2 , 0.88; P <0.0001 and R 2 , 0.89, P <0.0001; −0.21% and −0.18%, left ventricle and right ventricle model, respectively). Histological validation demonstrated equal performance of synthetic and measured ECV. Synthetic ECV as calculated by the common model showed a bias in the anemia cohort significantly reduced by the specific model (−2.45 to −1.28, right ventricle common and specific model, respectively). CONCLUSIONS: Synthetic ECV provided a promising way to calculate ECV without blood sampling. Specific models could provide the most accurate value, while common models could be more suitable in routine clinical practice because of their simplicity while maintaining adequate accuracy.

Kardiovaskuläre MRT in der Bewertung von Kardiomyopathien – ein aktueller Überblick

“…Die MRT kann dabei mithilfe von nativen und kontrastmittelverstärkten T1-Maps auch das extrazelluläre Volumen des Myokards quantifizieren. Dieses ist bei Amyloidinfiltration stark erhöht [47] und kann zuverlässig mit der MRT bestimmt werden [48]. Die Klassifizierung der ATTR-Amyloidose von der AL-Form wird klinisch noch nicht routinemäßig mit der Kardio-MRT durchgeführt.…”

Imaging Methods: Magnetic Resonance Imaging

“…65 A simplified approach for the assessment of ECV is introduced where the hematocrit can be estimated from native values of blood pool T1 (“synthetic ECV”). 66,67 The development of 3D T1-mapping acquisition are explored in 3D ECV quantification. 68…”

“…65 A simplified approach for the assessment of ECV is introduced where the hematocrit can be estimated from native values of blood pool T1 ("synthetic ECV"). 66,67 The development of 3D T1-mapping acquisition are explored in 3D ECV quantification. 68 ECV has been shown to be elevated in EMB-proven acute myocarditis, correlating with edema, and in subclinical myocardial disease in rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis, likely representing low-grade inflammation and diffuse fibrosis.…”

Detection of myocardial fibrosis: Where we stand

“…Based on the linear relationship between the hematocrit and the native T1 of blood, synthetic ECV is a new method to determine ECV without blood sampling ( 116 ). Recently, a large cohort study showed synthetic ECV presented no statistical difference from conventional ECV estimated by CMR and measured ECV by histological examination ( 117 ).…”