Abstract
BackgroundThe extracellular volume (ECV), derived from cardiovascular magnetic resonance (CMR) T1 mapping, is a biomarker of the extracellular space in the myocardium. The hematocrit (HCT), measured from venipuncture, is required for ECV measurement. We test the clinic values of synthetic ECV, which is derived from the longitudinal relaxation of blood–based (T1blood) synthetic hematocrit in 3 T CMR.MethodsA total of 226 subjects with CMR T1 mapping and HCT measurement taken on the same day as the CMR were retrospectively enrolled and randomly split into derivation (n = 121) and validation (n = 105) groups, comprising healthy subjects (n = 45), type 2 diabetes mellitus (T2DM) patients (n = 60), hypertrophic cardiomyopathy (HCM) patients (n = 93), and 28 other patients. Correlation of T1blood with the measured HCT (HCTm) was established in the derivation group and used in both the derivation and the validation groups. The relationships between the ECV values derived from both the synthetic HCT (HCTsyn) and HCTm were explored. In addition, the differences in the ECV values among the HC, T2DMs, and HCMs were compared.ResultsRegression between the HCTm and 1/T1blood was linear (R2 = 0.19, p < 0.001), and the regression equation was: HCTsyn = [561.6*(1/T1blood)] + 0.098 in the derivation group. The measured ECV (ECVm) was strongly correlated with the synthetic ECV (ECVsyn) (R2 = 0.87, p < 0.001) and mildly correlated with the difference between the ECVsyn and ECVm (R2 = 0.10, p < 0.001) in the derivation group. Also in this group, the ECVm was larger in T2DMs than that in healthy cohort (29.1 ± 3.1% vs. 26.4 ± 2.4%, p = 0.002), whereas, the ECVsyn did not differ between T2DMs and healthy cohort (28.3 ± 2.9% vs. 26.9 ± 2.2%, p = 0.064). Compared with the healthy cohort, the HCMs were associated with higher ECVsyn and ECVm of the mid-ventricle in both the derivation and the validation groups. Using our center’s normal cut-off of 31.8%, the use of ECVsyn would lead to a 6–25% incorrect categorization of patients in the derivation and validation groups.ConclusionsECVsyn derived from HCTsyn may lead to clinical errors in 3 T CMR, especially for patients who have only a subtle elevation in ECV.
Highlights
The extracellular volume (ECV), derived from cardiovascular magnetic resonance (CMR) T1 mapping, is a biomarker of the extracellular space in the myocardium
The study results indicated a very strong correlation between synthetic ECV (ECVsyn) and measured ECV (ECVm), which is consistent with another study at both 1.5 T and 3 T CMR [9]
Correlation between Measured hematocrit (HCTm) and Synthetic hematocrit (HCTsyn), and Measured extracellular volume fraction (ECVm) and Synthetic extracellular volume fraction (ECVsyn) in the derivation and validation groups Using the equation for the calculation of HCTsyn, there was modest correlation between HCTsyn and HCTm in the derivation group (Slope = 1.00, R2 = 0.19, p < 0.001, Fig. 2a) and slightly weaker correlation in the validation group (Slope = 0.93, R2 = 0.18, p < 0.001, Fig. 3a)
Summary
The extracellular volume (ECV), derived from cardiovascular magnetic resonance (CMR) T1 mapping, is a biomarker of the extracellular space in the myocardium. The additional blood test is cumbersome and costly, and it delays the process of CMR examination and ECV calculation It may cause difficulties for retrospective studies, for those patients without a measured HCT.Treibel et al [8] reported a linear correlation between the HCT and 1/T1blood at 1.5 T CMR. This correlation can be applied to estimate the synthetic HCT (HCTsyn) and subsequently, the ECV. Raucci et al [10] used the same method to study pediatric and young adult patients at 1.5 T CMR Their results showed that HCTsyn may cause clinically significant errors in ECV measurement. Whether it can be used in clinical routine workflow or not is still a subject of dispute, especially at 3 T CMR
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