Extracellular volume quantification by cardiac magnetic resonance imaging without hematocrit sampling

Abstract

SummaryBackgroundMyocardial tissue characterization by cardiovascular magnetic resonance (CMR) T1 mapping currently receives increasing interest as a diagnostic tool in various disease settings. The T1-mapping technique allows non-invasive estimation of myocardial extracellular volume (ECV) using T1-times before and after gadolinium administration; however, for calculation of the myocardial ECV the hematocrit is needed, which limits its utility in routine application. Recently, the alternative use of the blood pool T1-time instead of the hematocrit has been described.MethodsThe results of CMR T1 mapping data of 513 consecutive patients were analyzed for this study. Blood for hematocrit measurement was drawn when placing the i. v. line for contrast agent administration. Data from the first 200 consecutive patients (derivation cohort) were used to establish a regression formula allowing synthetic hematocrit calculation, which was then validated in the following 313 patients (validation cohort). Synthetic ECV was calculated using synthetic hematocrit, and was compared with conventionally derived ECV.ResultsAmong the entire cohort of 513 patients (mean age 57.4 ± 17.5 years old, 49.1% female) conventionally measured hematocrit was 39.9 ± 4.7% and native blood pool T1-time was 1570.6 ± 117.8 ms. Hematocrit and relaxivity of blood (R1 = 1/blood pool T1 time) were significantly correlated (r = 0.533, r2 = 0.284, p < 0.001). By linear regression analysis, the following formula was developed from the derivation cohort: synthetic hematocrit = 628.5 × R1 − 0.002. Synthetic and conventional hematocrit as well as ECV showed significant correlation in the validation (r = 0.533, r2 = 0.284, p < 0.001 and r = 0.943, r2 = 0.889, p < 0.001, respectively) as well as the overall cohort (r = 0.552, r2 = 0.305, p < 0.001 and r = 0.957, r2 = 0,916, p < 0.001). By Bland Altman analysis, good agreement between conventional and synthetic ECV was found in the validation cohort (mean difference: 0.007%, limits of agreement: −4.32 and 4.33%, respectively).ConclusionSynthetic ECV using native blood pool T1-times to calculate the hematocrit, is feasible and leads to almost identical results in comparison with the conventional method. It may allow fully automatic ECV-mapping and thus enable broader use of ECV by CMR T1 mapping in clinical practice.

Cardiac magnetic resonance T1 mapping. Part 1: Aspects of acquisition and evaluation

“…As T1 estimates generally depend on magnetic field strength, sequence type and protocol parameters, equations relating native blood T1 and hematocrit also depend (at least) on these confounders [5,43]. However, even when optimized regression equations are employed, deviations between ECV and synthetic ECV were shown not to be completely negligible [42][43][44][45].…”

Hereditary ATTR Amyloidosis in Austria: Prevalence and Epidemiological Hot Spots

“…Diagnosis of ATTR was either made by endomyocardial biopsy (EMB) or non-invasively according to the algorithm by Gillmore et al [ 11 , 12 ]. Cardiac magnetic resonance (CMR) was carried out in selected cases and was performed including gadolinium contrast application, T1 mapping and calculation of extracellular volume, as previously described [ 13 , 14 ]. The N-terminal prohormone of brain natriuretic peptide (NT-proBNP) plasma levels were analyzed in all patients.…”

Guidelines for Cardiovascular Magnetic Resonance Imaging from the Korean Society of Cardiovascular Imaging—Part 3: Perfusion, Delayed Enhancement, and T1- and T2 Mapping

“…A process that can perform the blood test near the time of CMR is needed. As a noninvasive test, the method of obtaining the synthetic ECV using the longitudinal relaxation rate of blood may be used; however, further research is needed [50][51][52].…”