Abstract：
OBJECTIVE: Calculation of extracellular volume fraction (ECV), a marker of myocardial fibrosis in cardiac magnetic resonance imaging (CMR), requires hematocrit (Hct). We aimed to correlate Hct levels with native blood T1 times, to derive a formula for estimating synthetic Hct (Hctsyn) and synthetic ECV (ECVsyn), to assess accuracy of ECVsyn and to compare our model with published formulas.
METHODS: In this retrospective study, a cohort of 250 CMR scans with T1 mapping (3T, MOLLI 5(3)3, endsystolic aquisition), was divided into a derivation and validation cohort. Native T1 times of the left ventricular blood pool (T1native,midLV) were correlated with Hct levels from blood sampling within 24 h (Hct24h) and a formula for calculation of Hctsyn was derived by linear regression.
RESULTS: In the derivation cohort (n = 167), Hct24h showed a good association with T1native,midLV (r = -0.711, p < 0.001). The resulting regression equation was Hctsyn = 1/T1native,midLV * 1355.52-0.310. In the validation cohort (n = 83), Hctsyn and Hct24h showed good correlation (r = 0.726, p < 0.001), while ECVsyn, and ECV24h demonstrated excellent correlation (r = 0.940, p < 0.001). ECVsyn had a minimal bias of 0.28 % and the misclassification rate (8.8 %) was comparable to the variability introduced by repeated Hct measurements (misclassification in 7.5 %). Applying published formulas in our cohort resulted in incorrect classification in up to 60 %.
CONCLUSIONS: We provide a formula for estimating Hctsyn from native blood T1 on a 3T scanner. The measurement error of ECVsyn is low and comparable to the error due to retest variability of conventional Hct. Scanner- and sequence-specific formulas should be used.
METHODS: In this retrospective study, a cohort of 250 CMR scans with T1 mapping (3T, MOLLI 5(3)3, endsystolic aquisition), was divided into a derivation and validation cohort. Native T1 times of the left ventricular blood pool (T1native,midLV) were correlated with Hct levels from blood sampling within 24 h (Hct24h) and a formula for calculation of Hctsyn was derived by linear regression.
RESULTS: In the derivation cohort (n = 167), Hct24h showed a good association with T1native,midLV (r = -0.711, p < 0.001). The resulting regression equation was Hctsyn = 1/T1native,midLV * 1355.52-0.310. In the validation cohort (n = 83), Hctsyn and Hct24h showed good correlation (r = 0.726, p < 0.001), while ECVsyn, and ECV24h demonstrated excellent correlation (r = 0.940, p < 0.001). ECVsyn had a minimal bias of 0.28 % and the misclassification rate (8.8 %) was comparable to the variability introduced by repeated Hct measurements (misclassification in 7.5 %). Applying published formulas in our cohort resulted in incorrect classification in up to 60 %.
CONCLUSIONS: We provide a formula for estimating Hctsyn from native blood T1 on a 3T scanner. The measurement error of ECVsyn is low and comparable to the error due to retest variability of conventional Hct. Scanner- and sequence-specific formulas should be used.
摘要：
目的：计算细胞外体积分数（ECV），心脏磁共振成像（CMR）中心肌纤维化的标志物，需要血细胞比容（Hct）。我们旨在将Hct水平与天然血液T1时间相关联，推导出估算合成Hct(Hctsyn)和合成ECV(ECVsyn)的公式，评估ECVsyn的准确性，并将我们的模型与公布的公式进行比较。
方法：在这项回顾性研究中，一组250次CMR扫描和T1映射(3T，MOLLI5（3）3，收缩后含水层），分为推导和验证队列。左心室血池的固有T1时间(T1native,midLV）与24小时内（Hct24h）抽血的Hct水平相关，并通过线性回归得出Hctsyn的计算公式。
结果：在派生队列中（n=167），Hct24h与T1native表现出良好的关联，midLV（r=-0.711，p<0.001）。得到的回归方程为Hctsyn=1/T1native，中型LV*1355.52-0.310。在验证队列中（n=83），Hctsyn和Hct24h表现出良好的相关性(r=0.726,p<0.001),而ECVsyn,与ECV24h表现出良好的相关性（r=0.940，p<0.001）。ECVsyn的最小偏倚为0.28％，错误分类率（8.8％）与重复Hct测量引入的变异性相当（错误分类为7.5％）。在我们的队列中应用已发布的公式导致高达60％的错误分类。
结论：我们提供了在3T扫描仪上从天然血液T1估算Hctsyn的公式。ECVsyn的测量误差较低，可与常规Hct的重测变异性引起的误差相媲美。应使用特定于扫描仪和序列的公式。
方法：在这项回顾性研究中，一组250次CMR扫描和T1映射(3T，MOLLI5（3）3，收缩后含水层），分为推导和验证队列。左心室血池的固有T1时间(T1native,midLV）与24小时内（Hct24h）抽血的Hct水平相关，并通过线性回归得出Hctsyn的计算公式。
结果：在派生队列中（n=167），Hct24h与T1native表现出良好的关联，midLV（r=-0.711，p<0.001）。得到的回归方程为Hctsyn=1/T1native，中型LV*1355.52-0.310。在验证队列中（n=83），Hctsyn和Hct24h表现出良好的相关性(r=0.726,p<0.001),而ECVsyn,与ECV24h表现出良好的相关性（r=0.940，p<0.001）。ECVsyn的最小偏倚为0.28％，错误分类率（8.8％）与重复Hct测量引入的变异性相当（错误分类为7.5％）。在我们的队列中应用已发布的公式导致高达60％的错误分类。
结论：我们提供了在3T扫描仪上从天然血液T1估算Hctsyn的公式。ECVsyn的测量误差较低，可与常规Hct的重测变异性引起的误差相媲美。应使用特定于扫描仪和序列的公式。
