Transverse water relaxation in whole blood and erythrocytes at 3T, 7T, 9.4T, 11.7T and 16.4T; determination of intracellular hemoglobin and extracellular albumin relaxivities.
Transverse water relaxation in whole blood and erythrocytes at 3T, 7T, 9.4T, 11.7T and 16.4T; determination of intracellular hemoglobin and extracellular albumin relaxivities.
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DOI：
10.1016/j.mri.2016.12.012
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发表时间：
2017-05
影响因子：
2.5
通讯作者：
van Zijl PC
中科院分区：
文献类型：
--
作者：
Grgac K;Li W;Huang A;Qin Q;van Zijl PC
血液是一种具有多个水室的生理物质，其中含有与水结合的蛋白质，如红细胞中的血红蛋白和血浆中的白蛋白。了解这些不同血室的水横向弛豫速率（R2）是量化血氧水平依赖性（BOLD）效应的先决条件。在这里，我们报告了在生理温度下灌注系统中循环的牛血液样品中基于carr - purcell - meiboomm - gill （CPMG）的水的横向弛豫率（R2CPMG），以模拟人类的血液灌注。在3t、7t、9.4 T、11.7 T和16.4 T时测定血浆、溶解红细胞、溶解血浆/红细胞混合物和全血的R2CPMG值，作为红细胞压积或血红蛋白浓度、氧合和CPMG回波间隔（τcp）的函数。R2CPMG在裂解细胞中表现出较小的τcp依赖性，这归因于游离水和血红蛋白结合水之间的水交换速率比τcp快得多。这与全血中的切向依赖性相反，全血中细胞和血浆之间的交换要慢得多。利用适用于交换和扩散对R2CPMG贡献的通用切向相关时间模型，将全血数据拟合为τcp的函数，并确定了无限短τcp处的r20血截距。采用不同红细胞压积下的r20血值和不同血红蛋白浓度下溶红细胞/血浆混合物的R2CPMG值测定血浆中红细胞内血红蛋白（r2Hb）和白蛋白（r2Alb）的弛豫度。在全氧作用下，从溶解红细胞和全血中获得的r2Hb值具有可比性。然而，虽然从裂解细胞中测定的r2Hb对氧合的依赖性呈线性，但在全血中这种依赖性变为二次型。这可能表明在完整细胞内有额外的松弛作用，可能是由于血红蛋白靠近红细胞膜。然而，我们不能排除这是用于从交换和扩散中去除松弛贡献的简单切向模型的结果。所提出的广泛的数据集应有助于未来的理论发展的横向松弛的血液。
Blood is a physiological substance with multiple water compartments, which contain water-binding proteins such as hemoglobin in erythrocytes and albumin in plasma. Knowing the water transverse (R2) relaxation rates from these different blood compartments is a prerequisite for quantifying the blood oxygenation level-dependent (BOLD) effect. Here, we report the Carr-Purcell-Meiboom-Gill (CPMG) based transverse (R2CPMG) relaxation rates of water in bovine blood samples circulated in a perfusion system at physiological temperature in order to mimic blood perfusion in humans. R2CPMG values of blood plasma, lysed packed erythrocytes, lysed plasma/erythrocyte mixtures, and whole blood at 3 T, 7 T, 9.4 T, 11.7 T and 16.4 T were measured as a function of hematocrit or hemoglobin concentration, oxygenation, and CPMG inter-echo spacing (τcp). R2CPMG in lysed cells showed a small τcp dependence, attributed to the water exchange rate between free and hemoglobin-bound water to be much faster than τcp. This was contrary to the tangential dependence in whole blood, where a much slower exchange between cells and blood plasma applies. Whole blood data were fitted as a function of τcp using a general tangential correlation time model applicable for exchange as well as diffusion contributions to R2CPMG, and the intercept R20blood at infinitely short τcp was determined. The R20blood values at different hematocrit and the R2CPMG values of lysed erythrocyte/plasma mixtures at different hemoglobin concentration were used to determine the relaxivity of hemoglobin inside the erythrocyte (r2Hb) and albumin (r2Alb) in plasma. The r2Hb values obtained from lysed erythrocytes and whole blood were comparable at full oxygenation. However, while r2Hb determined from lysed cells showed a linear dependence on oxygenation, this dependence became quadratic in whole blood. This possibly suggests an additional relaxation effect inside intact cells, perhaps due to hemoglobin proximity to the erythrocyte membrane. However, we cannot exclude that this is a consequence of the simple tangential model used to remove relaxation contributions from exchange and diffusion. The extensive data set presented should be useful for future theory development for the transverse relaxation of blood.