Morell Arvid, Lennmyr Fredrik, Jonsson Ove, Tovedal Thomas, Pettersson Jean, Bergquist Jonas, Zemgulis Vitas, Einarsson Gunnar Myrdal, Thelin Stefan, Ahlström Håkan, Bjørnerud Atle
Section of Radiology, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Uppsala, Sweden,
MAGMA. 2015 Apr;28(2):135-47. doi: 10.1007/s10334-014-0452-5. Epub 2014 Jun 28.
Perfusion assessment by monitoring the transport of a tracer bolus depends critically on conversion of signal intensity into tracer concentration. Two main assumptions are generally applied for this conversion; (1) contrast agent relaxivity is identical in blood and tissue, (2) change in signal intensity depends only on the primary relaxation effect. The purpose of the study was to assess the validity and influence of these assumptions.
Blood and cerebral tissue relaxivities r1, r2, and r2* for gadodiamide were measured in four pigs at 1.5 T. Gadolinium concentration was determined by inductively coupled plasma atomic emission spectroscopy. Influence of the relaxivities, secondary relaxation effects and choice of singular value decomposition (SVD) regularization threshold was studied by simulations.
In vivo relaxivities relative to blood concentration [in s(-1) mM(-1) for blood, gray matter (GM), white matter (WM)] were for r1 (2.614 ± 1.061, 0.010 ± 0.001, 0.004 ± 0.002), r2 (5.088 ± 0.952, 0.091 ± 0.008, 0.059 ± 0.014), and r2* (13.292 ± 3.928, 1.696 ± 0.157, 0.910 ± 0.139). Although substantial, by a nonparametric test for paired samples, the differences were not statistically significant. The GM to WM blood volume ratio was estimated to 2.6 ± 0.9 by r1, 1.6 ± 0.3 by r2, and 1.9 ± 0.2 by r2*. Secondary relaxation was found to reduce the tissue blood flow, as did the SVD regularization threshold.
Contrast agent relaxivity is not identical in blood and tissue leading to substantial errors. Further errors are introduced by secondary relaxation effects and the SVD regularization.
通过监测示踪剂团注的传输来进行灌注评估，关键取决于将信号强度转换为示踪剂浓度。通常为此转换应用两个主要假设；（1）造影剂在血液和组织中的弛豫率相同，（2）信号强度的变化仅取决于主要弛豫效应。本研究的目的是评估这些假设的有效性和影响。
在4头猪身上于1.5 T场强下测量钆双胺的血液和脑组织弛豫率r1、r2和r2*。通过电感耦合等离子体原子发射光谱法测定钆浓度。通过模拟研究弛豫率、二次弛豫效应以及奇异值分解（SVD）正则化阈值选择的影响。
相对于血液浓度的体内弛豫率[单位为s(-1) mM(-1)，血液、灰质（GM）、白质（WM）]，r1分别为（2.614±1.061，0.010±0.001，0.004±0.002），r2分别为（5.088±0.952，0.091±0.008，0.059±0.014），r2分别为（13.292±3.928，1.696±0.157，0.910±0.139）。虽然差异较大，但通过配对样本的非参数检验，差异无统计学意义。通过r1估计GM与WM的血容量比为（2.6±0.9），通过r2为（1.6±0.3），通过r2为（1.9±0.2）。发现二次弛豫会降低组织血流，SVD正则化阈值也会有此作用。
造影剂在血液和组织中的弛豫率不同，会导致显著误差。二次弛豫效应和SVD正则化会引入进一步的误差。
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