Lin W, Celik A, Paczynski R P, Hsu C Y, Powers W J
Mallinckrodt Institute of Radiology, Department of Electrical Engineering, Washington University, St. Louis, Missouri 63110, USA.
J Cereb Blood Flow Metab. 1999 Aug;19(8):853-62. doi: 10.1097/00004647-199908000-00004.
Acute hypercapnia simultaneously induces increases in regional cerebral blood volume (rCBV) and the oxygen saturation of cerebral venous blood (Yv). Changes in both physiologic parameters may influence the changes in R2 (deltaR2) that can be measured in the brain with gradient echo magnetic resonance imaging. The authors examined the effect of incorporating independent measurements of the change in rCBV (deltarCBV) on the fidelity of the relation between deltaR2 and deltaYv in the setting of experimental hypercapnia. A two-dimensional T2-weighted gradient echo sequence was used to measure deltaR2 in the brain parenchyma of anesthetized rats in response to hypercapnia with respect to the control state. In parallel, estimates of rCBV were obtained using a three-dimensional steady-state approach in conjunction with a paramagnetic contrast agent during both control and hypercapnic states so that a deltarCBV could be calculated. Regional CBV values of 2.96 +/- 0.82% and 5.74 +/- 1.21% were obtained during the control and hypercapnic states, respectively, and linear relations between rCBV and CO2 tension in both arterial (r = 0.80) and jugular venous (r = 0.76) blood samples were obtained. When correlating deltaR2 directly with deltaYv, no clear relation was apparent, but a strong linear relation (r = 0.76) was observed when correction for deltarCBV was incorporated into the data analysis. These results are consistent with the current understanding of the mechanisms of blood oxygen level-dependent (BOLD) contrast and underscore the potential importance of taking into account deltarCBV when quantitative estimates of deltaYv from the "BOLD effect" are intended.
急性高碳酸血症可同时引起局部脑血容量（rCBV）增加和脑静脉血氧饱和度（Yv）升高。这两个生理参数的变化可能会影响通过梯度回波磁共振成像在脑部测量的R2（ΔR2）变化。作者研究了在实验性高碳酸血症情况下，纳入rCBV变化（ΔrCBV）的独立测量值对ΔR2与ΔYv之间关系保真度的影响。使用二维T2加权梯度回波序列，测量麻醉大鼠脑实质在高碳酸血症相对于对照状态下的ΔR2。同时，在对照和高碳酸血症状态下，使用三维稳态方法结合顺磁性造影剂获得rCBV估计值，从而计算出ΔrCBV。对照和高碳酸血症状态下的局部CBV值分别为2.96±0.82%和5.74±1.21%，并且在动脉血（r = 0.80）和颈静脉血（r = 0.76）样本中均获得了rCBV与二氧化碳分压之间的线性关系。当直接将ΔR2与ΔYv进行关联时，未发现明显关系，但在数据分析中纳入ΔrCBV校正后，观察到了强线性关系（r = 0.76）。这些结果与当前对血氧水平依赖（BOLD）对比机制的理解一致，并强调了在打算从“BOLD效应”对ΔYv进行定量估计时考虑ΔrCBV的潜在重要性。
