Lin W, Paczynski R P, Celik A, Hsu C Y, Powers W J
Mallinckrodt Institute of Radiology, Department of Electrical Engineering, Washington University, St. Louis, Missouri 63110, USA.
Magn Reson Med. 1998 Dec;40(6):857-64. doi: 10.1002/mrm.1910400611.
Acute normovolemic hemodilution (HD) was induced in anesthetized rats to assess the effect of changes in hematocrit (Hct) on signal intensity in T2*-weighted magnetic resonance (MR) images. Other relevant physiological parameters were maintained invariant. Two degrees of HD were induced: mild (Hct reduced from 42.6+/-2.2% to 33.4+/-2.1%) and moderate (Hct reduced from 44.6+/-2.7% to 26.2+/-1.7%). A two-dimensional gradient-echo sequence was used to monitor signal changes with high temporal resolution before, during, and after HD protocols. The time course of signal intensity change was closely related to that of changes in Hct. Corresponding changes in R2* (deltaR2*) with respect to the pre-HD state were calculated for the brain parenchyma. Average deltaR2* values of -0.24+/-0.06 s(-1) and -0.40+/-0.07 s(-1) were obtained for the mild and moderate HD groups, respectively, during the final 2 min of MR imaging (proximal to correlative measurements of Hct). MR measured deltaR2* values were in close agreement with the expected changes in R2* predicted from theory when the measured changes in Hct were used as independent variables. These data are in good agreement with the current understanding of the effects of changes in the intravascular concentration of deoxyhemoglobin on induced magnetic susceptibility and hold promise for quantitative measurement of brain oxygenation in vivo.
在麻醉大鼠中诱导急性等容血液稀释（HD），以评估血细胞比容（Hct）变化对T2加权磁共振（MR）图像信号强度的影响。其他相关生理参数保持不变。诱导了两种程度的血液稀释：轻度（Hct从42.6±2.2%降至33.4±2.1%）和中度（Hct从44.6±2.7%降至26.2±1.7%）。使用二维梯度回波序列在血液稀释方案实施前、期间和之后以高时间分辨率监测信号变化。信号强度变化的时间进程与Hct变化的时间进程密切相关。计算脑实质相对于血液稀释前状态的R2（ΔR2*）的相应变化。在MR成像的最后2分钟（接近Hct的相关测量值），轻度和中度血液稀释组的平均ΔR2值分别为-0.24±0.06 s-1和-0.40±0.07 s-1。当将测量的Hct变化用作自变量时，MR测量的ΔR2值与根据理论预测的R2*预期变化非常一致。这些数据与目前对脱氧血红蛋白血管内浓度变化对诱导磁化率影响的理解高度一致，并有望用于体内脑氧合的定量测量。
