Wu Gaohong, Luo Feng, Li Zhu, Zhao Xiaoli, Li Shi-Jiang
Biophysics Research Institute, Medical College of Wisconsin, Milwaukee, Wisconsin 53226-0509, USA.
Magn Reson Med. 2002 Dec;48(6):987-93. doi: 10.1002/mrm.10317.
The transient relationship between arterial cerebral blood flow (CBF(A)) and total cerebral blood volume (CBV(T)) was determined in the rat brain. Five rats anesthetized with urethane (1.2 g/kg) were examined under graded hypercapnia conditions (7.5% and 10% CO(2) ventilation). The blood oxygenation level-dependent (BOLD) contrast was determined by a gradient-echo echo-planar imaging (GE-EPI) pulse sequence, and CBV(T) changes were determined after injection of a monocrystalline iron oxide nanocolloid (MION) contrast agent using an iron dose of 12 mg/kg. The relationship between CBV(T) and CBF(A) under transient conditions is similar to the power law under steady-state conditions. In addition, the transient relationship between CBV(T) and CBF(A) is region-specific. Voxels with > or =15% BOLD signal changes from hypercapnia (7.5% CO(2) ventilation) have a larger power index (alpha = 3.26), a larger maximum possible BOLD response (M = 0.85), and shorter T()(2) (32 ms) caused by deoxyhemoglobin, compared to voxels with <15% BOLD signal changes (alpha = 1.82, M = 0.16, and T()(2) = 169 ms). It is suggested that the biophysical model of the BOLD signal can be extended under the transient state, with a caution that alpha and M values are region-specific. To avoid overestimation of the cerebral metabolic rate of oxygen changes seen using fMRI, caution should be taken to not include voxels with large veins and a large BOLD signal.
在大鼠脑中测定了动脉脑血流量（CBF(A)）与总脑血容量（CBV(T)）之间的瞬态关系。对5只经氨基甲酸乙酯（1.2 g/kg）麻醉的大鼠在分级高碳酸血症条件下（7.5%和10% CO(2)通气）进行检查。通过梯度回波平面回波成像（GE-EPI）脉冲序列测定血氧水平依赖（BOLD）对比度，使用12 mg/kg的铁剂量注射单晶氧化铁纳米胶体（MION）造影剂后测定CBV(T)变化。瞬态条件下CBV(T)与CBF(A)之间的关系类似于稳态条件下的幂律关系。此外，CBV(T)与CBF(A)之间的瞬态关系具有区域特异性。与BOLD信号变化<15%的体素相比，高碳酸血症（7.5% CO(2)通气）导致BOLD信号变化≥15%的体素具有更大的幂指数（α = 3.26）、更大的最大可能BOLD反应（M = 0.85）以及由脱氧血红蛋白引起的更短的T()(2)（32 ms）（α = 1.82，M = 0.16，T()(2) = 169 ms）。这表明BOLD信号的生物物理模型可以在瞬态状态下扩展，但需注意α和M值具有区域特异性。为避免使用功能磁共振成像（fMRI）高估所观察到的脑氧代谢率变化，应谨慎避免纳入具有大静脉和大BOLD信号的体素。
