FUNCTIONAL IMAGING IN RODENT BRAIN USING INTRAVASCULAR IRON OXIDE CONTRAST

高分辨率功能磁共振 大鼠大脑皮质的成像(FMRI)提供了一种宝贵的技术 研究创伤后的可塑性和功能恢复。 Fmri已被用来显示麻醉状态下大脑皮质的激活。 利用动物的大胆效应和信号强度的变化 通常出现在几个百分点的数量级。方法：6名男性 用氟烷吸入氧气麻醉大鼠，静脉注射氟烷。 动脉插管后改用a-氯醛糖治疗 实验的其余部分和图像是在4.7T的VARIAN上获得的 伊诺瓦系统。每隔6小时采集一次梯度回波(GRE)图像 几秒钟。作为对比，高速T2加权自旋回波(SE)功能磁共振成像 是用一种罕见的序列进行的。提高对…的敏感性 显微磁化率变化，第一回波时间 增加到56ms。功能磁共振成像激活范式包括 关-开-关序列，每个周期持续60秒。前爪刺激 用持续时间为3ms、频率为3赫兹的3V脉冲序列执行， 通过插入的一对小针状电极传递 在左爪的皮下。实验是在这两种情况下进行的 注射Combidex前后的GRE和REARE序列 结果：GRE的信号强度增加了4-5% 激活过程中的成像(粗体效果)。在注射了 Combidex*，信号强度急剧下降15%-20% 在激活过程中反映CBV的变化。使用这些最佳配置 支持更高分辨率的128x128像素GRE图像 分辨率可达250 mm以上。该信号 在激活过程中用罕见序列测量的变化是 与使用粗体的GRE序列可比 机制。然而，注射造影剂后，减少了4-5% 在激活过程中检测到信号的变化。结论：高 大鼠大脑皮质感觉的分辨功能图 使用GRE序列或快速SE可以容易地获得刺激 与Combidex*结合的序列。定制的MR协议可以是 使激活的不同血管成分具有选择性 回应。这种方法对宏观因素相对不敏感。 敏感度高，因此非常适合高场fMRI 在动物身上做实验。

INTRODUCTION: High resolution functional magnetic resonance imaging (fMRI) of the rat cortex provides a valuable technique for investigating plasticity and functional recovery following trauma. fMRI has been used to demonstrate cortical activation in anaesthetized animals by exploiting the BOLD effect and the signal intensity changes typically seen are in the order of a few percent. METHODS: Six male rats were anesthetized with halothane in oxygen for venous and arterial catheterization then switched to a-chloralose for the remainder of the experiment and images were obtained on a 4.7T Varian INOVA system. Gradient echo (GRE) images were acquired every 6 seconds. For comparison high speed T2-weighted spin echo (SE) fMRI was performed using a RARE sequence. To increase the sensitivity to microscopic magnetic susceptibility variations, the first echo time was increased to 56ms. The fMRI activation paradigm consisted of off-on-off sequence with each period lasting 60s. Forepaw stimulation was performed with a train of 3V pulses of 3ms duration at 3Hz, delivered via a pair of small needle electrodes inserted subcutaneously in the left paw. Experiments were performed with both the GRE and RARE sequences before and after injection of Combidex*. RESULTS: A 4-5% increase in signal intensity was seen with the GRE imaging (BOLD effect) during activation. Following injection of Combidex*, there was a dramatic 15-20% decrease in signal intensity during activation reflecting a change in CBV. Using these optimal conditions higher resolution 128x128 pixel GRE images with in plane resolution of greater 250mm could be readily obtained. The signal change measured with the RARE sequence during activation was comparable to that seen with the GRE sequence using the BOLD mechanism. However, after injection of contrast agent 4-5% reduction in activation signal change was detected. CONCLUSIONS: High resolution functional maps of the rat cortex following sensory stimulation can be readily obtained using GRE sequences or fast SE sequences in conjunction with Combidex*. Tailored MR protocols can be made selective for different vascular components of the activation response. This approach is relatively insensitive to macroscopic susceptibility and is thus ideally suited to high fields fMRI experiments in animals.