Improved Visualization of Hypercutete Cerebral Intartion with Magnetization Transfer Contrast : Phantom and Animal Study

磁化转移造影剂（MTC）是一种相对较新的产生附加组织造影剂的技术。本研究的目的是评估Gd-DTPA给药后7 t MTC技术在实验性超急性脑缺血中的有效性。在初步研究中，我们在体外研究了MTC脉冲的波型、持续时间、振幅和偏移频率的最佳组合。最佳的MTC脉冲是持续时间较长、振幅最大、谐振频率约为3 kHz的高斯脉冲。在7t MR系统中，MTC脉冲对信号强度的降低是不可避免的。在动物实验中，使用的MTC脉冲为20 msec高斯脉冲，幅度为12.6muT，偏移频率为1 kHz。暂时阻断蒙古沙鼠颈总动脉后，静脉注射0.2 mmol/kg Gd-DTPA，获得无MTC脉冲和有MTC脉冲时的t1加权图像。没有颈动脉闭塞的对照组未见异常增强。在双侧暂时闭塞30分钟的组中，颈动脉闭塞1小时后，对比增强的t1加权图像显示双侧脑室周围异常增强。MTC脉冲增强区与正常脑组织的对比得到改善，但信号强度略有降低。单侧闭塞3小时组侧脑室周围也可见异常强化，以暂时性闭塞一侧为主。随着时间的推移，对比增强异常区域开始向基底神经节扩散。MTC脉冲对基底神经节的增强作用更为明显。MTC技术和Gd-DTPA可协同改善超急性脑缺血的描述。

The magnetization transfer contrast (MTC) is a relatively new technique to generate additional tissue contrast. The purpose of this study was to evaluate the effectiveness of MTC technique in experimental hyperacute brain ischemia after Gd-DTPA administration at 7 T.In the preliminary study, we investigated optimal combinations of the wave type, duration, amplitude, and offset frequency of MTC pulse in vitro. The optimal MTC pulse was the gauss pulse with longer duration, maximal amplitude and approximately 3 kHz off resonance. In 7 T MR system the signal intensity reduction with MTC pulse cannot be avoided.In the animal study, MTC pulse used was a 20 msec gauss pulse, the amplitude of 12.6muT,and the offset frequency of 1 kHz. Mongolian gerbils after temporarily occlusion of common carotid artery were administrated intravenously with 0.2 mmol/kg of Gd-DTPA and the T1-weighted images without and with the MTC pulse were obtained.No abnormal enhancements were observed in the control group without carotid occlusion. In the group with 30 minutes of bilateral temporary occlusion, the contrast enhanced T1-weighted images showed abnormal enhancement around the bilateral ventricles after one hour from carotid occlusion. Contrast between the enhancing area and the normal brian tissues was improved with MTC pulse, although the moderately signal intensity reduction was observed. In the group with 3 hours of unilateral occlusion, abnormal enhancement was also observed around the lateral ventricle dominantly in temporarily occluded side. As time passed, the area of abnormal contrast enhancement began to spread in the basal ganglia. The enhancement of basal ganglia was more conspicuous with application of the MTC pulse.MTC technique and Gd-DTPA can synergistically improve the depiction of hyperacute brain ischemia.