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

磁化传递对比度（MTC）是一种相对较新的技术，用于生成额外的组织对比度。本研究的目的是评估MTC技术在实验性超急性脑缺血Gd-DTPA给药后，在7 T的有效性。在初步研究中，我们研究了最佳组合的波型，持续时间，幅度，和偏移频率的MTC脉冲在体外。最佳MTC脉冲是具有较长持续时间、最大幅度和约3 kHz非共振的高斯脉冲。在7 T MR系统中，MTC脉冲的信号强度降低是不可避免的，动物实验中使用的MTC脉冲为20 msec高斯脉冲，幅度为12.6 μ T，偏频为1 kHz。暂时性阻断颈总动脉后，静脉注射Gd-DTPA 0.2mmol/kg，获得无MTC脉冲和有MTC脉冲的T1加权像，对照组无异常强化。双侧暂时阻断30分钟组，颈动脉阻断1小时后，增强T1加权像显示双侧脑室周围异常强化。MTC脉冲增强区与正常脑组织的对比度得到改善，但信号强度略有降低。单侧闭塞3 h组，侧脑室周围也可见异常强化，以暂时闭塞侧为主。随着时间的推移，异常对比增强的区域开始在基底节区扩散。MTC技术与Gd-DTPA联合应用可提高超急性期脑缺血的显示率。

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.