磁共振新技术在颈动脉狭窄诊断中的应用

Application of new techniques of MRI in the diagnosis of carotid artery stenosis

目的研究增强磁共振血管成像（CE—MRA）技术的成像影响因素，评价MR扫描序列对颈动脉狭窄硬化斑块的应用价值，探讨颈动脉狭窄血流动力学变化与临床症状的联系。方法颈动脉狭窄34例，男22例，女12例。年龄36～78岁，平均56岁。病人首先经多普勒超声（DUS）检查，然后行MRA及CE-MRA。22例同时采用亮血（Bright—blood）、黑血（Black—blood）技术、3例行血流测量分析（Flow measurements）。10例于磁共振检查后1周内接受颈动脉狭窄内膜剥除术。扫描技术：（1）MRA及CE-MRA：MRA：二维时间飞跃法MRA（2D TOF MRA）；CE-MRA：快速梯度回波扫描技术，冠状位采集。最佳扫描延迟时间主要采用造影剂团注试验（test-bolus）法。3例采用时间分辨回波分享血管成像技术（TRATE）。（2）斑块检查序列：亮血与黑血技术及增强前后T1序列。（3）血流测量分析：横断位心电门控2D相位对比序列，Argus系统分析血流方向、流速。结果血管覆盖范围：34例CE-MRA，23例良好显示颈部血管起始段至入颅段。2D TOF法11例。动脉狭窄评估程度：10例手术患者中，CE-MRA正确诊断血管狭窄者9例，低估狭窄程度1例。2D TOF正确诊断血管狭窄程度6例，高估3例，低估1例。22例亮血、黑血技术结合CE—MRA清晰显示血管壁及动脉硬化斑块。颈动脉单独成像24例中，Test—bolus法团注造影剂最佳扫描延迟时间为峰值时间-1s，且监视层面定于主动脉弓者18例。4例眩晕患者，颈动脉狭窄侧后交通动脉（PCOA）显示2例；PCOA粗大1例。狭窄侧未显示PCOA，同侧大脑后动脉主干增粗1例。2例锁骨下动脉窃血综合征血流方向异常，1例无名静脉狭窄，同侧颈静脉血流方向异常。结论（1）CE—MRA能完整、全程显示颈部血管，准确诊断颈动脉、椎动脉狭窄。（2）Test-bolus法确定扫描延迟时间为峰值时间-1s，并将监视层面定于主动脉弓时，可保证造影剂在动脉内达到高峰浓度时采集K空间数据，获得颈动脉单独成像的最佳图像。（3）亮血、黑血技术结合CE-MRA有助于显示颈动脉狭窄硬化斑块。（4）分析、测量颈动脉狭窄的血流动力学变化能全面评价狭窄后血流改变与临床症状的联系。

Objective To determine the factors of affecting imaging quality of contrast-enhanced magnetic resonance angiography（CE-MRA）, assess the value of MR scanning sequences for identification of carotid atherosclerotic plaque, and research the relationship between the dynamic circulation in carotid stenosis and carotid steal syndromes. Methods Thirty-four patients（male 22, female 12, aged 36-78 years） with carotid stenosis（diagnosed by Doppler ultrasound, DUS） were evaluated with CE-MRA and unenhanced two dimensional time of flight MRA（2D TOF MRA）. In CE-MRA, test-bolus and care-bolus were performed respectively in 25, 6. Next, Bright-Blood and Black-Blood techniques were used in 22 and ECG Gated 2D TOF PC sequences were done for the analysis of the flow direction and velocity in 3. Of thirtyfour patients, carotid endaterectomy was performed in 10. Results In CE-MRA, vessel segments from the aortic arch to the circle of Willis were imaged in 23;with 2D TOF MRA, 11. In cases with severe stenosis of carotid artery confirmed by operation, CE-MRA was in agreement with operation in 9, with underestimated in 1. 2D TOF MRA was in agreement with operation in 6,with overestimated in 3 and underestimated in 1. For test-bolus timing, the optimum delay time was that the peak time-lsecond with monitoring plane positioned in aorta, Bright-Blood and Black-Blood techniques demonstrated visualization of the abnormal vessel wall and specific plaque components in all cases. Of the 4 eases with vertigo, posterior communicating arteries （PCOA） on the ipsilateral carotid stenosis were displayed in 2, relative large in 1, and did not visualized while posterior cerebral artery was large on the same side in 1. Abnormal flow direction and velocity were analyzed in 2 eases of subclavian steal syndrome, 1 ease of brachiocephalic vein stenosis. Conclusion （1） CE-MRA is meaningful to provide a evaluation of the carotid artery including all vessel segments from aortic arch to the circle of Willis. Compared with 2D TOF, CE-MRA is more accurate in diagnosis of carotid artery stenosis. （2） For test-bolus timing, the optimum delay time was that the peak time -1 second with monitor plane in aorta, which is beneficial to achieve a good quality image during the first pass of the bolus. （3） Bright-Blood and Black-Blood techniques can be used to demonstrate the abnormal vessel wall and specific plaque components. （4） Flow measurement for dynamic flow in carotid artery stenosis provide a way to asses the relationship between carotid stenosis and some carotid steal syndromes.