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Variant Appearances of Intracranial Aneurysms’Flow Artifact on Different MRI Sequences
ZHANG Yong, CHENG Jingliang, REN Cuiping, etal
Department of Radiology, the first Affiliated Hospital,Zhengzhou University,
Zhengzhou, Henan Province 450052, P. R. China
【Abstract】 Objective:To evaluate the appearances of flow artifact on different MRI sequences and its diagnosis value for intracranial aneurysms. Materials and Methods:Flow artifacts of different MRI sequences and MRA findings of 19 patients with intracranial aneurysms confirmed by DSA and/or operation were analyzed, retrospectively. MRI examination were performed on GE Signa 1.0 T superconductive MRI unit. All of the cases had undergone SE sequence T1WI and T2WI, GRE sequence, FLAIR sequence and Gd-DTPA enhancement T1WI, 17 cases with 3D TOF MRA. Results:Flow artifacts were characterized by irregular strip shadow at the level of aneurismal residual sac, which were located in the phase coding direction. All of 19 cases of intracranial aneurysms had demonstrated flow artifact on FLAIR sequence, 18 cases on GRE sequence, 17 cases on T2WI, 9 cases on T1WI. All of the 7cases which underwent Gd-DTPA enhanced had demonstrated flow artifact in the phase coding direction. Flow artifacts on GRE and FLAIR sequence were bigger than SE sequence; and T2WI bigger than T1WI; flow artifacts on Gd-DTPA post-contrast T1WI bigger than pre-contrast imaging. Conclusion:MR flow artifact demonstrated variant appearances on different MRI sequences, reasonable application of flow artifact was helpful for the diagnosis and differentiation of intracranial aneurysm.
【Key words】 Flow Artifact Brain Magnetic Resonance Imaging Brain aneurysm
颅内动脉瘤是一种相对少见而危害较大的脑血管病，常伴发蛛网膜下腔出血和脑出血。迄今，虽然DSA仍被认为是诊断颅内动脉瘤的金标准，但MRI的应用为颅内动脉瘤的诊断提供了新的手段；且颅内动脉瘤MRI图像上的流动伪影有助于颅内动脉瘤的诊断和鉴别诊断。笔者搜集2000年10月～2006年6月经MRI、MRA以及DSA和手术确诊的同时合并有流动伪影的19例颅内动脉瘤进行分析，评价不同MRI序列上颅内动脉瘤流动伪影的表现及流动伪影对颅内动脉瘤的诊断价值。
1.资料与方法
19例MRI同时合并有流动伪影的颅内动脉瘤均经DSA或手术证实，其中男11例，女8例；年龄6～72岁，平均51.9岁。临床表现有头痛、恶心呕吐，意识障碍和相应部位的神经定位症状。
扫描参数为：T1WI：TR425ms，TE10ms，矩阵256×224；T2WI：TR4200ms，TE102ms，矩阵320×256；GRE序列扫描参数为：TR625ms，TE15ms，翻转角20度，矩阵512×256；FLAIR序列扫描参数为：TR8000ms，TE120ms，TI2000ms，矩阵256×192。FOV24×18，层厚6mm，层间距2mm。3D TOF MRA扫描参数为TR 36ms，TE 10ms，RF偏转角20度，层厚1mm，130～154层，随后行最大信号强度投影重建。Gd-DTPA增强扫描时，Gd-DTPA用量约为0.1mmol/kg体重，经肘静脉快速团注后行MRI增强扫描。统计学分析采用卡方独立性检验，以P<0.05为检验水准。
2.结果
19例颅内动脉瘤位于鞍旁7个，侧裂池5个，鞍上池4个，桥前池3个。横断面动脉瘤最大径线介于7mm×8mm～31mm×32mm。在所有MRI序列图像上均合并有动脉瘤开放瘤腔水平的不规则条带状影，且均位于相位编码方向。
19例颅内动脉瘤在横断面T2WI上显示17例次流动伪影，在横断面T1WI上显示9例次。相比较而言，SE序列横断面T2WI上显示的流动伪影数量明显多于横断面T1WI（卡方独立性检验，χ2值为0.013，P<0.05），且T2WI较T1WI上所显示的伪影更为粗大、明显（图1和图2）。
所有19例合并有流动伪影的颅内动脉瘤在横断面FLAIR序列上均可显示流动伪影，且FLAIR序列图像上的流动伪影强度均大于SE序列。本组19例颅内动脉瘤在GRE序列上显示流动伪影18例次，且其强度均大于SE序列。19例同时合并有流动伪影的颅内动脉瘤均行3D TOF MRA扫描，其中源自颈内动脉海绵窦段6例，大脑中动脉6例，基底动脉4例，颈内动脉虹吸段5例。MRA图像上，动脉瘤均呈类圆形囊袋状突出影像。（图3～6）。
本组19例颅内动脉瘤行Gd-DTPA对比增强者7例，增强前T1WI上显示流动伪影者4例，未显示者3例；7例Gd-DTPA T1WI图像均显示相位编码方向上的流动伪影，且其信号强度明显大于增强前T1WI（图7和图8）。
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