脊柱MRI成像中常见伪影总结 (artifacts)

2022-08-06 放射沙龙 放射沙龙

了解伪影是为了更好的诊断,但是阅片时,所见征象是否有临床意义的关键要看征象是否与症状体征相符。

磁共振由于复杂的成像原理和过程,容易产生各样式的伪影。如果不熟悉这些伪影特点,单纯阅片时容易错将伪影当成病变,导致误诊误治。现就脊柱MRI成像中常见伪影汇总如下:

1. 脑脊液流动伪影:易误诊为病变,应与椎管内占位相鉴别

图a和b提示脊髓背侧脑脊液中可见多个大的、不连续的低信号区(蓝色箭头)。此外,图a STIR序列脊髓内有一个线性高信号区,而在图b和c (FSE T2像)上高信号区消失了。蓝色箭头是脊髓腔内的脑脊液流动造成的流动伪影,白色箭头所指为截断伪影(下文会系统讲到)。蓝色和白色箭头征象均为伪影,椎管和脊髓都是正常的,星号区域为L1椎体血管瘤。

图:脊髓背侧低信号区为脑脊液流动造成的流动伪影

来源:https://radiopaedia.org/images/2101156

胸椎矢状面FSE T2加权像显示疑似硬膜内病变的脑脊液流动伪影(图a,箭头),在轴向脂肪抑制的FSE T2加权像上也观察到这种伪影(图b),然而在梯度回波T2加权像上却消除了这种伪影(图c)。PMID: 24515878

脑脊液流动伪影。轴向T2加权像显示环绕脊髓的蛛网膜下腔中的低信号(a,箭头)。梯度回波上的短TE消除了脊髓周围的流动伪影(b,箭头)。PMID: 30887091

在脊髓扫描时,随着脊髓腔的增大(胸椎常见,红箭头),常出现脑脊液流动伪影。图片来源:磁共振之家

2. 截断伪影(truncation artifact):在MR信号强度突然变化的组织界面上最容易看到,此伪影被视为平行于显示信号强度突然变化区域边缘的暗线或亮线。通常发生在脂肪-肌肉和脊髓-脑脊液界面,并可能导致脊髓内出现虚假的高信号强度区域,这可能被误解为脊髓空洞或损伤。

截断伪影被视为脊髓内高信号的线性区域(箭头),类似于脊髓空洞。在两个不同患者颈椎矢状面上脂肪抑制T2加权像(a)和梯度回波T2加权像(b)。PMID: 24515878

图a脊髓内看到的截断伪影(箭头),图b为校正后的图像。PMID: 24515878

使用错误的编码方向会导致颈脊髓出现假性空洞(图A箭头)。使用前后编码方向,伪影消失(图B箭头)。PMID: 18835643

3. 运动伪影

心脏和患者运动引起的运动伪影(箭头)。PMID: 18835643

颈部吞咽动作引起的运动伪影会被误认为脊髓病变(a,红箭头所示髓内高信号区),在颈前添加饱和带可有效抑制此伪影(b)。图片来源:磁共振之家

图b红箭头处为血管搏动伪影。图片来源:磁共振之家微信公众号

4. 化学位移伪影:在MRI成像过程中由于人体中水和脂肪内氢质子的进动频率差异而引起的伪影,常出现在水/脂界面。

化学位移伪影常被误认为硬脊膜结构(红箭头)。图片来源:磁共振之家

在右左(a)和前后(b)方向,脑脊液-脂肪分离区域(箭头)被视为暗带,脑脊液-脂肪重叠区域被视为亮带。图c为校正后的图像,伪影消失。PMID: 24515878

5. 其他容易识别的伪影

骨科金属植入物在3T时比在1.5T时引起更广泛的伪影。在脊髓背侧中表现为低信号强度(箭头),伴有脊髓变形。PMID: 18835643

外周信号伪影,常见于脊柱、四肢关节扫描中。所选择的线圈单元与扫描范围不匹配导致的伪影。可表现为条带状、在图像中心区域出现一个外来的“亮点”信号或图像的变形等。图片来源:磁共振之家

拼接伪影。在脊柱的扫描拼接中,很多时候由于某些因素(金属异物、参数不一致等)的干扰,上下两段的对比度不一致。图1:未经过任何处理,上下两段拼接后对比度差异较大。图2:经过图像滤过处理后,上下两段拼接后对比度得到很大改善。图片来源:磁共振之家

忽略的正常解剖结构。腰椎 MRI 可见明显椎基静脉孔,呈三角形(圆圈)

忽略的正常解剖结构。白箭头所指为椎基神经和血管在椎体中心形成的神经血管脂肪簇,黑箭头所指为椎基静脉孔(左图)。

了解伪影是为了更好的诊断,但是阅片时,所见征象是否有临床意义的关键要看征象是否与症状体征相符。

参考文献:

1.Semin Musculoskelet Radiol.2014;18:12-22.

2.J Neuroradiol. 2009;36(2):74-81.PMID:18835643

3.Clin Neuroradiol.2019;29(2):191-213.PMID:30887091

4.磁共振之家 (如有侵权,请联系微信spinejizhu删除)

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    2022-08-06 docwu2019

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