Clinical Value of Spectral Imaging Combined with MAR for CTA after Embolization of Intracranial Aneurysms
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摘要: 目的：评价颅内动脉瘤栓塞术后能谱CTA联合去金属伪影技术（MAR）的应用价值。方法：收集37例颅内动脉瘤栓塞术后需行能谱头颈CTA检查患者的CT原始数据。分别重建出70～140 keV单能级图像、120 kVp-like混合能量图像及70～140 keV MAR处理图像和120kVp-like MAR图像。感兴趣区（ROI）放置在伪影最严重层面的线圈附近，测量CT值及标准差（SD），计算伪影指数（AI)及信噪比（SNR）。在主观分析方面，由2名诊断医生采用Likert 5分量表法对所有图像的伪影程度和血管显示能力进行评估。比较MAR组和非MAR组图像的主观评分和客观参数。采用Wilcoxon秩和检验、配对样本t检验及独立样本t检验比较各组图像之间的差异。结果：8组单能量图像上，MAR图像的AI明显低于非MAR图像。在80～110 keV条件下，MAR图像SNR高于非MAR组，差异具有统计学意义。相同keV下，与非MAR组相比，MAR组图像的伪影评分及周围血管显示主观评分得分均更高。对于非MAR处理图像，AI值与周围血管显示评分在植入不同直径弹簧圈的患者图像上没有统计学差异。对于MAR图像，较大直径弹簧圈组（>8.79 mm）患者图像的AI值明显高于常规直径组，而周围血管显示主观评分明显低于常规直径组。结论：能谱CTA成像联合MAR可有效减少颅内动脉瘤栓塞植入物伪影，改善周围血管显示，对于小直径的弹簧圈MAR减少伪影效果最为显著。Abstract: Objective: To evaluate the application value of combining spectral imaging and metal artifact reduction (MAR) in head and neck CTA after the embolization of intracranial aneurysms. Methods: We collected 37 patients who experienced embolization of intracranial aneurysms then received spectral imaging of head and neck CTA. Monochromatic images with energy ranging from 70～140 keV, 120kVp-like mixed energic images, 70～140 keV MAR images, and 120 kVp-like MAR images were generated. The region of interest was placed on the area near the coil and with the most serious metal artifact. CT attenuation and standard deviation were measured, and artifact index (AI) and signal-noise ratio (SNR) were calculated. Two radiologists independently subjectively evaluated the metal artifact and the display of surrounding vessels using Likert 5 scales. The subjective scores and objective parameters between MAR and non-MAR images were compared. The Wilcoxon ranking test, paired sample t test, and independent sample t test were utilized to compare parameters between the groups. Results: MAR images had significantly lower AI than did non-MAR images for all eight monochromatic energies. When energies ranged from 80–110 keV, SNR was higher for MAR images than for non-MAR images, and the difference was statistically significant. With same energies, MAR images had higher artifact and vessel display scores than did non-MAR images. For non-MAR images, the different coil diameters did not make a statistical difference in AI and vessel display scores. For MAR images, a larger coil diameter (>8.79 mm) led to higher AI and lower vessel display scores than did normal diameters (≤8.79 mm). Conclusion: The combination of spectral imaging and MAR could effectively reduce the metal artifact of implants for the embolization of intracranial aneurysms and improve the surrounding vessel display. Moreover, the metal artifact reduction effect was more significant for the coils with smaller diameters.
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Key words:
- tomography /
- X-ray computed /
- spectral imaging /
- embolization of intracranial aneurysms /
- metal artifact
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图 1 典型病例图。女，49岁，左侧颈内动脉瘤术后
（a）（b）为120 kVp-like非MAR图像（血管窗），显示弹簧圈周围伪影较重，无法准确判定弹簧圈与邻近血管的关系；（c）（d）为120 kVp-like MAR图像（血管窗），弹簧圈周围伪影明显减轻，可清晰显示弹簧圈及周围血管。（e）为120 kVp-like联合MAR血管曲面重组图像，清晰显示后交通动脉起始部的弹簧圈，邻近血管未见明显狭窄及瘤样扩张。
Figure 1. Scheme diagram of a representative case. Female, 49 years old, after surgery for left internal carotid aneurysm
表 1 MAR图像与非MAR图像的伪影指数与信噪比比较
Table 1. Comparison of artifact index and signal to noise ratio between MAR and non-MAR images
电压 AI P SNR P MAR组 非MAR组 MAR组 非MAR组 70 keV 49.67±67.19 112.04±53.18 0.014 −2.74±2.27 −4.20±3.13 0.164 80 keV 45.91±67.05 100.32±52.39 0.012 −2.91±2.64 −4.82±3.90 0.009 90 keV 41.91±61.17 96.48±47.02 0.009 −3.08±2.85 −4.57±2.93 0.011 100 keV 36.97±51.77 93.45±44.13 0.014 −3.21±3.04 −4.70±3.10 0.034 110 keV 36.45±52.85 94.59±47.65 0.016 −3.26±3.16 −4.56±3.06 0.044 120 keV 36.22±53.74 93.46±48.67 0.017 −3.24±3.20 −4.61±3.25 0.050 130 keV 36.01±54.51 92.14±49.39 0.017 −3.26±3.27 −4.69±3.44 0.050 140 keV 35.96±55.17 91.30±50.16 0.018 −3.25±3.28 −4.76±3.63 0.055 120 kVp-like 47.20±70.50 110.1±55.9 0.015 −3.19±2.40 −4.51±3.63 0.059 注：MAR为去金属伪影；AI为伪影指数；SNR为信噪比。 
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表 2 植入不同直径弹簧圈的患者CT图像质量比较
Table 2. Image quality comparison among CT images of patients implanted with coils of different diameters
参数 常规直径组（＜8.79 mm） 直径较大组（>8.79 mm） P AI（MAR） 22.72±16.02 79.91±108.18 0.011 AI（非MAR） 108.88±43.15 111.84±81.17 0.195 SNR（MAR） -2.00±2.32 -4.79±1.57 0.124 SNR（非MAR） -2.62±1.25 -7.04±4.54 0.068 伪影评分（MAR） 4.40±0.23 3.70±0.53 0.093 伪影评分（非MAR） 3.28±0.10 3.10±0.10 0.830 周围血管显示（MAR） 4.55±0.17 3.43±0.58 0.032 周围血管显示（非MAR） 3.25±0.37 3.10±0.10 0.131 注：MAR为去金属伪影；AI为伪影指数；SNR为信噪比。
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表 3 MAR图像与非MAR图像的主观图像质量评分比较
Table 3. Comparison of subjective image quality scores between MAR and non-MAR images
伪影评分 P 周围血管显示评分 P MAR组 非MAR组 MAR组 非MAR组 70 keV 3.76±0.53 3.01±0.34 0.009 3.87±0.64 3.03±0.76 0.009 80 keV 3.90±0.53 3.13±0.10 0.005 3.93±0.60 3.11±0.22 0.007 90 keV 4.07±0.48 3.24±0.15 0.001 4.04±0.67 3.19±0.28 0.009 100 keV 4.20±0.51 3.32±0.18 0.001 4.10±0.71 3.24±0.31 0.011 110 keV 4.33±0.46 3.43±0.15 <0.001 4.06±0.66 3.23±0.31 0.010 120 keV 4.43±0.46 3.50±0.16 <0.001 3.97±0.62 3.19±0.24 0.014 130 keV 4.47±0.41 3.61±0.16 <0.001 3.88±0.56 3.17±0.21 0.010 140 keV 4.54±0.42 3.67±0.14 <0.001 3.77±0.51 3.10±0.15 0.008 120 kVp-like 4.10±0.51 3.20±0.13 0.001 4.10±0.70 3.19±0.28 0.011 注：MAR为去金属伪影。
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