光谱CT结合金属伪影去除技术降低乳腺癌患者胸部增强CT对比剂硬化伪影的临床价值

The clinical value of spectral CT combined with orthopedic metal artifact reduction technology in reducing artifacts from contrast media in enhanced chest CT of breast cancer patients

目的探讨光谱CT中单能谱成像结合金属伪影去除技术(O-MAR)降低对比剂注射侧静脉对比剂硬化伪影效果,寻找去除伪影的最佳单能谱范围,以提高腋窝淋巴结的显示。方法回顾性分析2022年12月至2023年2月四川大学华西医院行胸部增强CT扫描的35例乳腺癌患者影像资料。扫描数据重建为1组常规图像、17组单能谱图(能级范围为40~200 keV,每间隔10 keV为1组)和17组单能谱+O-MAR图像共35组图像。在重建图像的同层选择对侧胸大肌区,对比剂硬化高密度伪影区、低密度伪影区分别放置感兴趣区,并测量每组对比剂注射侧腋窝淋巴结检出个数、伪影最大层的伪影区面积及同层低密度伪影区、高密度伪影区、注射对侧胸大肌的CT值、SD值。分别计算高、低密度伪影区相对于同层对侧胸大肌CT值的差值ΔCT_(1)、ΔCT_(2)及伪影指数AI_(1)、AI_(2)。采用Friedman检验和Wilcoxon符号秩检验比较35组图像间ΔCT、AI、伪影区面积、淋巴结检出个数的差异,采用Kappa检验比较主观评价的差异。结果随着能级逐渐增高,单能谱图与常规图像、单能谱+O-MAR图相比,单能谱图ΔCT_(1)绝对值、ΔCT_(2)绝对值、AI_(1)、AI_(2)表现出先低后高的趋势;单能谱图的伪影面积减小及淋巴结检出个数增大(P<0.01)。相较于其他能级,当单能谱为100 keV时ΔCT_(1)值、140 keV时ΔCT_(2)值、120 keV时AI_(1)值、130 keV时AI_(2)值更接近于零,淋巴结检出个数在110~200 keV时检出率最高。而单能谱+O-MAR图像ΔCT_(1)绝对值表现出先低后高的趋势;ΔCT_(2)绝对值、AI_(1)、AI_(2)、伪影面积均显著减小;淋巴结检出个数显著增大(χ2分别为916.23、895.93、387.08、519.41、890.10、1027.98,P<0.01)。相较于其他能级,当单能谱+O-MAR图像在100 keV时的ΔCT_(1)值更接近于零,而ΔCT_(2)值随着能级增加更接近于零,淋巴结检出个数在110~200 keV时检出率最高。随着能级逐渐增高,相同能级间单能谱+O-MAR图像的ΔCT_(1)、AI_(1)、AI_(2)及伪影面积均显著小于单能谱图,淋巴结检出个数显著高于单能谱图(P均<0.01)。主观评分中110~200 keV单能谱图和100~200 keV单能谱+O-MAR图均高于4分,且单能谱+O-MAR图像的评分显著高于单能谱图像,2名放射医师主观评分一致性结果良好。结论光谱CT单能谱结合O-MAR成像技术在100~120 keV能级时,去除胸部增强CT对比剂硬化伪影及检出和显示的腋窝淋巴结效果最佳。

Objective To access the efficacy of monoenergetic imaging from spectral CT combined with metal artifact reduction for orthopedic implants(O-MAR)on reducing contrast hardening artifacts in the vein on the injection side,and determining the optimal monoenergetic spectral range to improve the display of axillary lymph node.Methods A total of 35 patients with breast cancer who underwent chest-enhanced CT scans were enrolled in this retrospective study.The original data were reconstructed to obtain a total of 35 sets of images,including one conventional image,17 groups of monoenergetic images,and 17 groups of monoenergetic+O-MAR images.The areas of interest were delineated in the high and low-density artifact area on the injection side of the same layer contrast agent,and the contralateral ectopectoralis.The CT value and its standard deviation(SD)were recorded respectively,the artifact area was measured,and the number of axillary lymph nodes was recorded.The difference in CT values(ΔCT_(1),ΔCT_(2))and the artifact index(AI_(1) and AI_(2))of the high and low-density artifact areas relative to the contralateral ectopectoralis in the same layer were calculated respectively.Friedman test and Wilcoxon signed-rank test were used to compare the differences ofΔCT,AI,artifact area,and number of lymph nodes among the three imaging modalities,and the Kappa test was used to compare the differences in subjective evaluation.Results As the energy level increased,compared to the conventional image,monoenergetic image,ΔCT_(1) absolute value,ΔCT_(2) absolute value,AI_(1),and AI_(2) showed a trend of initially low and then high,artifact area decreased,and the number of detected lymph nodes increased(P<0.01).Compared to other energy levels,when the monoenergetic image was 100 keV,ΔCT_(1) value,140 keV forΔCT_(2) value,120 keV for AI_(1) value,and 130 keV for AI_(2) value were close to zero,and the number of detected lymph nodes was highest at 110-200 keV.In contrast,in the monoenergetic+O-MAR images,ΔCT_(1) absolute value showed a trend of initially low and then high,but,ΔCT_(2) absolute value,AI_(1),AI_(2),and artifact area all significantly decreased,whereas the number of detected lymph nodes significantly increased(χ2 values were 916.23,895.93,387.08,519.41,890.10,and 1027.98,respectively.All P<0.01).Compared to other energy levels,when the monoenergetic+O-MAR image was at 100 keV,ΔCT_(1) value was close to zero,whileΔCT_(2) value became close to zero with increasing energy level,and the number of detected lymph nodes was highest at 110-200 keV.As the energy level increased,theΔCT_(1),AI_(1),AI_(2),and artifact area of monoenergetic+O-MAR images were significantly smaller than those of monoenergetic images at the same energy level,and the number of detected lymph nodes was significantly higher than that of monoenergetic images(P<0.01).The subjective scores for 110-200 keV monoenergetic images and 100-200 keV monoenergetic+O-MAR images were both higher than 4,and the score for monoenergetic+O-MAR images was significantly higher than that of single-energy spectrum images.The agreement between the two radiologists in assessing subjective scores was good.Conclusion At 100-120 keV level,spectral CT monoenergetic combined with O-MAR imaging technique has the best performance in removing hardening-induced artifacts of chest-enhanced CT contrast agent and detecting and displaying axillary lymph nodes.