光谱CT头部虚拟平扫图像:不同单能量图像质量的对比

目的:探讨双层探测器光谱CT不同单能量图像在头部影像诊断中的临床应用效能。方法:回顾性分析2019年6-12月因头晕、晕厥和头痛等临床症状而在本院行光谱CT(IQon Spectral CT)头部CT平扫检查的38例患者的影像资料。从光谱CT扫描中可获取常规混合能量图像和40~120 keV的光谱成像数据,以5 keV为间隔增量将光谱数据重建为17组单能级图像。分别测量每组图像上幕上灰质和白质的CT值和噪声值(SD),并计算信号噪声比(SNR)和对比信噪比(CNR)。同时对常规图像与120 keV单能级图像的伪影区域的脑组织结构(灰、白质)的对比及后颅窝伪影情况进行主、客观评分和比较。采用Bonferroni法进行统计学分析。结果:各组单能图像之间脑灰质CT值(P<0.001)、噪声(P=0.012)和CNR(P<0.001)的差异均有统计学意义,而脑白质CT值的差异无统计学意义(P=0.107)。其中65 keV图像的脑灰质CT值,脑灰、白质的噪声和SNR均高于其它单能级和常规混合能量图像(P<0.05),CNR亦高于其它单能级图像和常规图像(P<0.05)。与常规图像比较,120keV单能级图像上颅底层面伪影区域的脑灰、白质CT值(P=0.046)、噪声(P<0.01)、SNR(P<0.001)和CNR(P<0.001)的差异均具有统计学意义,且图像质量评分(P<0.001)和伪影评分(P<0.001)的差异亦有统计学意义。结论:和常规图像相比,从双层探测器光谱CT重建的单能图像在65 keV灰、白质对比度好,图像噪声降低、软组织分别率提高。120 keV单能级图像在由颅骨引起的X线束硬化伪影方面,能有效还原周围组织结构,提升图像质量。

A comparative study of head image quality of virtual monochromatic images at different energy levels on spectral CT

Objective:To investigate the influence of monoenergetic images of different energy levels in the double-layer detector spectral computed tomography(CT)on the image quality of head.Methods:The CT images of 38 patients with dizziness,fainting and headache who underwent head CT examination at a IQon spectral CT scanner from June to December 2019 were retrospective analyzed.The poly-energetic images and monoenergetic images were all reconstructed from the spectral CT data of 40~120keV.The monoenergetic images were reconstructed into17 sets with 5keV interval increments.The CT attenuation and noise of gray and white matter in each group were measured.Signal-to-noise ratio(SNR)and contrast-to-noise ratio(CNR)were calculated.At the same time,the contrast of the grey and white matter and artifacts in the artifact area of the posterior fossa were subjectively(ie.,visual rating)and objectively scored and compared between the conventional images and the monoenergetic images at 120keV.Bonferroni correction test was used for statistical analysis.Results:The differences of the CT values on the monoenergetic images of grey matter(P<0.001),noise(P=0.012)and CNR(P<0.001)were statistically significant among the groups,while the difference of the CT values of the white matter among the groups was not statistically significant(P=0.107).Among them,the CT values of grey matter,the noise of grey and white matter and SNR on 65keV monoenergetic images were higher than those on the other monoenergetic and conventional polyenergetic images(P<0.05),and the CNR was higher than that of other monoenergetic images and conventional images(P<0.05).Compared with those on conventional images,the CT values of the gray and white matter(P=0.046),noise(P<0.01),SNR(P<0.001)and CNR(P<0.001)in the artifact area on 120keV monoenergetic images were significantly different.There were significant differences in subjective evaluation on image quality(P<0.001)and artifact score(P<0.001).Conclusion:Compared with conventional polyenergetic image,the monoenergetic image at 65keV of the double-layer detector spectral CT has better,grey-white matter contrast,lower image noise and higher resolution on the soft tissue.At 120keV,beam-hardening artifacts on CT images caused by the skull are significantly reduced,which effectively restores the surrounding tissue structure and improves the image quality.