目的 探讨能谱CT单能量(85、90 keV)成像技术去除CT尿路成像(CTU)排泄期对比剂硬化伪影(BHA)的价值.方法 对15例成年患者于CTU排泄期应用能谱CT行尿路区能谱模式(GSI)扫描,在工作站以GSI viewer浏览器重建66、85和90 keV三组单能量图像.用66 keV图像代替传统120 kVp混合能量图像进行对比分析.由2名放射科医师在固定窗宽(350 HU)、窗位(40 HU)下对重建的1.25mm薄层轴位图像及重组VR图像质量进行主观目测评分,并测量图像指定区域(肾盂、肾盏旁BHA最明显处肾实质)的噪声值(以SD值表示),以腹壁下脂肪的噪声值为图像背景噪声(Nb),BHA(BHA)值为No与Nb平方差的平方根.结果 66、85和90 keV三组单能量图像的BHA分别为(28.12±8.89)HU、(16.75±8.05)HU及(16.05±7.78) HU,Nb分别为(13.01±1.96) HU、(19.83±2.84) HU及(20.13±2.83)HU.与66 keV组图像比较,85 keV和90 keV组图像的BHA分别降低了约40.43％和42.92％(P均＜0.001),Nb分别增加了约52.42％及54.72％(P均＜0.001),但85 keV和90 keV两组单能量图像间的BHA及Nb差异均无统计学意义(P=0.682、0.516).对图像的BHA面积、肾小盏边缘显示的锐利程度及重组VR图像质量进行主观评分,85和90 keV组图像的评分分别较66 keV组提高约100.75％、105.26％和94.49％(x2=26.82、28.71、24.88,P均＜0.001)；而85和90 keV两组图像间各主观评分差异均无统计学意义(P=1.00).结论 与相当于传统120 kVp混合能量模式的66 keV组图像相比,能谱CT可在85和90 keV单能量水平显著降低CTU排泄期肾盂肾盏内高浓度对比剂产生的BHA,提高图像质量.%Objective To assess the value of monochromatic images (85, 90 keV) of Gemstone spectral CT for reducing beam-hardening artifacts (BHAs) caused by contrast medium in CT urography (CTU) excretory phase. Methods With institutional review board approval, images of the excretory phase were acquired using gemstone spectral imaging (GSI) mode in 15 adult patients who underwent CTU examination. All data were transferred to AW4. 4 workstation to generate 3 sets of monochromatic images (66, 85 and 90 keV). The 66 keV image set was used to instead of the conventional 120 kVp polychromatic images for analyzing (according to the research data offered by GE company, 66 keV monochromatic images had the same imaging effect of 120 kVp polychromatic images). Two radiologists reviewed all images respectively, and image quality of 1. 25 mm thin section cross-sectional images and the reconstructed volume rending (VR) images with fixed window width (350 HU)and window level (40 HU) were assessed visually. The background image noise (Nb) was measured as the standard deviation of the pixel values from a ovoid ROI drawn in a homogeneous region of subcutaneous fat of the anterior abdominal wall, and the noises of the mostly affected region by the beam-hardening artifacts of the iodine contrast beside the opacified minor calyxes were measured in each three consecutive cross-section, while beam-hardening artifact was defined as square root of the difference between the square number of noise of ROI and noise of background. Results BHA of three sets of monochromatic images (66, 85 and 90 keV) was (28. 12 + 8. 89) HU, (16. 75 + 8. 05) HU and (16.05 + 7. 78) HU, respectively. Compared with 66 keV set, the reduction of BHA in 85 and 90 keV sets was 40. 43% and 42. 92% (both P<0. 001) , respectively, while there was no significant difference between 85 and 90 keV image sets(P = 0. 682). Nb of the three sets of monochromatic images was (13. 01 + 1. 96)HU, (19. 83 + 2. 84)HU and (20. 13 + 2. 83)HU, respectively. Compared with 66 keV set, the increase of Nb in 85 and 90 keV sets was 52. 42% and 54. 72% (both P< 0. 001) , respectively, while there was no significant difference between the two latters (P = 0. 516). When the areas of BHA, the sharpness of the edges, the opacified minor calyxes and the image quality of reconstructed VR images were com-. Pared, the subjective score of 85 and 90 keV sets both increased by 100. 75%, 105.26% and 94.49% (x2=26. 82, 28.71, 24. 88, respectively, both P<0. 001) than the 66 keV set, while there was no significant difference between the two latters (P=1.00). Conclusion Compared with 66 keV image set, which is similar to the conventional 120 kVp polychromatic mode, high-definition CT gemstone spectral imaging can considerably reduce BHA caused by contrast medium in CTU excretory phase at the monochromatic level of 85 and 90 keV, and improve image quality.
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