双层探测器光谱CT胰腺动态增强40 keV虚拟单能量图像优化窗口设置研究

Optimal window setting for 40 keV virtual monoenergetic images derived from dual-layer spectral detector CT pancreas dynamic enhanced scanning

目的探讨双层探测器光谱CT胰腺动态增强扫描40 keV虚拟单能量图像质量及优化窗口设置。方法回顾性分析2019年1月至7月上海交通大学医学院附属瑞金医院经手术病理证实为胰腺神经内分泌肿瘤的28例患者的影像资料,均于术前1周内接受双层探测器光谱CT胰腺动态增强扫描。扫描后重建常规120 kVp混合能量图像(PI)、40 keV虚拟单能量图像(VMI40 keV)。测量比较动脉期、门静脉期PI与VMI40 keV图像中正常胰腺实质、胰腺病灶、腹壁脂肪、腹主动脉及门静脉的CT值,计算病灶对比噪声比(CNR),采用配对t检验比较胰腺实质CT值、病灶CT值及CNR。调节并记录动脉期及门静脉期VMI40 keV的个性化窗口自设值(W-Ind,包括窗宽和窗位),通过对W-Ind与动脉期腹主动脉CT值、门静脉期门静脉CT值进行回归分析,获得动脉期和门静脉期的窗口校准值(W-Calc),并拟合出窗口优化值(W-Opt)。以5分法记录PI在标准腹部窗口(W-Std)设置下与VMI40 keV在W-Std、W-Ind、W-Calc、W-Opt各窗口设置下图像主观质量评分。采用Friedman检验比较VMI40 keV在W-Std、W-Ind、W-Calc、W-Opt各窗口设置下图像主观质量评分,采用Wilcoxon秩和检验比较动脉期、门静脉期VMI40 keV在W-Opt窗口设置下与PI在W-Std设置下图像主观评分。同时测量各组图像不同窗口设置下病灶的最大径,采用单因素方差分析进行组间比较。结果动脉期、门静脉期VMI40 keV中病灶CT值[(464.0±136.7)、(375.4±79.2)HU]高于PI中病灶CT值[(168.8±38.0)、(140.5±23.5)HU],差异均具有统计学意义(t=-16.107、-22.225,P均<0.001);CNR(16.5±11.1、10.9±6.1)明显优于PI(4.5±2.9、3.0±1.9),差异均具有统计学意义(t=-7.838、-9.781,P均<0.001);而图像噪声[(11.8±1.5)、(11.8±1.4)HU]小于PI[(13.1±1.5)、(12.9±1.3)HU],差异均具有统计学意义(t=6.356、3.891,P均<0.001)。动脉期PI在W-Std窗口设置下与VMI40 keV在W-Std、W-Ind、W-Calc、W-Opt各窗口设置下图像主观质量评分分别为4(1)、1(0)、5(0)、5(0.75)、5(1)分,门静脉期分别为3.5(1)、1(0)、5(0)、5(0)、5(1)分。动脉期、门静脉期VMI40 keV在W-Std、W-Ind、W-Calc和W-Opt窗口设置下主观评分组间差异有统计学意义(χ^2=76.143、76.000,P均<0.001)。动脉期、门静脉期VMI40 keV在W-Opt窗口设置下图像主观质量评分均优于PI在W-Std窗口设置下评分(Z=4.685、4.235,P均<0.001)。动脉期、门静脉期各组图像不同窗口设置下肿瘤病灶最大径测值组间差异无统计学意义(F=0.008、0.004,P均>0.999)。结论双层探测器光谱CT胰腺动态增强扫描VMI40 keV图像质量优于常规混合能量图像,但由于VMI40 keV图像中组织CT值改变明显,常规默认腹部观察窗口建议调整至合适的窗口设置(窗宽、窗位:动脉期880、230 HU,门静脉期840、260 HU),以获得最佳的图像效果。

Objective To explore the image quality of 40 keV virtual monoenergetic images(VMI)derived from dual-layer spectral detector CT(DLCT)pancreas dynamic enhanced scanning and its optimal window setting.Methods From January to July 2019,28 patients who underwent pancreas enhanced DLCT scan within one week before surgery and pathologically confirmed of pancreatic neuroendocrine tumors(pNETs)were retrospectively enrolled.Conventional polyenergetic images(PI)and 40 keV virtual monoenergetic images(VMI40 keV)were generated after scanning.CT value of normal pancreatic parenchyma,lesion,abdominal subcutaneous fat,abdominal aorta and portal vein were measured in PI and VMI40 keV.The contrast-to-noise ratio(CNR)of the pNETs lesion was calculated.All these objective results were compared between VMI40 keV and PI using paired t test.Individual window settings(W-Ind,including window width and window level)of VMI40 keV were recorded.Calculated window settings(W-Calc)were mathematically calculated via regression analysis and optimized window settings(W-Opt)were obtained.Subjective image quality was assessed with a 5-point scale and compared among VMI40 keV with different window settings(W-Std,W-Ind,W-Calc and W-Opt)using Friedman test,and compared PI with standard abdominal window setting(W-Std)and VMI40keV with W-Opt settings using Wilcoxon test.The maximum diameter of lesion was measured and compared with one-way ANOVA analysis among PI and VMI40 keV with different windows settings.Results For VMI40 keV in both arterial phase and portal vein phase,the CT attenuation[(464.0±136.7),(375.4±79.2)HU]of pNETs lesion were statistically significantly higher than those in PI[(168.8±38.0),(140.5±23.5)HU](t=-16.107,-22.225,P<0.001),CNR(16.5±11.1,10.9±6.1)were also statistically significantly higher than those in PI(4.5±2.9,3.0±1.9)(t=-7.838,-9.781,P<0.001),while with lower image noise in VMI40 keV[(11.8±1.5),(11.8±1.4)HU]than PI(13.1±1.5,12.9±1.3 HU)(t=6.356,3.891,P<0.001).The subjective score for PI with W-Std and VMI40 keV with W-Std,W-Ind,W-Calc,W-Opt in arterial phase were 4(1),1(0),5(0),5(0.75),5(1),and which in portal vein phase were 3.5(1),1(0),5(0),5(0),5(1).The subjective score of VMI40 keV with different window settings had statistical differences(χ²=76.143,76.000,P<0.001).Compared to the image quality of PI with W-Std settings,VMI40 keV with W-Opt settings have higher objective score(Z=4.685,4.235,P<0.001).The maximum diameter of lesion has no statistical difference among PI and VMI40 keV with different window settings(F=0.008,0.004,P>0.999)in both arterial phase and portal vein phase.Conclusions The VMI40 keV in pancreas dynamic enhancement scanning derived from dual-layer spectral detector CT have higher image quality than PI.Due to changes of CT value of tissue in VMI40 keV,it is recommended to optimize window settings(window width/window level,880/230 HU for arterial phase and 840/260 HU for portal vein phase)to obtain the best image quality.