双层探测器光谱CT肺动脉造影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 Pulmonary Angiography

目的探讨双层探测器光谱CT肺动脉造影(CTPA)40 keV虚拟单能量图像(VMI)质量及优化窗口设置。方法回顾性分析2020年12月至2021年5月在兰州大学第一医院Philips IQon双层探测器光谱CT上行CTPA的65例肺栓塞患者的资料。扫描后重组常规120 kVp混合能量图像(PI)、40 keV虚拟单能量图像(VMI_(40keV))。比较PI与VMI_(40keV)图像中肺动脉的CT值、图像噪声和对比噪声比(CNR)。调节并记录PI与VMI_(40keV)的个性化窗口自设值(Ind.-PI/Ind.-VMI_(40keV)),通过对Ind.-PI/Ind.-VMI_(40keV)与肺动脉CT值进行回归分析,获得PI与VMI_(40keV)的窗口校准值(Calc.-PI/Calc.-VMI_(40keV)),并拟合出PI与VMI_(40keV)的窗口优化值(Opt.-PI/Opt.-VMI_(40keV))。以4分法记录PI与VMI_(40keV)各窗口设置下图像主观质量评分,同时测量不同窗口设置下左上肺前段肺动脉直径。结果 VMI_(40keV)图像中肺动脉CT值[(1003.23±222.08) HU]、CNR(83.03±22.68)均高于PI[(354.06±73.76) HU]、CNR(23.44±7.03),差异具有统计学意义(t=46.089、t=39.321,P均<0.001);而VMI_(40keV)图像噪声[(11.72±2.11) HU]小于PI[(13.18±2.06) HU],差异具有统计学意义(t=9.811,P<0.001)。Opt.-PI/Opt.-VMI_(40keV)分别为890 HU、240 HU,1500 HU、500 HU。与标准窗口设置(Std.-)相比,所有调整后的窗口设置图像质量评分较高,且在VMI_(40keV)图像中,标准窗口设置高估了肺动脉直径。结论双层探测器光谱CT CTPA VMI_(40keV)图像质量优于PI图像,将常规默认肺动脉窗口调整至最佳窗口设置(窗宽、窗位:PI图像890 HU、240 HU,VMI_(40keV)图像1500 HU、500 HU),以获得观察肺栓塞的最佳图像质量。

Objective To explore the imaging quality of 40 keV virtual monoenergetic images(VMI)derived from duallayer spectral detector CT(DLCT)Pulmonary Angiography and its optimal window setting. Methods From December 2020 to May 2021,65 pulmonary embolism patients who underwent DLCTPulmonary Angiography were retrospectively enrolled.Conventional polyenergetic images(PI)and 40 keV virtual monoenergetic images(VMI_(40keV)) were generated after scanning. The CT value, image noise and contrast noise ratio(CNR) of the pulmonary artery were compared in PI and VMI_(40keV)images.Individual window settings(Ind.-PI/VMI_(40keV))of VMI_(40keV)were recorded.Calculated window settings(Calc.-PI/VMI_(40keV)) were mathematically calculated via regression analysis and optimized window settings(Opt.-PI/VMI_(40keV)) were obtained. Subjective image quality was assessed with a 4 point scale and measured the diameter of the upper left anterior pulmonary artery in PI and VMI_(40keV)with different window settings. Results The CT attenuation of the pulmonary artery in VMI_(40keV)[(1003.23±222.08) HU] and CNR(83.03±22.68) were higher than those in PI[(354.06±73.76) HU],CNR(23.44±7.03),the difference was statistically significant(t=46.089,t=39.321,P<0.001);while VMI_(40keV)image noise [(11.72±2.11) HU] was less than in PI[(13.18±2.06) HU],the difference was statistically significant(t= 9.811,P<0.001).The Opt.-of PI and VMI_(40keV)images are 890/240 HU and 1500/500 HU respectively.Compared with the standard window setting(Std.-),all the adjusted window settings have higher objective scores, and in VMI_(40keV),the standard window setting overestimated the pulmonary artery diameter. Conclusion The VMI_(40keV)Pulmonary Angiography derived from dual layer spectral detector CT have higher image quality than PI.It is recommended to adjust window settings(WW,WL:PI images 890,240 HU,VMI_(40keV)images 1500,500 HU) to obtain the best observation of pulmonary embolism image quality.