第一部分

双层探测器能谱CT低辐射剂量和低对比剂用量冠状动脉CTA：低keV和低kVp图像质量对比

摘要：

目的：本研究目的为探究双层探测器能谱CT行低辐射剂量和低对比剂用量的“双低剂量”冠状动脉CT血管造影（Coronary Computed Tomography Angiography，CCTA）的临床应用可行性，并探究低keV单能谱（mono-energetic）重建图像的临床应用价值。

材料和方法：纳入2017年4月到6月，就诊于北京协和医院，具有CCTA检查指征的可疑CAD患者，使用双层能谱探测器CT对患者行CCTA检查，将患者随机分配到A组和B组，A组、B组的管电压分别设为120 kVp和100 kVp，两组的对比剂用量均为36 mL,流速3 mL/s。A组重建40 - 80 keV 多个能级的单能能谱图像（40 - 80 keV图像）和120 kVp的混合能量常规图像（120 kVp图像），B组重建100 kVp的混合能量图像（100 kVp图像），对两组图像选取主动脉根部（Aortic root，Ao）和冠状动脉远段进行图像质量（Image Quality，IQ）定量和定性分析。

结果：共入组60例患者，每组30例（A组管电压120 kVp，平均管电流73.8 mAs；B组管电压100 kVp，平均管电流108.5 mAs）。两组病人的基本特征无统计学差异（P>0.05）。两组患者的有效辐射剂量无统计学差异（1.5 ± 0.3 mSv 和1.4 ± 0.3 mSv, P=0.20）。A、B两组图像对比，主动脉根部（Ao）和冠状动脉远段图像质量（IQ）定量分析结果显示，40–60 keV图像质量优于120 kVp或100 kVp混合能量图像质量（两组均P<0.05），所有单能能谱图像的图像噪声均低于120 kVp或100 kVp混合能量图像（两组均P<0.01）。A、B两组各图像对比，主动脉根部（Ao）和冠状动脉远段图像质量（IQ）定性分析结果显示，40 - 50 keV图像与100 kVp混合能量图像的主观图像质量评分并无统计学差异（P>0.8）。

结论：采用双层探测器能谱CT行CCTA“双低”剂量扫描具有良好的临床可行性，且与低电压（100 kVp）扫描方案相比，120 kVp扫描电压下采用40 - 50 keV能谱重建技术能够在不增加检查辐射剂量的前提下有效提高图像质量。

关键词：双能量CT，单能量重建，图像质量，能谱冠状动脉CTA，辐射剂量

第二部分

双层探测器能谱CT单能重建提高头部CT平扫图像质量应用价值研究

摘要：

目的：评价双层探测器能谱CT在改善头部CT平扫图像质量的应用价值，并将其与相同辐射剂量下120 kVp常规探测器CT的图像质量进行对比。

材料和方法：研究连续纳入2016年10月1日至11月1日在我院进行头部CT平扫的患者，对相同辐射剂量下双层探测器能谱CT (n=30)和常规探测器CT (n=30)患者的头部CT平扫的图像质量进行回顾性分析。将能谱CT的患者图像进行单能能谱重建，能量范围为40 - 140 keV，每5-keV为一个能级增量，其中65 - 70 keV区间内能级增量为1-keV（A1组）；能谱CT生成的120kVp混合能量常规图像为A2组；常规探测器CT的120kVp图像作为对照组（B组）。对单能量图像的CT值、图像噪声、信噪比（SNR）、对比噪声比（CNR）、后颅窝伪影进行定量分析；主观图像质量评分使用4分制评分标准（1分-图像质量很好，4分-图像质量差，不能用于诊断）由2个放射诊断医师独立完成，以确定最佳的重建keV。

结果：在65 - 70 keV水平，图像具有最佳的信噪比（SNR）和主观图像质量评分；在这个范围内，68 keV具有较高的SNR (68 keV组, A2 组和B组分别为18.48 ± 1.94, 15.55 ± 1.56和14.33 ± 1.38，P<0.001)，CNR (68 keV组, A2 组和B组分别为4.09 ± 0.65, 3.43 ± 0.56和3.52 ± 0.55，P<0.001) 和较低的图像噪声(68 keV组, A2 组和B组分别为1.80 ± 0.19, 2.11 ± 0.19和2.25 ± 0.25，P<0.001)

结论：与相同辐射剂量的常规探测器CT相比，能谱CT在68keV单能量重建能够提高头部CT平扫图像质量，同时减少图像伪影。

关键词：双层探测器能谱CT，单能量成像，图像对比度和图像质量，神经系统放射学

PART 1

Low Dose and Low Contrast Medium Coronary CT Angiography Using Dual-Layer Spectral Detector CT

Low keV versus Low kVp

Abstract

Purpose: The aim of the present study was to investigate the performance of low keV mono-energetic reconstructions in spectral coronary computed tomography angiography (CCTA) using dual-layer spectral detector CT with reduced contrast media and radiation dose.

Material and Methods: Sixty patients were randomly assigned to Groups A and B (both n=30) to undergo CCTA on a dual-layer spectral detector CT with tube voltage 120 kVp and 100 kVp (average tube current: 73.8 and 108.5 mAs, respectively), with contrast media volume of 36 mL used in both groups. The mono-energetic 40 - 80 keV and conventional 120 kVp images in Group A and conventional 100 kVp images in Group B were reconstructed. Quantitative and qualitative image quality (IQ) were evaluated in the aortic root and distal segments of the coronary arteries. 

Results: The patient characteristics were not significantly different between the two groups (all P>0.05), nor was the effective radiation dose (1.5 ± 0.3 and 1.4 ± 0.3 mSv, P=0.20). The quantitative IQ in aorta and coronary arteries of mono-energetic 40-60 keV was superior to conventional 120 kVp and 100 kVp images (all P<0.05). The noise in spectral images was lower compared to conventional images (all P<0.01). The subjective IQ score of 40 - 50 keV images was not significantly different from that of 100 kVp images (P>0.8).

Conclusion: The mono-energetic 40 - 50 keV reconstructions from spectral CCTA using dual-layer spectral detector CT provide improved IQ compared to conventional techniques while facilitating reduced radiation dose and contrast media.

Key words: Dual energy computed tomography, Mono-energetic reconstruction, Image quality, Spectral coronary CT angiography, Radiation dose

PART 2

Dual-layer spectral detector CT monoenergetic reconstruction improves image quality of non-contrast cerebral CT as compared with conventional single energy CT

Abstract

Purpose: To investigate and compare image quality of monoenergetic reconstructions from spectral NCCT to conventional 120kVp images acquired at a similar dose.

Materials and methods: Patients undergoing NCCT on a dual-layer spectral detector CT (n=30) and a conventional CT (n=30) were enrolled in the study. The spectral detector CT data was reconstructed at monoenergetic images from 40-140keV in 5-keV increments and 65-70keV in 1-keV increments (Group A1) and using single energy CT equivalent reconstruction (Group A2). The reference conventional 120kVp images (Group B) were acquired using a standard-of-care protocol with the same radiation dose. We evaluated the image quality of monoenergetic images and determined the optimal keV level using HU attenuation, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), artifact evaluation in posterior fossa by placing region-of-interest (ROI) and subjective image score by 2 radiologists independently using a 4-point scale (1–excellent, 4–undiagnostic). 

Results: The SNR and subjective image score were optimal at 66-70keV, while monoenergetic 68keV images with a higher SNR (18.48±1.94, 15.55±1.56 and 14.33±1.38 for Group 68keV, A2 and B respectively, P<0.001), CNR (4.09±0.65, 3.43±0.56 and 3.52±0.55 for Group 68keV, A2 and B respectively, P<0.001) and a lower noise (1.80±0.19, 2.11±0.19 and 2.25±0.25 for Group 68keV, A2 and B respectively, P<0.001). 

Conclusion: Spectral NCCT monoenergetic reconstructions at 68keV improve image quality and reduce artifact compared to conventional single energy CT without radiation dose penalty.

Keywords: dual-energy computed tomography, monoenergetic imaging, image contrast and quality, neuroradiology