Volume 42 Issue 5
Oct.  2018
Article Contents

Citation:

Evaluation of the image quality of integrated imaging in coronary combined with carotid and cerebrovascular computed tomography angiography

  • Corresponding author: Kai Sun, Henrysk@163.com ; Bin Lyu, blu@vip.sina.com
  • Received Date: 2018-02-27
    Fund Project:

    Science and Technology Planning Project of Baotou 2015S2004-1-5

    National Natural Science Foundation of China 81560286

  • Objective To evaluate the image quality, radiation dose and key technologies of integrated imaging in coronary combined with carotid and cerebrovascular computed tomography angiography (CTA), which hopes to offer a non-invasive imaging method for cardiovascular and cerebrovascular diseases evaluation.Methods A total of 493 symptomatic patients referred for simultaneous coronary, carotid, and cerebrovascular CTA were prospectively included. The subjects were divided into two groups according to CT model. Group A (300 cases), on which 3rd generation dual-source CT was performed, was further divided into groups A1 (n=69, HR ≤ 65 bpm) and A2 (n=231, HR>65 bpm), while group B (113 cases), on which 2nd generation dual-source CT was performed, was further divided into groups B1 (n=92, HR ≤ 65 bpm) and B2 (n=101, HR>65 bpm).Objective and subjective image quality and radiation dose were nalyzed, factors influencing image quality were determined, and the key technologies of the method were described. The measurement data were tested by independent sample t test, the frequency parameter composition ratio in the patient's clinical data was tested by chi-square χ2 test, and Cohen Kappa analysis was used to evaluate the consistency of the image quality score.Results (1) No statistically significant difference between groups A and B was found in terms of age (t=0.58, P=0.847), gender (χ2=1.45, P=0.228), and body mass index (t=1.20, P=0.277). (2)Objective evaluation of image quality:Common carotid artery, internal carotid artery, middle cerebral artery, and vertebral artery CT values and noise in group A were significantly lower than those in group B (t=1.98-4.49, all P < 0.05), although no statistically significant difference between groups was found in terms of aortic root CT values (t=0.68, P=0.495) and noise score (t=0.31, P=0.755). (3) The consistency of the image quality assessment was good (Kappa value=0.912). ① Subjective evaluation of image quality:The average coronary CTA image quality score of group A was better than that of group B (t=0.018, P=0.001), and the rate of non-diagnostic coronary grade 4 vessels based on number of patients in group A was lower than that in group B (χ2=6.63, P=0.014). ② Carotid-cerebrovascular CTA score of group A was better than group B (t=0.013, P=0.004), and carotid-cerebrovascular grade 4 vessels were less likely to be diagnosed in group A than in group B (χ2=4.38, P=0.036). ③ The effective radiation dose of group A was significantly lower than that of group B[(1.48±0.33) mSv vs. (2.14±0.52) mSv; t=14.79, P=0.001].Conclusions Integrated imaging by coronary and cerebrovascular CTA is a non-invasive imaging method which adopted different heart rates were captured by different scan time windows can providing high image quality with significant reduction of radiation for evaluation of coronary and cerebrovascular disease.
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Evaluation of the image quality of integrated imaging in coronary combined with carotid and cerebrovascular computed tomography angiography

    Corresponding author: Kai Sun, Henrysk@163.com
    Corresponding author: Bin Lyu, blu@vip.sina.com
  • 1. Department of Radiology, Baotou Central Clinical Medicine College, Inner Mongolia Medical University, Inner Mongolia 014040, China
  • 2. Key Laboratory of Arrhythmias of Ministry of Education, Research Center of Translational Medicine, Shanghai East Hospital, Tongji University School of Medicine, Shanghai 200120, China
  • 3. Department of Cardiology, Center of Translational medicine, Baotou Central Hospital, Baotou 014040, China
  • 4. Department of Radiology, Xuanwu Hospital, Capital Medical University, Beijing 100037, China
  • 5. State Key Laboratory of Cardiovascular Disease, Fu Wai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100053, China
Fund Project:  Science and Technology Planning Project of Baotou 2015S2004-1-5National Natural Science Foundation of China 81560286

Abstract: Objective To evaluate the image quality, radiation dose and key technologies of integrated imaging in coronary combined with carotid and cerebrovascular computed tomography angiography (CTA), which hopes to offer a non-invasive imaging method for cardiovascular and cerebrovascular diseases evaluation.Methods A total of 493 symptomatic patients referred for simultaneous coronary, carotid, and cerebrovascular CTA were prospectively included. The subjects were divided into two groups according to CT model. Group A (300 cases), on which 3rd generation dual-source CT was performed, was further divided into groups A1 (n=69, HR ≤ 65 bpm) and A2 (n=231, HR>65 bpm), while group B (113 cases), on which 2nd generation dual-source CT was performed, was further divided into groups B1 (n=92, HR ≤ 65 bpm) and B2 (n=101, HR>65 bpm).Objective and subjective image quality and radiation dose were nalyzed, factors influencing image quality were determined, and the key technologies of the method were described. The measurement data were tested by independent sample t test, the frequency parameter composition ratio in the patient's clinical data was tested by chi-square χ2 test, and Cohen Kappa analysis was used to evaluate the consistency of the image quality score.Results (1) No statistically significant difference between groups A and B was found in terms of age (t=0.58, P=0.847), gender (χ2=1.45, P=0.228), and body mass index (t=1.20, P=0.277). (2)Objective evaluation of image quality:Common carotid artery, internal carotid artery, middle cerebral artery, and vertebral artery CT values and noise in group A were significantly lower than those in group B (t=1.98-4.49, all P < 0.05), although no statistically significant difference between groups was found in terms of aortic root CT values (t=0.68, P=0.495) and noise score (t=0.31, P=0.755). (3) The consistency of the image quality assessment was good (Kappa value=0.912). ① Subjective evaluation of image quality:The average coronary CTA image quality score of group A was better than that of group B (t=0.018, P=0.001), and the rate of non-diagnostic coronary grade 4 vessels based on number of patients in group A was lower than that in group B (χ2=6.63, P=0.014). ② Carotid-cerebrovascular CTA score of group A was better than group B (t=0.013, P=0.004), and carotid-cerebrovascular grade 4 vessels were less likely to be diagnosed in group A than in group B (χ2=4.38, P=0.036). ③ The effective radiation dose of group A was significantly lower than that of group B[(1.48±0.33) mSv vs. (2.14±0.52) mSv; t=14.79, P=0.001].Conclusions Integrated imaging by coronary and cerebrovascular CTA is a non-invasive imaging method which adopted different heart rates were captured by different scan time windows can providing high image quality with significant reduction of radiation for evaluation of coronary and cerebrovascular disease.

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  • 冠状动脉粥样硬化与颈动脉、脑动脉粥样硬化密切相关[1-5]。研究表明,32.4%无心脏症状的脑梗死患者同时合并有冠状动脉重度狭窄[6]。因此,全面准确地评价心脑血管动脉粥样硬化的程度及两者的关系,能够进行早期干预,对降低心脑血管事件的发生具有重要的临床意义。传统上,用多层螺旋CT行冠状动脉、头颈部动脉一体化成像时,总辐射剂量高、对比剂用量大、操作费时,且心率均需控制在60次/min。本研究旨在突破心率限制,通过评价CT心脑血管一体化成像的客观图像质量、主观图像质量和辐射剂量,分析图像质量的影响因素,探讨该方法的关键技术点,为临床提供一种无创的评价心脑血管的影像学方法。

1.   资料与方法

    1.1.   临床资料

  • 前瞻性选择2015年10月至2017年7月在内蒙古医科大学包头临床医学院临床上需要同时进行冠状动脉和头颈部动脉CT血管造影(CT angiography,CTA)的连续性患者493例。入选标准:①有心血管或脑血管疾病易患因素的高危人群,如有糖尿病、高血脂、高血压、吸烟史、心脑血管疾病家族史;②无CTA检查禁忌证;③了解CTA扫描及研究方案,并签署知情同意书。排除标准:①有对比剂过敏史;②严重肝、肾功能不全病史(肾小球滤过率 < 60 mL/min);③心功能不全;④患瓣膜病或其他心脏疾病,如心肌病或先天性心脏病;⑤各种病因的肺动脉高压;⑥怀孕或育龄、哺乳期妇女;⑦研究相关数据不全者。

    根据CT扫描机型将患者分为A、B两组。A组采用第三代双源CT(Force,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描,共300例,其中男性199例,女性101例;年龄27~92岁,平均年龄(54±9)岁;体重指数(body mass index,BMI)为10.8~32.6 kg/m2,平均BMI为(22.50±2.37)kg/m2;心率为52~128次/min,平均心率为(74±11)次/min。根据心率不同将A组分为A1组(n=69,心率≤65次/min)和A2组(n=231,心率>65次/min)。B组采用第二代双源CT(Definiton Flash,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描,共193例,其中男性64例,女性129例;年龄34~83岁,平均年龄(54±10)岁;BMI为19.8~27.5 kg/m2,平均BMI为(22.15±2.01)kg/m2;心率为56~108次/min,平均心率为(57±5)次/min。根据心率不同将B组分为B1组(n=92,心率≤65次/min)和B2组(n=101,心率>65次/min)。全部患者中怀疑心脑血管病变和体检者共454例;枕骨术后1例;怀疑头颈血管动脉瘤1例;冠状动脉支架或经皮冠状动脉介入治疗术后18例;合并头颈血管支架3例,其中2例在颅脑动脉,1例颈动脉;仅头颈血管支架者1例;冠脉搭桥者2例,其中1例合并头颈血管支架术后;心脏起搏器者术后1例;主动脉弓壁间血肿1例;其他11例。

  • 1.2.   检查方法

  • A组扫描参数如下:探测器准直为2 mm×192 mm×0.6 mm,旋转时间为0.25 s,螺距3.2,管电压自动调节(CARE kV,德国西门子Healthcare公司)[7-8],管电流采用自动调节技术(CAREDose 4D,德国西门子Healthcare公司)。扫描前行呼吸训练,常规舌下喷硝酸甘油2喷。先行冠状动脉钙化评分扫描,然后实施“一站式”血管联合增强扫描。扫描方向为从足部向头部,扫描范围从隔顶至颅顶(心脏+头颈部范围)。心率≤65次/min,扫描时采用舒张期成像,即RR间期的55%;心率>65次/min,采用收缩期成像,即RR间期的30%。B组扫描参数如下:准直为2 mm×128 mm×0.6 mm,旋转时间为0.28 s,螺距3.2,管电压为100~120 kV,管电流为360~430 mAs。具体扫描方法与A组相同。

    注射对比剂采用Bolus-tracking方法,应用碘海醇(OmniPaque 350,美国GE Healthcare公司):A组对比剂总量为50 mL,B组对比剂总量为60 mL,采用双筒高压注射器(德国Ulrich Medical公司)以5.0 mL/s的流率肘静脉注射,在升主动脉根部设置ROI(阈值为100 HU),峰值时间延迟8 s开始扫描,流速和对比剂总量可根据不同的BMI进行调节。

  • 1.3.   图像后处理

  • 两组患者均采用迭代算法进行轴位图像重建。横断位图像传送至工作站(Syngo.Via CTA,德国西门子Healthcare公司)进行后处理。A组采用高级模拟迭代重建技术进行后处理,B组采用正弦图确定迭代重建技术[7]。将原始数据传到工作站后,采用Circulation软件和用软组织卷积核(B36f)对两组患者进行血管重建,有血管壁钙化者,采用锐利组织卷积核重建图像(B46)来补偿伪像。经最大密度投影、曲面重建、容积再现和心血管优化分析软件进行处理。脑血管重建方法:A组采用数字减影血管造影术(digital subtraction angiography,DSA)减影软件;B组采用Inspace重建,行最大密度投影和容积再现,重建层厚1 mm,间隔0.9 mm,卷积核D30f。

    采用美国心脏病协会推荐的18分段法[9],闭塞血管远段不计入分析。头颈部动脉血管分段:颈内动脉分为C1~C5段;大脑中动脉分为M1~M5段,大脑前动脉分为A1~A5段。

  • 1.4.   图像质量评价

  • 图像质量客观评价[9]:测量体轴横断位图像。①冠状动脉显影强度评价:测量主动脉根部(左主干起源层面)的CT值(ROI约100 mm2);②头颈动脉显影强度评价:分别测量颈总动脉起始部(ROI约10 mm2)、颈内动脉起始部(ROI约2 mm2)、大脑中动脉M1段(ROI约2 mm2)、椎动脉V4段(ROI约2 mm2)的CT值;③噪声值取图像CT值的标准差;④信噪比(signal noise ratio,SNR)和对比噪声比(contrast noise ratio,CNR):在主动脉根部选取ROI区域,分别测量增强前和增强后的CT值,将二者之差定义为血管强化值,CNR为血管强化值与图像噪声之比。于主动脉根部测量强化后的CT值,计算平均CT值作为主动脉信号强度(signal intensity,SI)(简称SI主动脉),取其CT值的平均标准差作为图像噪声,测量升主动脉起始部水平胸壁前空气的CT值的标准差为背景噪声(background noise,BN),测量主动脉弓层面胸大肌CT值,计算其平均值为背景信号强度(简称SI肌肉),ROI测量面积均为0.5 cm2 [7]

    SNR=SI主动脉/BN;CNR=(SI主动脉-SI肌肉)/BN

    图像质量主观评价[9]:由两名主治以上医师进行分析与评价。将冠状动脉、头颈部动脉图像质量分为4级,相应评为1~4分:1级为血管显示良好,边界清晰,无伪影或血管中断;2级为血管边界模糊,有轻度伪影;3级为血管有中度伪影,尚能满足诊断要求;4级为血管显示不清,有严重伪影,不能作出诊断。

  • 1.5.   辐射剂量

  • 通过CT自动计算得到剂量长度乘积(dose length product,DLP),单位有效剂量(effective dose,ED)=k×DLP(心脏k值参照2017年Sigal Trattner[10]研究,心脏k值为0.026 mSv·mGy-1·cm-1;头颈部k值参照欧盟委员会关于CT的质量标准指南,头颈部k值为0.0031 mSv·mGy-1·cm-1)。取两部位有效辐射剂量相加计算[9]。心脏、头颈部扫描时间及DLP从患者扫描参数中获得。

  • 1.6.   统计学分析

  • 采用SPSS 21.0软件进行统计学分析。定量资料以x±s表示,符合正态分布且方差齐,两组间的计量资料比较采用独立样本t检验;采用χ2检验对两组患者临床资料中的频数参数构成比进行比较。P < 0.05表示差异有统计学意义。图像质量评分一致性采用Cohen Kappa分析,Kappa值>0.81为一致性极好、0.61~0.80为一致性良好、0.41~0.60为一致性中等、0.21~0.40为一致性一般,Kappa值< 0.20为一致性差。

2.   结果

    2.1.   患者基线资料

  • 表 1可见,A组和B组患者间年龄(t=0.58,P>0.05)、性别(χ2=1.45,P>0.05)、BMI(t=1.20,P>0.05)差异无统计学意义;在平均心率、心率变异性方面进行比较,差异均有统计学意义(t=12.48、3.48,均P<0.05);其余方面的比较差异均无统计学意义。

    变量 A组/n=300 B组/n=193 检验值 P
    年龄/岁 54.27±9.63 53.56±10.64 t=0.58 0.847
    性别/%(男) 66.33(199) 33.16(64) χ2=1.45 0.228
    体重指数/(kg/m2) 22.50±2.37(10.6~32.6) 22.15±2.01(19.8~27.5) t=1.20 0.277
    最低心率/(次/min) 71.60±11.91(45~128) 61.12±4.10(53~103) t=7.84 0.001
    最高心率/(次/min) 78.50±21.62(54~285) 73.33±21.28(57~130) t=1.93 0.055
    平均心率/(次/min) 74.00±11.00(52~128) 57.00±5.00(56~108) t=12.48 0.001
    心率变异性 6.90±20.63(0~299) 16.00±22.18(0~67) t=3.48 0.001
    扫描长度/mm 478.98(26.41 486.51±56.24 t=1.84 0.067
    管电流/mAs 359.70±83.66 373.83±15.78 t=1.77 0.077
    管电压/kV 98.60±9.53 100.17±1.88 t=1.73 0.083
    注:表中,A组采用第三代双源CT(Force,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描;B组米用第二代双源CT(Definiton Flash,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描。

    Table 1.  Characteristics of 493 patients subjected to integrated imaging in coronary combined with carotid and cerebrovascular CT angiography

  • 2.2.   图像质量、辐射剂量的客观评价结果

  • 通过对A组和B组心脑血管一体化成像的客观图像质量进行比较,A组颈总动脉、颈内动脉、大脑中动脉和椎动脉V4段的CT值、噪声均低于B组,差异均有统计学意义(t=1.98~4.49,均P<0.05);A组的剂量长度乘积明显低于B组,且差异有统计学意义(t=18.69,P=0.001);A组有效辐射剂量较B组降低了30%,差异有统计学意义(t=14.79,P=0.001)。A组的对比剂用量、扫描时间、时间分辨率均明显低于B组,且差异有统计学意义(t=45.51、12.27、14.79,均P=0.001),图像质量其他方面的差异均无统计学意义(表 2)。

    患者图像质量比较参数/ (HU,x±s) A组/n=300 B组/n=193 t P
    主动脉根部CT值 449.46±109.24 457.29±86.43 0.68 0.495
    主动脉根部噪声 23.86±7.76 24.11±5.46 0.31 0.755
    颈总动脉CT值 454.94±125.44 512.83±87.83 4.49 0.001
    颈总动脉噪声 14.57±5.94 16. ±5.96 2.17 0.031
    颈内动脉CT值 452.79±121.53 488.82±102.18 2.46 0.004
    颈内动脉噪声 15.32±10.48 18.56±8.72 2.91 0.002
    大脑中动脉CT值 406.49±112.16 470.83±87.96 5.48 0.001
    大脑中动脉噪声 19.22±8.87 26.85±16.14 6.09 0.001
    椎动脉V4段CT/ 384.53±102.75 470.18±97.37 7.63 0.049
    椎动脉V4段噪声 20.24±8.44 22.08±8.17 1.98 0.049
    主动脉层面SNR 25.09±12.03 23.10±6.12 1.67 0.095
    主动脉层面CNR 22.07±11.25 19.96±6.49 1.87 0.062
    剂量长度乘积/mGy.cm 138.57±31.62 219.57±54.62 18.69 0.001
    (73.5-258.0) (142.0-399.0)
    时间分辨率/ms 66 75 14.79 0.001
    扫描时间/s 0.78±0.12 0.94±0.06 12.27 0.001
    对比剂/mL 50.00±0.00 60.00±0.00 45.51 0.001
    有效辐射剂量/mSv 1.48±0.33 2.14±0.52 14.79 0.001
    (0.79-2.77) (1.36-4.08)
    注:表中,A组采用第三代双源CT(Force,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描;B组米用第二代双源CT(Definiton Flash,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描。SNR:信噪比;CNR:对比噪声比。

    Table 2.  Comparision of objective integrated imaging in coronary combined with carotid and cerebrovascular CT angiography between 3rd and 2nd dual-source CT

  • 2.3.   图像质量主观评价结果

  • 对图像质量进行评价的一致性检验Kappa值为0.912。A1、A2、B1、B2各组患者间年龄(t=0.18~0.37,P>0.05)、性别(χ2=0.42~2.82,P>0.05)、BMI(t=0.30~0.82,P>0.05)差异均无统计学意义。由表 3可知:①与B组进行比较,A组的冠状动脉CTA平均图像质量的评分更好(t=0.018,P < 0.05)、冠状动脉4级血管基于患者数的不可诊断率更低(χ2=6.63,P < 0.05),且差异均有统计学意义;②与B组进行比较,A组的头颈部CTA评分更好(t=0.013,P < 0.05)、头颈部4级血管基于患者数的不可诊断率更低(χ2=4.38,P < 0.05),且差异均有统计学意义;③不同扫描间期A1组和A2组的图像质量进行比较,A2组可取得与A1组同样的图像质量评分,差异均无统计学意(t=0.82、0.88,χ2=0.18、0.82,均P>0.05)。高心率患者采用第三代双源CT成像较二代CT成像的成功率高(88.74% vs.67.32%,χ2=22.06,P < 0.05),典型病例的图像见图 1图 2

    变量 冠状动脉CTA平均图像质量评分 头颈部CTA平均图像质量评分 冠状动脉4级血管基于患者数/%(例) 头颈部4级血管基于患者数/%(例)
    A组/n=300 1.09±0.42 1.05±0.34 1.00(3/300) 0.06(2/300)
      A1组/n=69,心率≤65次/min 1.08±0.44 1.08±0.41 1.44(1/69) 1.44(1/69)
      A2组/n=201,心率 > 65次/min 1.09±0.38 1.04±0.32 0.86(2/231) 0.43(1/231)
    B组/n=193 1.44±0.88a 1.19±0.61a 4.66(9/193)a 3.11(6/193)a
      B1组/n=92,心率≤65次/min 1.26±0.73 1.07±0.45 5.43(5/92) 2.17(2/92)
      B2组/n=101,心率 > 65次/min 1.60±0.98b 1.30±0.71b 4.95(5/101)b 3.96(4/101)
    注:表中,A组采用第三代双源CT(Force,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描;B组采用第二代双源CT(Defmiton Flash,德国西门子Healthcare公司)前瞻性心电门控大螺距模式扫描。a:与A组比较,差异均有统计学意义t=0.018、0.013, ;χ2=6.63、4.38,均P < 0.05); b:与A2组比较,差异均有统计学意义t=2.013、4.357, χ2=5.68、5.89,均P < 0.05)。CTA: CT血管造影。

    Table 3.  Comparision of subjective integrated imaging in coronary combined with carotid and cerebrovascular CT angiography between 3rd and 2nd dual source CT in different scan interval

    Figure 1.  A typical case of 3rd generation dual-source CT of integrated imaging in coronary combined with carotid and cerebrovascular CT angiography

    Figure 2.  A typical case of 2nd generation dual-source CT of integrated imaging in coronary combined with carotid and cerebrovascular CT angiography

3.   讨论
  • 本研究通过评价CT心脑血管一体化成像的客观图像质量、主观图像质量和辐射剂量,分析影响图像质量的因素,结果表明:①双源CT心脑血管一体化成像的关键技术点为采用大螺距扫描模式从足到头部方向扫描,低心率患者(心率≤65次/min)扫描时间窗采用舒张期成像(RR间期55%),高心率患者(心率>65次/min)采用收缩期成像(RR间期30%);②与第二代双源CT相比,第三代双源CT头颈部动脉可以去骨重建,明显提高了图像质量,提高了高心率患者的成像成功率;③与第二代双源CT相比,第三代双源CT辐射剂量降低了30%。双源CT心脑血管一体化成像为临床提供了一种评价心脑血管疾病的无创性影像学方法。

    我们团队的前期研究已证实了CT心脑血管一体化成像的可行性[9, 11],大螺距双源CT在相对较低辐射剂量条件下对评估冠状动脉、颈动脉和脑动脉狭窄提供了质量良好的图像和较高的诊断准确率,但前期研究具有一定局限性:样本量较小(82例),仅用第二代双源CT成像,选择的患者心率均在65次/min以下。本研究在前期研究基础上进行了进一步研究,样本量扩大为493例,入选患者的心率平均(74±11)次/min,最高心率可达128次/min。

    在本研究中我们发现,心脑一体化成像失败的原因大多在于冠状动脉成像的失败。影响因素有以下4点:①心率变异性较大,如房颤、心率不齐患者一次性图像成功的可能性较小,Gramer等[12]运用256排CT的研究也发现,心率变异性高的患者冠状动脉图像质量评分低。②高心率患者冠状动脉成像的成功率低,Gordic等[13]在对高心率(心率>65次/min)患者的最初的研究发现基于血管节段评价失败率可达12.5%,基于患者评价失败率达36%。③错误的时间窗选择,低心率应选择舒张期(RR间期的55%)成像,高心率应选择收缩期(RR间期的30%)成像,如落在QRS波峰(QRS波是指正常心电图中幅度最大的波群,反映心室除极的全过程)上,则成像成功的可能性减小。Zimmerman等[14]运用双源CT对心率大于90次/min的患者采用30%~80%RR间期成像,获得了质量良好的图像。一项研究结果也表明,应对高心率患者(心率>65次/min)采用双源CT大螺距前瞻性心电门控螺旋扫描,在RR间期20%~30%成像[15]。Nitesh等[16]也在研究中提出了时间窗的选择,高心率采用收缩期成像。④与我们的前期研究结果相比,本研究结果显示,与第二代双源CT时间分辨率(75 ms)相比[9],第三代A代双源CT时间分辨率(66 ms)[17]较前提升,差异有统计学意义。与第二代双源CT相比,第三代双源CT明显提高了图像质量,提高了高心率患者成像的成功率,并且头颈部动脉可以去骨重建,这些表明CT的时间分辨率是影响图像质量的一个重要因素。

    我们前期进行心脑一体化成像用时(0.97±0.09)s[18],而Wang等[19]运用第二代双源CT进行心脑联合扫描,时间为(1.31±0.06)s。Zhang等[20]研究结果发现,心脑血管CTA扫描时间为12.9~18.6 s,平均(14.7±1.7)s。本研究进行心脑一体化成像仅用时(0.78±0.12)s,这表明第三代双源CT缩短了扫描时间。随着分辨率的提高和扫描时间的缩短,因此降低了辐射剂量。我们前期研究结果显示,进行心脑一体化成像时的辐射剂量为(1.42±0.44)mSv[9]。Furtado等[21]对120例脑卒中患者采用64排CT完成颅内动脉、颈动脉、和冠状动脉CTA三部位分期扫描,头颈部DLP为(726.4±41.5)mGy·cm,冠状动脉DLP为(374.7±28.9)mGy·cm。Tognolini等[22]对33例患者采用二期扫描,头颈动脉采用螺旋模式,心脏扫描采用前瞻性心电门控序列,辐射剂量达4.3 mSv。Zhang等[23]进行的心脑联扫有效辐射剂量达7.0 mSv,Zhang等[20]降低为(2.21±1.38)mSv。本研究心脑联合扫描中高心率患者扫描时选取收缩期成像,低心率患者选取舒张期成像,DLP较前明显降低,有效辐射剂量较前明显降低。随着第三代双源CT扫描速度的提升[8-9],对比剂的用量可进一步减少。据文献报道,第二代双源CT及256排螺旋CT心脑一体化成像使用对比剂用量为65~90 mL[18-20],在本研究中对比剂用量仅为50 mL,较前明显降低,表明第三代双源CT减少了对比剂用量。

    局限与不足:①本研究并未评价第三代双源CT一体化血管成像诊断血管狭窄的准确性,应进一步研究证实;②本研究未对斑块进行分析,未对各类型斑块的危险因素进行分析。

    本研究结果表明,第三代双源CT心脑血管一体化成像在相对低辐射剂量及头颈部动脉自动去骨重建的条件下为高心率患者评估冠状动脉、颈动脉和脑动脉狭窄提供了较好的图像质量,提高了一体化成像的成功率,为临床提供了一种评价心脑血管疾病的无创性影像学方法。

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